This study conducted temporary plugging and diversion fracturing(TPDF)experiments using a true triaxial fracturing simulation system within a laboratory setting that replicated a lab-based horizontal well completion w...This study conducted temporary plugging and diversion fracturing(TPDF)experiments using a true triaxial fracturing simulation system within a laboratory setting that replicated a lab-based horizontal well completion with multi-cluster sand jetting perforation.The effects of temporary plugging agent(TPA)particle size,TPA concentration,single-cluster perforation number and cluster number on plugging pressure,multi-fracture diversion pattern and distribution of TPAs were investigated.A combination of TPAs with small particle sizes within the fracture and large particle sizes within the segment is conducive to increasing the plugging pressure and promoting the diversion of multi-fractures.The addition of fibers can quickly achieve ultra-high pressure,but it may lead to longitudinal fractures extending along the wellbore.The temporary plugging peak pressure increases with an increase in the concentration of the TPA,reaching a peak at a certain concentration,and further increases do not significantly improve the temporary plugging peak pressure.The breaking pressure and temporary plugging peak pressure show a decreasing trend with an increase in single-cluster perforation number.A lower number of single-cluster perforations is beneficial for increasing the breaking pressure and temporary plugging peak pressure,and it has a more significant control on the propagation of multi-cluster fractures.A lower number of clusters is not conducive to increasing the total number and complexity of artificial fractures,while a higher number of clusters makes it difficult to achieve effective plugging.The TPAs within the fracture is mainly concentrated in the complex fracture areas,especially at the intersections of fractures.Meanwhile,the TPAs within the segment are primarily distributed near the perforation cluster apertures which initiated complex fractures.展开更多
Multistage fracturing of horizontal wells is a critical technology for unconventional oil and gas reservoir stimulation. Ball-throwing temporary plugging fracturing is a new method for realizing uniform fracturing alo...Multistage fracturing of horizontal wells is a critical technology for unconventional oil and gas reservoir stimulation. Ball-throwing temporary plugging fracturing is a new method for realizing uniform fracturing along horizontal wells and plays an important role in increasing oil and gas production. However,the transportation and sealing law of temporary plugging balls(TPBs) in the perforation section of horizontal wells is still unclear. Using COMSOL computational fluid dynamics and a particle tracking module, we simulate the transportation process of TPBs in a horizontal wellbore and analyse the effects of the ball density, ball diameter, ball number, fracturing fluid injection rate, and viscosity on the plugging efficiency of TPB transportation. This study reveals that when the density of TPBs is close to that of the fracturing fluid and a moderate diameter of the TPB is used, the plugging efficiency can be substantially enhanced. The plugging efficiency is greater when the TPB number is close to twice the number of perforations and is lower when the number of TPBs is three times the number of perforations.Adjusting the fracturing fluid injection rate from low to high can control the position of the TPBs,improving plugging efficiency. As the viscosity of the fracturing fluid increases, the plugging efficiency of the perforations decreases near the borehole heel and increases near the borehole toe. In contrast, the plugging efficiency of the central perforation is almost unaffected by the fracturing fluid viscosity. This study can serve as a valuable reference for establishing the parameters for temporary plugging and fracturing.展开更多
Using the visualized experimental device of temporary plugging in hydraulic fractures, the plugging behaviors of temporary plugging particles with different sizes and concentrations in hydraulic fractures were experim...Using the visualized experimental device of temporary plugging in hydraulic fractures, the plugging behaviors of temporary plugging particles with different sizes and concentrations in hydraulic fractures were experimentally analyzed under the conditions of different carrier fluid displacements and viscosities. The results show that the greater the carrier fluid viscosity and displacement, the more difficult it is to form a plugging layer, and that the larger the size and concentration of the temporary plugging particle, the less difficult it is to form a plugging layer. When the ratio of particle size to fracture width is 0.45, the formation of the plugging layer is mainly controlled by the mass concentration of the temporary plugging particle and the viscosity of the carrier fluid, and a stable plugging layer cannot form if the mass concentration of the temporary plugging particle is less than 20 kg/m^(3)or the viscosity of the carrier fluid is greater than 3 mPa·s. When the ratio of particle size to fracture width is 0.60, the formation of the plugging layer is mainly controlled by the mass concentration of the temporary plugging particle, and a stable plugging layer cannot form if the mass concentration of the temporary plugging particle is less than 10 kg/m^(3). When the ratio of particle size to fracture width is 0.75, the formation of the plugging layer is basically not affected by other parameters, and a stable plugging layer can form within the experimental conditions. The formation process of plugging layer includes two stages and four modes. The main controlling factors affecting the formation mode are the ratio of particle size to fracture width, carrier fluid displacement and carrier fluid viscosity.展开更多
Temporary plugging agent(TPA)is widely used in many fields of petroleum reservoir drilling and production,such as temporary plugging while drilling and petroleum well stimulation by diverting in acidizing or fracturin...Temporary plugging agent(TPA)is widely used in many fields of petroleum reservoir drilling and production,such as temporary plugging while drilling and petroleum well stimulation by diverting in acidizing or fracturing operations.The commonly used TPA mainly includes hard particles,fibers,gels,and composite systems.However,current particles have many limitations in applications,such as insufficient plugging strength and slow degradation rate.In this paper,a degradable pre-formed particle gel(DPPG)was developed.Experimental results show that the DPPG has an excellent static swelling effect and self-degradation performance.With a decrease in the concentration of total monomers or cross-linker,the swelling volume of the synthesized DPPG gradually increases.However,the entire self-degradation time gradually decreases.The increase in 2-acrylamide-2-methylpropanesulfonic acid(AMPS)in the DPPG composition can significantly increase its swelling ratio and shorten the self-degradation time.Moreover,DPPG has excellent high-temperature resistance(150°C)and high-salinity resistance(200,000 mg/L NaCl).Core displacement results show that the DPPG has a perfect plugging effect in the porous media(the plugging pressure gradient was as high as 21.12 MPa),and the damage to the formation after degradation is incredibly minor.Therefore,the DPPG can be used as an up-and-coming TPA in oil fields.展开更多
In this paper,a viscoelasticity-plastic damage constitutive equation for naturally fractured shale is deduced,coupling nonlinear tensile-shear mixed fracture mode.Dynamic perforation-erosion on fluid re-distribution a...In this paper,a viscoelasticity-plastic damage constitutive equation for naturally fractured shale is deduced,coupling nonlinear tensile-shear mixed fracture mode.Dynamic perforation-erosion on fluid re-distribution among multi-clusters are considered as well.DFN-FEM(discrete fracture network combined with finite element method)was developed to simulate the multi-cluster complex fractures propagation within temporary plugging fracturing(TPF).Numerical results are matched with field injection and micro-seismic monitoring data.Based on geomechanical characteristics of Weiyuan deep shale gas reservoir in Sichuan Basin,SW China,a multi-cluster complex fractures propagation model is built for TPF.To study complex fractures propagation and the permeability-enhanced region evolution,intersecting and competition mechanisms between the fractures before and after TPF treatment are revealed.Simulation results show that:fracture from middle cluster is restricted by the fractures from side-clusters,and side-clusters plugging is benefit for multi fractures propagation in uniformity;optimized TPF timing should be delayed within a higher density or strike of natural fractures;Within a reservoir-featured natural fractures distribution,optimized TPF timing for most clustered method is 2/3 of total fluid injection time as the optimal plugging time under different clustering modes.展开更多
The development of unconventional petroleum resources has gradually become an important succession for increasing oil production.However,the related engineers and researchers are paying more and more attention to the ...The development of unconventional petroleum resources has gradually become an important succession for increasing oil production.However,the related engineers and researchers are paying more and more attention to the application of temporary plugging agents(TPAs)for their efficient development.TPAs can expand the stimulated reservoir volume(SRV)and facilitate the flow of oil and gas to the bottom of the well.Particle-gels used as temporary plugging agents have the characteristics of the simple injection process,good deformation,high plugging strength,and complete self-degradation performance,which have been widely applied in recent years.In this paper,five samples of DPPG polymerized by different molecular weights of cross-linking agents were prepared.In addition,infrared spectroscopy analysis,differential calorimetry scanning(DSC)analysis,static particle gel swelling and degradation performance evaluation experiments,and dynamic temporary plugging performance experiments in cores were conducted at 34°C.Results show that as the molecular weight of the cross-linking agent(at 0.01 g)in the DPPG molecule decreased from 1,000 to 200 Da,the fewer cross-linking sites of DPPG,the looser the microscopic three-dimensional mesh structure formed.The swelling ratio increased from 7 to 33 times.However,the complete degradation time increased from 40 to 210 min.Moreover,the DSC results confirmed that the higher the molecular weight of the cross-linking agent,the worse is chemical stability and the more prone it to self-degradation.DPPG samples had good temporary plugging performance in reservoir cores.DPPGs prepared by the cross-linking agent with smaller molecular weight has a stronger swelling ratio,higher gel strength,and greater plugging strength in the core permeabilities.Moreover,the degraded DPPG is less damaging to the cores.However,their slower degradation rates take a slightly longer times to reach complete degradation.The results of this paper can provide new ideas and a theoretical basis for the development of particle gel-type temporary plugging agents(TPA)with controllable degradation time in low-temperature reservoirs.It can help to expand the application range of existing DPPG reservoir conditions.展开更多
When deep and ultra-deep shale gas well fracturing is carried out,multi-cluster fracturing can hardly realize synchronous initiation and propagation of hydraulic fractures due to the combined effects of heterogeneity ...When deep and ultra-deep shale gas well fracturing is carried out,multi-cluster fracturing can hardly realize synchronous initiation and propagation of hydraulic fractures due to the combined effects of heterogeneity of deep in-situ stress and"dense cluster"fracture arrangement,and the strong interference between fractures aggravates the unbalanced fracture propagation degree.Field practice proves that the fracture-opening temporary plugging fracturing technology can effectively control the unbalanced propagation of multiple fractures.In addition,the application effect of temporary plugging process can be improved by developing a method for simulating fracture control during fracture-opening temporary plugging fracturing of deep/ultra-deep shale-gas horizontal wells.Based on rock mechanics,elasticity mechanics,fluid mechanics and fracture propagation theory,combined with the flow distribution equation of horizontal-well multi-cluster fracturing and the plugging equation of temporary plugging balls,this paper establishes a fracture propagation model and a fracture control simulation method for the fracture-opening temporary plugging fracturing of deep/ultra-deep shale gas horizontal wells.Then,the influences of the number of temporary plugging balls and the times and timing of temporary plugging on temporary plugging control are simulated,and the influences of temporary plugging balls on fracture propagation morphology and SRV(stimulated reservoir volume)distribution are analyzed by taking Sinopec's one deep shale gas well in Dingshan-Dongxi structure of southeast Sichuan Basin as an example.And the following research results are obtained.First,fracture-opening temporary plugging can significantly promote the balanced propagation of multiple fractures,and the simulation confirms that the number of temporary plugging balls and the times and timing of temporary plugging play an important role in fracture control.Second,as the number of temporary plugging balls increase,the SRV increases firstly and then decreases,so there is an optimal number of temporary plugging balls.Third,increasing the times of temporary plugging can improve the fault tolerance rate of temporary plugging and diverting process,but it is necessary to increase the number of temporary plugging balls appropriately.Fourth,when the timing of temporary plugging is appropriate,the balanced propagation of multiple fractures is achieved and the maximum SRV is reached.In conclusion,this method is of great significance to optimizing the design of temporary plugging fracturing,improve the implementation level of field process and develop deep and ultra-deep shale gas efficiently.展开更多
Due to downhole complexities,shale-gas horizontal well fracturing in the Sichuan Basin suffered from casing deformation and failure to apply the technique of cable-conveyed perforation bridge plug.In view of these pro...Due to downhole complexities,shale-gas horizontal well fracturing in the Sichuan Basin suffered from casing deformation and failure to apply the technique of cable-conveyed perforation bridge plug.In view of these problems,a new technique of staged volume fracturing with temporary plugging by sand filling is employed.Based on theoretical analyses and field tests,a design of optimized parameters of coiled tubingconveyed multi-cluster sand-blasting perforation and temporary plugging by sand filling was proposed.It was applied in the horizontalWell ZJ-1 in which casing deformation occurred.The following results are achieved in field operations.First,this technique enables selective staged fracturing in horizontal sections.Second,this technique can realize massive staged fracturing credibly without mechanical plugging,with the operating efficiency equivalent to the conventional bridge plug staged fracturing.Third,full-hole is preserved after fracturing,thus it is possible to directly conduct an open flow test without time consumption of a wiper trip.The staged volume fracturing with temporary plugging by sand filling facilitated the 14-stage fracturing in Well ZJ-1,with similar SRV to that achieved by conventional bridge plug staged fracturing and higher gas yield than neighboring wells on the same well pad.Thus,a new and effective technique is presented in multi-cluster staged volume fracturing of shale gas horizontal wells.展开更多
At present, the oil and water wells in Liaohe Oilfield have entered the middle and later stages of development. The pressure of the oil and water wells has decreased year by year and the contradiction between injectio...At present, the oil and water wells in Liaohe Oilfield have entered the middle and later stages of development. The pressure of the oil and water wells has decreased year by year and the contradiction between injection and production has become increasingly prominent. In order to maximize its recovery, various new processes and technologies have been widely applied in different oilfields. The loss of workover fluid during workover operation not only increases the dosage of workover fluid, but also causes more serious pollution to the oil layer (formation). Affect oil production after workover operation.展开更多
This study explores the transport dynamics of temporary plugging balls in multi-cluster horizontal wellbores through a three-dimensional Computational Fluid Dynamics(CFD)model based on field dimensions.An experimental...This study explores the transport dynamics of temporary plugging balls in multi-cluster horizontal wellbores through a three-dimensional Computational Fluid Dynamics(CFD)model based on field dimensions.An experimental setup mimicking the transport of these balls was utilized to validate the model,revealing a maximum discrepancy of less than 22.2% in ball allocation proportions under identical conditions.This validation substantiates the model's precision in predicting transport dynamics across various operational scenarios.Key parameters,including pump rate,fluid viscosity,perforation discharge capacity,ball diameter,ball density,and the number of balls,were examined using the validated model.Findings indicate that pump rate,ball density,and perforation discharge capacity markedly influence ball distribution,followed by fluid viscosity.The number of balls has a lesser effect.Elevated pump rates augment inertial forces,prompting balls to migrate towards the toe-side of the wellbore.Moderate fluid viscosities enhance distribution uniformity,whereas extreme viscosities do not.Perforation clusters with higher discharge capacities attract more balls,thereby improving plugging efficiency.Lower ball density and smaller diameter yield more uniform distribution,while higher values lead to ball accumulation at the toe-end.This study offers valuable insights for optimizing parameters in temporary plugging fracturing technology,thereby improving the efficiency and effectiveness of hydraulic fracturing treatments.展开更多
Temporary plugging and diversion fracturing(TPDF)is widely used to promote the uniform and complex distribution of multi-clustered hydraulic fractures(HFs)in a horizontal well of the unconventional formations.However,...Temporary plugging and diversion fracturing(TPDF)is widely used to promote the uniform and complex distribution of multi-clustered hydraulic fractures(HFs)in a horizontal well of the unconventional formations.However,the migration behavior of temporary plugging agent(TPA),as a function of the concentration and particle size of TPA and cluster-perforation numbers,etc.,determining the effectiveness of this technique,remains unclear.Therefore,this study conducted innovatively a series of TPDF simulation experiments on transparent polymethyl methacrylate(PMMA)specimens(cubic block of 30 cm×30 cm×30 cm)to explore visually the migration behavior of TPA in multi-clustered HFs in a horizontal well.A laboratory hydraulic sandblasting perforation completion technique was implemented to simulate the multi-cluster perforations.All the distributions of wellbore,perforations,HFs,and TPA can be seen clearly inside the PMMA specimen post the experiment.The results show that there are four characteristic plugging positions for the TPA:mouth of HF,middle of HF,tip of HF,and the intersection of HFs.Small particle size TPA tends to migrate to the fracture tip for plugging,while large particle size TPA tends to plug at the fracture mouth.The migration of the TPA is influenced obviously by the morphology of the fracture wall.A smooth fracture wall is conducive to the migration of the TPA to the far end of HFs,but not conducive to generating the plugging zone and HF diversion.In contrast,a"leaf vein"fracture of rough wall is conducive to generating the plugging layer and the diversion of HFs,but not conducive to the migration of the TPA to the far end of HFs.The migration ability of TPA in a"shell"pattern is intermediate between the two above cases.Increasing TPA concentration can encourage TPA to migrate more quickly to the characteristic plugging position,and thereby to promote the creation of effective plugging and subsequently the multi-stage diversion of the HFs.Nevertheless,excessive concentration may cause the TPA to settle prematurely,affecting the propagation of the HFs to the far end.Increasing the number of clusters to a certain extent can encourage TPA to migrate into the HFs and form plugging,and promote the diversion.An evaluation system for the migration ability of granular TPA has been established,and it was calculated that when there is no plugging expectation target,the comprehensive migration ability of small particle size TPA is stronger than that of large particle size TPA.This research provides theoretical foundation for the optimization of temporary plugging parameters.展开更多
Multi-stage and multi-cluster fracturing(MMF)is a crucial technology in unconventional oil and gas development,aiming to enhance production by creating extensive fracture networks.However,achieving uniform expansion o...Multi-stage and multi-cluster fracturing(MMF)is a crucial technology in unconventional oil and gas development,aiming to enhance production by creating extensive fracture networks.However,achieving uniform expansion of multi-cluster hydraulic fractures(HFs)in MMF remains a significant challenge.Field practice has shown that the use of temporary plugging and diversion fracturing(TPDF)can promote the balanced expansion of multi-cluster HFs.This study conducted TPDF experiments using a true triaxial fracturing simulation system setting a horizontal well completion with multi-cluster jetting perforations to investigate the equilibrium initiation and extension of multi-cluster fractures.The influence of key parameters,including cluster spacing,fracturing fluid viscosity,differential stress,and fracturing fluid injection rate,on fracture initiation and propagation was systematically examined.The results indicate that while close-spaced multi-cluster fracturing significantly increases the number of HFs,it also leads to uneven extension of HFs in their propagation.In contrast,TPDF demonstrates effectiveness in mitigating uneven HF extension,increasing the number of HFs,and creating a larger stimulated reservoir volume,ultimately leading to improved oil and gas well productivity.Moreover,under conditions of high differential stress,the differential stress within the formation exerts a stronger guiding effect in HFs,which are more closely aligned with the minimum principal stress.Low-viscosity fluids facilitate rapid and extensive fracture propagation within the rock formation.High-volume fluid injection,on the other hand,more comprehensively fills the formation.Therefore,employing lowviscosity and high-volume fracturing is advantageous for the initiation and extension of multi-cluster HFs.展开更多
Hydraulic fracturing,an effective method for enhancing coal seam productivity,largely determines coalbed methane(CBM)production,which is significantly influenced by geological and engineering factors.This study focuse...Hydraulic fracturing,an effective method for enhancing coal seam productivity,largely determines coalbed methane(CBM)production,which is significantly influenced by geological and engineering factors.This study focuses on the L block to investigate the mechanisms influencing efficient fracture propagation and enhanced stimulated reservoir volume(SRV)in fracturing.To explore the mechanisms influencing effective fracture propagation and enhanced SRV,the L block was selected as the research object,with a comprehensive consideration of geological background,reservoir properties,and dynamic production data.By combining the discrete lattice method with numer-ical analysis and true triaxial experimental simulation,the fracture morphology of a single cluster and the propagation patterns of multiple clusters of complex fractures were obtained.Additionally,the optimization of temporary plugging timing and the fracture map under multiple factors were innovatively proposed.Results indicate that greater flow rate and viscosity can effectively overcome the stress shadow effect of the outermost fractures(1st and 6th clusters),increasing the fracture pressure of the single cluster and the equilibrium degree of multiple fracture propagation,thus forming a more complex fracture network.Moreover,when viscosity exceeds 45 pressure concentrates at fracture mPa⋅s,tips,promoting discontinuous propagation and reducing flow resistance.Conversely,increased gangue thickness and spacing between horizontal wells increase the vertical propagation pressure,suppressing fracture growth and reducing central flow velocity.This study provides a multi-cluster fracture propagation map for optimizing volumetric fracturing in coal seams and suggests that the optimal temporary plugging time significantly enhances the SRV.展开更多
Refracturing is an importa nt technique to tap the potential of reservoirs and boost production in depleted oil and gas fields.However,fracture propagation during refracturing,including both conventional refracturing ...Refracturing is an importa nt technique to tap the potential of reservoirs and boost production in depleted oil and gas fields.However,fracture propagation during refracturing,including both conventional refracturing and temporary-plugging refracturing remains poorly understood,especially for cases with non-uniform distribution of formation pressure due to long-term oil production and water injection.Therefore,taking pilot tests of refracturing with sidetracking horizontal wells in tight reservoirs in the Changqing Oilfield,China as an example,we establish a three-dimensional numerical model of conventional refracturing and a numerical model of temporary-plugging refracturing based on the discrete lattice method.Non-uniform distributions of formation pressure are imported in these models.We discuss the effects of key operating parameters such as injection rate,cluster spacing,and number of clusters on the propagation of multi-cluster fractures for conventional refracturing.For temporaryplugging refracturing,we examine the impacts of controlling factors such as the timing and number of temporary plugging on fracture propagation.In addition,we analyze a field case of temporaryplugging refracturing using well P3 in the Changqing Oilfield.The results show that fractures during re fracturing tend to propagate preferentially and dominantly in the depleted areas.Improved stimulation effect can be obtained with an optimal injection rate and a critical cluster spacing.The proposed model of temporary-plugging refracturing can well describe the temporary plugging of dominant existingfractures and the creation of new-fractures after fracturing fluid is forced to divert into other clusters from previous dominant clusters.Multiple temporary plugging can improve the balanced propagation of multi-cluster fractures and obtain the maximum fracture area.The established numerical model and research results provide theoretical guidance for the design and optimization of key operating parameters for refracturing,especially for temporary-plugging refracturing.展开更多
Temporary plugging and diverting fracturing(TPDF),involving inner-fracture temporary plugging(IFTP)and inner-stage temporary plugging(ISTP),has been proposed as a widely applied technique in China,for promoting the un...Temporary plugging and diverting fracturing(TPDF),involving inner-fracture temporary plugging(IFTP)and inner-stage temporary plugging(ISTP),has been proposed as a widely applied technique in China,for promoting the uniform initiation and propagation of multi-clustered hydraulic fractures(HFs)in a horizontal well of the shale oil/gas reservoirs.However,how the key plugging parameters controlling the multi-fracture growth and the pumping pressure response during TPDF in shale with dense bedding planes(BPs)and natural fractures(NFs)is still unclear,which limits the optimization of TPDF scheme.In this paper,a series of TPDF simulation experiments within a stage of multi-cluster in a horizontal well were carried out on outcrops of Longmaxi Formation shale using a large-scale true tri-axial fracturing simulation system,combined with the acoustic emission(AE)monitor and computed tomography(CT)scanning techniques.Each experiment was divided into three stages,including the conventional fracturing(CF),IFTP and ISTP.Multi-fracture initiation and propagation behavior,and the dominant controlling parameters were examined,containing the particle sizes,concentration of temporary plugging agent(TPA),and cluster number.The results showed that the number of transverse HFs(THFs)and the overall complexity of fracture morphology increase with the increase in TPA concentration and perforation cluster number.Obviously,the required concentration of TPA is positively correlated with the cluster number.Higher peak values and continuous fluctuations of pumping pressure during TPDF may indicate the creation of diversion fractures.The creation of standard THFs during CF is favorable to the creation of diversion fractures during TPDF.Moreover,the activation of BPs nearby the wellbore during CF is unfavorable to the subsequent pressure buildup during TPDF,resulting in poor plugging and diverting effect.Notably,under the strike-slip fault stress regime,the diversion of THFs is not likely during IFTP,which is similar as the results of ISTP to initiate mainly the un-initiated or under-propagated perforation clusters.Three typical pressure curve types during TPDF can be summarized to briefly identify the hydraulic fracture diversion effects,including good(multiple branches or/and THFs can be newly created),fair(HF initiation along the slightly opened BPs and then activating the NFs),and bad(HF initiation along the largely opened BPs and then connecting with the NFs).展开更多
Casing deformation and frac-hit pose significant challenges to the development of deep shale gas in southern Sichuan Basin.By analyzing the mechanism and main control factors of casing deformation and frac-hit,two kin...Casing deformation and frac-hit pose significant challenges to the development of deep shale gas in southern Sichuan Basin.By analyzing the mechanism and main control factors of casing deformation and frac-hit,two kinds of risk assessment methods were defined,and the overall prevention and control concept and practice were formulated.The results show that initial stress,pore pressure,fault development and large scale fracturing in local block are the main factors leading to the deformation.The development of fracture through well group and uncontrolled fracturing fluid volume are the main factors leading to pressure channeling.Based on this,the risk classification technology of casing deformation and frac-hit is established,and the dual-optimal,dual-control concept and technology are formed.In terms of the prevention and control of casing deformation,the formation of small-diameter bridge plug fracturing,large section combined fracturing,glass beads cementing,singlewell staggered and platform straddle fracturing mode,dual-dimension controlled and lift fracturing,hyperbolic diagnosis,etc.Frac-hit prevention and control formed pump sequence optimization mode,physical and chemical temporary plugging and other methods.The above technology achieved casing deformation rate decreased from 50.4%to 25.4%,frac-hit rate decreased from 58.6%to 33.9%,and the average well kilometer EUR reached 0.52e0.7 million square meters,an increase of 7.7%compared with the previous research,with remarkable results.展开更多
Due to the reservoir heterogeneity and the stress shadow effect, multiple hydraulic fractures within one fracturing segment cannot be initiated simultaneously and propagate evenly, which will cause a low effectiveness...Due to the reservoir heterogeneity and the stress shadow effect, multiple hydraulic fractures within one fracturing segment cannot be initiated simultaneously and propagate evenly, which will cause a low effectiveness of reservoir stimulation. Temporary plugging and diverting fracturing(TPDF) is considered to be a potential uniform-stimulation method for creating multiple fractures simultaneously in the oilfield. However, the multi-fracture propagation morphology during TPDF is not clear now. The purpose of this study is to quantitatively investigate the multi-fracture propagation morphology during TPDF through true tri-axial fracturing experiments and CT scanning. Critical parameters such as fracture spacing, number of perforation clusters, the viscosity of fracturing fluid, and the in-situ stress have been investigated. The fracture geometry before and after diversion have been quantitively analyzed based on the two-dimensional CT slices and three-dimensional reconstruction method. The main conclusions are as follows:(1) When injecting the high viscosity fluid or perforating at the location with low in-situ stress, multiple hydraulic fractures would simultaneously propagate. Otherwise, only one hydraulic fracture was created during the initial fracturing stage(IFS) for most tests.(2) The perforation cluster effectiveness(PCE) has increased from 26.62% during the IFS to 88.86% after using diverters.(3) The diverted fracture volume has no apparent correlation with the pressure peak and peak frequency during the diversion fracturing stage(DFS) but is positively correlated with water-work.(4) Four types of plugging behavior in shale could be controlled by adjusting the diverter recipe and diverter injection time, and the plugging behavior includes plugging the natural fracture in the wellbore, plugging the previous hydraulic fractures, plugging the fracture tip and plugging the bedding.展开更多
Excess water production has become an important issue in the oil and gas extraction process.Preformed particle gels(PPGs),show the capability to control the conformance and reduce excess water cut.However,conventional...Excess water production has become an important issue in the oil and gas extraction process.Preformed particle gels(PPGs),show the capability to control the conformance and reduce excess water cut.However,conventional PPGs have poor mechanical properties and their swollen particles are easily damaged by shearing force when passing through the fractures in formations,meanwhile PPGs can be also degraded into various byproducts,leading to permanent damage to the reservoir permeability after temporary plugging.Herein,a novel type of dual cross-linked PPGs(dPPGs)was designed and synthesized using sodium alginate(SA)and acrylamide(AAm),cross-linked with N,N’-methylenebisacrylamide(MBA)and Fe^(3+).Results show that dPPGs have excellent mechanical properties with a storage modulus up to 86,445 Pa,which is almost 20 times higher than other reported PPGs.Meanwhile,dPPGs can be completely degraded into liquid without any solid residues or byproducts and the viscosity of dPPGs degraded liquid was found to be lower than 5 mPa·s.A laboratory coreflooding test showed that the plugging efficiency of dPPGs was up to 99.83%on open fractures.The obtained results demonstrated that dPPGs could be used as economical and environment-friendly temporary plugging agent with high-strength,self-degradation,thermal stability,and salt stability,thus making it applicable to a wide range of conformance control to enhance oil recovery.展开更多
Based on analysis of the reasons for low efficiency and low production after fracturing of some wells in the ultra-deep fractured tight reservoirs of the Kuqa piedmont zone, Tarim Basin and the matching relationship b...Based on analysis of the reasons for low efficiency and low production after fracturing of some wells in the ultra-deep fractured tight reservoirs of the Kuqa piedmont zone, Tarim Basin and the matching relationship between the in-situ stress field and natural fractures, technological methods for creating complex fracture networks are proposed. Through theoretical study and large-scale physical simulation experiments, the mechanical conditions for forming complex fracture network in the Kuqa piedmont ultra-deep reservoirs are determined. The effectiveness of temporary plugging and diversion, and multi-stage fracturing to activate natural fractures and consequently realize multi-stage diversion is verified. The coupling effect of hydraulic fractures and natural fractures activating each other and resulting in "fracture swarms" is observed. These insights provide theoretical support for improving fracture-controlled stimulated reservoir volume(FSRV) in ultra-deep tight reservoirs. In addition, following the concept of volume fracturing technology and based on the results of fracture conductivity experiments of different processes, fracturing technologies such as multi-stage fracture-network acid fracturing, "multi-stage temporary plugging + secondary fracturing", fracturing of multiple small layers by vertically softness-and-hardness-oriented subdivision, and weighted-fluid refracturing are proposed to increase the FSRV. New environment-friendly weighted-fluid with low cost and new fracturing fluid system with low viscosity and high proppant-carrying capacity are also developed. These techniques have achieved remarkable results in field application.展开更多
To solve the problem that the production of Mahu conglomerate reservoir is not up to expectation after the multi-cluster plus temporary plugging fracturing technology is applied in horizontal wells, stages 2–6 in the...To solve the problem that the production of Mahu conglomerate reservoir is not up to expectation after the multi-cluster plus temporary plugging fracturing technology is applied in horizontal wells, stages 2–6 in the test well MaHW6285 are selected to carry out erosion tests with different pumping parameters. The downhole video imaging technology is used to monitor the degree of perforations erosion, and then the fracture initiation and proppant distribution of each cluster are analyzed. The results showed that proppant entered 76.7% of the perforations. The proppant was mainly distributed in a few perforation clusters, and the amount of proppant entered in most of the clusters was limited. The proppant distribution in Stage 4 was relatively uniform, and the fracture initiation of each cluster in the stage is more uniform. The proppant distribution in stages 2, 3, 5, and 6 was significantly uneven, and the uniform degree of fracture initiation in each cluster is low. More than 70% of the proppant dose in the stage entered clusters near the heel end, so the addition of diverters did not promote the uniform initiation of hydraulic fractures. There was a positive correlation between the amount of proppant added and the degree of perforations erosion, and the degree of perforations erosion ranged from 15% to 352%, with an average value of 74.5%, which was far higher than the statistical results of shale reservoir tests in North America. The use of 180° phase perforation(horizontal direction) can reduce the “Phase Bias” of perforations erosion, promote uniform perforations erosion and fluid inflow. The research results provide the basis for optimizing the pumping procedure, reducing the perforation erosion and improving the success rate of diversion.展开更多
基金Supported by the National Natural Science Foundation of China(51974332).
文摘This study conducted temporary plugging and diversion fracturing(TPDF)experiments using a true triaxial fracturing simulation system within a laboratory setting that replicated a lab-based horizontal well completion with multi-cluster sand jetting perforation.The effects of temporary plugging agent(TPA)particle size,TPA concentration,single-cluster perforation number and cluster number on plugging pressure,multi-fracture diversion pattern and distribution of TPAs were investigated.A combination of TPAs with small particle sizes within the fracture and large particle sizes within the segment is conducive to increasing the plugging pressure and promoting the diversion of multi-fractures.The addition of fibers can quickly achieve ultra-high pressure,but it may lead to longitudinal fractures extending along the wellbore.The temporary plugging peak pressure increases with an increase in the concentration of the TPA,reaching a peak at a certain concentration,and further increases do not significantly improve the temporary plugging peak pressure.The breaking pressure and temporary plugging peak pressure show a decreasing trend with an increase in single-cluster perforation number.A lower number of single-cluster perforations is beneficial for increasing the breaking pressure and temporary plugging peak pressure,and it has a more significant control on the propagation of multi-cluster fractures.A lower number of clusters is not conducive to increasing the total number and complexity of artificial fractures,while a higher number of clusters makes it difficult to achieve effective plugging.The TPAs within the fracture is mainly concentrated in the complex fracture areas,especially at the intersections of fractures.Meanwhile,the TPAs within the segment are primarily distributed near the perforation cluster apertures which initiated complex fractures.
基金supported by the National Natural Science Foundation of China (No. 52074250)。
文摘Multistage fracturing of horizontal wells is a critical technology for unconventional oil and gas reservoir stimulation. Ball-throwing temporary plugging fracturing is a new method for realizing uniform fracturing along horizontal wells and plays an important role in increasing oil and gas production. However,the transportation and sealing law of temporary plugging balls(TPBs) in the perforation section of horizontal wells is still unclear. Using COMSOL computational fluid dynamics and a particle tracking module, we simulate the transportation process of TPBs in a horizontal wellbore and analyse the effects of the ball density, ball diameter, ball number, fracturing fluid injection rate, and viscosity on the plugging efficiency of TPB transportation. This study reveals that when the density of TPBs is close to that of the fracturing fluid and a moderate diameter of the TPB is used, the plugging efficiency can be substantially enhanced. The plugging efficiency is greater when the TPB number is close to twice the number of perforations and is lower when the number of TPBs is three times the number of perforations.Adjusting the fracturing fluid injection rate from low to high can control the position of the TPBs,improving plugging efficiency. As the viscosity of the fracturing fluid increases, the plugging efficiency of the perforations decreases near the borehole heel and increases near the borehole toe. In contrast, the plugging efficiency of the central perforation is almost unaffected by the fracturing fluid viscosity. This study can serve as a valuable reference for establishing the parameters for temporary plugging and fracturing.
基金Supported by National Natural Science Foundation of China (U21A20105)Science and Technology Innovation Fund of PetroChina (2020D-5007-0208)。
文摘Using the visualized experimental device of temporary plugging in hydraulic fractures, the plugging behaviors of temporary plugging particles with different sizes and concentrations in hydraulic fractures were experimentally analyzed under the conditions of different carrier fluid displacements and viscosities. The results show that the greater the carrier fluid viscosity and displacement, the more difficult it is to form a plugging layer, and that the larger the size and concentration of the temporary plugging particle, the less difficult it is to form a plugging layer. When the ratio of particle size to fracture width is 0.45, the formation of the plugging layer is mainly controlled by the mass concentration of the temporary plugging particle and the viscosity of the carrier fluid, and a stable plugging layer cannot form if the mass concentration of the temporary plugging particle is less than 20 kg/m^(3)or the viscosity of the carrier fluid is greater than 3 mPa·s. When the ratio of particle size to fracture width is 0.60, the formation of the plugging layer is mainly controlled by the mass concentration of the temporary plugging particle, and a stable plugging layer cannot form if the mass concentration of the temporary plugging particle is less than 10 kg/m^(3). When the ratio of particle size to fracture width is 0.75, the formation of the plugging layer is basically not affected by other parameters, and a stable plugging layer can form within the experimental conditions. The formation process of plugging layer includes two stages and four modes. The main controlling factors affecting the formation mode are the ratio of particle size to fracture width, carrier fluid displacement and carrier fluid viscosity.
基金This work was supported by the Research Foundation of China University of Petroleum-Beijing at Karamay(No.XQZX20200010)the Natural Science Foundation of Xinjiang Uygur Autonomous Region(No.2019D01B57)+3 种基金the University Scientific Research Project of Xinjiang Uygur Autonomous Region(No.XJEDU2019Y067)the Xinjiang Uygur Autonomous Region Innovation Environment Construction Project(No.2019Q025)the Sichuan Province Regional Innovation Cooperation Project(No.2020YFQ0036)the CNPC Strategic Cooperation Science and Technology Project(ZLZX2020-01-04-04)。
文摘Temporary plugging agent(TPA)is widely used in many fields of petroleum reservoir drilling and production,such as temporary plugging while drilling and petroleum well stimulation by diverting in acidizing or fracturing operations.The commonly used TPA mainly includes hard particles,fibers,gels,and composite systems.However,current particles have many limitations in applications,such as insufficient plugging strength and slow degradation rate.In this paper,a degradable pre-formed particle gel(DPPG)was developed.Experimental results show that the DPPG has an excellent static swelling effect and self-degradation performance.With a decrease in the concentration of total monomers or cross-linker,the swelling volume of the synthesized DPPG gradually increases.However,the entire self-degradation time gradually decreases.The increase in 2-acrylamide-2-methylpropanesulfonic acid(AMPS)in the DPPG composition can significantly increase its swelling ratio and shorten the self-degradation time.Moreover,DPPG has excellent high-temperature resistance(150°C)and high-salinity resistance(200,000 mg/L NaCl).Core displacement results show that the DPPG has a perfect plugging effect in the porous media(the plugging pressure gradient was as high as 21.12 MPa),and the damage to the formation after degradation is incredibly minor.Therefore,the DPPG can be used as an up-and-coming TPA in oil fields.
基金Supported by the National Natural Science Foundation of China(52192622,52204005,U20A20265)Sichuan Outstanding Young Scientific and Technological Talents Project(2022JDJQ0007).
文摘In this paper,a viscoelasticity-plastic damage constitutive equation for naturally fractured shale is deduced,coupling nonlinear tensile-shear mixed fracture mode.Dynamic perforation-erosion on fluid re-distribution among multi-clusters are considered as well.DFN-FEM(discrete fracture network combined with finite element method)was developed to simulate the multi-cluster complex fractures propagation within temporary plugging fracturing(TPF).Numerical results are matched with field injection and micro-seismic monitoring data.Based on geomechanical characteristics of Weiyuan deep shale gas reservoir in Sichuan Basin,SW China,a multi-cluster complex fractures propagation model is built for TPF.To study complex fractures propagation and the permeability-enhanced region evolution,intersecting and competition mechanisms between the fractures before and after TPF treatment are revealed.Simulation results show that:fracture from middle cluster is restricted by the fractures from side-clusters,and side-clusters plugging is benefit for multi fractures propagation in uniformity;optimized TPF timing should be delayed within a higher density or strike of natural fractures;Within a reservoir-featured natural fractures distribution,optimized TPF timing for most clustered method is 2/3 of total fluid injection time as the optimal plugging time under different clustering modes.
基金supported by the Research Foundation of China University of Petroleum-Beijing at Karamay (No. YJ2018B02002 and XQZX20200010)the Natural Science Foundation of Xinjiang Uygur Autonomous Region (No. 2021D01E23 and 2019D01B57)+3 种基金the University Scientific Research Project of Xinjiang Uygur Autonomous Region (No. XJEDU2019Y067)the Xinjiang Uygur Autonomous Region Innovation Environment Construction Project (No. 2019Q025)the Sichuan Province Regional Innovation Cooperation Project (No. 2020YFQ0036)the CNPC Strategic Cooperation Science and Technology Project (ZLZX2020-01-04-04)
文摘The development of unconventional petroleum resources has gradually become an important succession for increasing oil production.However,the related engineers and researchers are paying more and more attention to the application of temporary plugging agents(TPAs)for their efficient development.TPAs can expand the stimulated reservoir volume(SRV)and facilitate the flow of oil and gas to the bottom of the well.Particle-gels used as temporary plugging agents have the characteristics of the simple injection process,good deformation,high plugging strength,and complete self-degradation performance,which have been widely applied in recent years.In this paper,five samples of DPPG polymerized by different molecular weights of cross-linking agents were prepared.In addition,infrared spectroscopy analysis,differential calorimetry scanning(DSC)analysis,static particle gel swelling and degradation performance evaluation experiments,and dynamic temporary plugging performance experiments in cores were conducted at 34°C.Results show that as the molecular weight of the cross-linking agent(at 0.01 g)in the DPPG molecule decreased from 1,000 to 200 Da,the fewer cross-linking sites of DPPG,the looser the microscopic three-dimensional mesh structure formed.The swelling ratio increased from 7 to 33 times.However,the complete degradation time increased from 40 to 210 min.Moreover,the DSC results confirmed that the higher the molecular weight of the cross-linking agent,the worse is chemical stability and the more prone it to self-degradation.DPPG samples had good temporary plugging performance in reservoir cores.DPPGs prepared by the cross-linking agent with smaller molecular weight has a stronger swelling ratio,higher gel strength,and greater plugging strength in the core permeabilities.Moreover,the degraded DPPG is less damaging to the cores.However,their slower degradation rates take a slightly longer times to reach complete degradation.The results of this paper can provide new ideas and a theoretical basis for the development of particle gel-type temporary plugging agents(TPA)with controllable degradation time in low-temperature reservoirs.It can help to expand the application range of existing DPPG reservoir conditions.
基金Major Project of National Natural Science Foundation of China Basic Theory of Efficient Development of Shale Oil and Gas(No.51490653)Theory and Method of Efficient Con struction of Fracture Network in Deep and Ultra-Deep Shale Gas Horizontal Wells(No.U19A2043)National Natural Science Foundation of China Theory and Method of Long term Propping for Deep Shale Gas Hydraulic Fractures based on DEM-LBM Hydro-Mechanical Coupling(No.52104039).
文摘When deep and ultra-deep shale gas well fracturing is carried out,multi-cluster fracturing can hardly realize synchronous initiation and propagation of hydraulic fractures due to the combined effects of heterogeneity of deep in-situ stress and"dense cluster"fracture arrangement,and the strong interference between fractures aggravates the unbalanced fracture propagation degree.Field practice proves that the fracture-opening temporary plugging fracturing technology can effectively control the unbalanced propagation of multiple fractures.In addition,the application effect of temporary plugging process can be improved by developing a method for simulating fracture control during fracture-opening temporary plugging fracturing of deep/ultra-deep shale-gas horizontal wells.Based on rock mechanics,elasticity mechanics,fluid mechanics and fracture propagation theory,combined with the flow distribution equation of horizontal-well multi-cluster fracturing and the plugging equation of temporary plugging balls,this paper establishes a fracture propagation model and a fracture control simulation method for the fracture-opening temporary plugging fracturing of deep/ultra-deep shale gas horizontal wells.Then,the influences of the number of temporary plugging balls and the times and timing of temporary plugging on temporary plugging control are simulated,and the influences of temporary plugging balls on fracture propagation morphology and SRV(stimulated reservoir volume)distribution are analyzed by taking Sinopec's one deep shale gas well in Dingshan-Dongxi structure of southeast Sichuan Basin as an example.And the following research results are obtained.First,fracture-opening temporary plugging can significantly promote the balanced propagation of multiple fractures,and the simulation confirms that the number of temporary plugging balls and the times and timing of temporary plugging play an important role in fracture control.Second,as the number of temporary plugging balls increase,the SRV increases firstly and then decreases,so there is an optimal number of temporary plugging balls.Third,increasing the times of temporary plugging can improve the fault tolerance rate of temporary plugging and diverting process,but it is necessary to increase the number of temporary plugging balls appropriately.Fourth,when the timing of temporary plugging is appropriate,the balanced propagation of multiple fractures is achieved and the maximum SRV is reached.In conclusion,this method is of great significance to optimizing the design of temporary plugging fracturing,improve the implementation level of field process and develop deep and ultra-deep shale gas efficiently.
基金supported by the National Major Science and Technology Project“Experimental study on shale gas production in Zhaotong County,Yunnan Province”(No.:2012ZX0518-006)Major Project of CNPC“Field test of shale gas drilling and production engineering technology in Zhaotong demonstration zone”(No.:2012F-47-02).
文摘Due to downhole complexities,shale-gas horizontal well fracturing in the Sichuan Basin suffered from casing deformation and failure to apply the technique of cable-conveyed perforation bridge plug.In view of these problems,a new technique of staged volume fracturing with temporary plugging by sand filling is employed.Based on theoretical analyses and field tests,a design of optimized parameters of coiled tubingconveyed multi-cluster sand-blasting perforation and temporary plugging by sand filling was proposed.It was applied in the horizontalWell ZJ-1 in which casing deformation occurred.The following results are achieved in field operations.First,this technique enables selective staged fracturing in horizontal sections.Second,this technique can realize massive staged fracturing credibly without mechanical plugging,with the operating efficiency equivalent to the conventional bridge plug staged fracturing.Third,full-hole is preserved after fracturing,thus it is possible to directly conduct an open flow test without time consumption of a wiper trip.The staged volume fracturing with temporary plugging by sand filling facilitated the 14-stage fracturing in Well ZJ-1,with similar SRV to that achieved by conventional bridge plug staged fracturing and higher gas yield than neighboring wells on the same well pad.Thus,a new and effective technique is presented in multi-cluster staged volume fracturing of shale gas horizontal wells.
文摘At present, the oil and water wells in Liaohe Oilfield have entered the middle and later stages of development. The pressure of the oil and water wells has decreased year by year and the contradiction between injection and production has become increasingly prominent. In order to maximize its recovery, various new processes and technologies have been widely applied in different oilfields. The loss of workover fluid during workover operation not only increases the dosage of workover fluid, but also causes more serious pollution to the oil layer (formation). Affect oil production after workover operation.
基金supported by the National Natural Science Foundation of China(Nos.52404052,51804268)the Open Project Program of the State Energy Center for Shale Oil Research and Development(No.33550000-22-ZC0613-0376).
文摘This study explores the transport dynamics of temporary plugging balls in multi-cluster horizontal wellbores through a three-dimensional Computational Fluid Dynamics(CFD)model based on field dimensions.An experimental setup mimicking the transport of these balls was utilized to validate the model,revealing a maximum discrepancy of less than 22.2% in ball allocation proportions under identical conditions.This validation substantiates the model's precision in predicting transport dynamics across various operational scenarios.Key parameters,including pump rate,fluid viscosity,perforation discharge capacity,ball diameter,ball density,and the number of balls,were examined using the validated model.Findings indicate that pump rate,ball density,and perforation discharge capacity markedly influence ball distribution,followed by fluid viscosity.The number of balls has a lesser effect.Elevated pump rates augment inertial forces,prompting balls to migrate towards the toe-side of the wellbore.Moderate fluid viscosities enhance distribution uniformity,whereas extreme viscosities do not.Perforation clusters with higher discharge capacities attract more balls,thereby improving plugging efficiency.Lower ball density and smaller diameter yield more uniform distribution,while higher values lead to ball accumulation at the toe-end.This study offers valuable insights for optimizing parameters in temporary plugging fracturing technology,thereby improving the efficiency and effectiveness of hydraulic fracturing treatments.
基金supported by the National Natural Science Foundation of China Joint Fund for Enterprise Innovation and Development,Enrichment Mechanism and Stereoscopic Development of Shale Oil in Continental Rift Basins(No.U24B6002).
文摘Temporary plugging and diversion fracturing(TPDF)is widely used to promote the uniform and complex distribution of multi-clustered hydraulic fractures(HFs)in a horizontal well of the unconventional formations.However,the migration behavior of temporary plugging agent(TPA),as a function of the concentration and particle size of TPA and cluster-perforation numbers,etc.,determining the effectiveness of this technique,remains unclear.Therefore,this study conducted innovatively a series of TPDF simulation experiments on transparent polymethyl methacrylate(PMMA)specimens(cubic block of 30 cm×30 cm×30 cm)to explore visually the migration behavior of TPA in multi-clustered HFs in a horizontal well.A laboratory hydraulic sandblasting perforation completion technique was implemented to simulate the multi-cluster perforations.All the distributions of wellbore,perforations,HFs,and TPA can be seen clearly inside the PMMA specimen post the experiment.The results show that there are four characteristic plugging positions for the TPA:mouth of HF,middle of HF,tip of HF,and the intersection of HFs.Small particle size TPA tends to migrate to the fracture tip for plugging,while large particle size TPA tends to plug at the fracture mouth.The migration of the TPA is influenced obviously by the morphology of the fracture wall.A smooth fracture wall is conducive to the migration of the TPA to the far end of HFs,but not conducive to generating the plugging zone and HF diversion.In contrast,a"leaf vein"fracture of rough wall is conducive to generating the plugging layer and the diversion of HFs,but not conducive to the migration of the TPA to the far end of HFs.The migration ability of TPA in a"shell"pattern is intermediate between the two above cases.Increasing TPA concentration can encourage TPA to migrate more quickly to the characteristic plugging position,and thereby to promote the creation of effective plugging and subsequently the multi-stage diversion of the HFs.Nevertheless,excessive concentration may cause the TPA to settle prematurely,affecting the propagation of the HFs to the far end.Increasing the number of clusters to a certain extent can encourage TPA to migrate into the HFs and form plugging,and promote the diversion.An evaluation system for the migration ability of granular TPA has been established,and it was calculated that when there is no plugging expectation target,the comprehensive migration ability of small particle size TPA is stronger than that of large particle size TPA.This research provides theoretical foundation for the optimization of temporary plugging parameters.
基金funded by the National Natural Science Foundation of China(52104046).
文摘Multi-stage and multi-cluster fracturing(MMF)is a crucial technology in unconventional oil and gas development,aiming to enhance production by creating extensive fracture networks.However,achieving uniform expansion of multi-cluster hydraulic fractures(HFs)in MMF remains a significant challenge.Field practice has shown that the use of temporary plugging and diversion fracturing(TPDF)can promote the balanced expansion of multi-cluster HFs.This study conducted TPDF experiments using a true triaxial fracturing simulation system setting a horizontal well completion with multi-cluster jetting perforations to investigate the equilibrium initiation and extension of multi-cluster fractures.The influence of key parameters,including cluster spacing,fracturing fluid viscosity,differential stress,and fracturing fluid injection rate,on fracture initiation and propagation was systematically examined.The results indicate that while close-spaced multi-cluster fracturing significantly increases the number of HFs,it also leads to uneven extension of HFs in their propagation.In contrast,TPDF demonstrates effectiveness in mitigating uneven HF extension,increasing the number of HFs,and creating a larger stimulated reservoir volume,ultimately leading to improved oil and gas well productivity.Moreover,under conditions of high differential stress,the differential stress within the formation exerts a stronger guiding effect in HFs,which are more closely aligned with the minimum principal stress.Low-viscosity fluids facilitate rapid and extensive fracture propagation within the rock formation.High-volume fluid injection,on the other hand,more comprehensively fills the formation.Therefore,employing lowviscosity and high-volume fracturing is advantageous for the initiation and extension of multi-cluster HFs.
基金the project of the State Key Laboratory of Petroleum Resources and Engineering(No.PRE/open-2307)the CNOOC Research Institute(No.2020PFS-03).
文摘Hydraulic fracturing,an effective method for enhancing coal seam productivity,largely determines coalbed methane(CBM)production,which is significantly influenced by geological and engineering factors.This study focuses on the L block to investigate the mechanisms influencing efficient fracture propagation and enhanced stimulated reservoir volume(SRV)in fracturing.To explore the mechanisms influencing effective fracture propagation and enhanced SRV,the L block was selected as the research object,with a comprehensive consideration of geological background,reservoir properties,and dynamic production data.By combining the discrete lattice method with numer-ical analysis and true triaxial experimental simulation,the fracture morphology of a single cluster and the propagation patterns of multiple clusters of complex fractures were obtained.Additionally,the optimization of temporary plugging timing and the fracture map under multiple factors were innovatively proposed.Results indicate that greater flow rate and viscosity can effectively overcome the stress shadow effect of the outermost fractures(1st and 6th clusters),increasing the fracture pressure of the single cluster and the equilibrium degree of multiple fracture propagation,thus forming a more complex fracture network.Moreover,when viscosity exceeds 45 pressure concentrates at fracture mPa⋅s,tips,promoting discontinuous propagation and reducing flow resistance.Conversely,increased gangue thickness and spacing between horizontal wells increase the vertical propagation pressure,suppressing fracture growth and reducing central flow velocity.This study provides a multi-cluster fracture propagation map for optimizing volumetric fracturing in coal seams and suggests that the optimal temporary plugging time significantly enhances the SRV.
基金funded by the National Natural Science Foundation of China(41772286,42077247)the Fundamental Research Funds for the Central UniversitiesOpen Research Fund of State Key Laboratory of Geomechanics and Geotechnical Engineering,Institute of Rock and Soil Mechanics,Chinese Academy of Sciences(Z020009)。
文摘Refracturing is an importa nt technique to tap the potential of reservoirs and boost production in depleted oil and gas fields.However,fracture propagation during refracturing,including both conventional refracturing and temporary-plugging refracturing remains poorly understood,especially for cases with non-uniform distribution of formation pressure due to long-term oil production and water injection.Therefore,taking pilot tests of refracturing with sidetracking horizontal wells in tight reservoirs in the Changqing Oilfield,China as an example,we establish a three-dimensional numerical model of conventional refracturing and a numerical model of temporary-plugging refracturing based on the discrete lattice method.Non-uniform distributions of formation pressure are imported in these models.We discuss the effects of key operating parameters such as injection rate,cluster spacing,and number of clusters on the propagation of multi-cluster fractures for conventional refracturing.For temporaryplugging refracturing,we examine the impacts of controlling factors such as the timing and number of temporary plugging on fracture propagation.In addition,we analyze a field case of temporaryplugging refracturing using well P3 in the Changqing Oilfield.The results show that fractures during re fracturing tend to propagate preferentially and dominantly in the depleted areas.Improved stimulation effect can be obtained with an optimal injection rate and a critical cluster spacing.The proposed model of temporary-plugging refracturing can well describe the temporary plugging of dominant existingfractures and the creation of new-fractures after fracturing fluid is forced to divert into other clusters from previous dominant clusters.Multiple temporary plugging can improve the balanced propagation of multi-cluster fractures and obtain the maximum fracture area.The established numerical model and research results provide theoretical guidance for the design and optimization of key operating parameters for refracturing,especially for temporary-plugging refracturing.
基金supported by the National Natural Science Foundation of China(Grant No.51974332)。
文摘Temporary plugging and diverting fracturing(TPDF),involving inner-fracture temporary plugging(IFTP)and inner-stage temporary plugging(ISTP),has been proposed as a widely applied technique in China,for promoting the uniform initiation and propagation of multi-clustered hydraulic fractures(HFs)in a horizontal well of the shale oil/gas reservoirs.However,how the key plugging parameters controlling the multi-fracture growth and the pumping pressure response during TPDF in shale with dense bedding planes(BPs)and natural fractures(NFs)is still unclear,which limits the optimization of TPDF scheme.In this paper,a series of TPDF simulation experiments within a stage of multi-cluster in a horizontal well were carried out on outcrops of Longmaxi Formation shale using a large-scale true tri-axial fracturing simulation system,combined with the acoustic emission(AE)monitor and computed tomography(CT)scanning techniques.Each experiment was divided into three stages,including the conventional fracturing(CF),IFTP and ISTP.Multi-fracture initiation and propagation behavior,and the dominant controlling parameters were examined,containing the particle sizes,concentration of temporary plugging agent(TPA),and cluster number.The results showed that the number of transverse HFs(THFs)and the overall complexity of fracture morphology increase with the increase in TPA concentration and perforation cluster number.Obviously,the required concentration of TPA is positively correlated with the cluster number.Higher peak values and continuous fluctuations of pumping pressure during TPDF may indicate the creation of diversion fractures.The creation of standard THFs during CF is favorable to the creation of diversion fractures during TPDF.Moreover,the activation of BPs nearby the wellbore during CF is unfavorable to the subsequent pressure buildup during TPDF,resulting in poor plugging and diverting effect.Notably,under the strike-slip fault stress regime,the diversion of THFs is not likely during IFTP,which is similar as the results of ISTP to initiate mainly the un-initiated or under-propagated perforation clusters.Three typical pressure curve types during TPDF can be summarized to briefly identify the hydraulic fracture diversion effects,including good(multiple branches or/and THFs can be newly created),fair(HF initiation along the slightly opened BPs and then activating the NFs),and bad(HF initiation along the largely opened BPs and then connecting with the NFs).
文摘Casing deformation and frac-hit pose significant challenges to the development of deep shale gas in southern Sichuan Basin.By analyzing the mechanism and main control factors of casing deformation and frac-hit,two kinds of risk assessment methods were defined,and the overall prevention and control concept and practice were formulated.The results show that initial stress,pore pressure,fault development and large scale fracturing in local block are the main factors leading to the deformation.The development of fracture through well group and uncontrolled fracturing fluid volume are the main factors leading to pressure channeling.Based on this,the risk classification technology of casing deformation and frac-hit is established,and the dual-optimal,dual-control concept and technology are formed.In terms of the prevention and control of casing deformation,the formation of small-diameter bridge plug fracturing,large section combined fracturing,glass beads cementing,singlewell staggered and platform straddle fracturing mode,dual-dimension controlled and lift fracturing,hyperbolic diagnosis,etc.Frac-hit prevention and control formed pump sequence optimization mode,physical and chemical temporary plugging and other methods.The above technology achieved casing deformation rate decreased from 50.4%to 25.4%,frac-hit rate decreased from 58.6%to 33.9%,and the average well kilometer EUR reached 0.52e0.7 million square meters,an increase of 7.7%compared with the previous research,with remarkable results.
基金the National Natural Science Foundation of China fund (Project number: 52174045 and No. 52104011)Research Foundation of China University of Petroleum-Beijing at Karamay (No. XQZX20210001)PetroChina Innovation Foundation (2020D50070207)。
文摘Due to the reservoir heterogeneity and the stress shadow effect, multiple hydraulic fractures within one fracturing segment cannot be initiated simultaneously and propagate evenly, which will cause a low effectiveness of reservoir stimulation. Temporary plugging and diverting fracturing(TPDF) is considered to be a potential uniform-stimulation method for creating multiple fractures simultaneously in the oilfield. However, the multi-fracture propagation morphology during TPDF is not clear now. The purpose of this study is to quantitatively investigate the multi-fracture propagation morphology during TPDF through true tri-axial fracturing experiments and CT scanning. Critical parameters such as fracture spacing, number of perforation clusters, the viscosity of fracturing fluid, and the in-situ stress have been investigated. The fracture geometry before and after diversion have been quantitively analyzed based on the two-dimensional CT slices and three-dimensional reconstruction method. The main conclusions are as follows:(1) When injecting the high viscosity fluid or perforating at the location with low in-situ stress, multiple hydraulic fractures would simultaneously propagate. Otherwise, only one hydraulic fracture was created during the initial fracturing stage(IFS) for most tests.(2) The perforation cluster effectiveness(PCE) has increased from 26.62% during the IFS to 88.86% after using diverters.(3) The diverted fracture volume has no apparent correlation with the pressure peak and peak frequency during the diversion fracturing stage(DFS) but is positively correlated with water-work.(4) Four types of plugging behavior in shale could be controlled by adjusting the diverter recipe and diverter injection time, and the plugging behavior includes plugging the natural fracture in the wellbore, plugging the previous hydraulic fractures, plugging the fracture tip and plugging the bedding.
基金supported by Shanxi Provincial Key Research and Development Project(No.20201102002)the Science Foundation of China University of Petroleum,Beijing(No.2462020BJRC007,2462020YXZZ003)State Key Laboratory of Petroleum Resources and Prospecting,China University of Petroleum(No.PRP/DX-2216)
文摘Excess water production has become an important issue in the oil and gas extraction process.Preformed particle gels(PPGs),show the capability to control the conformance and reduce excess water cut.However,conventional PPGs have poor mechanical properties and their swollen particles are easily damaged by shearing force when passing through the fractures in formations,meanwhile PPGs can be also degraded into various byproducts,leading to permanent damage to the reservoir permeability after temporary plugging.Herein,a novel type of dual cross-linked PPGs(dPPGs)was designed and synthesized using sodium alginate(SA)and acrylamide(AAm),cross-linked with N,N’-methylenebisacrylamide(MBA)and Fe^(3+).Results show that dPPGs have excellent mechanical properties with a storage modulus up to 86,445 Pa,which is almost 20 times higher than other reported PPGs.Meanwhile,dPPGs can be completely degraded into liquid without any solid residues or byproducts and the viscosity of dPPGs degraded liquid was found to be lower than 5 mPa·s.A laboratory coreflooding test showed that the plugging efficiency of dPPGs was up to 99.83%on open fractures.The obtained results demonstrated that dPPGs could be used as economical and environment-friendly temporary plugging agent with high-strength,self-degradation,thermal stability,and salt stability,thus making it applicable to a wide range of conformance control to enhance oil recovery.
基金National Science and Technology Major Project(2016ZX05023)PetroChina Science and Technology Major Project(2018E-1809)。
文摘Based on analysis of the reasons for low efficiency and low production after fracturing of some wells in the ultra-deep fractured tight reservoirs of the Kuqa piedmont zone, Tarim Basin and the matching relationship between the in-situ stress field and natural fractures, technological methods for creating complex fracture networks are proposed. Through theoretical study and large-scale physical simulation experiments, the mechanical conditions for forming complex fracture network in the Kuqa piedmont ultra-deep reservoirs are determined. The effectiveness of temporary plugging and diversion, and multi-stage fracturing to activate natural fractures and consequently realize multi-stage diversion is verified. The coupling effect of hydraulic fractures and natural fractures activating each other and resulting in "fracture swarms" is observed. These insights provide theoretical support for improving fracture-controlled stimulated reservoir volume(FSRV) in ultra-deep tight reservoirs. In addition, following the concept of volume fracturing technology and based on the results of fracture conductivity experiments of different processes, fracturing technologies such as multi-stage fracture-network acid fracturing, "multi-stage temporary plugging + secondary fracturing", fracturing of multiple small layers by vertically softness-and-hardness-oriented subdivision, and weighted-fluid refracturing are proposed to increase the FSRV. New environment-friendly weighted-fluid with low cost and new fracturing fluid system with low viscosity and high proppant-carrying capacity are also developed. These techniques have achieved remarkable results in field application.
基金Supported by the PetroChina–China University of Petroleum (Beijing) Strategic Cooperation Project (ZLZX2020-04)。
文摘To solve the problem that the production of Mahu conglomerate reservoir is not up to expectation after the multi-cluster plus temporary plugging fracturing technology is applied in horizontal wells, stages 2–6 in the test well MaHW6285 are selected to carry out erosion tests with different pumping parameters. The downhole video imaging technology is used to monitor the degree of perforations erosion, and then the fracture initiation and proppant distribution of each cluster are analyzed. The results showed that proppant entered 76.7% of the perforations. The proppant was mainly distributed in a few perforation clusters, and the amount of proppant entered in most of the clusters was limited. The proppant distribution in Stage 4 was relatively uniform, and the fracture initiation of each cluster in the stage is more uniform. The proppant distribution in stages 2, 3, 5, and 6 was significantly uneven, and the uniform degree of fracture initiation in each cluster is low. More than 70% of the proppant dose in the stage entered clusters near the heel end, so the addition of diverters did not promote the uniform initiation of hydraulic fractures. There was a positive correlation between the amount of proppant added and the degree of perforations erosion, and the degree of perforations erosion ranged from 15% to 352%, with an average value of 74.5%, which was far higher than the statistical results of shale reservoir tests in North America. The use of 180° phase perforation(horizontal direction) can reduce the “Phase Bias” of perforations erosion, promote uniform perforations erosion and fluid inflow. The research results provide the basis for optimizing the pumping procedure, reducing the perforation erosion and improving the success rate of diversion.
