Lithologic Reservoirs

The sandstone property is closely related to the chlorite film of Yanchang Formation in Ordos Basin. The data of cast thin slice and scanning electron microscope with energy disperse spectroscopy were used to analyze the chlorite film of Chang 8 sandstone,so as to study the growth pattern of the chlorite film and its influence on physical properties. The result shows that the chlorite film consists of inner layer film and outer layer film, and the outer layer film can be separated into small crystal sub-layer film and big crystal sub-layer film according to the grain size of crystal chlorite. The small crystal sub-layer film developed in the early diagenetic stage B, and the crystal has small size, poor shape and dense arrangement after rapid crystallization,and the chlorite film had the capacity to retard fluid exchange between the primary pore and the small cavity formed by the dissolution of the framework grain. The inner layer film developed in the small cavity and had low Fe and Mg content with high Si content under the bidirectional block of the small crystal sub-layer film, whose crystal is small in size and poor in shape and disorderly packed because of too narrow space for the growth. As the connectivity of the primary pore changed for the worse and the oil emplaced in the middle diagenetic stage, the velocity of the fluid decreased and the supply of the substance slowed down, which reduced the growth rate of chlorite. In such a process, some crystal chlorites increased in size and sparsely arranged and formed the big crystal sub-layer above the small crystal sub-layer film. The small crystal sub-layer film on the surface of quartziferous clastic particle inhibited quartz overgrowth by occupying the crystalline substrate. The small crystal sub-layer film on the surface of feldspathic clastic particle retarded the dissolution of the feldspathic clastic particle, and the inner layer film in the surface of the framework grain consumed the silicic fluid,which both led to insufficient silicic fluid to generate large amounts of authigenic quartz particles in the primary pore. The chlorite film protected the primary pore from quartz cement.

Deep-water turbidite characteristics and its reservoir development of Chang 7 oil layers in southwestern Ordos Basin

WANG Jianmin, WANG Jiayuan

2017, Vol.29(4): 11–19 Abstract ( 420 ) PDF (6009 KB) ( 629 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2017.04.002

Aiming at the genesis of the deep-water reservoir in lacustrine basin and the potential of petroleum exploration, the deep-water turbidite characteristics and its influence on the reservoirs development of Chang 7 oil layers in LM well field in the southwestern Ordos Basin were studied according to logging,testing,experiments and producing test data, based on single well facies and logging facies analysis. The results show that Chang 7 oil layers can be divided into three sub oil layers and four sub-layers. Chang 73 sub oil layers in the lower Chang 7 developed a large set of oil shale,and Chang 72 and Chang 71 sub oil layers in the middle and upper Chang 7 developed a large set of turbidite and typical Bouma sequence,all of which constituted a complete deep-water turbi-dite facies sequence. The sedimentation can be sequentially divided into three subfacies including turbidite middle fan, turbidite lower fan and deep-water basin, as well as six microfacies types including turbidite channel, interchannel overflow,front channel overflow, turbidite endings, mud shale and oil shale. This large deep-water turbidite fan is dominated by turbidite middle fan and controlled by the southwest provenance and drainage system,with good sandbody continuity,connectivity and composition,and became the major genetic types for Chang 7 effective deep-water reservoir. With good oil show,and great exploration potential, the turbidite fan is an effective prospect for petroleum exploration on deep-water sediments.

Hydrocarbon accumulation rules of Neogene in Xinchun area,Junggar Basin

YANG Yuanliang, ZHU Xiaomin, MA Ruiguo, DONG Yanlei, HOU Shuaijun, JIANG Qiang, LIU Chengquan

2017, Vol.29(4): 20–29 Abstract ( 356 ) PDF (3851 KB) ( 557 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2017.04.003

The hydrocarbon accumulation conditions and rules of Neogene Shawan Formation(N1s)in Xinchun area are unclear,resulting in the failure of several exploratory wells. The regional structure,oil-source correlation,migration system and reservoir accumulation characteristics were analyzed. The results show that the favorable reservoir accumulation conditions include structural evolution, source rock, reservoir, seal and trap. Hydrocarbon generated from Jurassic in Sikeshu Sag,migrated northward and enriched in the first member(N1s1)and second member(N1 s1)of Shawan Formation. The sand group I of N1 s1 developed thick sands with large single layer thickness,which plays an important role in hydrocarbon migration and accumulation. N1 s2 and sand group Ⅱ of N1 s1 mainly developed sand-shale interbed. Under the vertical communication of small Himalayan faults,the thin sandstone of N1 s2 is finally accumulated. It is believed that two sets of thick layers of sandstone supply the lateral pathway for the hydrocarbon migration and enrichment,the coupling relationship of unconformity with pinchout sandstones controls the hydrocarbon enrichment of the sand group I of N1s1,and the coupling relationship of sandstones with small Himalayan faults developed controls the hydrocarbon accumulation of N1 s2 and sand group Ⅱ of N1s1.

Characteristics of sequence stratigraphy of the Lower Triassic Feixianguan Formation in Dachuan-Wanxian area,northeastern Sichuan Basin

SUN Chunyan, HU Mingyi, HU Zhonggui

2017, Vol.29(4): 30–37 Abstract ( 306 ) PDF (4542 KB) ( 338 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2017.04.004

In order to clarify the development, evolution and distribution of oolitic beach reservoir and dolomite reservoir of the Lower Triassic Feixianguan Formation in Dachuan-Wanxian area, based on the theory of Vail sequence stratigraphy, combined with sequence boundary markers, such as the exposed surface, lithological mutation and sequence unconformity surface, the sequence of the typical single well was divided. According to the change of relative sea level rising and falling, the Feixianguan Formation can be divided into two third-order sequences(Sq1 and Sq2)and four system tracts. Sq1 consists of the first and second members of Feixianguan For-mation, and Sq2 consists of the third and fourth members of Feixianguan Formation. Both Sq1 and Sq2 are made up of transgressive and highstand systems tracts, lacking of the lowstand systems tract. The sequence stratigraphic framework of this area was established by comparing the sequence stratigraphic sections of the cross facies zone. The results show that each systems tract in the region can be comparative, platform margin oolitic facies and intraplatform oolitic facies developed in the late period of highstand systems tract, and the strong dolomitization improved the porosity and permeability. Under the condition of deep burial, the primary pore of dolomite is easy to be preserved, and it has a certain anti-compaction and anti-pressure solution, which lays a foundation for the formation of high quality reservoir. The result has important geological significance for further exploration in Sichuan Basin.

Characteristics and controlling factors of tight sandstone and shale reservoirs of the fifth member of Xujiahe Formation in the Western Sichuan Depression

SHI Hongliang, YANG Keming, WANG Tong

2017, Vol.29(4): 38–46 Abstract ( 372 ) PDF (7404 KB) ( 708 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2017.04.005

The exploration of nonmarine unconventional tight gas is still in the early stage. In order to explore the research methods of tight gas in nonmarine shale sequence,the data of cores,cast thin sections, scanning electron microscope, X-ray diffraction and mercury injection,were used to study the petrology,reservoir space, physical properties and main controlling factors of the fifth member of Xujiahe Formation in the Western Sichuan Depression. The results show that the lithology was composed of three types:shale(56%),siltstone(25%)and fine sandstone(19%). There are high content of matrix and debris, low content of feldspar in sandstone,and high content of quartz mineral in shale. The reservoir spaces include organic pores,mixed matrix pores and intragranular dissolved pores,intergranular dissolved pores and microfractures. The average porosity and permeability of sandstone are 1.41% and 0.1 mD,respectively,so it belongs to tight sandstone reservoir,and mainly in high power subaqueous distributary channel. The average porosity and permeability of siltstone are 1.41% and 0.1 mD,respectively,and the average porosity and permeability of shale reservoir are 1.95% and 0.068 mD,respectively. The reservoir properties are mainly controlled by deposition conditions, diagenesis and structural fracture. Strong compaction and pressure dissolution are the main factors leading to the tightness of sandstone. Secondary pores are mainly formed by dissolution. The transformation of clay minerals and the thermal evolution of organic matter provide a large amount of reservoir spaces for shale,and microfracture greatly improves the reservoir permeability. The results can provide a reference for tight gas exploration in this area.

Shale gas accumulation conditions of Neoproterozoic Doushantuo Formation in NW Hunan province

PENG Bo, LIU Yuchen, QI Fucheng, WANG Zhenyun

2017, Vol.29(4): 47–54 Abstract ( 361 ) PDF (8380 KB) ( 444 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2017.04.006

Shale of the Neoproterozoic Doushantuo Formation is widely developed in Northwestern Hunan province. With better gas show in shale gas wells,it revealed better gas potential of the Doushantuo Formation shale. Based on outcrop observation,combined with analysis of organic geochemical test, SEM, X-ray diffraction, low-temperature nitrogen adsorption-desorption and isothermal adsorption,the accumulation conditions and characteristics of shale gas of the Neoproterozoic Doushantuo Formation were studied. The results show that the shale development in the study area is not uniform,and the relatively large cumulative depositional thickness is 20-50m in Dayong syncline. The TOC mass fraction of shale is 0.5%-3.0%,the organic matter is mainly type Ⅰ, and the Ro is 3%-4%,which has reached over-mature evolution stage,with favorable conditions for gas generation. The reservoir minerals of shale are mainly of brittle minerals,with mass fraction of 21.0%-78.7%. The various types of pore spaces developed in shale support high specific surface area and pore volume. The maximum methane absorbance is 0.80-1.77 m3/t. All of the characteristics of shale mean the advantageous geological conditions of shale gas enrichment and accumulation. With steady tectonic setting, favorable preservation conditions and advantageous shale gas accumulation conditions, Dayong syncline is favorable for shale gas exploration.

Fine description method of dynamic provenance and its application:a case from Yanan Sag,Qiongdongnan Basin

WU Aijun, XU Jianyong, TENG Binbin, XIAO Lingli, KANG Bo, LI Fanyi, YIN Binhao

2017, Vol.29(4): 55–63 Abstract ( 321 ) PDF (4064 KB) ( 574 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2017.04.007

With the development of lithologic trap exploration,the conventional provenance analysis method cannot meet the demand of oil and gas exploration. Based on the concept of dynamic provenance,a systematic method of fine description of dynamic provenance was established, which enriches the research methods of provenance analysis. Based on the sequence boundary recognition and systems tract division,combined with the constrain of compaction correction and reestablishing of paleo-water depth,this method uses quantitative back-striping technique to restore the paleogeomorphology at early age of different systems tracts. The development scale of clastic reservoir was determined by characterizing the provenance of the initial sediments in each systems tract, so as to predict the development position of the reservoir. This method was applied to lithologic trap research in Yanan Sag of Qiongdongnan Basin. The result shows that there is a short-term but comparatively large-scale provenance region in LST of Lingshui Formation(E3l1), which could provide abundant sandbodies to form a large lithologic trap associated with fan delta. This lithologic trap has excellent hydrocarbon accumulation conditions,and it might be a break-through of lithologic reservoir exploration in Yanan Sag.

Significance of central transfer zone on lithologic reservoir exploration:a case of Abu Gabra Formation in Fula Sag,Muglad Basin,Sudan

WU Dong, ZHU Xiaomin, LIU Changni, NAN Zhengbing, SHI Yanli

2017, Vol.29(4): 64–72 Abstract ( 510 ) PDF (3859 KB) ( 555 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2017.04.008

In order to demonstrate the distribution of sedimentary sandbodies and effectively guide the exploration and development of lithologic and stratigraphic reservoirs of Abu Gabra Formation in Fula Sag, Muglad Basin, Sudan, under the guidance of the theories and methods of sequence stratigraphy and sedimentology,based on the analysis of seismic and well data, typical seismic sequence boundary and well logging sequence boundary were identified. The formation can be further subdivided into five third-order sequences,which are named as SQa1-SQa5. Based on the sequence framework, the characteristics of formation thickness distribution were analyzed. It is considered that the Abu Gabra Formation is thick in the southwest and thin in the northeast of Fula Sag, which is closely related to the influence of the central transfer zone. The center transfer zone, formed and developed during the sedimentation of SQa1-SQa5, is located in the center of Fula Sag, and it also affects the basin architecture, paleogeomorphology, sedimentary facies zone, sequence filling, and distribution of lithologic and stratigraphic traps. It is revealed that fan delta and turbidite in the west and the normal delta in the east of northern central transfer zone, and braided delta, turbidite and beach bar around the east of southern central transfer zone, are potential exploration targets.

Petroleum geological significance of pyrite in glutenite reservoirs:a case of Qigu Formation in Che 60 well field,Junggar Basin

XIONG Lianqiao, YU Fusheng, YAO Genshun, GAO Chonglong, WANG Yu

2017, Vol.29(4): 73–80 Abstract ( 313 ) PDF (18259 KB) ( 472 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2017.04.009

A large number of authigenic pyrites with perfect crystalline were found in the glutenite reservoirs of Jurassic Qigu Formation in Che 60 well field, northwestern margin of Junggar Basin. These pyrites were concentrated in the braided river delta sandbodies with low shale content, high oil saturation and good physical properties. However, strata with pyrite were interpreted as shale intervals in the previous studies based on the well logging interpretation, which directly led to the misunderstanding of sandbody connectivity and remaining oil distri-bution and resulted in the omission of potential oil and gas reserves in the reservoirs. Based on well longing data and core observation, identification charts of pyrite-rich sandbodies were established, and combined with the geologic settings of the study area, 3 D geological modeling technique was applied to establish the formation model of pyrite. And then porosity and pyrite content of the pyrite-rich sandbodies were recalculated through equivalent volume model. The results show that the distribution of pyrite-rich sandbodies was controlled by faults, and pyrite in the glutenite reservoirs could indicate the distribution of oil-bearing sandbodies, and these sandbodies are not shale intervals. The porosity obtained from the equivalent volume model was much closer to the data of core sample analysis than the old interpretation model. These pyrite-rich sandbodies might be the favorable accumulations of remaining oil or potential areas of reserves. This result could enrich the understanding of pyrite and it is significant for the study of remaining oil and the oilfield flooding development.

Influences of fractal characteristics of reservoir rocks on permeability

YIN Shuai, XIE Runcheng, DING Wenlong, SHAN Yuming, ZHOU Wen

2017, Vol.29(4): 81–90 Abstract ( 354 ) PDF (1829 KB) ( 648 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2017.04.010

In order to characterize the pore structure of different types of reservoirs and cognize its influence on rock permeability,based on the mercury intrusion,nuclear magnetic resonance(NMR)and N2 adsorption experiments,the fractal characteristics of sandstone,coal and shale were compared and analyzed by using the fractal theory, the equivalent capillary tortuosity models were established, and the influences of fractal characteristic parameters of conventional and unconventional reservoir rocks on permeability were discussed. The results show that the fractal dimension(Df)of the three kinds of rocks is in the range of 2.6-3.0,the capillary average tortuosity fractal dimension(DT)is in the range of 1.1-2.3,and the fractal dimension is negatively correlated with rock permeability. The microscopic pore structure factors that influence the rock permeability include heterogeneity of the rock,pore throat size distribution,pore surface roughness and capillary tortuosity,among which the capillary tortuosity has the biggest influence on rock permeability. The equivalent capillary tortuosity of coal,sandstone and shale is relatively small, medium and big, respectively. Finally, the theory of fractal model was used to forecast the permeability of 39 sets of rock samples,the prediction results of sandstone and coal are good. But for shale with strong heterogeneity, its permeability reached nD level. Although the prediction results have a certain degree of coincidence,the prediction accuracy still needs to be further improved. The knowledge obtained in this paper has important reference value in in-depth knowing microscopic percolation mechanism of different kinds of reservoirs.

Influencing factors and quantitative evaluation for pore structure of tight glutenite reservoir:a case of the Triassic Baikouquan Formation in Ma 131 well field,Mahu Sag

KUANG Yan, SIMA Liqiang, QU Jianhua, WEN Danni, CHEN Meng, WU Feng

2017, Vol.29(4): 91–100 Abstract ( 365 ) PDF (11049 KB) ( 612 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2017.04.011

In order to study the quantitative evaluation method of pore structure of tight glutenite reservoir and to provide an effective method for oilfield development,the tight glutenite reservoir of Baikouquan Formation in Ma 131 well field of Mahu Sag was taken as an example, the data of cast thin sections, scanning electron microscope images, mercury injection curves and nuclear magnetic resonance(NMR)T2 spectra were used to study the pore structure and its influencing factors. Based on the statistical relationship between characteristic parameters for pore structure evaluation(average pore-throat radius,saturation median pressure, variation coefficient, displacement pressure, NMR macroporous ratio and T2 geometric mean values)and reservoir quality factors(quantitative characterization parameter of pore structure),the quantitative evaluation method of pore structure of glu-tenite reservoir was discussed,and then the calculation model for continuously characterizing the reservoir quality factor was established by using conventional well log data. The calculation result has a good consistence with experimental data and oil well test data. The continuous and quantitative characterization of reservoir quality factor of Baikouquan Formation in Ma 131 well field was carried out. This result could provide reference for the quantitative characterization of pore structure in Mahu Sag or other similar area.

Application of auto-adaptive dip-steering technique to fault recognition

DUAN Youxiang, CAO Jing, SUN Qifeng

2017, Vol.29(4): 101–107 Abstract ( 314 ) PDF (8742 KB) ( 390 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2017.04.012

The development of fault and fracture is an important issue in 3D seismic interpretation during hydrocarbon exploration and development. The random noises contained in seismic data often affect the depiction accuracy of faults, so denoising technique is often used in the interpretation process to reduce noise and improve the accuracy of fault description. The conventional denoising technique can not only improve the S/N of seismic data, but also destroy the edge information of the reflection structure and the sharpness of fault, which affects the accuracy of structural interpretation and reservoir description. In order to solve the problems of structure protection denoising and fault detection, a method of fault recognition based on auto-adaptive dip-steering was proposed. A steering cube was generated by auto-adaptive dip-steering technology which contains dip and azimuth information of sampling point, and then the steering cube was used as a filter input for constraint denoising to improve S/N and retain important structural information, and finally, the similarity attributes were extracted from filtered seismic volume under the guidance of dip-steering so as to recognize fault and improve the accuracy of fault interpretation. The result shows that the similarity attributes extracted by auto-adaptive dip-steering technique effectively highlight the discontinuity of fault, and it has a good noise reduction result. Auto-adaptive dip-steering technique effectively enhances the fault recognition ability, so it is an effective method to describe the faults and the geological boundary, and has a good application prospect in complex reservoir exploration.

Log calculation method of geochemical parameters of lacustrine shale and its application:a case of lower Es₃ in Bonan subsag,Zhanhua Sag

YAN Jianping, LIANG Qiang, GENG Bin, FENG Chunzhen, KOU Xiaopan, HU Yong

2017, Vol.29(4): 108–116 Abstract ( 334 ) PDF (2748 KB) ( 608 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2017.04.013

The Geochemical index is an important parameter in the study of source rock and unconventional shale oil and gas, and it is of great significance for evaluating hydrocarbon potential of source rocks and reservoir effectiveness. The classic Passey formula was used to calculate the TOC content of lacustrine shale of the lower third member of Shahejie Formation(Es3)in Bonan subsag of Zhanhua Sag, but the error is larger. Through the analysis of the relationship between TOC and log response, it is found that TOC has a good correlation with tripo-rosity curve. The TOC calculation model was established on account of different lithologies(oil mudstone, mudstone and oil shale), and the calculation accuracy was obviously improved. The calculation models of pyrolysis hydrocarbon(S2), hydrogen index(HI)and maximum pyrolysis temperature(Tmax)were established indirectly by TOC and depth variables, and then the kerogen types and organic matter abundance were quantitatively evaluated by using the data of continuous HI, Tmax and TOC. Finally, combining with the information of mineral composition and physical properties obtained from well log data, the shale lithofacies were identified effectively, which is abundant of type Ⅰ and Ⅱ1 kerogen. This result provides a theoretical basis for the favorable reservoir prediction of lacustrine shale in Bonan subsag.

Application of Sonic Scanner logging to fracture effectiveness evaluation of carbonate reservoir:a case from Sinian in Sichuan Basin

XIE Bing, BAI Li, ZHAOAilin, ZHANG Hongying, WANGYue

2017, Vol.29(4): 117–123 Abstract ( 375 ) PDF (4269 KB) ( 540 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2017.04.014

The detection depth of borehole electrical imaging logging is shallow, so it is hard to determine whether the fractures observed on the image developed away from the wellbore. The fracture strike identified by electrical imaging logging was integrated with the shear wave anisotropy orientation measured by Sonic Scanner logging to carry out modeling. The anisotropy caused by fractures in reservoir and the extension of the fractures in the borehole were determined, and then the effectiveness of fractures was evaluated. This methodology was successfully applied in effectiveness evaluation of fracture-vug carbonate reservoir of Sinian Dengying Formation in Sichuan Basin. The combination of Sonic Scanner logging and electrical imaging logging can accurately evaluate the fracture effectiveness around the wellbore, and it provides a reliable basis for reservoir evaluation and optimization of test interval.

Acoustic emission characteristics of rocks with different brittleness

ZHAO Wanchun, MA Yunpeng, WANG Tingting, CHENG Dong, CHEN Yanqiu, FENG Xiaohan

2017, Vol.29(4): 124–130 Abstract ( 365 ) PDF (18221 KB) ( 425 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2017.04.015

Current researches on acoustic emission test of rock are mostly focused on the mechanical properties of rock,and the acoustic emission test of rock brittleness is relatively a few. The uniaxial test and acoustic emission tests were carried out on four kinds of rock samples with different brittleness which are cement mortar rocks with different sand ratio,so as to obtain the stress-strain curves and the acoustic emission count curves. The result shows that the sand ratio of samples is positively related with rock brittleness. The greater the rock brittleness is,the greater the slope of the elastic deformation section is,the faster the stress drops and the larger the strain is after the peak on the stress-strain curves. On the acoustic emission count curves,the more brittle the rock sample is,the earlier the time that acoustic emission signal appears and the greater the maximum value of the acoustic emission count is. The acoustic emission count curves before the peak show that with the increase of rock brittleness,the fracture mode of samples transits from progressive fracture to burst fracture,and the fracture morphology of samples is changed from tensile crack to shear crack and mixed cracks. Overall,rocks with different brittleness have different acoustic emission characteristics,so acoustic emission characteristics can be used to judge the rock brittleness. This test result has theoretical reference value and practical significance for the evaluation of rock brittleness and hydraulic fracturing scheme design.

Acoustic anisotropy of water-saturated and desiccated carbonate rocks

CHEN Chao, LOU Zhanghua, JIN Aimin

2017, Vol.29(4): 131–137 Abstract ( 261 ) PDF (1742 KB) ( 405 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2017.04.016

In order to understand the propagation rules of acoustic wave of carbonate rocks in the condition of desiccated and water-saturated,the desiccated and water-saturated quadrate samples of carbonate rocks were taken the acoustic testing and numerical simulation testing,and the acoustic waveform,propagation velocity and spectral features of carbonate rocks were studied. The results show that when the acoustic waves through the samples,the waveform is loose,and the cycle is obviously increased. The period increases further after saturated with water,and the maximum amplitude position moves forward. There are obvious anisotropic characteristics of the wave velocity and dominant frequency of the rock samples. The more the fracture develops,the greater the anisotropy coefficient of wave velocity and dominant frequency is,and the P-wave velocity and dominant frequency decreases obviously along the vertical direction of fracture. The anisotropy coefficient of the wave velocity and the dominant frequency of the desiccated samples can be used to evaluate the anisotropic characteristics. The dominant frequency is more sensitive for the anisotropy. The anisotropy coefficient is greatly reduced after saturated with water. This study result is helpful for us to use acoustic logging correctly and to recognize the anisotropic characteristics of carbonate reservoir.

Reservoir modeling of tight sandstone gas reservoir based on geological knowledge database:a case from Su X block in Sulige Gas Field

YANG Tebo, WANG Jiping, WANG Yi, FU Bin, XUE Wen, HAO Qian

2017, Vol.29(4): 138–145 Abstract ( 407 ) PDF (1498 KB) ( 556 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2017.04.017

The tight sandstone gas reservoirs in Sulige Gas Field are characterized by unclear understanding of effective reservoir, lack of suitable modeling methods and low effective reservoir drilling rate of horizontal wells. Based on logging curves correlation of 169 wells in Su X block and geological understanding of braided river, the reservoir geological knowledge database was established, and combined with 3D image training, a new 3D multiplepoint geostatistics modeling method was put forward. The results show that the width, thickness, length and width-thickness ratio of braided river point bar are 200-450 m, 3-10 m, 450-1 000 m, 45:1-55:1,respectively, and the width of single braided river is 1 000-2 500 m. By using the geological knowledge database in the process of 3D image training, the geological model is more suitable to display the proportion between braided river and point bar, and reflects the overlap and migration characteristics of braided river sedimentary systems. Multi-point geostatistics method could apply 3D training image to 3D geological modeling of braided river, and presents a structure of"sand pack sand"in effective reservoir. Horizontal well drilling results confirm that the geological model could accurately predict the effective sandbodies and guide the geo-steering of the horizontal well in tight sandstone gas reservoir. This study will play a certain reference role to tight sandstone gas reservoir modeling.

Remaining oil distribution of point bar reservoir based on reservoir architecture and reservoir numerical simulation

ZHANG Jianxing, LIN Chengyan, ZHANG Xianguo, SUN Zhifeng, CHEN Jiayun

2017, Vol.29(4): 146–153 Abstract ( 337 ) PDF (3784 KB) ( 590 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2017.04.018

In order to enhance the remaining oil recovery of point bar reservoir in the extra-high water cut stage, taking the west 7th block of Gudong Oilfield in Shengli Oilfield as a case,based on fine reservoir architecture analysis of meandering river point bar reservoir,lateral accretion body modeling method based on reservoir architecture unit was used to establish a reservoir architecture model,and then numerical simulation technology was used to predict the remaining oil distribution and analyze the main controlling factors. The results show that reservoir architecture,performation intervals and injection direction have great implications for the remaining oil distribution in meandering point bar reservoir. Five patterns of remaining oil were summed up,including upper injection-upper production,lower injection-upper production,commingling production-injection,upper injection-lower production and lower injection-lower production. The enrichment degree of these five patterns of remaining oil is increasing in turn. According to comprehensive comparison of the five patterns of remaining oil, the favorable enrichment area of remaining oil is located in the upper reservoir where the injection direction is opposite to the dip direction of lateral accretion beddings. It is considered that investing horizontal well is an effective adjustment measure to improve the development effect of meandering river point bar reservoir, which can enhance the recovery of remaining oil.

Productivity calculation method for gas-water two phase fractured horizontal wells in tight gas reservoir

HE Jixiang, JIANG Ruizhong, MAO Yu, YUAN Lin

2017, Vol.29(4): 154–161 Abstract ( 329 ) PDF (1710 KB) ( 525 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2017.04.019

Tight gas is a potential of unconventional natural gas resources,while duo to the low porosity, low permeability, producing water and production adjusting, unsteady flow model and conventional Darcy law are no longer applicable to predict the production of gas wells. Based on the percolation mechanism of fractured horizontal wells in tight gas reservoir, considered the effects of stress sensitivity in reservoir and fractures, gas slippage and non-Darcy percolation caused by high velocity in fractures on productivity, the gas-water two phase generalized pseudo pressure in reservoir and fractures was defined respectively, and the gas-water two phase productivity calculation model for tight gas reservoir was built. Case study shows that the relative error of absolute open flow calculated by the new model is small compared with that calculated by productivity testing, which proves high accuracy and reliability of the new model. With the increase of fracture number, half-length and conductivity, the absolute open flow of gas well increases, while with the increase of water-gas volume ratio and stress sensitivity index in reservoir and fractures, the absolute open flow of gas well decreases, meanwhile gas slippage has little influence on gas well productivity,which can be neglected. The method could provide a theoretical basis for studying inflow performance relationship(IPR)of fractured horizontal wells and optimizing the fracture parameters in tight gas reservoir.

Scaling tendency prediction and influencing factors of formation and injected water in Huabei Oilfield

YOU Jing, WANG Zhikun, YU Jiliang, ZHANG Chao, SUN Shuangqing, HU Songqing

2017, Vol.29(4): 162–168 Abstract ( 275 ) PDF (1488 KB) ( 684 )

doi: https://doi.org/10.3969/j.issn.1673-8926.2017.04.020

During water flooding development,scaling of oil layer or production system would greatly affect the production efficiency. Studying the scaling rule and mechanism of formation and injected water could provide theoretical guidance for field descaling technology. Davis-Stiff saturation index method and Ryznar stability index method were used to predict the scaling tendency of the formation and injected water of Jing-11 block in Huabei Oilfield under different temperatures,pH values and concentrations of scaling ions,and the scale rules were investigated by the static scaling test. The results show that the components and concentration of the formation and injected water samples are quite close to each other,both water samples have serious scaling tendency,and the scaling tendency of formation water is slightly higher than that of injected water. In addition,the scale sample of Jing-11 block is mainly composed of calcium carbonate. The scale formation ratio of simulated water sam-ple is 61% under normal conditions,and it can be highly increased by raising temperature,pH and concentration of scaling ions. The increase rate of the scale formation ratio increases by the temperature and pH,but decreases by the concentration of the scaling ions in the solution.