Milling bridge plugs in shale gas wells with severe casing deformation often leads to the accumulation of cuttings,increasing the risk of stuck drill bits.Friction in the wellbore further complicates tool deployment i...Milling bridge plugs in shale gas wells with severe casing deformation often leads to the accumulation of cuttings,increasing the risk of stuck drill bits.Friction in the wellbore further complicates tool deployment into the horizontal section,posing challenges to efficient plug drilling and achieving wellbore access to the target layer.This paper integrates the theory of positive displacement motors and models their actual working characteristics to study the milling of bridge plugs in severely deformed horizontal wells.It examines the effects of coiled tubing diameter and wall thickness on the bending load of horizontal sections and discusses key technical requirements,including the timing of plug drilling,extending the run in the horizontal section,parameter control,and real-time field analysis.Field practices have shown that after casing deformation occurs,priority should be given to drilling out the bridge plugs below the point of deformation.The primary factors contributing to stuck drills in deformed wells include smaller mill shoe sizes and larger cuttings sizes.Short well-washing cycles and targeted cuttings removal can effectively reduce sticking risks.If sticking occurs,high-tonnage pulling should be avoided.Instead,releasing the stick through up-anddown string motion,combined with high-volume nozzle spraying and annulus pumping,is recommended.The selection of coiled tubing should consider diameter,wall thickness,and steel grade to handle complex situations.Larger diameters,thicker walls,and low-frequency,multi-head hydraulic oscillators are more effective for unlocking horizontal sections.This approach can reduce the risk of drill sticking and solve the problem of horizontal section lock-ups,offering a reliable solution for smooth drilling and efficient production in wells with severe casing deformation.展开更多
The casing deformation prevention technology based on the optimization of cement slurry is proposed to reduce the casing deformation of shale oil and gas wells during hydraulic fracturing. In this paper, the fracture ...The casing deformation prevention technology based on the optimization of cement slurry is proposed to reduce the casing deformation of shale oil and gas wells during hydraulic fracturing. In this paper, the fracture mechanism of hollow particles in cement sheath was firstly analyzed by discrete element method, and the effect of hollow particles in cement on casing deformation was investigated by laboratory experiment method. Finally, field test was carried out to verify the improvement effect of the casing deformation based on cement slurry modification. The results show that the formation displacement can be absorbed effectively by hollow particles inside the cement transferring the excessive deformation away from casing. The particles in the uncemented state provide deformation space during formation slipping. The casing with diameter of 139.7 mm could be passed through by bridge plug with the diameter of 99 mm when the mass ratio of particle/cement reaches 1:4. According to the field test feedback, the method based on optimization of cement slurry can effectively reduce the risk of casing deformation, and the recommended range of hollow microbeads content in the cement slurry is between 15% and 25%.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
To study the casing deformation(CD)in shale gas well fracturing caused by natural fracture slip,a fracture face stress model is built based on stress analysis,and a CD prediction model is established based on complex ...To study the casing deformation(CD)in shale gas well fracturing caused by natural fracture slip,a fracture face stress model is built based on stress analysis,and a CD prediction model is established based on complex function to analyze factors affecting wellbore shear stress and CD.(1)The fracture and wellbore approach angles have significant impacts on the wellbore shear stress.In Weiyuan shale gas field,Sichuan Basin,under the common wellbore approach angle of nearly 90°,the wellbore is subjected to large shear stress and high risk of CD at the fracture approach angle range of 20° to 55° or its supplementary angle range.(2)When the fracture is partially opened,the wellbore shear stress is positively correlated with the fluid pressure,and negatively correlated with the fracture friction coefficient;when the fracture is fully opened,the wellbore shear stress is positively correlated with the natural fracture area.(3)The lower the elastic modulus and the longer the fracture length,the more serious the CD will be,and the Poisson’s ratio has a weak influence on the CD.The deformation first increases and then decreases with the increase of fracture approach angle,and reaches the maximum when the fracture approach angle is 45°.(4)At a given fracture approach angle,appropriately adjusting the wellbore approach angle can avoid high shear stress acting on wellbore,and reasonable control of the fluid pressure in the fracture can reduce the CD risk.The shear stress acting on casing is usually much greater than the shear strength of casing,so increasing casing strength or cementing quality have limited effect on reducing the risk of CD.Caliper logging data has verified that the CD prediction model is reliable,so the model can be used to establish risk analysis chart and calculate deformation value,to provide a reference for quick CD risk prediction in fracturing design.展开更多
Based on structural distribution and fault characteristics of the Luzhou block,southern Sichuan Basin,as well as microseismic,well logging and in-situ stress data,the casing deformation behaviors of deep shale gas wel...Based on structural distribution and fault characteristics of the Luzhou block,southern Sichuan Basin,as well as microseismic,well logging and in-situ stress data,the casing deformation behaviors of deep shale gas wells are summarized,and the casing deformation mechanism and influencing factors are identified.Then,the risk assessment chart of casing deformation is plotted,and the measures for preventing and controlling casing deformation are proposed.Fracturing-activated fault slip is a main factor causing the casing deformation in deep shale gas wells in the Luzhou block.In the working area,the approximate fracture angle is primarily 10°-50°,accounting for 65.34%,and the critical pore pressure increment for fault-activation is 6.05-9.71 MPa.The casing deformation caused by geological factors can be prevented/controlled by avoiding the faults at risk and deploying wells in areas with low value of stress factor.The casing deformation caused by engineering factors can be prevented/controlled by:(1)keeping wells avoid faults with risks of activation and slippage,or deploying wells in areas far from the faulting center if such avoidance is impossible;(2)optimizing the wellbore parameters,for example,adjusting the wellbore orientation to reduce the shear force on casing to a certain extent and thus mitigate the casing deformation;(3)optimizing the casing program to ensure that the curvature radius of the curved section of horizontal well is greater than 200 m while the drilling rate of high-quality reservoirs is not impaired;(4)optimizing the fracturing parameters,for example,increasing the evasive distance,lowering the single-operation pressure,and increasing the stage length,which can help effectively reduce the risk of casing deformation.展开更多
Formation subsidence is inevitable during marine hydrate decomposition,and the consequent casing deformation seriously threatens the security of sustainable hydrate production.Owing to insufficient observed data of fo...Formation subsidence is inevitable during marine hydrate decomposition,and the consequent casing deformation seriously threatens the security of sustainable hydrate production.Owing to insufficient observed data of formation subsidence in field,displacement boundary condition of casing is undetermined.Thus the conventional static methods are inapplicable for the calculation of casing deformation in hydrate production well.The present work aims at proposing an approach to investigate dynamic deformation of the casing during hydrate production.In the proposed methodology,based on the movement theory of hydrate decomposition front,hydrate decomposition process can be simulated,in which hydrate reservoir strength formation subsidence showed time-dependent characteristics.By considering the actual interactions among casing,cement and formation,three models of hydrate production well are developed to reveal the static and dynamic deformation mechanisms of the casing.The application of the proposed methodology is demonstrated through a case study.Results show that buckling deformation and bending deformation of casing reduce the passing ability of downhole tools in deformed casing by 4.2%and 7.5%,respectively.With the progress of hydrate production,buckling deformation will increase obviously,while a little increase of bending deformation will occur,as the formation slippage induced by formation inclination is much larger than that caused by hydrate decomposition.The proposed approach can provide theoretical reference for improving casing integrity of marine hydrate production.展开更多
In the course of completion of an ultra-deep well newly drilled in the Yuanba Gasfield,Sichuan Basin,long-section and large-scale deformation occurred in the heavy casing section and nickel base alloy casing section o...In the course of completion of an ultra-deep well newly drilled in the Yuanba Gasfield,Sichuan Basin,long-section and large-scale deformation occurred in the heavy casing section and nickel base alloy casing section of the sealing Triassic limestone interval,so a new hole had to be sidetracked,which impels us to rediscover the applicability of conventional drilling and completion technology in ultra-deep wells.In this paper,based on the borehole condition and field operation data of this well,the borehole pressure field variation initiated by lost circulation in the low-pressure formation was analyzed from the perspective of dynamics,then,the variation pattern of differential pressure inside and outside the well bore at different time intervals was depicted,and the primary cause of such complication was theoretically revealed,i.e.,the pressure wave generated by instant lost circulation in low-pressure formation would result in redistribution of pressure inside the downhole confined space,and then the crush of casing in the vicinity of local low-pressure areas.Pertinent proposals for avoiding these kinds of engineering complexities were put forward:①when downhole sealing casing operation is conducted in open hole completion,liner completion or perforated hole,the potential damage of lost circulation to casing should be considered;②the downhole sealing point and sealing mode should be selected cautiously:the sealing point had better be selected in the section with good cementing quality or as close to the casing shoe as possible,and the sealing mode can be either cement plug or mechanical bridge plug.This paper finally points out that good cementing quality plays an important role in preventing this type of casing deformation.展开更多
Casing deformation occurs during the development of ChangningeWeiyuan national shale gas demonstration Area in the Sichuan Basin.In view of this,the correlation between the casing deformation and the geological charac...Casing deformation occurs during the development of ChangningeWeiyuan national shale gas demonstration Area in the Sichuan Basin.In view of this,the correlation between the casing deformation and the geological characteristics as well as hydraulic fracturing was analyzed.It is shown that fracture and bedding(hereinafter collectively referred to as fractures)in faults are the internal cause for casing deformation and hydraulic fracturing is the external cause.Then,the mechanism of casing deformation was clarified.As the fracturing fluid flows along a certain passage into the natural fracture,the pore pressure in the fracture rises.When the critical pressure is reached,the natural fracture is activated to move,and consequently casing deformation occurs.Fluid may flow along three pathways,i.e.,the hydraulic fracture,the axial fracture along the borehole axis created during hydraulic fracturing and the micro-annulus of cement sheath induced by repeated fracturing.Finally,some specific preventive measures were put forward.First,install packers in the whole sections with fractures and beddings.Second,improve the properties of slurry to avoid the formation of micro-annulus of cement sheath.And third,adopt the fracturing technologies to avoid the casing from repeated high pressure.The study results provide the guidance for the solution to shale gas casing deformation.展开更多
Horizontal shale gas well fracturing is mostly carried out by pumping bridge plugs.In the case of casing deformation,the bridge plug can not be pumped down to the designated position,so the hole sections below the def...Horizontal shale gas well fracturing is mostly carried out by pumping bridge plugs.In the case of casing deformation,the bridge plug can not be pumped down to the designated position,so the hole sections below the deformation could not be stimulated according to the design program.About 30%of horizontal shale gas wells in the Changning and Weiyuan Blocks,Sichuan Basin,suffer various casing deformation after fracturing.Previously,the hole sections which could not be stimulated due to casing deformation were generally abandoned.As a result,the resources controlled by shale gas wells weren't exploited effectively and the fracturing effect was impacted greatly.There are a lot of difficulties in investigating casing deformation,such as complex mechanisms,various influencing factors and unpredictable deformation time.Therefore,it is especially important to seek a staged fracturing technology suitable for the casing deformation sections.In this paper,the staged fracturing technology with sand plugs inside fractures and the staged fracturing technology with temporary plugging balls were tested in casing deformation wells.The staged fracturing technology with sand plugs inside fractures was carried out in the mode of single-stage perforation and single-stage fracturing.The staged fracturing technology with temporary plugging balls was conducted in the mode of single perforation,continuous fracturing and staged ball dropping.Then,two kinds of technologies were compared in terms of their advantages and disadvantages.Finally,they were tested on site.According to the pressure response,the pressure monitoring of the adjacent wells and the microseismic monitoring in the process of actual fracturing,both technologies are effective in the stimulation of the casing deformation sections,realizing well control reserves efficiently and guaranteeing fracturing effects.展开更多
Shale gas horizontal wells have severe problems of casing deformation and failure due to formation displacement during fracturing.Statistics show that casing deformation problems occur frequently in the development of...Shale gas horizontal wells have severe problems of casing deformation and failure due to formation displacement during fracturing.Statistics show that casing deformation problems occur frequently in the development of shale gas,especially in Sichuan Basin.Furthermore,the phe-nomenon of formation extrusion and fault slip is serious,which has caused great obstacles to the development of shale gas in China.In view of the current lack of casing deformation control methods,afinite element model of a wellbore under formation displacement load is established in this paper.The stress and deformation of the casing are simulated,and the mitigating effects of new annular materials such as a modified cement sheath and rubber are evaluated.Results indicate that the formation extrusion and fault slip can cause radial oval deformation and axial S-shaped deformation of the production casing,respectively.The use of a modified cement sheath can provide a little mitigating effect on casing deformation.Meanwhile,using rubber cementing can play a strong protective role for the production casing and avoid casing deformation to a certain extent.This research can provide a new way and important reference for the prevention and control of casing deformation in shale gas wells.展开更多
Casing deformation is a widespread problem in a certain block of Jiaoshiba Shale Gas Field in Sichuan Basin,China,and it severely limits the development benefits of shale gas in that block.Based on the spatiotemporal ...Casing deformation is a widespread problem in a certain block of Jiaoshiba Shale Gas Field in Sichuan Basin,China,and it severely limits the development benefits of shale gas in that block.Based on the spatiotemporal characteristics of block formation,fracture development,and casing deformation occurrence,this paper employs an integrated geological—engineering research approach to identify the primary mechanisms governing casing deformation within the block and proposes countermeasures to prevent such deformation.The present research indicates the following findings:(1)The block has undergone multiple phases of tectonic superposition,with fracture development serving as the geological factor causing casing deformation.(2)Fracturing activation constitutes the engineering factor causing casing deformation,with 4 mm of formation slip inducing deformation.(3)The fracture activation risk map shows that Class Ⅰ and Class Ⅱ fractures account for 73.36%of the total recorded in the block.Within the most susceptible Class I risk zone,the critical activation pressure increment for fracturing operations ranges from 13.43 MPa to 13.99 MPa.Based on the distribution of casing failure risk zones identified in the fracture activation risk map,this paper proposes relevant technical countermeasures for preventing casing failure from three perspectives:shale gas well location deployment,drilling techniques,and fracturing techniques.These measures provide robust support for safeguarding the integrity of casing systems within the studied block.展开更多
With the rapid development of shale gas exploration and development in China,casing deformation in shale gas horizontal wells happens frequently,which directly impacts the development efficiency and benefits of shale ...With the rapid development of shale gas exploration and development in China,casing deformation in shale gas horizontal wells happens frequently,which directly impacts the development efficiency and benefits of shale gas.In order to explore casing deformation prediction,prevention and treatment methods,this paper analyzes the geological and engineering causes of casing deformation in shale-gas horizontal wells through laboratory work,such as the casing resistance to internal pressure alternating test,the ground simulation test and systematical casing deformation characteristic analysis of MIT24 caliper logging,and the large-scale physical simulation test and numerical simulation of casing deformation.Then,combined with the generalized shear activity criterion,a new method for evaluating casing deformation risk points and some technical measures for preventing casing deformation were formulated.And the following research results were obtained.First,the deformation characteristics of 119 casing deformation points in 23 wells interpreted by MIT24 caliper logging are consistent with the mechanical behaviors of shear compression deformation test.Second,the large-scale physical simulation test shows that natural fault-fractures slip obviously under the state of strike-slip stress.Third,numerical simulation shows that the compression stress on casing increases with the increase of fault-fracture slip.When the fault-fracture slip is between 7.5 mm and 9.0 mm,the casing reaches the critical yield strength and begins to undergo plastic deformation.The“temporary fracture plugging+long segment and multi-cluster”and other technologies are field tested in 28 wells in Weiyuan area of southern Sichuan Basin.The casing deformation rate decreases from 54%(before this research)to 14.3%,and the segment loss rate decreases from 7.8%to 0,which reveals remarkable achievements in casing deformation treatment.In conclusion,the shear slip of fault and macro fractures(referred to as fault-fracture)is the main cause of casing deformation in shale gas horizontal wells,and some measures(e.g.“temporary fracture plugging+long segment and multi-cluster”,reducing fracturing scale and releasing wellbore pressure properly)shall be taken in advance to reduce the fault-fracture activity before the risk point of casing deformation is fractured,so as to reach the goal of casing deformation prevention.展开更多
In the Huangjinba Block of the Zhaotong National Shale Gas Demonstration Zone in the periphery of the Sichuan Basin,two horizontal shale gas wells suffer severe casing deformation.In this paper,the geological and engi...In the Huangjinba Block of the Zhaotong National Shale Gas Demonstration Zone in the periphery of the Sichuan Basin,two horizontal shale gas wells suffer severe casing deformation.In this paper,the geological and engineering characteristics of the strata around the deformed casing interval were analyzed based on the 24-arm caliper measurement of casing deformation,open-hole caliper,electrical resistivity,drilling time and gas logging,cementing CBLyVDL and CBL imaging.Then,24-arm caliper measurement data were analyzed and 3D imaged by 3D imaging analysis software,to figure out the morphologic characteristics of deformed casing.It is shown that severe casing deformation tends to occur where structural fractures are developed.Besides,casing deformation is mainly in the form of“S”-shape bending vertically.The severely deformed casing is also characterized by obviously transverse shear deformation caused by the high-angle sliding compression of rocks.Therefore,some suggestions were proposed correspondingly.First,the countermeasures in this block shall focus on shear casing deformation caused by the sliding of rocks along the fracture face.Wellbore trajectory shall be designed based on the structural contours map of pay zones to bypass the“ridge”and“valley bottom”area in the local high and steep structural zones.Second,the distribution information of fractured zones shall be predicted based on the ant-tracking attribute volume distribution map of pay zones,so that the wellbore trajectory can run along the strike of fractured zone.And third,it is recommended to use plug-drilling free big bore bridge plug or full-bore infinite stage completion technique,so that the conventional bridge plug milling operation after fracturing can be omitted and each fractured layer can be put into production after fracturing.展开更多
The effects of plastic deformation and H2 S on fracture toughness of high strength casing steel（C110 steel） were investigated. The studied casing specimens are as follows： original casing, plastic deformation（PD）...The effects of plastic deformation and H2 S on fracture toughness of high strength casing steel（C110 steel） were investigated. The studied casing specimens are as follows： original casing, plastic deformation（PD） casing and PD casing after being immersed in NACE A solution saturated with H2S（PD＋H2S）. Instrumented impact method was employed to evaluate the impact behaviors of the specimens, meanwhile, dynamic fracture toughness（JId） was calculated by using Rice model and Schindler model. The experimental results show that dynamic fracture toughness of the casing decreases after plastic deformation. Compared with that of the original casing and PD casing, the dynamic fracture toughness decreases further when the PD casing immersed in H2 S, moreover, there are ridge-shaped feature and many secondary cracks present on the fracture surface of the specimens. Impact fracture mechanism of the casing is proposed as follows： the plastic deformation results in the increase of defect density of materials where the atomic hydrogen can accumulate in reversible or irreversible traps and even recombine to form molecular hydrogen, subsequently, the casing material toughness decreases greatly.展开更多
Hydraulic rolling reshaper is an advanced reshaping tool to solve the problem of casing deformation,which has been widely used in recent years.When it is used for well repair operation,the reshaping force provided by ...Hydraulic rolling reshaper is an advanced reshaping tool to solve the problem of casing deformation,which has been widely used in recent years.When it is used for well repair operation,the reshaping force provided by ground devices is generally determined by experience.However,too large reshaping force may destroy the deformed casing,and too small reshaping force may also prolong the construction period and affect the repairing effect.In this paper,based on Hertz contact theory and elastic-plastic theory,combined with the process parameters of shaping,and considering the structural characteristics of the deformed casing and reshaper,we propose a mathematical model for calculating the reshaping force required for repairing deformed casing by hydraulic rolling reshaper.Meanwhile,the finite element model and numerical method of hydraulic rolling reshaper repairing deformed casing are established by using the finite element method,and the reliability of the mathematical model is verified by several examples.On this basis,the control variable method is used to investigate the influence of each parameter on the reshaping force,and the influence degree of each parameter is explored by orthogonal simulation test and Pearson correlation analysis.The research results not only provide an important theoretical basis for the prediction of reshaping force in on-site construction,but also provide a reference for the subsequent improvement of the shaping process.展开更多
In the enhanced geothermal systems wells, casing temperature variation produces casing thermal stresses, resulting in casing uplift or bucking. When the induced thermal stresses exceed casing material's yield stre...In the enhanced geothermal systems wells, casing temperature variation produces casing thermal stresses, resulting in casing uplift or bucking. When the induced thermal stresses exceed casing material's yield strength, the casing deforms and collapses. The traditional casing design standard only considers the influence of temperature variation on casing material's yield strength. Actually, for commonly used grades of steel pipe, casing's material properties-such as yield strength, coefficient of thermal expansion, and modulus of elasticity change with temperature variation. In this paper, the modified thermal stress equation is given. Examples show that the allowable temperature of the material grade N80's casing is only 164 ℃, which is much lower than that of the traditional design standard. The effective method to improve the casing pipe's allowable temperature is pre-stressed cementing technology. Pre-stressed cementing includes pre-tension stress cementing and pre-pressure stress cementing. This paper focuses on the design method of full casing pre-tension stress cementing and the ground anchor full casing string pre-tension cementing construction process.展开更多
During volume fracturing of shale gas reservoirs,hydraulic fractures may readily communicate with natural fractures to propagate forward and induce the formations to slip along the fracture surfaces.The resulted inter...During volume fracturing of shale gas reservoirs,hydraulic fractures may readily communicate with natural fractures to propagate forward and induce the formations to slip along the fracture surfaces.The resulted inter-well frac-hit and casing deformation affect the safe and efficient operation of shale gas fracturing.In addition,unpropped fractures caused by small natural fracture width lead to deteriorating fracture conductivity,which in turn impacts the stimulation effect of shale gas reservoirs.This paper discusses the three key issues,i.e.inter-well frac-hit,casing deformation and unpropped microfractures,that impact the economic exploration and exploitation of shale gas,and proposes engineering prevention and control measures through literature review and research on mechanism by integrating theoretical and experimental analysis,which have been applied on site.Firstly,after clarifying the mechanism and main controlling factors of inter-well frac-hit,an evaluation model and prediction method of frac-hit based on machine learning were established.The measures for preventing and controlling inter-well frac-hit,including temporary plugging at fracture tip and shut-in of old wells,were determined after evaluation with the well-cluster fracture model.Secondly,an analysis model of casing deformation caused by fracture shear and slippage was established after stress analysis.According to the analysis of stress on casing intersected with fractures during fracturing,it is ascertained that increase of fluid pressure within natural fractures is the main factor that causes casing deformation.The methods for preventing casing deformation were proposed in terms of fracturing operation and well construction.Thirdly,the mechanism of micro-proppant migration was analyzed by integrating the model of particle migration and the transport experiment in large-scale plate,and the experiment confirms that micro-proppant can effectively improve the fracture conductivity.It is concluded after field application that the prevention and control measures proposed for inter-well frac-hit and casing deformation can mitigate frac-hit and casing deformation significantly,and micro-proppants are conducive to improving post-frac shale gas production.The measures provide a support for large-scale and economic development of deep shale gas.展开更多
Stimulation of hydraulic fracturing of horizontal shale gas wells in Weirong Block has always been facing many difficulties due to many factors such as complicated geological conditions,small differences between the h...Stimulation of hydraulic fracturing of horizontal shale gas wells in Weirong Block has always been facing many difficulties due to many factors such as complicated geological conditions,small differences between the horizontal principal stress and the vertical principal stress,high working pump pressures,and low sensitive sand ratios.In view of this,by combing the geological structure,engineering geological characteristics and the difficulties of fracturing of deep shale gas wells in Weirong Block,learning from the general idea of volumetric fracturing for shale gas reservoirs at home and abroad,we determined the main ideas and technical countermeasures for fracturing in the area and applied them to the subsequent fracturing practices of shale gas wells.And the following achievements were obtained.First,the conventional fracturing technology applied to the shale gas wells in Weirong Block resulted in low fracture complexity,small stimulated reservoir volume(SRV),difficulties in guaranteeing the effectiveness of perforation clusters,low strength of proppant adding,difficulties in obtaining higher conductivity,poor stable production capacity after stimulation,and difficulties in meeting the need of well fracturing with casing deformation.Second,in view of the difficulties of fracturing stimulation in deep shale gas wells of Weirong Block,super high pressure,huge displacement,large fluid volume,temporary plugging and diverting in fracturing,and variable displacement technology can effectively increase SRV and the complexity of fractures in distant wells.The effectiveness of multi-cluster perforation can be guaranteed by comprehensive utilization of multi-cluster perforation optimization technology,big displacement technology and temporary plugging and diverting&fracturing technology at slots.The continuous proppant-adding technology with huge displacement,high viscosity,low sand ratio,low density and small particle size can improve sand adding strength and fracture conductivity.Besides,the stimulation technology for casing deformed wells using coiled tubing fast processing+small diameter bridge plug and separate pumping technology of perforating gun have been formed.Third,after the above fracturing technologies have been applied in five shale gas horizontal wells in Weirong Block,the average absolute open flow(QAOF)reached 26.11×10^(4)m^(3)/d,indicating a good stimulation effect.In conclusion,this paper can provide meaningful reference for the development of deep shale gas wells of the similar type.展开更多
So far,large-scale development of shale gas wells above 3500 m in the Changning Block of the Sichuan Basin has been realized by means of the large-scale hydraulic fracturing technology.As the main process parameters a...So far,large-scale development of shale gas wells above 3500 m in the Changning Block of the Sichuan Basin has been realized by means of the large-scale hydraulic fracturing technology.As the main process parameters arefinally set,however,the improvement rate of its stimulation effect tends to slow down,while in North America,single-well production has increased significantly by shortening cluster spacing and increasing proppant volumes.In order to provide a reliable practice basis for optimizing the parameters of shale gas fracturing process,this paper analyzes the productivity increasing mechanism of the new fracturing technology of intensive stageþhigh-intensity proppant injection by virtue of the model for calculating induced stress and multi-stage and multi-cluster productivity of horizontal wells.And accordingly,the main en-gineering factors of fracturing stimulation technology were ascertained.Then,after the pilot test scheme on this new fracturing technology was formulated according to the geological parameters of this block,the pilot test was carried out.Finally,the fracturing process parameters were optimized based on actual production effects and experimental results.And the following research results were obtained.First,shortening the spacing between main fractures,increasing the interference degree of induced stress and improving the stimulation degree of hydraulic fractures to shale reservoirs are the technical keys to the intense stage,and increasing the proppant volume,reducing the influence degree of proppant embedding and breaking on the attenuation of fracture conductivity and ensuring the long-term conductivity of propped fractures are the internal causes of significant production increase through high-intensity proppant injection.Second,the optimized implementation parameters of this new process in the Changning Block are as follows.The cluster spacing is in the range of 15e20 m,the proppant injection intensity is 2.0e2.5 t/m,and the liquid consuming intensity is 30e35 m3/m.It is concluded that this new process increases the single-well production of shale gas wells and the development benefit of the Changning Block and provides technical support for improving the comprehensive development benefit of shale gas wells in this block.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
基金supported by Major Technology Promotion Project of CNPC,China(No.2022ZT01)Major Field Test Project of CNPC,China(No.2019F-31-04)CNPC Chuanqing Drilling Engineering Company Science and Technology Special Project,China(No.CQ2024B-11-Z2-4).
文摘Milling bridge plugs in shale gas wells with severe casing deformation often leads to the accumulation of cuttings,increasing the risk of stuck drill bits.Friction in the wellbore further complicates tool deployment into the horizontal section,posing challenges to efficient plug drilling and achieving wellbore access to the target layer.This paper integrates the theory of positive displacement motors and models their actual working characteristics to study the milling of bridge plugs in severely deformed horizontal wells.It examines the effects of coiled tubing diameter and wall thickness on the bending load of horizontal sections and discusses key technical requirements,including the timing of plug drilling,extending the run in the horizontal section,parameter control,and real-time field analysis.Field practices have shown that after casing deformation occurs,priority should be given to drilling out the bridge plugs below the point of deformation.The primary factors contributing to stuck drills in deformed wells include smaller mill shoe sizes and larger cuttings sizes.Short well-washing cycles and targeted cuttings removal can effectively reduce sticking risks.If sticking occurs,high-tonnage pulling should be avoided.Instead,releasing the stick through up-anddown string motion,combined with high-volume nozzle spraying and annulus pumping,is recommended.The selection of coiled tubing should consider diameter,wall thickness,and steel grade to handle complex situations.Larger diameters,thicker walls,and low-frequency,multi-head hydraulic oscillators are more effective for unlocking horizontal sections.This approach can reduce the risk of drill sticking and solve the problem of horizontal section lock-ups,offering a reliable solution for smooth drilling and efficient production in wells with severe casing deformation.
基金the supports of project funded by China Postdoctoral Science Foundation(2023M743886)Project of Shale Gas Evaluation and Exploitation Key Laboratory of Sichuan Province(YSK2023004)youth project funded by Shaanxi Province Natural Science Basic Research Program(2024JC-YBQN-0522)。
文摘The casing deformation prevention technology based on the optimization of cement slurry is proposed to reduce the casing deformation of shale oil and gas wells during hydraulic fracturing. In this paper, the fracture mechanism of hollow particles in cement sheath was firstly analyzed by discrete element method, and the effect of hollow particles in cement on casing deformation was investigated by laboratory experiment method. Finally, field test was carried out to verify the improvement effect of the casing deformation based on cement slurry modification. The results show that the formation displacement can be absorbed effectively by hollow particles inside the cement transferring the excessive deformation away from casing. The particles in the uncemented state provide deformation space during formation slipping. The casing with diameter of 139.7 mm could be passed through by bridge plug with the diameter of 99 mm when the mass ratio of particle/cement reaches 1:4. According to the field test feedback, the method based on optimization of cement slurry can effectively reduce the risk of casing deformation, and the recommended range of hollow microbeads content in the cement slurry is between 15% and 25%.
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Supported by National Natural Science Foundation of China(51904258,51874250)Project of Science and Technology of Shale Gas Exploration&Development of CCDC(2019-JS-941)National Major Project of Science and Technology(2016ZX05048-004-006)。
文摘To study the casing deformation(CD)in shale gas well fracturing caused by natural fracture slip,a fracture face stress model is built based on stress analysis,and a CD prediction model is established based on complex function to analyze factors affecting wellbore shear stress and CD.(1)The fracture and wellbore approach angles have significant impacts on the wellbore shear stress.In Weiyuan shale gas field,Sichuan Basin,under the common wellbore approach angle of nearly 90°,the wellbore is subjected to large shear stress and high risk of CD at the fracture approach angle range of 20° to 55° or its supplementary angle range.(2)When the fracture is partially opened,the wellbore shear stress is positively correlated with the fluid pressure,and negatively correlated with the fracture friction coefficient;when the fracture is fully opened,the wellbore shear stress is positively correlated with the natural fracture area.(3)The lower the elastic modulus and the longer the fracture length,the more serious the CD will be,and the Poisson’s ratio has a weak influence on the CD.The deformation first increases and then decreases with the increase of fracture approach angle,and reaches the maximum when the fracture approach angle is 45°.(4)At a given fracture approach angle,appropriately adjusting the wellbore approach angle can avoid high shear stress acting on wellbore,and reasonable control of the fluid pressure in the fracture can reduce the CD risk.The shear stress acting on casing is usually much greater than the shear strength of casing,so increasing casing strength or cementing quality have limited effect on reducing the risk of CD.Caliper logging data has verified that the CD prediction model is reliable,so the model can be used to establish risk analysis chart and calculate deformation value,to provide a reference for quick CD risk prediction in fracturing design.
基金Supported by the PetroChina Scientific Research and Technology Development Project (2022KT1205)。
文摘Based on structural distribution and fault characteristics of the Luzhou block,southern Sichuan Basin,as well as microseismic,well logging and in-situ stress data,the casing deformation behaviors of deep shale gas wells are summarized,and the casing deformation mechanism and influencing factors are identified.Then,the risk assessment chart of casing deformation is plotted,and the measures for preventing and controlling casing deformation are proposed.Fracturing-activated fault slip is a main factor causing the casing deformation in deep shale gas wells in the Luzhou block.In the working area,the approximate fracture angle is primarily 10°-50°,accounting for 65.34%,and the critical pore pressure increment for fault-activation is 6.05-9.71 MPa.The casing deformation caused by geological factors can be prevented/controlled by avoiding the faults at risk and deploying wells in areas with low value of stress factor.The casing deformation caused by engineering factors can be prevented/controlled by:(1)keeping wells avoid faults with risks of activation and slippage,or deploying wells in areas far from the faulting center if such avoidance is impossible;(2)optimizing the wellbore parameters,for example,adjusting the wellbore orientation to reduce the shear force on casing to a certain extent and thus mitigate the casing deformation;(3)optimizing the casing program to ensure that the curvature radius of the curved section of horizontal well is greater than 200 m while the drilling rate of high-quality reservoirs is not impaired;(4)optimizing the fracturing parameters,for example,increasing the evasive distance,lowering the single-operation pressure,and increasing the stage length,which can help effectively reduce the risk of casing deformation.
基金financially supported by the National Natural Science Foundation of China(Grant No.51890914)the Major Scientific and Technological Projects of CNPC(Grant No.ZD2019-184-004-003)the Innovation fund project for graduate student of China University of Petroleum(East China)(Grant No.22CX04034A)。
文摘Formation subsidence is inevitable during marine hydrate decomposition,and the consequent casing deformation seriously threatens the security of sustainable hydrate production.Owing to insufficient observed data of formation subsidence in field,displacement boundary condition of casing is undetermined.Thus the conventional static methods are inapplicable for the calculation of casing deformation in hydrate production well.The present work aims at proposing an approach to investigate dynamic deformation of the casing during hydrate production.In the proposed methodology,based on the movement theory of hydrate decomposition front,hydrate decomposition process can be simulated,in which hydrate reservoir strength formation subsidence showed time-dependent characteristics.By considering the actual interactions among casing,cement and formation,three models of hydrate production well are developed to reveal the static and dynamic deformation mechanisms of the casing.The application of the proposed methodology is demonstrated through a case study.Results show that buckling deformation and bending deformation of casing reduce the passing ability of downhole tools in deformed casing by 4.2%and 7.5%,respectively.With the progress of hydrate production,buckling deformation will increase obviously,while a little increase of bending deformation will occur,as the formation slippage induced by formation inclination is much larger than that caused by hydrate decomposition.The proposed approach can provide theoretical reference for improving casing integrity of marine hydrate production.
文摘In the course of completion of an ultra-deep well newly drilled in the Yuanba Gasfield,Sichuan Basin,long-section and large-scale deformation occurred in the heavy casing section and nickel base alloy casing section of the sealing Triassic limestone interval,so a new hole had to be sidetracked,which impels us to rediscover the applicability of conventional drilling and completion technology in ultra-deep wells.In this paper,based on the borehole condition and field operation data of this well,the borehole pressure field variation initiated by lost circulation in the low-pressure formation was analyzed from the perspective of dynamics,then,the variation pattern of differential pressure inside and outside the well bore at different time intervals was depicted,and the primary cause of such complication was theoretically revealed,i.e.,the pressure wave generated by instant lost circulation in low-pressure formation would result in redistribution of pressure inside the downhole confined space,and then the crush of casing in the vicinity of local low-pressure areas.Pertinent proposals for avoiding these kinds of engineering complexities were put forward:①when downhole sealing casing operation is conducted in open hole completion,liner completion or perforated hole,the potential damage of lost circulation to casing should be considered;②the downhole sealing point and sealing mode should be selected cautiously:the sealing point had better be selected in the section with good cementing quality or as close to the casing shoe as possible,and the sealing mode can be either cement plug or mechanical bridge plug.This paper finally points out that good cementing quality plays an important role in preventing this type of casing deformation.
基金supported by the National Major Science and Technology Project“Factory drilling techniques and integrated application”(No.2016ZX05022001)CNPC Major Shale Gas Project“Shale gas drilling and production engineering field tests”(No.2014F-4702-05).
文摘Casing deformation occurs during the development of ChangningeWeiyuan national shale gas demonstration Area in the Sichuan Basin.In view of this,the correlation between the casing deformation and the geological characteristics as well as hydraulic fracturing was analyzed.It is shown that fracture and bedding(hereinafter collectively referred to as fractures)in faults are the internal cause for casing deformation and hydraulic fracturing is the external cause.Then,the mechanism of casing deformation was clarified.As the fracturing fluid flows along a certain passage into the natural fracture,the pore pressure in the fracture rises.When the critical pressure is reached,the natural fracture is activated to move,and consequently casing deformation occurs.Fluid may flow along three pathways,i.e.,the hydraulic fracture,the axial fracture along the borehole axis created during hydraulic fracturing and the micro-annulus of cement sheath induced by repeated fracturing.Finally,some specific preventive measures were put forward.First,install packers in the whole sections with fractures and beddings.Second,improve the properties of slurry to avoid the formation of micro-annulus of cement sheath.And third,adopt the fracturing technologies to avoid the casing from repeated high pressure.The study results provide the guidance for the solution to shale gas casing deformation.
基金Project supported by the National Key Basic Research and Development Program(973 Program)“Theory and Technology Adaptability of Shale Gas Development in Typical Marine Blocks in South China”(No.2013CB228006).
文摘Horizontal shale gas well fracturing is mostly carried out by pumping bridge plugs.In the case of casing deformation,the bridge plug can not be pumped down to the designated position,so the hole sections below the deformation could not be stimulated according to the design program.About 30%of horizontal shale gas wells in the Changning and Weiyuan Blocks,Sichuan Basin,suffer various casing deformation after fracturing.Previously,the hole sections which could not be stimulated due to casing deformation were generally abandoned.As a result,the resources controlled by shale gas wells weren't exploited effectively and the fracturing effect was impacted greatly.There are a lot of difficulties in investigating casing deformation,such as complex mechanisms,various influencing factors and unpredictable deformation time.Therefore,it is especially important to seek a staged fracturing technology suitable for the casing deformation sections.In this paper,the staged fracturing technology with sand plugs inside fractures and the staged fracturing technology with temporary plugging balls were tested in casing deformation wells.The staged fracturing technology with sand plugs inside fractures was carried out in the mode of single-stage perforation and single-stage fracturing.The staged fracturing technology with temporary plugging balls was conducted in the mode of single perforation,continuous fracturing and staged ball dropping.Then,two kinds of technologies were compared in terms of their advantages and disadvantages.Finally,they were tested on site.According to the pressure response,the pressure monitoring of the adjacent wells and the microseismic monitoring in the process of actual fracturing,both technologies are effective in the stimulation of the casing deformation sections,realizing well control reserves efficiently and guaranteeing fracturing effects.
基金supported by the National Natural Science Foundation of China(No.51904038)the Natural Science Foundation of Sichuan Province(No.2022NSFSC0249).
文摘Shale gas horizontal wells have severe problems of casing deformation and failure due to formation displacement during fracturing.Statistics show that casing deformation problems occur frequently in the development of shale gas,especially in Sichuan Basin.Furthermore,the phe-nomenon of formation extrusion and fault slip is serious,which has caused great obstacles to the development of shale gas in China.In view of the current lack of casing deformation control methods,afinite element model of a wellbore under formation displacement load is established in this paper.The stress and deformation of the casing are simulated,and the mitigating effects of new annular materials such as a modified cement sheath and rubber are evaluated.Results indicate that the formation extrusion and fault slip can cause radial oval deformation and axial S-shaped deformation of the production casing,respectively.The use of a modified cement sheath can provide a little mitigating effect on casing deformation.Meanwhile,using rubber cementing can play a strong protective role for the production casing and avoid casing deformation to a certain extent.This research can provide a new way and important reference for the prevention and control of casing deformation in shale gas wells.
文摘Casing deformation is a widespread problem in a certain block of Jiaoshiba Shale Gas Field in Sichuan Basin,China,and it severely limits the development benefits of shale gas in that block.Based on the spatiotemporal characteristics of block formation,fracture development,and casing deformation occurrence,this paper employs an integrated geological—engineering research approach to identify the primary mechanisms governing casing deformation within the block and proposes countermeasures to prevent such deformation.The present research indicates the following findings:(1)The block has undergone multiple phases of tectonic superposition,with fracture development serving as the geological factor causing casing deformation.(2)Fracturing activation constitutes the engineering factor causing casing deformation,with 4 mm of formation slip inducing deformation.(3)The fracture activation risk map shows that Class Ⅰ and Class Ⅱ fractures account for 73.36%of the total recorded in the block.Within the most susceptible Class I risk zone,the critical activation pressure increment for fracturing operations ranges from 13.43 MPa to 13.99 MPa.Based on the distribution of casing failure risk zones identified in the fracture activation risk map,this paper proposes relevant technical countermeasures for preventing casing failure from three perspectives:shale gas well location deployment,drilling techniques,and fracturing techniques.These measures provide robust support for safeguarding the integrity of casing systems within the studied block.
基金supported by the Scientific Research and Technology Development Project of CNPC“Research and field test of key technologies for effective exploitation of deep shale gas”(No.2019F-31JT).
文摘With the rapid development of shale gas exploration and development in China,casing deformation in shale gas horizontal wells happens frequently,which directly impacts the development efficiency and benefits of shale gas.In order to explore casing deformation prediction,prevention and treatment methods,this paper analyzes the geological and engineering causes of casing deformation in shale-gas horizontal wells through laboratory work,such as the casing resistance to internal pressure alternating test,the ground simulation test and systematical casing deformation characteristic analysis of MIT24 caliper logging,and the large-scale physical simulation test and numerical simulation of casing deformation.Then,combined with the generalized shear activity criterion,a new method for evaluating casing deformation risk points and some technical measures for preventing casing deformation were formulated.And the following research results were obtained.First,the deformation characteristics of 119 casing deformation points in 23 wells interpreted by MIT24 caliper logging are consistent with the mechanical behaviors of shear compression deformation test.Second,the large-scale physical simulation test shows that natural fault-fractures slip obviously under the state of strike-slip stress.Third,numerical simulation shows that the compression stress on casing increases with the increase of fault-fracture slip.When the fault-fracture slip is between 7.5 mm and 9.0 mm,the casing reaches the critical yield strength and begins to undergo plastic deformation.The“temporary fracture plugging+long segment and multi-cluster”and other technologies are field tested in 28 wells in Weiyuan area of southern Sichuan Basin.The casing deformation rate decreases from 54%(before this research)to 14.3%,and the segment loss rate decreases from 7.8%to 0,which reveals remarkable achievements in casing deformation treatment.In conclusion,the shear slip of fault and macro fractures(referred to as fault-fracture)is the main cause of casing deformation in shale gas horizontal wells,and some measures(e.g.“temporary fracture plugging+long segment and multi-cluster”,reducing fracturing scale and releasing wellbore pressure properly)shall be taken in advance to reduce the fault-fracture activity before the risk point of casing deformation is fractured,so as to reach the goal of casing deformation prevention.
文摘In the Huangjinba Block of the Zhaotong National Shale Gas Demonstration Zone in the periphery of the Sichuan Basin,two horizontal shale gas wells suffer severe casing deformation.In this paper,the geological and engineering characteristics of the strata around the deformed casing interval were analyzed based on the 24-arm caliper measurement of casing deformation,open-hole caliper,electrical resistivity,drilling time and gas logging,cementing CBLyVDL and CBL imaging.Then,24-arm caliper measurement data were analyzed and 3D imaged by 3D imaging analysis software,to figure out the morphologic characteristics of deformed casing.It is shown that severe casing deformation tends to occur where structural fractures are developed.Besides,casing deformation is mainly in the form of“S”-shape bending vertically.The severely deformed casing is also characterized by obviously transverse shear deformation caused by the high-angle sliding compression of rocks.Therefore,some suggestions were proposed correspondingly.First,the countermeasures in this block shall focus on shear casing deformation caused by the sliding of rocks along the fracture face.Wellbore trajectory shall be designed based on the structural contours map of pay zones to bypass the“ridge”and“valley bottom”area in the local high and steep structural zones.Second,the distribution information of fractured zones shall be predicted based on the ant-tracking attribute volume distribution map of pay zones,so that the wellbore trajectory can run along the strike of fractured zone.And third,it is recommended to use plug-drilling free big bore bridge plug or full-bore infinite stage completion technique,so that the conventional bridge plug milling operation after fracturing can be omitted and each fractured layer can be put into production after fracturing.
基金Funded by the Construction of Key Disciplines for Young Teacher Science Foundation of the Southwest Petroleum University(No.P209)the Research Fund for the Doctoral Program of Higher Education(No.20105121120002)the National Natural Science Foundation of China(Nos.51004084 and 51374177)
文摘The effects of plastic deformation and H2 S on fracture toughness of high strength casing steel（C110 steel） were investigated. The studied casing specimens are as follows： original casing, plastic deformation（PD） casing and PD casing after being immersed in NACE A solution saturated with H2S（PD＋H2S）. Instrumented impact method was employed to evaluate the impact behaviors of the specimens, meanwhile, dynamic fracture toughness（JId） was calculated by using Rice model and Schindler model. The experimental results show that dynamic fracture toughness of the casing decreases after plastic deformation. Compared with that of the original casing and PD casing, the dynamic fracture toughness decreases further when the PD casing immersed in H2 S, moreover, there are ridge-shaped feature and many secondary cracks present on the fracture surface of the specimens. Impact fracture mechanism of the casing is proposed as follows： the plastic deformation results in the increase of defect density of materials where the atomic hydrogen can accumulate in reversible or irreversible traps and even recombine to form molecular hydrogen, subsequently, the casing material toughness decreases greatly.
基金financially supported by the National Natural Science Foundation of China (51674088)Natural Science Foundation of Heilongjiang Province of China (LH 2021E011)。
文摘Hydraulic rolling reshaper is an advanced reshaping tool to solve the problem of casing deformation,which has been widely used in recent years.When it is used for well repair operation,the reshaping force provided by ground devices is generally determined by experience.However,too large reshaping force may destroy the deformed casing,and too small reshaping force may also prolong the construction period and affect the repairing effect.In this paper,based on Hertz contact theory and elastic-plastic theory,combined with the process parameters of shaping,and considering the structural characteristics of the deformed casing and reshaper,we propose a mathematical model for calculating the reshaping force required for repairing deformed casing by hydraulic rolling reshaper.Meanwhile,the finite element model and numerical method of hydraulic rolling reshaper repairing deformed casing are established by using the finite element method,and the reliability of the mathematical model is verified by several examples.On this basis,the control variable method is used to investigate the influence of each parameter on the reshaping force,and the influence degree of each parameter is explored by orthogonal simulation test and Pearson correlation analysis.The research results not only provide an important theoretical basis for the prediction of reshaping force in on-site construction,but also provide a reference for the subsequent improvement of the shaping process.
基金supported by the Hydrogeology Survey And Comprehensive Evaluation of Large Basin and Deep Typical Southeast Coastal Region(No.12120114025101)
文摘In the enhanced geothermal systems wells, casing temperature variation produces casing thermal stresses, resulting in casing uplift or bucking. When the induced thermal stresses exceed casing material's yield strength, the casing deforms and collapses. The traditional casing design standard only considers the influence of temperature variation on casing material's yield strength. Actually, for commonly used grades of steel pipe, casing's material properties-such as yield strength, coefficient of thermal expansion, and modulus of elasticity change with temperature variation. In this paper, the modified thermal stress equation is given. Examples show that the allowable temperature of the material grade N80's casing is only 164 ℃, which is much lower than that of the traditional design standard. The effective method to improve the casing pipe's allowable temperature is pre-stressed cementing technology. Pre-stressed cementing includes pre-tension stress cementing and pre-pressure stress cementing. This paper focuses on the design method of full casing pre-tension stress cementing and the ground anchor full casing string pre-tension cementing construction process.
文摘During volume fracturing of shale gas reservoirs,hydraulic fractures may readily communicate with natural fractures to propagate forward and induce the formations to slip along the fracture surfaces.The resulted inter-well frac-hit and casing deformation affect the safe and efficient operation of shale gas fracturing.In addition,unpropped fractures caused by small natural fracture width lead to deteriorating fracture conductivity,which in turn impacts the stimulation effect of shale gas reservoirs.This paper discusses the three key issues,i.e.inter-well frac-hit,casing deformation and unpropped microfractures,that impact the economic exploration and exploitation of shale gas,and proposes engineering prevention and control measures through literature review and research on mechanism by integrating theoretical and experimental analysis,which have been applied on site.Firstly,after clarifying the mechanism and main controlling factors of inter-well frac-hit,an evaluation model and prediction method of frac-hit based on machine learning were established.The measures for preventing and controlling inter-well frac-hit,including temporary plugging at fracture tip and shut-in of old wells,were determined after evaluation with the well-cluster fracture model.Secondly,an analysis model of casing deformation caused by fracture shear and slippage was established after stress analysis.According to the analysis of stress on casing intersected with fractures during fracturing,it is ascertained that increase of fluid pressure within natural fractures is the main factor that causes casing deformation.The methods for preventing casing deformation were proposed in terms of fracturing operation and well construction.Thirdly,the mechanism of micro-proppant migration was analyzed by integrating the model of particle migration and the transport experiment in large-scale plate,and the experiment confirms that micro-proppant can effectively improve the fracture conductivity.It is concluded after field application that the prevention and control measures proposed for inter-well frac-hit and casing deformation can mitigate frac-hit and casing deformation significantly,and micro-proppants are conducive to improving post-frac shale gas production.The measures provide a support for large-scale and economic development of deep shale gas.
基金supported by the Scientific Research Project of Sinopec Oilfield Service Corporation“Key technologies for deep shale gas fracturing and gas testing in Weiyuan-Yongchuan”(No.:SG1704-02K).
文摘Stimulation of hydraulic fracturing of horizontal shale gas wells in Weirong Block has always been facing many difficulties due to many factors such as complicated geological conditions,small differences between the horizontal principal stress and the vertical principal stress,high working pump pressures,and low sensitive sand ratios.In view of this,by combing the geological structure,engineering geological characteristics and the difficulties of fracturing of deep shale gas wells in Weirong Block,learning from the general idea of volumetric fracturing for shale gas reservoirs at home and abroad,we determined the main ideas and technical countermeasures for fracturing in the area and applied them to the subsequent fracturing practices of shale gas wells.And the following achievements were obtained.First,the conventional fracturing technology applied to the shale gas wells in Weirong Block resulted in low fracture complexity,small stimulated reservoir volume(SRV),difficulties in guaranteeing the effectiveness of perforation clusters,low strength of proppant adding,difficulties in obtaining higher conductivity,poor stable production capacity after stimulation,and difficulties in meeting the need of well fracturing with casing deformation.Second,in view of the difficulties of fracturing stimulation in deep shale gas wells of Weirong Block,super high pressure,huge displacement,large fluid volume,temporary plugging and diverting in fracturing,and variable displacement technology can effectively increase SRV and the complexity of fractures in distant wells.The effectiveness of multi-cluster perforation can be guaranteed by comprehensive utilization of multi-cluster perforation optimization technology,big displacement technology and temporary plugging and diverting&fracturing technology at slots.The continuous proppant-adding technology with huge displacement,high viscosity,low sand ratio,low density and small particle size can improve sand adding strength and fracture conductivity.Besides,the stimulation technology for casing deformed wells using coiled tubing fast processing+small diameter bridge plug and separate pumping technology of perforating gun have been formed.Third,after the above fracturing technologies have been applied in five shale gas horizontal wells in Weirong Block,the average absolute open flow(QAOF)reached 26.11×10^(4)m^(3)/d,indicating a good stimulation effect.In conclusion,this paper can provide meaningful reference for the development of deep shale gas wells of the similar type.
基金supported by the National Major Science and Technology Project"Changning-Weiyuan Shale Gas Development Demonstration Project"(No.:2016ZX05062)PetroChina Major Science and Technology Project"Research and Application of Key Technologies in Gas Production of 30 billion cubic meters in Southwest Oil&Gas Field Company"(No.:2016E-0612).
文摘So far,large-scale development of shale gas wells above 3500 m in the Changning Block of the Sichuan Basin has been realized by means of the large-scale hydraulic fracturing technology.As the main process parameters arefinally set,however,the improvement rate of its stimulation effect tends to slow down,while in North America,single-well production has increased significantly by shortening cluster spacing and increasing proppant volumes.In order to provide a reliable practice basis for optimizing the parameters of shale gas fracturing process,this paper analyzes the productivity increasing mechanism of the new fracturing technology of intensive stageþhigh-intensity proppant injection by virtue of the model for calculating induced stress and multi-stage and multi-cluster productivity of horizontal wells.And accordingly,the main en-gineering factors of fracturing stimulation technology were ascertained.Then,after the pilot test scheme on this new fracturing technology was formulated according to the geological parameters of this block,the pilot test was carried out.Finally,the fracturing process parameters were optimized based on actual production effects and experimental results.And the following research results were obtained.First,shortening the spacing between main fractures,increasing the interference degree of induced stress and improving the stimulation degree of hydraulic fractures to shale reservoirs are the technical keys to the intense stage,and increasing the proppant volume,reducing the influence degree of proppant embedding and breaking on the attenuation of fracture conductivity and ensuring the long-term conductivity of propped fractures are the internal causes of significant production increase through high-intensity proppant injection.Second,the optimized implementation parameters of this new process in the Changning Block are as follows.The cluster spacing is in the range of 15e20 m,the proppant injection intensity is 2.0e2.5 t/m,and the liquid consuming intensity is 30e35 m3/m.It is concluded that this new process increases the single-well production of shale gas wells and the development benefit of the Changning Block and provides technical support for improving the comprehensive development benefit of shale gas wells in this block.
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.
