During drilling operations in deep fractured tight gas reservoirs,lost circulation of working fluid frequently occurs due to the formationʼs low pressure-bearing capacity.Adding lost circulation materials(LCMs)to dril...During drilling operations in deep fractured tight gas reservoirs,lost circulation of working fluid frequently occurs due to the formationʼs low pressure-bearing capacity.Adding lost circulation materials(LCMs)to drilling fluids is the most common method for controlling lost circulation.Among these,granular LCMs are widely used,but the application frequency of flaky LCMs has been increasing annually due to their unique morphology.However,the migration and plugging behavior of flaky LCMs within fractures,and the mechanisms enhancing the pressure-bearing capacity of the plugging zone are not well understood.Therefore,this study conducted visual plugging experiments and dynamic fracture plugging experiments to evaluate the plugging mode and pressure-bearing capacity of the plugging slurry with various particle sizes and concentrations of flaky LCMs.The experimental results demonstrate that the fracture plugging process can be divided into four stages:uniform flow stage of the plugging slurry,formation and development stage of the bridging area,formation and development stage of the plugging area,and pressure-bearing stage of the plugging zone.The inclusion of flaky LCMs notably reduces the duration of stages 1 and 2,while simultaneously increasing the proportion of the plugging zone and enhancing its surface porosity.Flaky LCMs reduce the effective fracture width through“interception”and“co-bridging”modes,thus improving plugging zone formation efficiency.Appropriate particle size and concentration of flaky LCMs increase the area and length of the plugging zone.This reduces the fracture width increment caused by injection pressure and enhances frictional force between the plugging zone and fracture surface,thereby improving the pressure-bearing capacity of the plugging zone.However,excessively high concentrations of flaky LCMs result in decreased structural stability of the plugging zone,and excessively large particle sizes increase the risk of plugging outside fracture inlet.The recommended concentration of flaky LCMs in the plugging slurry is 2%–3%,with a particle size 1.2 to 1.5 times that of the bridging granular LCMs and not exceeding twice the fracture width.This study provides a theoretical foundation for selecting LCMs and designing plugging formulations for field applications.展开更多
Lost circulation of drilling fluid is one of the most common and costly problems in drilling operations.This highlights the importance of wellbore strengthening treatment sthat can utilize lost circulation materials(L...Lost circulation of drilling fluid is one of the most common and costly problems in drilling operations.This highlights the importance of wellbore strengthening treatment sthat can utilize lost circulation materials(LCMs)to seal fractures associated with the wellbore.In this work,a numerical model accounting for the deformation of surrounding rock,fluid flow in the fracture,fracture propagation,and the transport of LCMs is presented to investigate the wellbore strengthening,from the fracture initiation to the fracture arrest,due to plugs formed by LCMs.The equations governing the rock deformation and fluid flow are solved by the dual boundary element method and the finite volume method,respectively.The transport of LCMs is solved based on an empirical constitutive model in suspension flow,and several characteristic quantities are derived by dimensional analysis.It is found that two dimensionless parameters,dimensionless toughness and normalized initial particle concentration,control the migration of LCM particles.The numerical results show that the dimensionless toughness influences the entrance and bridging of LCMs while the initial concentration controls the location of the particle bridging.When the initial concentration is larger than 0.8,the particle bridging tends to occur near the fracture entry.Conversely,when the initial concentration is less than 0.8,the particle bridging occurs near the fracture tip.This work provides an effective tool to predict the LCM transport and plugging in the wellbore strengthening process.展开更多
By reviewing the mechanisms of drilling fluid lost circulation and its control in fractured formations, the applicability and working mechanisms of different kinds of lost circulation materials in plugging fractured f...By reviewing the mechanisms of drilling fluid lost circulation and its control in fractured formations, the applicability and working mechanisms of different kinds of lost circulation materials in plugging fractured formations have been summarized. Meanwhile, based on the types of lost circulation materials, the advantages, disadvantages, and application effects of corresponding plugging technologies have been analyzed to sort out the key problems existing in the current lost circulation control technologies. On this basis, the development direction of plugging technology for severe loss have been pointed out. It is suggested that that the lost circulation control technology should combine different disciplines such as geology, engineering and materials to realize integration, intelligence and systematization in the future. Five research aspects should be focused on:(1) the study on mechanisms of drilling fluid lost circulation and its control to provide basis for scientific selection of lost circulation material formulas, control methods and processes;(2) the research and development of self-adaptive lost circulation materials to improve the matching relationship between lost control materials and fracture scales;(3) the research and development of lost circulation materials with strong retention and strong filling in three-dimensional fracture space, to enhance the retention and filling capacities of materials in fractures and improve the lost circulation control effect;(4) the research and development of lost circulation materials with high temperature tolerance, to ensure the long-term plugging effect of deep high-temperature formations;(5) the study on digital and intelligent lost circulation control technology, to promote the development of lost circulation control technology to digital and intelligent direction.展开更多
Fractured carbonate reservoirs are susceptible to blowout and lost circulation during drilling,which not only restricts drilling speed,but also poses big threat to well control.Moreover,there are few technical means a...Fractured carbonate reservoirs are susceptible to blowout and lost circulation during drilling,which not only restricts drilling speed,but also poses big threat to well control.Moreover,there are few technical means available to reconstruct pressure balance in the borehole.Accordingly,the fine managed pressure drilling was used in the drilling of Well GS19 in the Qixia Formation with super-high pressure and narrow density window,which is a success:①back pressure in the annular spaces will be adjusted to maintain a slightly over-balanced bottom-hole hydraulic pressure,and fluid level in the circulation tank will be kept in a slight dropping state to ensure that natural gas in the formation would not invade into the borehole in a massive volume;②inlet drilling fluid density will be controlled at around 2.35 g/cm^(3),back pressures in the annular be maintained at 2-5 MPa,and bottom-hole pressure equivalent circulation density be controlled at 2.46-2.52 g/cm^(3);③during managed pressure drilling operations,if wellhead pressure exceeds or expects to exceed 7 MPa,semi-blind rams will be closed.Fluids will pass through the choke manifold of the rig to the choke manifold specifically for pressure control before entering gas/liquid separators to discharge gas;④during tripping back pressure will be kept at less than 5 MPa,volume of injected drilling fluid will be higher than the theoretical volume during tripping out,whereas the volume of returned drilling fluid will be higher than the theoretical volume during the out-tripping.This technique has been applied successfully in the drilling of the Qixia Formation,Liangshan Formation and Longmaxi Formation with a total footage of 216.60 m,as a good attempt in complicated wells with both blowout and lost circulation risks,which can provide valuable experiences and guidance for handling similar complexities in the future.展开更多
Lost circulation of drilling fluid is one of the most common engineering problems in the drilling process of fractured formations.In this study,an oil-absorbing polymer gel synthesized using compound monomers with rig...Lost circulation of drilling fluid is one of the most common engineering problems in the drilling process of fractured formations.In this study,an oil-absorbing polymer gel synthesized using compound monomers with rigid and flexible chains was applied to control the oil-based drilling fluid loss while drilling.The microstructure,oil-absorbing performance,and plugging performance the gel was investigated.A large number of dense pores on the surface of the gel were observed,which allowed the oil molecules to enter the internal space of the gel.The initial oil absorption capacity of the gel was fast,and it increased with the increase in the temperature and decrease in the particle size,reaching 20.93 g/g at140℃.At a high temperature of 140℃,the bearing pressure capacity of the gel formula containing particles of different particle sizes reached 7.6 MPa for a fracture of a width of 3 mm,showing that the oil-absorbing gel have excellent plugging performance at high temperature.Plugging mechanism of the gel was investigated through visualized fracture plugging experiments.Results show that the dynamic migratio n,particle-swelling,particle-bridging,particle-aggregation,deformation-filling,and compaction-plugging contribute to the whole lost circulation control process,reflecting that the plugging performance can be effectively enhanced by improving the aggregation and filling degrees of the gel with different particle sizes.展开更多
Loss of drilling fluids in large porous and fractured zones inevitably up-regulates the overall cost of drilling.As a type of acid-soluble cement,magnesium oxysulfate(MOS)cement is arousing huge attention for the less...Loss of drilling fluids in large porous and fractured zones inevitably up-regulates the overall cost of drilling.As a type of acid-soluble cement,magnesium oxysulfate(MOS)cement is arousing huge attention for the less hygroscopic nature and less damaging to steel casings compared with magnesium oxychloride(MOC)cement.The present study developed MOS cement as a fast setting,high strength and acid-soluble lost circulation material to reduce the problem of losses.As suggested in this study,a higher strength of MOS cement at 70℃could be achieved by elevating M_(g)O/MgSO_(4)·7 H_(2)O molar ratio or downregulating H_(2)O/MgSO_(4)·7 H_(2)O molar ratio.Boric acid and borax could act as effective retarders.Plugging slurry based on MOS cement could effectively block the simulated porous loss zones exhibiting a diameter from 1.24 mm to 1.55 mm,as well as the fractured loss zones with a width from 2 mm to 5 mm and bearing a pressure difference up to 8 MPa.Permeability recovery test demonstrated that it facilitated future oil and gas production.The successful field application in the Junggar Basin,Xinjiang,China verified the significant plugging effect of MOS cement for severe loss problems.展开更多
Focused on the lost circulation control in deep naturally fractured reservoirs, the multiscale structure of fracture plugging zone is proposed based on the theory of granular matter mechanics, and the structural failu...Focused on the lost circulation control in deep naturally fractured reservoirs, the multiscale structure of fracture plugging zone is proposed based on the theory of granular matter mechanics, and the structural failure pattern of plugging zone is developed to reveal the plugging zone failure mechanisms in deep, high temperature, high pressure, and high in-situ stress environment. Based on the fracture plugging zone strength model, key performance parameters are determined for the optimal selection of loss control material(LCM). Laboratory fracture plugging experiments with new LCM are carried out to evaluate the effect of the key performance parameters of LCM on fracture plugging quality. LCM selection strategy for fractured reservoirs is developed. The results show that the force chain formed by LCMs determines the pressure stabilization of macro-scale fracture plugging zone. Friction failure and shear failure are the two major failure patterns of fracture plugging zone. The strength of force chain depends on the performance of micro-scale LCM, and the LCM key performance parameters include particle size distribution, fiber aspect ratio, friction coefficient, compressive strength, soluble ability and high temperature resistance. Results of lab experiments and field test show that lost circulation control quality can be effectively improved with the optimal material selection based on the extracted key performance parameters of LCMs.展开更多
During well-killing operations for the workover of low-pressure gas wells,formation pressure should be balanced so as to guarantee well control safety by preventing natural gas overflow.In this paper,a laboratory eval...During well-killing operations for the workover of low-pressure gas wells,formation pressure should be balanced so as to guarantee well control safety by preventing natural gas overflow.In this paper,a laboratory evaluation was conducted with fuzzy-ball fluids as killing fluids.The results show that,the fuzzy-ball fluid,with a density of 0.5e1.5 g/cm^(3) and a viscosity up to 78,50,000 mPa$s at a low shear rate,realizes controllable performance and forms piston-like plugging slugs of solid-free high structural strength on natural gas wellbore after bonding.During well workover,multiple fluid column pressures were set up by injecting fuzzy-ball fluids with different densities at various rates.Owing to high structural strength of the fluids at a low shear rate,natural gas breaks through only inside the piston-like slug and cannot flow upwards to the ground,so the pathways of natural gas in the wellbore are isolated from the ground surface.Moreover,the fluid can wholly move up and down like a piston-like plug,with the change of formation pressures or the tripping of pipe strings.Like the conventional operations,the production can be restored after the workover,so long as the fluid in wellbore is cleaned by means of gas lift.In a natural gas field in NW China,where the formation pressure coefficient dropped to 0.60e0.82,three wells were fully filled with fuzzy-ball workover fluids for 7 days and another three wells were treated with the piston-like plugs of fuzzy-ball workover fluids for only 3 days.They all presented better technical results.The technology provides a new way for low-pressure gas well workover.展开更多
Lost circulations have presented great challenges to the petroleum industry, causing great expenditures of cash and time to fighting the problem. Probably the most problematic situations are the naturally fractured fo...Lost circulations have presented great challenges to the petroleum industry, causing great expenditures of cash and time to fighting the problem. Probably the most problematic situations are the naturally fractured formations where the operator may face total loss with no mud return in the annular. The voids or large fracture encountered in this case are often far too large to be plugged with conventional Lost Circulation Material. This paper will give a detailed introduction on a novel composite gel material usable to control severe losses and pressurization sealing. The plugging mechanics of this new composite gel material, which is different from conventional lost circulation materials, were elaborated as well. In addition, the properties of the new composite gel material such as thermostability, sealing strength and bearing resistance are characterized with specific experimental devices. The experimental results proved that the breakdown pressure of the new plugging reached more than 20MPa, and the maximum degraded temperature can be exceed 130℃. The field application at 4 wells in Puguang gas field, SINOPEC, demonstrated that the new composite gel material solved the serious loss in Ordovician carbonate fractured formation successfully and guaranteed the following completion cement operation smoothly. The composite gel sealing slurries, which was easily prepared on site, gives remarkable properties regarding pumping through drill pipes, adjustment of setting time and excellent sealing strength of the lost zone sealing, additionally, the whole pressurization sealing process was complicated within only ten hours. The on-site results show that the plugging ratio of the new composite gel was reached 100%, and the success rate of sealing operation kept above 80%.Thus the new LCM can guarantee safe drilling jobs and save operation cost more effectively.展开更多
The well-known“lost circulation”problem refers to the uncontrolled flow of whole mud into a formation.In order to address the problem related to the paucity of available data,in the present study,a model is introduc...The well-known“lost circulation”problem refers to the uncontrolled flow of whole mud into a formation.In order to address the problem related to the paucity of available data,in the present study,a model is introduced for the lost-circulation risk sample profile of a drilled well.The model is built taking into account effective data(the Block L).Then,using a three-dimensional geological modeling software,relying on the variation function and sequential Gaussian simulation method,a three-dimensional block lost-circulation risk model is introduced able to provide relevant information for regional analyses.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
Ultra-deep geological conditions are complex, often leading to leakage issues. As the depth increases during ultra-deep bridging lost-circulation operations, the varying settling velocities of different types of lost ...Ultra-deep geological conditions are complex, often leading to leakage issues. As the depth increases during ultra-deep bridging lost-circulation operations, the varying settling velocities of different types of lost circulation materials(LCMs) lead to gravitational differentiation. This causes stratification of the LCMs, forming an unevenly dispersed system and reduced plugging efficacy. An experimental methodology is described for assessing the density suitability between LCMs and drilling fluids, which calculates the density suitability factor(DSF) by measuring the density of the plugging slurry at various locations after a designated resting period, ultimately evaluating its density suitability based on the DSF. Experimental results indicate that LCMs with lower densities demonstrate superior density suitability compared to those with higher densities. Smaller particle sizes(10-40 mesh) show better density suitability than larger ones(2-6 mesh). Fracture-plugging experiments validated this method, the plugging slurry composed of a good density suitability material, such as walnut shells, exhibited no notable gravitational differentiation after 2 h, achieving a maximum plugging pressure of 16.4 MPa with88 m L of total volume loss. In contrast, the slurry formed with poorly density suitability materials, such as calcite, showed significant gravitational differentiation after 2 h, achieving only 9.6 MPa in maximum plugging pressure and a total volume loss of 96 m L. These findings highlight that LCMs with superior density suitability enhance plugging efficiency, highlighting the critical role of density suitability testing and the optimization of plugging formulations to improve the success of plugging operations.展开更多
Lost circulation of drilling fluid is an international engineering problem during drilling.Aiming at the problems of the first-time lost circulation control success rate and poor adaptability of traditional lost circu...Lost circulation of drilling fluid is an international engineering problem during drilling.Aiming at the problems of the first-time lost circulation control success rate and poor adaptability of traditional lost circulation materials,a new self-healing lost circulation material based on dynamic disulfide bonds was prepared and named CKSH.In this paper,the particle size of self-healing lost circulation material was from 0.1 to 5 mm.The structure was analyzed by modern characterization means,and the drilling fluid compatibility,self-healing performance were evaluated.The self-healing and bridging-filling-sealing mechanism of CKSH were revealed.The results showed that the healing rate of CKSH could reach100%after 12 h over 70℃.It showed good compatibility with drilling fluid,with no effect on rheology or filtration loss.It could be stably suspended in drilling fluid,and the temperature resistance reached140℃.Healing by self-healing lost circulation materials of different particle size,the pressure bearing capacity of plugging zone were over 12 MPa for fracture opening of 1–5 mm.It could play a synergistic role with traditional lost circulation materials by chemical bonding,and the repeated loss caused by physical plugging was avoided.The research results of this paper can improve the bridging plugging bearing pressure strength and the first-time lost circulation control success rate,which is of great significance for improving drilling efficiency and reducing non-productive time.展开更多
Due to complex geological structures and a narrow safe mud density window,offshore fractured formations frequently encounter severe lost circulation(LC)during drilling,significantly hindering oil and gas exploration a...Due to complex geological structures and a narrow safe mud density window,offshore fractured formations frequently encounter severe lost circulation(LC)during drilling,significantly hindering oil and gas exploration and development.Predicting LC risks enables the targeted implementation of mitigation strategies,thereby reducing the frequency of such incidents.To address the limitations of existing 3D geomechanical modeling in predicting LC,such as arbitrary factor selection,subjective weight assignment,and the inability to achieve pre-drilling prediction along the entire well section,an improved prediction method is proposed.This method integrates multi-source data and incorporates three LC-related sensitivity factors:fracture characteristics,rock brittleness,and in-situ stress conditions.A quantitative risk assessment model for LC is developed by combining the subjective analytic hierarchy process with the objective entropy weight method(EWM)to assign weights.Subsequently,3D geomechanical modeling is applied to identify regional risk zones,enabling digital visualization for pre-drilling risk prediction.The developed 3D LC risk prediction model was validated using actual LC incidents from drilled wells.Results were generally consistent with field-identified LC zones,with an average relative error of 19.08%,confirming its reliability.This method provides practical guidance for mitigating potential LC risks and optimizing drilling program designs in fractured formations.展开更多
Working fluids loss is a major contributor to low productivity during production process of fractured tight reservoirs.Lost circulation control effect directly related to the tribological behavior between fracture sur...Working fluids loss is a major contributor to low productivity during production process of fractured tight reservoirs.Lost circulation control effect directly related to the tribological behavior between fracture surface and lost circulation materials(LCMs).In this study,the friction coefficient(FC)was investigated using typical clastic rocks and LCMs by considering multiple effect factors divided into external condition and internal condition.The results show that normal load had a relatively high effect on sliding model.A positive correlation was observed between FC and asperities heights.FC decreased induced by particle size degradation of rigid LCMs.Elastic LCMs manifested higher FC compared with rigid LCMs.Under the lubrication condition by working fluid,FC of rigid LCMs was mainly controlled by their surface wettability.FC of organic LCMs is more sensitive to high temperature aging than inorganic LCMs.Fracture plugging experiments show that LCMs optimized based on the research results can effectively improve the efficiency and strength of fracture plugging.展开更多
A new model was established based on the flow model of the drilling fluid in one-dimensional radial fracture to research the influencing factors on conversion time between lost circulation and overflow for multi-press...A new model was established based on the flow model of the drilling fluid in one-dimensional radial fracture to research the influencing factors on conversion time between lost circulation and overflow for multi-pressure system in fractured reservoirs.And the equation of the conversion time between lost circulation and overflow is obtained by solving the mathematical model.The model were validated by reproducing the field data from Sichuan oil field and the simulation results of references.The influences of consistency index,liquidity index,dynamic shear force,drilling fluid density,drilling fluid intrusion depth,pressure of lost circulation layer,crack width,decreased height of annular liquid level,pressure of high-pressure layer were analyzed.Results indicate that conversion time between lost circulation and overflow increases with the increasing consistency index,liquidity index,dynamic shear force,drilling fluid density,drilling fluid intrusion depth,pressure of lost circulation layer.Conversion time between lost circulation and overflow decreases with the increasing crack width,decreased height of annular liquid level,pressure of high-pressure layer.The time interval of“Hang's Muddingoff”operating should be appropriately less than the conversion time between lost circulation and overflow.Under the premise of ensuring wellbore safety,appropriately increasing the consistency index,liquidity index and dynamic shear force of the drilling fluid can effectively increase the conversion time between lost circulation and overflow in large fractured stratum.展开更多
Lost circulation is the most common problem encountered while drilling oil wells.Occurrence of such a problem can cause a lot of time and cost wastes.In order to drill oil wells,a fast and profitable way is necessary ...Lost circulation is the most common problem encountered while drilling oil wells.Occurrence of such a problem can cause a lot of time and cost wastes.In order to drill oil wells,a fast and profitable way is necessary to predict and solve lost circulation problem.Expert system is a method used lately for problems that deal with uncertainty.In this paper,three approaches are carried out for prediction of lost circulation problem.These approaches include design of experiments(DOE),data mining,and adaptive neuro-fuzzy inference system(ANFIS).Data of 61 wells of Maroon oilfield are selected and sorted as the feed of the systems.Seventeen variables are used as inputs of the approaches and one variable is used as the output.First,DOE is conducted to observe the effects of variables.Plackett-Burman method is used to determine the effects of variables on lost circulation.After that,data mining is conducted to predict the amount of lost circulation.The class of regression is used to determine a function to model the data and the error of the model.Then,ANFIS is applied to predict the amount of lost circulation.The chosen data are used in order to train,test,and control the ANFIS.Furthermore,subtractive clustering is used to train the fuzzy inference system(FIS)of the model.The performance of the ANFIS model is assessed through the root mean squared error(RMSE).The results suggest that ANFIS method can be successfully applied to establish lost circulation prediction model.In addition,results of ANFIS and data mining are investigated through their prediction performances.The comparison of both methods reveals that ANFIS error is much lower than data mining.展开更多
Oil and gas operators worldwide are expecting service companies to deliver integrated techniques to minimize,if not prevent,drilling problems.Drilling fluids perform vital functions to ensure the success of drilling o...Oil and gas operators worldwide are expecting service companies to deliver integrated techniques to minimize,if not prevent,drilling problems.Drilling fluids perform vital functions to ensure the success of drilling operations.The technical challenges often associated with water-based drilling fluids are loss of critical properties,such as fluid loss control and rheology,under demanding conditions,such as in drilling deeper,high-temperature and high-pressure wells.Fluid loss during drilling operations has a very significant effect in both reservoir formation damage and monetary terms.The use of durian rind(DR)as a new additive in controlling lost circulation would provide another opportunity to reduce waste and avoid pollution.Therefore,DR was used to improve the rheological properties of water-based mud,and it was prepared for use as a fluid loss additive.For a better understanding of the influence of pectin on drilling mud properties,the rheological evaluation of untreated DR was compared to that of mud samples containing treated DR.The pectin in DR was extracted using four different solvents,namely,ethanol,methanol,sodium hydroxide and hydrogen peroxide,and the most effective solvent to remove the pectin was then determined.The Fourier transform infrared spectroscopy(FTIR)results showed that NaOH was the best solvent for removing pectin from DR.Thermogravimetric analysis(TGA)was used to determine the thermal stability of DR before and after treatments.The TGA results demonstrated that the treated DR had improved thermal stability compared to untreated DR.The sizes of DR used were coarse,medium,and fine.The untreated DR presented better rheological properties than the treated DR.The experimental investigation showed that a concentration of 20 lb/bbl of intermediate-sized DR was the best concentration among the tested samples.展开更多
Lost circulation is an expensive and critical problem in the drilling operations.Millions of dollars are spent every year to mitigate or stop this problem.In this work,data from over 3000 wells were collected from mul...Lost circulation is an expensive and critical problem in the drilling operations.Millions of dollars are spent every year to mitigate or stop this problem.In this work,data from over 3000 wells were collected from multiple sources.The data went through a processing step where all outliers were removed and decision rules were set up.Multiple machine learning methods(support vector machine,decision trees,logistic regression,artificial neural networks,and ensemble trees)were used to create a model that can predict the best lost circulation treatment based on the type of loss and the reason of loss.5-fold cross-validation was conducted to ensure no overfitting in the created model.After using all the aforementioned machine learning methods to train models to choose the best lost circulation treatment,overall,the results showed that support vector machine had the highest accuracy among the other algorithms.Thus,it was selected to train the model.The created model went through quality control/quality assurance(QC/QA)to limit the results of incorrect classification.Two treatments were suggested to treat partial loss,four to treat severe loss,and seven for complete loss,based on the reason of loss.In addition,a formalized methodology to respond to lost circulation was provided to help the drilling personnel handling lost circulation in the field.展开更多
A major cause of some of serious issues encountered in a drilling project,including wellbore instability,formation damage,and drilling string stuck e which are known to increase non-productive time(NPT)and hence the d...A major cause of some of serious issues encountered in a drilling project,including wellbore instability,formation damage,and drilling string stuck e which are known to increase non-productive time(NPT)and hence the drilling cost e is what we know as mud loss.The mud loss can be prevented or at least significantly reduced by taking proper measures beforehand provided the position and intensity of such loss can be properly predicted using an accurate predictor model.Accordingly,in this study,we used the convolutional neural network(CNN)and hybridized forms of multilayer extreme learning machine(MELM)and least square support vector machine(LSSVM)with the Cuckoo optimization algorithm(COA),particle swarm optimization(PSO),and genetic algorithm(GA)for modeling the mud loss rate based on drilling data,mud properties,and geological information of 305 drilling wells penetrating the Marun Oilfield.For this purpose,we began by a pre-processing step to attenuate the effect of noise using the Savitzky-Golay method.The whole set of available data was divided into the modeling(including 2300 data points)and the validation(including 483 data points)subsets.Next,the second generation of the non-dominated sorting genetic algorithm(NSGA-Ⅱ)was applied to the modeling data to identify the most significant features for estimating the mud loss.The results showed that the prediction accuracy increased with the number of selected features,but the increase became negligible when the number of selected features exceeded 9.Accordingly,the following 9 features were selected as input to the intelligent algorithms(IAs):pump pressure,mud weight,fracture pressure,pore pressure,depth,gel 10 min/gel 10 s,fan 600/fan 300,flowrate,and formation type.Application of the hybrid algorithms and simple forms of LSSVM and CNN to the training data(80%of the modeling data,i.e.1840 data points)showed that all of the models tend to underestimate the mud loss at higher mud loss rates,although the CNN exhibited lower underestimation levels.Error analysis on different models showed that the CNN provided for a significantly higher degree of accuracy,as compared to other models.The more accurate outputs of the hybrid LSSVM model than those of the simple LSSVM indicated the large potentials of metaheuristic algorithms for achieving optimal solutions.The lower error levels obtained with the CNN model in the testing phase highlighted the excellent generalizability of this model for unseen data.The more accurate predictions obtained with this model,rather than the other models,in the validation phase further proved this latter finding.Therefore,application of this method to other wells in the same field is highly recommended.展开更多
基金support from the National Natural Science Foundation of China(Grant No.52274009).
文摘During drilling operations in deep fractured tight gas reservoirs,lost circulation of working fluid frequently occurs due to the formationʼs low pressure-bearing capacity.Adding lost circulation materials(LCMs)to drilling fluids is the most common method for controlling lost circulation.Among these,granular LCMs are widely used,but the application frequency of flaky LCMs has been increasing annually due to their unique morphology.However,the migration and plugging behavior of flaky LCMs within fractures,and the mechanisms enhancing the pressure-bearing capacity of the plugging zone are not well understood.Therefore,this study conducted visual plugging experiments and dynamic fracture plugging experiments to evaluate the plugging mode and pressure-bearing capacity of the plugging slurry with various particle sizes and concentrations of flaky LCMs.The experimental results demonstrate that the fracture plugging process can be divided into four stages:uniform flow stage of the plugging slurry,formation and development stage of the bridging area,formation and development stage of the plugging area,and pressure-bearing stage of the plugging zone.The inclusion of flaky LCMs notably reduces the duration of stages 1 and 2,while simultaneously increasing the proportion of the plugging zone and enhancing its surface porosity.Flaky LCMs reduce the effective fracture width through“interception”and“co-bridging”modes,thus improving plugging zone formation efficiency.Appropriate particle size and concentration of flaky LCMs increase the area and length of the plugging zone.This reduces the fracture width increment caused by injection pressure and enhances frictional force between the plugging zone and fracture surface,thereby improving the pressure-bearing capacity of the plugging zone.However,excessively high concentrations of flaky LCMs result in decreased structural stability of the plugging zone,and excessively large particle sizes increase the risk of plugging outside fracture inlet.The recommended concentration of flaky LCMs in the plugging slurry is 2%–3%,with a particle size 1.2 to 1.5 times that of the bridging granular LCMs and not exceeding twice the fracture width.This study provides a theoretical foundation for selecting LCMs and designing plugging formulations for field applications.
基金support of the National Natural Science Foundation of China(Grant No.52371279)the Program for International Exchange and Cooperation in Education by the Ministry of Education of the People's Republic of China(Grant No.57220500123).
文摘Lost circulation of drilling fluid is one of the most common and costly problems in drilling operations.This highlights the importance of wellbore strengthening treatment sthat can utilize lost circulation materials(LCMs)to seal fractures associated with the wellbore.In this work,a numerical model accounting for the deformation of surrounding rock,fluid flow in the fracture,fracture propagation,and the transport of LCMs is presented to investigate the wellbore strengthening,from the fracture initiation to the fracture arrest,due to plugs formed by LCMs.The equations governing the rock deformation and fluid flow are solved by the dual boundary element method and the finite volume method,respectively.The transport of LCMs is solved based on an empirical constitutive model in suspension flow,and several characteristic quantities are derived by dimensional analysis.It is found that two dimensionless parameters,dimensionless toughness and normalized initial particle concentration,control the migration of LCM particles.The numerical results show that the dimensionless toughness influences the entrance and bridging of LCMs while the initial concentration controls the location of the particle bridging.When the initial concentration is larger than 0.8,the particle bridging tends to occur near the fracture entry.Conversely,when the initial concentration is less than 0.8,the particle bridging occurs near the fracture tip.This work provides an effective tool to predict the LCM transport and plugging in the wellbore strengthening process.
基金Supported by National Natural Science Foundation of China(51991361,52074327,U1762212)Major Engineering Technology Field Tes Project of CNPC(2020F-45)。
文摘By reviewing the mechanisms of drilling fluid lost circulation and its control in fractured formations, the applicability and working mechanisms of different kinds of lost circulation materials in plugging fractured formations have been summarized. Meanwhile, based on the types of lost circulation materials, the advantages, disadvantages, and application effects of corresponding plugging technologies have been analyzed to sort out the key problems existing in the current lost circulation control technologies. On this basis, the development direction of plugging technology for severe loss have been pointed out. It is suggested that that the lost circulation control technology should combine different disciplines such as geology, engineering and materials to realize integration, intelligence and systematization in the future. Five research aspects should be focused on:(1) the study on mechanisms of drilling fluid lost circulation and its control to provide basis for scientific selection of lost circulation material formulas, control methods and processes;(2) the research and development of self-adaptive lost circulation materials to improve the matching relationship between lost control materials and fracture scales;(3) the research and development of lost circulation materials with strong retention and strong filling in three-dimensional fracture space, to enhance the retention and filling capacities of materials in fractures and improve the lost circulation control effect;(4) the research and development of lost circulation materials with high temperature tolerance, to ensure the long-term plugging effect of deep high-temperature formations;(5) the study on digital and intelligent lost circulation control technology, to promote the development of lost circulation control technology to digital and intelligent direction.
文摘Fractured carbonate reservoirs are susceptible to blowout and lost circulation during drilling,which not only restricts drilling speed,but also poses big threat to well control.Moreover,there are few technical means available to reconstruct pressure balance in the borehole.Accordingly,the fine managed pressure drilling was used in the drilling of Well GS19 in the Qixia Formation with super-high pressure and narrow density window,which is a success:①back pressure in the annular spaces will be adjusted to maintain a slightly over-balanced bottom-hole hydraulic pressure,and fluid level in the circulation tank will be kept in a slight dropping state to ensure that natural gas in the formation would not invade into the borehole in a massive volume;②inlet drilling fluid density will be controlled at around 2.35 g/cm^(3),back pressures in the annular be maintained at 2-5 MPa,and bottom-hole pressure equivalent circulation density be controlled at 2.46-2.52 g/cm^(3);③during managed pressure drilling operations,if wellhead pressure exceeds or expects to exceed 7 MPa,semi-blind rams will be closed.Fluids will pass through the choke manifold of the rig to the choke manifold specifically for pressure control before entering gas/liquid separators to discharge gas;④during tripping back pressure will be kept at less than 5 MPa,volume of injected drilling fluid will be higher than the theoretical volume during tripping out,whereas the volume of returned drilling fluid will be higher than the theoretical volume during the out-tripping.This technique has been applied successfully in the drilling of the Qixia Formation,Liangshan Formation and Longmaxi Formation with a total footage of 216.60 m,as a good attempt in complicated wells with both blowout and lost circulation risks,which can provide valuable experiences and guidance for handling similar complexities in the future.
基金financially supported by the National Natural Science Foundation of China(Grant 52074327,51991361)the Natural Science Foundation of Shandong Province,China(ZR2020QE107)
文摘Lost circulation of drilling fluid is one of the most common engineering problems in the drilling process of fractured formations.In this study,an oil-absorbing polymer gel synthesized using compound monomers with rigid and flexible chains was applied to control the oil-based drilling fluid loss while drilling.The microstructure,oil-absorbing performance,and plugging performance the gel was investigated.A large number of dense pores on the surface of the gel were observed,which allowed the oil molecules to enter the internal space of the gel.The initial oil absorption capacity of the gel was fast,and it increased with the increase in the temperature and decrease in the particle size,reaching 20.93 g/g at140℃.At a high temperature of 140℃,the bearing pressure capacity of the gel formula containing particles of different particle sizes reached 7.6 MPa for a fracture of a width of 3 mm,showing that the oil-absorbing gel have excellent plugging performance at high temperature.Plugging mechanism of the gel was investigated through visualized fracture plugging experiments.Results show that the dynamic migratio n,particle-swelling,particle-bridging,particle-aggregation,deformation-filling,and compaction-plugging contribute to the whole lost circulation control process,reflecting that the plugging performance can be effectively enhanced by improving the aggregation and filling degrees of the gel with different particle sizes.
基金supported by the National Natural Science Foundation(Grant No.51874329 and Grant No.52004297 and Grant No.51991361)the National Natural Science Innovation Population of China(Grant No.51821092)+1 种基金the Strategic Cooperation Technology Projects of CNPC and CUPB(Grant No.ZLZX2020-01)Cooperation projects of CCDC and CUPB(CQ2021B-33-Z2-3)。
文摘Loss of drilling fluids in large porous and fractured zones inevitably up-regulates the overall cost of drilling.As a type of acid-soluble cement,magnesium oxysulfate(MOS)cement is arousing huge attention for the less hygroscopic nature and less damaging to steel casings compared with magnesium oxychloride(MOC)cement.The present study developed MOS cement as a fast setting,high strength and acid-soluble lost circulation material to reduce the problem of losses.As suggested in this study,a higher strength of MOS cement at 70℃could be achieved by elevating M_(g)O/MgSO_(4)·7 H_(2)O molar ratio or downregulating H_(2)O/MgSO_(4)·7 H_(2)O molar ratio.Boric acid and borax could act as effective retarders.Plugging slurry based on MOS cement could effectively block the simulated porous loss zones exhibiting a diameter from 1.24 mm to 1.55 mm,as well as the fractured loss zones with a width from 2 mm to 5 mm and bearing a pressure difference up to 8 MPa.Permeability recovery test demonstrated that it facilitated future oil and gas production.The successful field application in the Junggar Basin,Xinjiang,China verified the significant plugging effect of MOS cement for severe loss problems.
基金Supported by the National Natural Science Foundation of China(Grant No.51604236)Science and Technology Program of Sichuan Province(Grant No.2018JY0436)the Sichuan Province Youth Science and Technology Innovation Team Project(Grant No.2016TD0016)
文摘Focused on the lost circulation control in deep naturally fractured reservoirs, the multiscale structure of fracture plugging zone is proposed based on the theory of granular matter mechanics, and the structural failure pattern of plugging zone is developed to reveal the plugging zone failure mechanisms in deep, high temperature, high pressure, and high in-situ stress environment. Based on the fracture plugging zone strength model, key performance parameters are determined for the optimal selection of loss control material(LCM). Laboratory fracture plugging experiments with new LCM are carried out to evaluate the effect of the key performance parameters of LCM on fracture plugging quality. LCM selection strategy for fractured reservoirs is developed. The results show that the force chain formed by LCMs determines the pressure stabilization of macro-scale fracture plugging zone. Friction failure and shear failure are the two major failure patterns of fracture plugging zone. The strength of force chain depends on the performance of micro-scale LCM, and the LCM key performance parameters include particle size distribution, fiber aspect ratio, friction coefficient, compressive strength, soluble ability and high temperature resistance. Results of lab experiments and field test show that lost circulation control quality can be effectively improved with the optimal material selection based on the extracted key performance parameters of LCMs.
文摘During well-killing operations for the workover of low-pressure gas wells,formation pressure should be balanced so as to guarantee well control safety by preventing natural gas overflow.In this paper,a laboratory evaluation was conducted with fuzzy-ball fluids as killing fluids.The results show that,the fuzzy-ball fluid,with a density of 0.5e1.5 g/cm^(3) and a viscosity up to 78,50,000 mPa$s at a low shear rate,realizes controllable performance and forms piston-like plugging slugs of solid-free high structural strength on natural gas wellbore after bonding.During well workover,multiple fluid column pressures were set up by injecting fuzzy-ball fluids with different densities at various rates.Owing to high structural strength of the fluids at a low shear rate,natural gas breaks through only inside the piston-like slug and cannot flow upwards to the ground,so the pathways of natural gas in the wellbore are isolated from the ground surface.Moreover,the fluid can wholly move up and down like a piston-like plug,with the change of formation pressures or the tripping of pipe strings.Like the conventional operations,the production can be restored after the workover,so long as the fluid in wellbore is cleaned by means of gas lift.In a natural gas field in NW China,where the formation pressure coefficient dropped to 0.60e0.82,three wells were fully filled with fuzzy-ball workover fluids for 7 days and another three wells were treated with the piston-like plugs of fuzzy-ball workover fluids for only 3 days.They all presented better technical results.The technology provides a new way for low-pressure gas well workover.
文摘Lost circulations have presented great challenges to the petroleum industry, causing great expenditures of cash and time to fighting the problem. Probably the most problematic situations are the naturally fractured formations where the operator may face total loss with no mud return in the annular. The voids or large fracture encountered in this case are often far too large to be plugged with conventional Lost Circulation Material. This paper will give a detailed introduction on a novel composite gel material usable to control severe losses and pressurization sealing. The plugging mechanics of this new composite gel material, which is different from conventional lost circulation materials, were elaborated as well. In addition, the properties of the new composite gel material such as thermostability, sealing strength and bearing resistance are characterized with specific experimental devices. The experimental results proved that the breakdown pressure of the new plugging reached more than 20MPa, and the maximum degraded temperature can be exceed 130℃. The field application at 4 wells in Puguang gas field, SINOPEC, demonstrated that the new composite gel material solved the serious loss in Ordovician carbonate fractured formation successfully and guaranteed the following completion cement operation smoothly. The composite gel sealing slurries, which was easily prepared on site, gives remarkable properties regarding pumping through drill pipes, adjustment of setting time and excellent sealing strength of the lost zone sealing, additionally, the whole pressurization sealing process was complicated within only ten hours. The on-site results show that the plugging ratio of the new composite gel was reached 100%, and the success rate of sealing operation kept above 80%.Thus the new LCM can guarantee safe drilling jobs and save operation cost more effectively.
文摘The well-known“lost circulation”problem refers to the uncontrolled flow of whole mud into a formation.In order to address the problem related to the paucity of available data,in the present study,a model is introduced for the lost-circulation risk sample profile of a drilled well.The model is built taking into account effective data(the Block L).Then,using a three-dimensional geological modeling software,relying on the variation function and sequential Gaussian simulation method,a three-dimensional block lost-circulation risk model is introduced able to provide relevant information for regional analyses.
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support from the National Natural Science Foundation of China(Grant Nos.52274009,51604236)the Sichuan Province Youth Science and technology innovation team project(No.2021JDTD0017)the Sichuan Province Science and Technology Project(Grant No.2018JY0436).
文摘Ultra-deep geological conditions are complex, often leading to leakage issues. As the depth increases during ultra-deep bridging lost-circulation operations, the varying settling velocities of different types of lost circulation materials(LCMs) lead to gravitational differentiation. This causes stratification of the LCMs, forming an unevenly dispersed system and reduced plugging efficacy. An experimental methodology is described for assessing the density suitability between LCMs and drilling fluids, which calculates the density suitability factor(DSF) by measuring the density of the plugging slurry at various locations after a designated resting period, ultimately evaluating its density suitability based on the DSF. Experimental results indicate that LCMs with lower densities demonstrate superior density suitability compared to those with higher densities. Smaller particle sizes(10-40 mesh) show better density suitability than larger ones(2-6 mesh). Fracture-plugging experiments validated this method, the plugging slurry composed of a good density suitability material, such as walnut shells, exhibited no notable gravitational differentiation after 2 h, achieving a maximum plugging pressure of 16.4 MPa with88 m L of total volume loss. In contrast, the slurry formed with poorly density suitability materials, such as calcite, showed significant gravitational differentiation after 2 h, achieving only 9.6 MPa in maximum plugging pressure and a total volume loss of 96 m L. These findings highlight that LCMs with superior density suitability enhance plugging efficiency, highlighting the critical role of density suitability testing and the optimization of plugging formulations to improve the success of plugging operations.
基金supported by National Natural Science Foundation of China(52304006,52274032,and 51774062)the General Project of the Chongqing Natural Science Foundation(CSTB2022NSCQ-MSX1554 and CSTB2022NSCQ-MSX0349)Shaanxi Province Key Laboratory of Environmental Pollution Control and Reservoir Protection Technology of Oilfields and Engineering Research Center of Oil and Gas Field Chemistry,Universities of Shaanxi Province(XSYU-CCCE-2402).
文摘Lost circulation of drilling fluid is an international engineering problem during drilling.Aiming at the problems of the first-time lost circulation control success rate and poor adaptability of traditional lost circulation materials,a new self-healing lost circulation material based on dynamic disulfide bonds was prepared and named CKSH.In this paper,the particle size of self-healing lost circulation material was from 0.1 to 5 mm.The structure was analyzed by modern characterization means,and the drilling fluid compatibility,self-healing performance were evaluated.The self-healing and bridging-filling-sealing mechanism of CKSH were revealed.The results showed that the healing rate of CKSH could reach100%after 12 h over 70℃.It showed good compatibility with drilling fluid,with no effect on rheology or filtration loss.It could be stably suspended in drilling fluid,and the temperature resistance reached140℃.Healing by self-healing lost circulation materials of different particle size,the pressure bearing capacity of plugging zone were over 12 MPa for fracture opening of 1–5 mm.It could play a synergistic role with traditional lost circulation materials by chemical bonding,and the repeated loss caused by physical plugging was avoided.The research results of this paper can improve the bridging plugging bearing pressure strength and the first-time lost circulation control success rate,which is of great significance for improving drilling efficiency and reducing non-productive time.
基金supported by the National Natural Science Foundation of China(No.52074312)the CNPC Science and Technology Innovation Foundation(No.2021DQ02-0505)+1 种基金the Open Fund Project of the National Key Laboratory for the Enrichment Mechanism and Efficient Development of Shale Oil and Gas(No.36650000-24-ZC0609-0006)the Major Science and Technology Project of Karamay City(No.20232023zdzx0003).
文摘Due to complex geological structures and a narrow safe mud density window,offshore fractured formations frequently encounter severe lost circulation(LC)during drilling,significantly hindering oil and gas exploration and development.Predicting LC risks enables the targeted implementation of mitigation strategies,thereby reducing the frequency of such incidents.To address the limitations of existing 3D geomechanical modeling in predicting LC,such as arbitrary factor selection,subjective weight assignment,and the inability to achieve pre-drilling prediction along the entire well section,an improved prediction method is proposed.This method integrates multi-source data and incorporates three LC-related sensitivity factors:fracture characteristics,rock brittleness,and in-situ stress conditions.A quantitative risk assessment model for LC is developed by combining the subjective analytic hierarchy process with the objective entropy weight method(EWM)to assign weights.Subsequently,3D geomechanical modeling is applied to identify regional risk zones,enabling digital visualization for pre-drilling risk prediction.The developed 3D LC risk prediction model was validated using actual LC incidents from drilled wells.Results were generally consistent with field-identified LC zones,with an average relative error of 19.08%,confirming its reliability.This method provides practical guidance for mitigating potential LC risks and optimizing drilling program designs in fractured formations.
基金the Science and technology program of Sichuan Province(2018JY0436)the Innovation Fund for Postgraduates Research of Southwest Petroleum University(2019cxyb027)+2 种基金Important and Special Project of China(No.2016ZX05052)sponsored by the Ministry of Science and Technology of ChinaNational Natural Science Foundation of China(51604236).
文摘Working fluids loss is a major contributor to low productivity during production process of fractured tight reservoirs.Lost circulation control effect directly related to the tribological behavior between fracture surface and lost circulation materials(LCMs).In this study,the friction coefficient(FC)was investigated using typical clastic rocks and LCMs by considering multiple effect factors divided into external condition and internal condition.The results show that normal load had a relatively high effect on sliding model.A positive correlation was observed between FC and asperities heights.FC decreased induced by particle size degradation of rigid LCMs.Elastic LCMs manifested higher FC compared with rigid LCMs.Under the lubrication condition by working fluid,FC of rigid LCMs was mainly controlled by their surface wettability.FC of organic LCMs is more sensitive to high temperature aging than inorganic LCMs.Fracture plugging experiments show that LCMs optimized based on the research results can effectively improve the efficiency and strength of fracture plugging.
基金The authors gratefully acknowledge the financial support of the National Key R&D Program of China(No.2018YFC031020201)the Sichuan Science and Technology Project(2019YFS0045).
文摘A new model was established based on the flow model of the drilling fluid in one-dimensional radial fracture to research the influencing factors on conversion time between lost circulation and overflow for multi-pressure system in fractured reservoirs.And the equation of the conversion time between lost circulation and overflow is obtained by solving the mathematical model.The model were validated by reproducing the field data from Sichuan oil field and the simulation results of references.The influences of consistency index,liquidity index,dynamic shear force,drilling fluid density,drilling fluid intrusion depth,pressure of lost circulation layer,crack width,decreased height of annular liquid level,pressure of high-pressure layer were analyzed.Results indicate that conversion time between lost circulation and overflow increases with the increasing consistency index,liquidity index,dynamic shear force,drilling fluid density,drilling fluid intrusion depth,pressure of lost circulation layer.Conversion time between lost circulation and overflow decreases with the increasing crack width,decreased height of annular liquid level,pressure of high-pressure layer.The time interval of“Hang's Muddingoff”operating should be appropriately less than the conversion time between lost circulation and overflow.Under the premise of ensuring wellbore safety,appropriately increasing the consistency index,liquidity index and dynamic shear force of the drilling fluid can effectively increase the conversion time between lost circulation and overflow in large fractured stratum.
文摘Lost circulation is the most common problem encountered while drilling oil wells.Occurrence of such a problem can cause a lot of time and cost wastes.In order to drill oil wells,a fast and profitable way is necessary to predict and solve lost circulation problem.Expert system is a method used lately for problems that deal with uncertainty.In this paper,three approaches are carried out for prediction of lost circulation problem.These approaches include design of experiments(DOE),data mining,and adaptive neuro-fuzzy inference system(ANFIS).Data of 61 wells of Maroon oilfield are selected and sorted as the feed of the systems.Seventeen variables are used as inputs of the approaches and one variable is used as the output.First,DOE is conducted to observe the effects of variables.Plackett-Burman method is used to determine the effects of variables on lost circulation.After that,data mining is conducted to predict the amount of lost circulation.The class of regression is used to determine a function to model the data and the error of the model.Then,ANFIS is applied to predict the amount of lost circulation.The chosen data are used in order to train,test,and control the ANFIS.Furthermore,subtractive clustering is used to train the fuzzy inference system(FIS)of the model.The performance of the ANFIS model is assessed through the root mean squared error(RMSE).The results suggest that ANFIS method can be successfully applied to establish lost circulation prediction model.In addition,results of ANFIS and data mining are investigated through their prediction performances.The comparison of both methods reveals that ANFIS error is much lower than data mining.
文摘Oil and gas operators worldwide are expecting service companies to deliver integrated techniques to minimize,if not prevent,drilling problems.Drilling fluids perform vital functions to ensure the success of drilling operations.The technical challenges often associated with water-based drilling fluids are loss of critical properties,such as fluid loss control and rheology,under demanding conditions,such as in drilling deeper,high-temperature and high-pressure wells.Fluid loss during drilling operations has a very significant effect in both reservoir formation damage and monetary terms.The use of durian rind(DR)as a new additive in controlling lost circulation would provide another opportunity to reduce waste and avoid pollution.Therefore,DR was used to improve the rheological properties of water-based mud,and it was prepared for use as a fluid loss additive.For a better understanding of the influence of pectin on drilling mud properties,the rheological evaluation of untreated DR was compared to that of mud samples containing treated DR.The pectin in DR was extracted using four different solvents,namely,ethanol,methanol,sodium hydroxide and hydrogen peroxide,and the most effective solvent to remove the pectin was then determined.The Fourier transform infrared spectroscopy(FTIR)results showed that NaOH was the best solvent for removing pectin from DR.Thermogravimetric analysis(TGA)was used to determine the thermal stability of DR before and after treatments.The TGA results demonstrated that the treated DR had improved thermal stability compared to untreated DR.The sizes of DR used were coarse,medium,and fine.The untreated DR presented better rheological properties than the treated DR.The experimental investigation showed that a concentration of 20 lb/bbl of intermediate-sized DR was the best concentration among the tested samples.
文摘Lost circulation is an expensive and critical problem in the drilling operations.Millions of dollars are spent every year to mitigate or stop this problem.In this work,data from over 3000 wells were collected from multiple sources.The data went through a processing step where all outliers were removed and decision rules were set up.Multiple machine learning methods(support vector machine,decision trees,logistic regression,artificial neural networks,and ensemble trees)were used to create a model that can predict the best lost circulation treatment based on the type of loss and the reason of loss.5-fold cross-validation was conducted to ensure no overfitting in the created model.After using all the aforementioned machine learning methods to train models to choose the best lost circulation treatment,overall,the results showed that support vector machine had the highest accuracy among the other algorithms.Thus,it was selected to train the model.The created model went through quality control/quality assurance(QC/QA)to limit the results of incorrect classification.Two treatments were suggested to treat partial loss,four to treat severe loss,and seven for complete loss,based on the reason of loss.In addition,a formalized methodology to respond to lost circulation was provided to help the drilling personnel handling lost circulation in the field.
文摘A major cause of some of serious issues encountered in a drilling project,including wellbore instability,formation damage,and drilling string stuck e which are known to increase non-productive time(NPT)and hence the drilling cost e is what we know as mud loss.The mud loss can be prevented or at least significantly reduced by taking proper measures beforehand provided the position and intensity of such loss can be properly predicted using an accurate predictor model.Accordingly,in this study,we used the convolutional neural network(CNN)and hybridized forms of multilayer extreme learning machine(MELM)and least square support vector machine(LSSVM)with the Cuckoo optimization algorithm(COA),particle swarm optimization(PSO),and genetic algorithm(GA)for modeling the mud loss rate based on drilling data,mud properties,and geological information of 305 drilling wells penetrating the Marun Oilfield.For this purpose,we began by a pre-processing step to attenuate the effect of noise using the Savitzky-Golay method.The whole set of available data was divided into the modeling(including 2300 data points)and the validation(including 483 data points)subsets.Next,the second generation of the non-dominated sorting genetic algorithm(NSGA-Ⅱ)was applied to the modeling data to identify the most significant features for estimating the mud loss.The results showed that the prediction accuracy increased with the number of selected features,but the increase became negligible when the number of selected features exceeded 9.Accordingly,the following 9 features were selected as input to the intelligent algorithms(IAs):pump pressure,mud weight,fracture pressure,pore pressure,depth,gel 10 min/gel 10 s,fan 600/fan 300,flowrate,and formation type.Application of the hybrid algorithms and simple forms of LSSVM and CNN to the training data(80%of the modeling data,i.e.1840 data points)showed that all of the models tend to underestimate the mud loss at higher mud loss rates,although the CNN exhibited lower underestimation levels.Error analysis on different models showed that the CNN provided for a significantly higher degree of accuracy,as compared to other models.The more accurate outputs of the hybrid LSSVM model than those of the simple LSSVM indicated the large potentials of metaheuristic algorithms for achieving optimal solutions.The lower error levels obtained with the CNN model in the testing phase highlighted the excellent generalizability of this model for unseen data.The more accurate predictions obtained with this model,rather than the other models,in the validation phase further proved this latter finding.Therefore,application of this method to other wells in the same field is highly recommended.
