Lithologic Reservoirs

Focusing on the facts that the type and accuracy of sequence boundaries identified on seismic is lower than that on logging and the established sequence framework cannot favorably meet the needs of lithologic reservoir exploration,a method of seismic subtle sequence boundary identification and high-frequency sequence framework establishment was proposed based on logging-seismic time-frequency matching analysis and seismic all-reflector tracking. Technically,it involves the time-frequency analysis of logging,logging calibration to seismic and seismic all-reflector tracking based on seismic time-frequency analysis,and the relationship of seismic reflection cycles matching to logging was obtained and the high-resolution spatial sequence framework was established. The sequence boundaries within this framework not only have clear geological meanings of sedimentary cycles,but also have high resolution. It can effectively identify the subtle sequence boundary which is difficult to be recognized by conventional method,and favorably meet the accuracy requirements for lithologic trap identification and description in sequence stratigraphy study. The Jurassic in the western margin of Turpan-Kumul Basin demonstrated the application of this method and good result was achieved. It is helpful for tapping the potential of seismic interpretation,high-resolution sequence stratigraphy study and lithologic reservoir exploration.

Distribution characteristics and controlling factors of movable fluid in tight sandstone gas reservoir: a case study of the eighth member of Xiashihezi Formation and the first member of Shanxi Formation in western Sulige Gas Field

LIU Na, ZHOU Zhaohua, REN Dazhong, NAN Junxiang, LIU Dengke, DU Kun

2019, Vol.31(6): 14–25 Abstract ( 345 ) PDF (7609 KB) ( 392 )

doi: https://doi.org/10.12108/yxyqc.20190602

The tight sandstone gas reservoir in Ordos Basin has great development potential. However,the existence of micro-nanopore structure increases the difficulty of fluid seepage and the development. The eighth member of Xiashihezi Formation(He 8)and the first member of Shanxi Formation(Shan 1)in the western of Sulige Gas Field were taken as an example to understand the distribution characteristics and controlling factors of movable fluid by using various experiments,including nuclear magnetic resonance(NMR),scanning electron microscopy(SEM),physical property tests and rate-controlled mercury intrusion(RCMI). The results show that:(1)The characteristics of the movable fluid distribution of He 8 and Shan 1 were different,and the average of the movable fluid saturation of the He 8 and Shan 1 sandstones was 48.75% and 23.64%,respectively.(2)The distribution characteristics of movable fluids of He 8 sandstone were controlled by physical properties and porethroat structure,and abundant seepage pathways and pores with relatively large radius led to the high movable fluid saturation,while that of Shan 1 sandstone were hard to be found due to the complex pore-throat network. (3)According to the comprehensive evaluation model,strong signal of residual and dissolved pores derived from NMR,high transitional radius and mercury saturation were the key factors of high movable fluid saturations. The research results clarify the controlling factors of movable fluids in different sections of tight sandstone gas reservoirs,and could provide a theoretical basis for predicting "sweet point" of tight sandstone gas reservoirs and play a guiding role in gas reservoir development.

Sedimentary facies distribution characteristics of Chang 4+5 reservoir in Longdong area,Ordos Basin

ZHENG Qinghua, LIU Qiao, LIANG Xiuling, ZHANG Jiankui, ZHANG Jianna, LIU Tao

2019, Vol.31(6): 26–35 Abstract ( 316 ) PDF (7749 KB) ( 374 )

doi: https://doi.org/10.12108/yxyqc.20190603

In order to study the distribution characteristics of sedimentary facies of Chang 4+5 reservoir in Longdong area of Ordos Basin,core observation,casting thin section identification,heavy mineral testing and log rockelectricity relationship analysis were carried out in outcrop profile and drilling coring. The results show that:(1)The deposits of Chang 4+5 reservoir in Longdong area are mainly controlled by three provenance areas in northeast, southwest and south;(2)Three types of sedimentary facies are mainly developed in the study area,inclu-ding meandering river delta facies in the northeast,braided river delta facies in the southwest and south,and lacu-strine facies in the central region,which can be further divided into five types of subfacies and 10 types of microfacies; (3)The Chang 4+5 reservoir in the study area is mainly characterized by "lake retreat-sand progradation". The lake basin area of Chang 4+51 sublayer is smaller than that of Chang 4+52 sublayer,but the scale of sand body is larger;(4)Compared with the southwest and south,the northeast has a more abundant supply of provenances and many underwater distributary channels converge. As a result,thick sand bodies with overlapping and continuous distribution are more developed. The research results show the exploration potential of Chang 4+5 reser-voir in Longdong area,which can provide reference for further fine exploration.

Distribution and genetic mechanism of overpressure in western Sichuan foreland basin

WANG Zhihong, HAO Cuiguo, LI Jianming, FENG Zhenzhi, HUANG Changwu

2019, Vol.31(6): 36–43 Abstract ( 309 ) PDF (1791 KB) ( 700 )

doi: https://doi.org/10.12108/yxyqc.20190604

Formation overpressure is one of the main driving forces for hydrocarbon migration and accumulation. In order to study the distribution and genetic mechanism of the Triassic-Jurassic overpressure system and its contribution to natural gas reservoir formation in western Sichuan,a quantitative study on the genetic mechanism based on comprehensive compaction models and differential stress models was carried out. The results show that:(1)There are four types of overpressure distributed vertically in the Upper Triassic-Jurassic in western Sichuan:bell-shaped,spindle-shaped,step-shaped and composite type,which are distributed in the front edge of nappe,southwest Sichuan,northwest Sichuan and central Sichuan respectively. The first two types have a weak preservation ability of fluids,while the latter two ones have a strong storage retention ability to fluids.(2)The central and northern parts are the center of the overpressure zone in the Upper Triassic strata,while the overpressure center in the Jurassic strata is in the central area with the abnormal amplitudes descending to its periphery areas, and the hydrostatic pressure is maintained in the piedmont area of the Longmen Mountains.(3)The development of abnormal formation pressure in western Sichuan Basin has undergone the stages of sedimentary overpressure (Late Triassic-Eocene)and tectonic overpressure(Oligocene to present),of which the Late Triassic-Early Cretaceous is the supercharging stage of the sedimentary overpressure,and the Late Cretaceous-Eocene is the dissipation stage of the sedimentary overpressure.(4)The present overpressure is superimposed by residual sedimentary overpressure and overpressure resulted from tectonic compression. For the overpressure in the central and northern regions,the contribution of tectonic compression pressurization is 30% to 60%,while the overpressure in the south is mostly caused by the tectonic compression pressurization. The residual sedimentary overpressure is mainly formed by hydrocarbon generation in the middle and late stages of Yanshanian movement period. The research results have guiding significance for finding overpressure reservoirs.

Hydrothermal action of Middle Permian Qixia Formation in northwestern Sichuan Basin and its effect on reservoirs

YANG Yuran, ZHANG Ya, XIE Chen, CHEN Cong, ZHANG Xiaoli, CHEN Shuangling, GAO Zhaolong

2019, Vol.31(6): 44–53 Abstract ( 279 ) PDF (7620 KB) ( 331 )

doi: https://doi.org/10.12108/yxyqc.20190605

Deep hydrothermal fluids can improve the reservoir properties of carbonate rocks in northwestern Sichuan Basin. In order to study the effect of hydrothermal fluid on the reservoir of Middle Permian Qixia Formation in northwestern Sichuan Basin,the core and thin section observation and geochemical analysis of trace elements and strontium isotopes were analyzed. The results show that:(1)The reservoir of Middle Permian Qixia Formation was reformed by deep hydrothermal fluid. Hydrothermal minerals such as saddle-shaped dolomite,pyrite,chlorite and quartz were found in part of dissolved holes,and hydrothermal breccia carbonate rocks,an important lithofacies indicator of hydrothermal activity,were found in drilling coring.(2)Compared with limestone without hydrothermal modification,pinhole dolomite and saddle-shaped dolomite show the characteristics of delta δ18O negative migration,87Sr/86Sr positive migration,high Mn and low Sr.(3)Multi-stage magma-tectonism took place in Late Permian to Late Triassic in the study area,and a large number of deep hydrothermal fluids entered the sedimentary strata through deep and large faults,resulting in significant dissolution of surrounding rocks,forming a good reservoir space. The research results are of great significance for the deep exploration of high quality dolomite reservoirs.

Diagenesis and secondary pore evolution of Middle and Upper Permian clastic rocks in Wu-Xia area,Junggar Basin

LI Jiasi, FU Lei, ZHANG Jinlong, CHEN Jing, NIU Bin, ZHANG Shuncun

2019, Vol.31(6): 54–66 Abstract ( 322 ) PDF (11768 KB) ( 292 )

doi: https://doi.org/10.12108/yxyqc.20190606

The Middle and Upper Permian clastic reservoirs in Wu-Xia area of Junggar Basin are deeply buried and poor in reservoir properties,mainly with secondary pores. Diagenesis is the most important factor affecting the development of secondary pores in middle-deep reservoirs. Based on casting thin section identification,scanning electron microscopy(SEM),X-ray diffraction analysis method with logging and mud logging data,the diagenesis and secondary pore evolution of the Middle and Upper Permian clastic rocks in Wu-Xia area were studied. The results show that the reservoir compositional maturity and textural maturity were low and the most pores were secondary pores. The average porosity of lower Urho Formation and Xiazijie Formation was 8.15% and 7.85% respectively,secondary pores account for 77.18% and 80.90% respectively,and the amount of hyperplasia of pores was 6.49% and 4.74% respectively. The clastic reservoir in the study area was mainly at the A-B stage of the middle diagenetic stage,and the diagenesis was dominated by compaction,cementation and dissolution. The degree of porosity loss caused by compaction and cementation was 24.5% and 6.14% respectively. Dissolution was the main cause of secondary pores and the dissolution of feldspar and debris particles contributed the most to secondary pore growth. Lower Urho Formation and Xiazijie Formation have the rate of 47.62% and 55.86% respectively. Affected by atmospheric water dissolution,fault zone and dissolution of organic acids,there are three secondary pore development zones vertically developed in the reservoir of the study area. The secondary pore development zones are important zones for finding relatively favorable reservoirs under low porosity and low permeability conditions.

Thermal evolution history and prediction of favorable zones in Lunpola Basin

GENG Tao, MAO Xiaoping, WANG Haochen, FAN Xiaojie, WU Chonglong

2019, Vol.31(6): 67–78 Abstract ( 277 ) PDF (8413 KB) ( 276 )

doi: https://doi.org/10.12108/yxyqc.20190607

Lunpola Basin is the most oil-gas exploration potential basin found in Tibet,and has a broad prospect for exploration. In order to study the thermal evolution history of source rocks and the law of oil and gas migration and accumulation in this area,drilling core analysis,2-D seismic data interpretation,single well thermal evolution history modeling,simulation analysis of oil-gas migration and accumulation were carried out. The results show that:(1)Thick turbidite sand bodies were identified at the bottom of the lower submember of the third member of Niubao Formation in wells W1 and W2.(2)At the end of Eocene,affected by the double action of high heat flow and high geothermal gradient,the source rocks of the middle submember of the second member of the Niubao Formation began to generate hydrocarbons and the process has been continuing to this day. The maturation of source rocks tended to be early in the west and late in the east. During this period,a small amount of hydrocarbon mainly migrated in Jiangri Aco Sag and Jiangjiaco Sag,and accumulated in the uplift zone and its periphery in the sag.(3)In the early Oligocene,large-scale hydrocarbon migration took place in Pacuo Sag. Hydrocarbon migrated northward and southward along the dominant migration pathway and upward through faults. It is inferred that there are 10 favorable oil-gas accumulation zones in the middle part of the thrust nappe belt in the northern basin and in the middle and western part of the southern thrust uplift belt in the southern basin,as well as in the eastern part of Jiangjiacuo Sag and the western part of Pacuo Sag. The study results provide a basis for oil and gas exploration in Lunpola Basin.

EXPLORATION TECHNOLOGY

Application of PP-wave and SS-wave joint interpretation technology in gas cloud area

CHEN Guowen, DENG Zhiwen, JIANG Tailiang, ZHANG Junyong, YU Xuejiao, QI Chengye, XI Xiaoping

2019, Vol.31(6): 79–87 Abstract ( 234 ) PDF (12151 KB) ( 287 )

doi: https://doi.org/10.12108/yxyqc.20190608

Sanhu area in Qaidam Basin is the main natural gas producing area of Qinghai Oilfield. However, Quaternary biogas reservoirs in this area have many geologic characteristics,such as new stratigraphic sedimentary age,poor diagenesis and loose rock structure,which lead to poor seismic structural imaging and low prediction accuracy of low abundance gas reservoirs in gas cloud area. Based on the high-quality P-wave and pure SSwave data acquired from the 2-D joint excitation test of"low frequency+S-wave"for oil and gas exploration,the joint calibration,joint interpretation and joint attribute analysis of PP-wave and SS-wave were adopted. The results show that there are micro-faults,and many low-amplitude structural traps and seismic anomaly traps have been found in the shallow layer of sanhu area. A set of PP-wave and SS-wave joint interpretation supporting technologies applicable for the shallow biogas in Sanhu area was formed,which fully shows the good application prospects of the PP-wave and SS-wave joint seismic exploration technology.

Time-varying wavelet deconvolution method based on zero-offset VSP data

ZHAO Yan, MAO Ningbo

2019, Vol.31(6): 88–94 Abstract ( 239 ) PDF (7622 KB) ( 302 )

doi: https://doi.org/10.12108/yxyqc.20190609

An effective way to improve the resolution of surface seismic data is to extract deconvolution operators from VSP data and use them for surface seismic data. However,the conventional VSP wavelet deconvolution method commonly extracts a fixed deconvolution operator without considering the time-varying characteristics of seismic wavelet. Since seismic wavelet is time-varying,it is not accurate to extract a wavelet deconvolution operator from VSP for surface seismic records. A method was proposed for extracting time-varying wavelet deconvolution operators by using VSP data. It takes the down-going direct wave of zero-offset VSP data as oneway VSP seismic wavelet,and converts its amplitude spectrum of the direct wave to that of two-way seismic wavelet by using the attenuation function of subsurface medium. Under the assumption of minimum phase,the time-varying deconvolution operator can be obtained from the amplitude spectrum,and then applied to poststack surface seismic data. Synthetic data and real data examples demonstrate that the proposed method can effectively compensate the amplitude energy and improve the resolution of seismic records.

A set of recognition techniques for thin reservoirs with unconsolidated high-argillaceous sandstone: a case study from X oilfield in Pearl River Mouth Basin

LUO Ze, XIE Mingying, TU Zhiyong, WEI Xihui, CHEN Yiming

2019, Vol.31(6): 95–101 Abstract ( 315 ) PDF (5126 KB) ( 477 )

doi: https://doi.org/10.12108/yxyqc.20190610

Aiming at the problems of poor quality of logging curves,serious overlapping of wave impedance attributes,thin reservoir and strong heterogeneity caused by serious expansion of unconsolidated high-argillaceous sandstone of Hanjiang Formation in X oilfield,Pearl River Mouth Basin,a fine characterization technology for thin reservoir was formed,which is summarized as "three-step method".(1)The elastic curve reflecting real formation characteristics can be obtained by reconstructing logging curves with genetic neural network technology,and then the problem of poor quality of logging curves caused by the serious expansion of unconsolidated sandstone can be solved.(2)A new sensitive characteristic parameter DVT for the identification of thin reservoirs with unconsolidated high-argillaceous sandstone was constructed to distinguish sandstone from mudstone.(3)High resolution inversion method with waveform indication was used to predict the spatial distribution of thin reservoirs with unconsolidated high-argillaceous sandstone. Practical application shows that this technology achieved good application results in water injection efficiency,optimization implementation of adjustment wells and well pattern design of development adjustment scheme in X oilfield. A complete set of technical process has been formed for the prediction of thin reservoir with unconsolidated high-argillaceous sandstone,which solves the difficulty of accurate description of 3-5 m thin reservoir in the oilfield. This technology has reference significance for the characterization of similar reservoirs and the efficient development of oilfields.

Fracture effectiveness evaluation and reservoir quality classification based on electrical imaging data: a case study of Cretaceous in Yaerxia Oilfield

WU Wei, SHAO Guanghui, GUI Pengfei, ZHANG Qian, WEI Haoyuan, LI Guoli, REN Panliang

2019, Vol.31(6): 102–108 Abstract ( 308 ) PDF (2875 KB) ( 428 )

doi: https://doi.org/10.12108/yxyqc.20190611

K1g0 member of Yaerxia Oilfield is a fractured glutenite reservoir with fan delta front subfacies in Liubei area,Jiuquan Basin. Effective fracture is not only the main reservoir space and seepage channel,but also the main controlling factor of productivity. In order to study the validity of fracture in K1g0 member and the classification method of reservoir quality,the effects of three key parameters including fracture width,density and dip angle, on fracture validity were analyzed by using electrical imaging and production test data. Through key parameters and fracture development thickness,the fracture development degree and fracture opening degree were constructed to quantitatively characterize the effectiveness of fractures,and the quantitative evaluation charts of the above two characterization parameters and index of oil production per meter were established. The results show that the fracture development and fracture opening index can better evaluate the effectiveness of fractures in the study area, and the evaluation chart of fracture effectiveness index and reservoir oil production can carry out quantitative and rapid classification of fractured glutenite reservoir quality. The study results can provide a basis for the review of old wells and production prediction of new wells in fractured reservoirs in the study area.

Well logging prediction models of TOC content in source rocks: a case of Wenchang Formation in Lufeng Sag

JIANG Dexin, JIANG Zhenglong, ZHANG He, YANG Shuyue

2019, Vol.31(6): 109–117 Abstract ( 333 ) PDF (2938 KB) ( 590 )

doi: https://doi.org/10.12108/yxyqc.20190612

There is a certain response relationship between well logging parameters and total organic carbon (TOC)content of source rocks,so TOC content can be predicted by well logging parameters. The multi-variate regression model,BP artificial neural network model and curve overlapping model were established between TOC and conventional well log data,including resistivity log,acoustic log,neutron porosity log,gamma-ray log and density log of Wenchang Formation source rocks in Lufeng Sag. The differences of the three models in TOC prediction effect were discussed. The results show that the multi-variate regression model has better TOC prediction effect for semi-deep lake facies and delta front facies,but worse for shore-shallow lake facies. The prediction effect of BP artificial neural network model is better than that of multi-variate regression model,while the curve overlapping model has worse prediction effect. In practical application,the BP artificial neural network model is suitable for areas where logging parameters and TOC are difficult to express with explicit functions and have a large enough data volume,the multi-variate regression model is suitable for areas where logging parameters are significantly correlated with TOC,while the curve overlapping model is suitable for areas where gamma curve responds significantly to clay and organic matter content,and the target curve can be well superposed in non-hydrocarbon source rock beds. Through the analysis of the above models,it can be applied to other sub-sags in the depression.

OIL AND GAS FIELD DEVELOPMENT

Fractal nonlinear seepage model of horizontal wells in fractured-vuggy carbonate reservoirs

JIANG Ruizhong, ZHANG Chunguang, GAO Yihua, GENG Yanhong, YU Hui, LI Haoyuan

2019, Vol.31(6): 118–126 Abstract ( 311 ) PDF (1916 KB) ( 633 )

doi: https://doi.org/10.12108/yxyqc.20190613

Traditional seepage theory based on Euclidean space has limitations in characterizing multi-scale characteristics and heterogeneity of fractured-vuggy carbonate reservoirs. Considering the influence of boundary layer and fluid yield stress,the nonlinear seepage characteristics of dense matrix blocks were described. In addition, the fractal theory was applied to describe the fractal characteristics of the fracture system and the stress sensitivity of reservoirs were considered. The fractal nonlinear seepage model of horizontal well in fractured-vuggy carbonate reservoir was established accordingly. The dynamic pressure curves of the horizontal well were drawn by applying finite element method to solve the seepage model. The seepage law was analyzed by comparing the dynamic pressure curves of different seepage models,and the seepage process was divided into nine flow stages. Then,the sensitivity analyses of parameters such as fractal index and nonlinear parameter were conducted,and combined with logging data,the new model was applied to mine field to explain the seepage parameters. The results show that the nonlinear parameters mainly affect the intensity of cross flow from matrix blocks to fracture system while the fractal index makes the dynamic pressure curves gradually upturned in the middle and late stages of the seepage, and the upwarping degree increases with the increase of the fractal index. The application of the fractal nonlinear model to the field shows that the model meets the actual production status of the reservoir and has a guiding significance for improving the accuracy of the well test interpretation.

Application of flow potential control in water control and oil stabilization of fractured-vuggy carbonate reservoirs

REN Wenbo

2019, Vol.31(6): 127–134 Abstract ( 262 ) PDF (3559 KB) ( 563 )

doi: https://doi.org/10.12108/yxyqc.20190614

In order to solve the production decline caused by water breakthrough and water cut rise in fractured-vuggy reservoirs,based on the existing conventional flow potential characterization of sandstone reservoir and the geologic characteristics of fractured-vuggy reservoirs,a corresponding flow potential characterization method was proposed. Through calculation and simulation,it is clear that the flow potential of fractured-vuggy carbonate reservoir is mainly composed of potential energy and pressure energy. According to the fact that the flow potential is the decisive factor to control the flow of underground fluid,the technical strategy of water control was put forward to control the flow potential by changing the production pressure difference so as to change the flow direction of underground fluid,and the key technologies of flow potential control,such as well selection and adjustment design,which are related to water invasion direction and aquifer size,were formed. Finally,through case analysis,it is further proved that flow potential regulation is an effective means to control water and stabilize oil in fractured-vuggy carbonate reservoirs. Up to now,13 well groups have been implemented in Tahe Oilfield,11 effective wells have been implemented,and the cumulative oil increase is nearly 100,000 tons.

Water-cut rising patterns and optimal water injection techniques of horizontal wells in thin carbonate reservoir with bottom water

SUN Liang, LI Yong, YANG Jing, LI Baozhu

2019, Vol.31(6): 135–144 Abstract ( 366 ) PDF (3577 KB) ( 578 )

doi: https://doi.org/10.12108/yxyqc.20190615

The problem of water cut rising in horizontal wells is becoming more and more prominent,which has a great impact on oil field productivity construction. Water-cut rising performance of horizontal wells in a thin carbonate reservoir with bottom water in A oilfield in the Middle East was studied by analyzing main controlling factors and water flood models. Accordingly,optimal development techniques of water injection were also put forward. Through the analyses of core description,XRMI,thin section and CT scanning,the influencing factors including high-permeability zone,fracture belt,high viscosity oil,bottom water,injection-production ratio,injectionproduction intensity and the relationship between horizontal segments and reservoir were determined,which resulted in the uneven displacement and the rapid rise of water cut. The water-out rising rule was characterized by injected water or bottom water flowing along the high-permeability zone and"strip"flooding of horizontal well. Thus the optimum technical measures including the pattern balancing injection-production,the cyclic flood with variable water injection rate,and the horizontal well sidetracking were proposed,and the development effects of oil stabilization and water-out control have been achieved. These techniques can be applied to similar oil fields.

Optimization adjustment of injection-production structure based on meandering river reservoir architecture

LONG Ming, LIU Yingxian, CHEN Xiaoqi, WANG Meinan, YU Dengfei

2019, Vol.31(6): 145–154 Abstract ( 323 ) PDF (3931 KB) ( 445 )

doi: https://doi.org/10.12108/yxyqc.20190616

In order to study the effect of lateral layer on the injection-production structure,taking the high-curvature meandering river reservoir in the southern part of Bohai L oilfield as the research object,the influence of reservoir architecture on fluid flow was determined based on fine anatomy of sand body configuration,and the reservoir architecture model of meandering river was established. The control effect of reservoir architecture model on fluid flow was studied from the aspects of porosity,permeability,thickness,occurrence,spreading range and formation inclination by numerical simulation. The empirical formula of reservoir control coefficient of meandering river reservoir was established by regression. According to B-L water flooding theory,the expression equation of water flooding sweep coefficient affected by reservoir architecture model was deduced,and the vector adjustment chart of injection-production structure based on meandering river reservoir architecture model was established. The results show that the control effect of the lateral layer on the fluid motion in the meandering river dam does not change with the increase of porosity of the lateral layer. The control effect of the lateral layer is weakened with the increase of the permeability of lateral layer. Increasing the thickness,horizontal width,distribution frequency and formation angle of the lateral layer can enhance the control effect of the lateral layer on fluid flow. After optimizing the D12 well group in the southern Bohai L oilfield by using the injection-production structure vector adjustment chart,the daily oil production increased by 123 m3/d,and the adjustment effect was remarkable,which laid a foundation for further optimization of water injection and tapping of remaining oil under the control of reservoir architecture.

Maxwell model of oil production forecasting

WANG Xin, CHENG Ximing

2019, Vol.31(6): 155–160 Abstract ( 398 ) PDF (1419 KB) ( 571 )

doi: https://doi.org/10.12108/yxyqc.20190517

When using generalized Weng's model to study the prediction of oil production,linear trial and error method is often used to estimate the parameters of the model. This method needs to set one parameter value beforehand and obtain the other two parameters under this condition,which is easy to be influenced by some artificial factors. Based on Maxwell distribution in statistics,a two-parameter Maxwell model was established. Furthermore, three different parameter estimation methods,such as nonlinear optimization,univariate polynomial regression and binary linear regression,were proposed to solve two parameters in the Maxwell model. Taking oil production from 1971 to 2016 in Norway as training data set,the solving processes and calculation results of the three methods were compared,and the advantages and disadvantages of the three methods were analyzed. The results show that the oil production data obtained by the three methods are in good agreement with the actual data, which proves the applicability of the Maxwell model and the accuracy of the parameter estimation method. In addition,the mean square deviations obtained by two regression methods are very small,which shows that the precisions of regression modeling methods are higher,and the maximum production year fitted by non-linear optimization method is more accurate. This study provides a new model and an effective parameter estimation method for oil and gas field production prediction.

PETROLEUM ENGINEERING

Influencing factors of fracture geometry in deep shale gas wells

BIAN Xiaobing, HOU Lei, JIANG Tingxue, GAO Dongwei, ZHANG Chi

2019, Vol.31(6): 161–168 Abstract ( 346 ) PDF (2873 KB) ( 580 )

doi: https://doi.org/10.12108/yxyqc.20190618

There are abundant deep shale gas resources in China. For deep shale gas wells,the casing pressure is usually very high and it is difficult to pump proppants during hydraulic fracturing treatment,however,the production is low as well. How to generate effective fracture system remains an urgent and unresolved issue in deep shale gas wells. Thus,based on lab experiments together with microseismic monitoring data,a fracture propagation model was established using discrete fracture network model of Meyer,especially for deep shale gas wells in southeast Sichuan Basin,and the simulation accuracy is above 85%. Through orthogonal design and variance analysis,it is defined that fracturing fluid viscosity is the main controlling factor affecting fracture geometry especially for fracture width and SRV in deep shale gas wells,and there are two stages for the fracture propagation progress:the rapid growth stage in the early 1/5-1/4 pump time,and the following moderate growth stage. The fracturing design principle was put forward for the target block:fine field control with larger fluid displacement and moderate operation scale,hybrid hydraulic fluid with various viscosity to achieve fully fracture propagation, and continuous smaller proppant loading mode with lower concentration to prop fracture effectively. The fracturing parameters were optimized such as fracturing fluid volume,proppant volume and fluid displacement. A sample horizontal well buried more than 3 900 m was fractured with comprehensive sand-liquid ratio up to 3.51% and maximum sand volume per stage up to 80.6 m3,and the testing production was 11.4×104m3. The research could provide fracturing references for similar horizontal wells in deep shale gas play.