Table of Content

08 April 2016, Volume 37 Issue 2

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Forming conditions of large-scale gas fields in Permo-Carboniferous in the northern Ordos Basin

Hao Shumin, Li Liang, Zhang Wei, Qi Rong, Ma Chao, Chen Jingyi

2016, 37(2):  149-154.  doi:10.11743/ogg20160201

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The Hangjinqi area in the northern margin of the Ordos Basin has been explored for natural gas for about 40 years.However, it wasn't until a decade ago that a systematic investigation of gas reservoiring conditions in this area has been initiated.As a result, exploration breakthrough had been made here after aiming at the large-scale lithological traps.The Permo-carboniferous tight clastic rocks were found to contain more than 700 billion m³ of gas-in-place.A comprehensive study shows that large-scale gas fields in the area were mostly formed within the pervasive near-source layered petroleum system in the transitional sequences at the lower Permo-Carboniferous.This petroleum system has widely-distributed coal-measure source rocks in the Upper Carboniferous, huge Lower Permian channel sandstone reservoirs, short distance between the source and the reservoirs, massive hydrocarbon generation and charging during the Early Cretaceous and large area of Upper Permian cap rocks.The Upper Paleozoic gas reservoirs in the area feature in lithological traps, large gas-bearing area and low abundance of reserves.As newly found reservoirs are mostly tight and low-permeability, how to locate sweet spots to realize a highly effective gas discovery is a challenge for all those engaging in petroleum industry.

Diagenesis and diagenetic facies of low porosity and permeability sandstone in Member 8 of the Yanchang Formation in Daijiaping area, Ordos Basin

Zhou Xiang, He Sheng, Chen Zhaoyou, Wang Furong, Zhou Sibin, Liu Ping

2016, 37(2):  155-164.  doi:10.11743/ogg20160202

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Member 8 sandstone of the Upper Triassic Yanchang Formation is the major exploration target in Daijiaping area, Ordos Basin.Member 8 sandstone of the Yanchang Formation mainly consists of feldspathic litharenite and lithic arkose, currently is at the A phase of middle diagenesis stage, and is categorized into low-porosity and extremely low-permeability reservoir.The intensive diagenesis is main cause of reservoir densification.Compaction and carbonate cementation largely reduce the primary porosity, while chlorite cementation and feldspar dissolution improve the reservoir quality, and the alkaline-acidic-alkaline change of digenetic environment control the formation of clay mineral, the precipitation of carbonate cements, and the dissolution of feldspar.Five types of diagenetic facies are identified in the Member 8 sandstone of the Yanchang Formation according to multiple qualitative and quantitative parameters.Quantitative calculation of porosity evolution in different digenesis facies shows that the differences of primitive compositions among different diagenetic facies as a result of sedimentation is the material basis of the cementation types and the dissolution strength, while the differences of diagenesis types and intensity is the main cause of the differences in porosity evolution and reservoir quality.The distribution of high quality reservoirs is closely related to the diagenesis facies.The weakly-compacted chlorite cement facies and modera-tely-compacted secondary dissolution facies in subaqueous distributary channel sandstone show the best reservoir quality, thus are the most favorable diagenesis facies in the Member 8 sandstone of the Yanchang Formation reservoir.

Unconformity structure types and hydrocarbon migration characteristics in Hangjinqi area of Ordos Basin

Sun Xiao, Li Liang, Ding Chao

2016, 37(2):  165-172.  doi:10.11743/ogg20160203

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Hangjinqi Block is located in northern Ordos Basin and has three unconformities including the Upper Paleozoic-Lower Paleozoic, Upper Paleozoic-Paleozoic and Upper Paleozoic-Archean.Logging data, core data and cutting logging data were integrated to study the characteristics of unconformity space structure in detail.In addition, hydrocarbon migration characteristics of various types of unconformity structure were also analyzed in combination with the carriers above and below the conformities and distribution of gas reservoir.It also figured out the distribution area of advantageous migration pathways.The research shows that there are nine unconformity configuration types in Hangjinqi Block, namely sand-mud-sand, sand-mud-limestone, sand-mud-metamorphic rock, sand-metamorphic rock, sand-limestone, mud-mud-sand, mud-mud-limestone, mud-mud-metamorphic rock and sand-mud-mud.And there are three kinds of migration pathways, namely double migration pathway I-type, single migration pathway Ⅱ₁-type and single migration pathway Ⅱ₂-type, among which the double migration pathway I-type is the primary pathway and is mainly distributed in three areas.The largest area is in the central-eastern part of the block, and its target traps are Shilijiahan in the south of fault and ShiguhaoYin the north of fault.And the second area lies in the western block and its target trap is Xinzhao.The smallest area lies in the eastern block and its target trap is Azhen.Double migration pathway is poorly developed in Shilijiahan trap and is favorable for the in-situ enrichement and accumulation of gas.

Discovery and significance of the Mesozoic igneous carbonate rock at the southwestern margin of Ordos Basin

Xi Shengli, Li Zhenhong, Liu Xinshe

2016, 37(2):  173-179.  doi:10.11743/ogg20160204

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Ordos basin is a stable cratonic basin in the central-west China.Along the margin of the basin, tectonic activity was intense, thrust-nappe structures were well developed and magmatic events were common.On the contrary, the inner part of the basin was very stable and no magmatic events have been recorded.Lately, we found some igneous carbonate rock dikes intruded into the dolomite of the Jixian System in Qingshen 1 well at the south-western margin of the Ordos basin.These intrusive dykes provide new clues for us to reconsider the tectonic activity inside the basin.In the REE distribution patterns, its characteristics are basically consistent with igneous carbonate rock without significant Eu anomaly.Besides, all data points fall within the range of igneous carbonate rock in the C-O isotope crossplot.According to the zircon U-Pb dating results, the age of the intrusive igneous carbonate rock is 176.2±3.3 Ma.Therefore, the intrusive dykes formed during the regional extension after the subduction between Yangtze Craton and North China Craton, under the control of minor activities of the NE-SW trending basement faults in the Early-Middle Jurassic.These intrusive igneous dykes at the south-western margin of the Ordos basin provide new evidences for us to understand the regional extension background of North China Craton in the Early Jurassic.

Accumulation patterns of natural gas in the Upper Paleozoic in Longdong area, Ordos Basin

Li Jun, Wang Yunuo, Zhao Jingzhou, Li Lei, Zheng Jie, Hu Weiqiang

2016, 37(2):  180-188.  doi:10.11743/ogg20160205

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Based on the analysis of source rocks, reservoirs and cap rocks in the Upper Paleozoic, Longdong eara, Ordos Basin, studies were performed on the controlling factors of natural gas accumulation.It's shown that the formation and distribution of gas reservoirs in the Upper Paleozoic are mainly controlled by the source rocks, reservoirs and cap rocks and the coupling relationship among them.Source rocks and cap rocks of the Shanxi Formation jointly control the formation and distribution of the gas reservior in the region.The gas play fairway of the first member of Shanxi Formation(P₂s¹) are distributed in area with high gas generation intensity and thick P₂s¹ cap rock over 35 meters.In contrast, gas play fairway of the eighth member of Shihezi Formation(P₂h⁸) occurs in area where the thickness of P₂s¹ cap rock is less than 35 meters.Local enrichment of gas is dermermined by the reservior conditions.When the source rocks and cap rocks of the first member of the Shanxi Formation are similiar, "sweet spot" controls gas distribution, that is to say the better the quality of the reservoir is, the more enrichment the natural gas is.When both the source rocks and cap rocks of the first member of Shanxi Formation are favorable, gas reservoir can also be formed in the relatively poor formations.It is worth noting that best gas enrichment area is not the one where the gas source, seal and reservoir conditions are all favorable, rather the one where the gas source, seal and reservoir conditions match and compensate best.

Reservoir-forming dynamics and gas-water distribution characteristics of lithologic traps in the 1^st Member of Xiashihezi Formation in the Shilijiahan zone,Hangjinqi area,Ordos Basin

Zhang Wei, Li Liang, Jia Huichong

2016, 37(2):  189-196.  doi:10.11743/ogg20160206

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Low-permeability sandstone gas reservoir is the main reservoir type in Shilijiahan zone of Hangjinqi area, Ordos Basin.The 1^st Member of Xiashihezi Formation, which is the major gas bearing reservoir, is characterized by strong heterogeneity and locally complex gas-water contact.Making clear of the occurrence, distribution characteristics and main controlling factors of gas and water is the key to explore and develop gas reservoirs in Shilijiahan zone.In order to analyze the vertical water-gas differentiation under the control of buoyancy in tight reservoir, the capillary resistance in three types of reservoirs were calculated on the basis of mercury injection experiment and gas-water relative flow experiment.The results show that there is no sign of water -gas differentiation in the 1^st Member of Xiashihezi Formation because the buoyancy of continuous gas column in the reservoir is less than the mean capillary pressure due to the strong reservoir heterogeneity and the small continuous thickness.With a gentle tectonic setting, buoyancy can hardly be the charging force of low permeability reservoir with a large area.Instead, overpressure is the main reservoir-forming dynamics.Reservoir-forming dynamics of three lithologic traps in the study area are deduced by analyzing the gas saturation and differences of capillary pressure curves of gas, gas-water and water reservoirs.Duguijiahan trap which is located in the western part of the study area is defined as a strong dynamic trap because of its strongest reservoir-forming energy, while Subuerga trap which is located in the eastern part is defined as a weak dynamic trap because of the minimum reservoir-forming dynamics.Based on the study of reservoir-forming dynamics, six modes of water and gas layer are recognized in the three traps according to the occurrence and overlapping patterns of gas and water layers.After analyzing the differences of geological conditions, trap dynamics and water-gas differentiation, it is suggested that hydrocarbon generation intensity and trap sealing condition are the main controlling factors of reservoir-forming dynamics.Trap dynamics and reservoir heterogeneity conjointly control the distribution of gas and water.

Characteristics of braided river sedimentary system zones in Sulige gasfield, Ordos Basin

Guo Zhi, Jia Ailin, He Dongbo, Tang Haifa, Liu Qunming

2016, 37(2):  197-204.  doi:10.11743/ogg20160207

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The 8^th Member of the Shihezi Formation and the 1^st Member of the Shanxi Formation of the Upper Paleozoic in Sulige gasfield are mainly of fluvial facies, and the crosscutting and superimposition of multiple-stage channels resulted in a large "braided river system" in geologic history.According to different sedimentary environments and sedimentation characteristics, the braided river system can be divided into superimposed zone, transitional zone and inter-channel zone.This study deepens and develops the concept and deposit connotation of the braided river system, establishes a sedimentary hierarchy of sedimentary facies-braided river system-braided river system zone, and proposes multiple-parameter quantitative classification standards for Sulige's braided river system.Through integrated analysis of core, logging and drilling data, it is concluded that braided river system zone is the key geological factor for sedimentation and reservoir characteristics of Sulige gasfield, as it strongly controls the sedimentary microfacies distribution and scale, sand bodies' superimposition style and effective sand bodies' type and centralization.The superimposed zones of the braided river system feature in highly develo-ped and large channel bars, superimposition of multiple stage sand bodies and clustering of effective sand bodies, thus is the favorable facies zone for gas production.In transitional zone, channel filling is more developed and effective sand bodies are mainly distributed in isolation in space.In contrast, the inter-channel zone is characterized by scattered and sparse sand bodies, thus its exploitation potential is poor.In addition, the criteria of geological target selection for horizontal wells are set up for the superimposed zone and transitional zone of braided river system respectively, and horizontal well trajectory is optimized, providing a more reliable basis for geo-steering while drilling of horizontal wells.

Origin and source of natural gas in the Upper Paleozoic of the Yimeng Uplift,Ordos Basin

Chen Jingyi, Jia Huichong, Li Yongjie, An Chuan, Li Wei, Liu Sihong

2016, 37(2):  205-209.  doi:10.11743/ogg20160208

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No consensus has been reached on the origin and source of natural gas in the Upper Paleozoic of Yimeng Uplift, Ordos Basin.Based on a comprehensive analysis of carbon isotope and light hydrocarbon, the δ¹³C₂ values are gene-rally more than -25.4‰, alkane carbon isotope values change in normal order and the relative content of methylcyclohexane is more than 50%, which show that natural gas is coal-derived gas.The Upper Paleozoic source rocks in Yimeng Uplift are dominated by coals.In Shiguhao area, the thickness of coalbeds ranges from 6 to 10 m.The source rocks with a vitrinite reflectance from 0.8% to 1.2% reached the major stage of hydrocarbon generation.So the local source rocks have an important contribution to near-source gas accumulation.Average methane content of Yimeng Uplift is 94.5%, which is higher than that of Shilijiahan area (91.2%); δ¹³C value was alos significantly heavier than that of Shilijiah area with the difference value of 3‰.It is believed that component differentiation and carbon isotope fractionation occurred in natural gas migration process.So some natural gas in the Upper Paleozoic of Yimeng Uplift may come from the south of Boerjianghaizi fault.

Development patterns of collapse-type karst reservoirs in the Ordovician of Daniudi gasfield, Ordos Basin

Ding Xiaoqi, Zhang Shaonan, Pan Huaixiao, Li Liang, Jia Huichong

2016, 37(2):  210-217.  doi:10.11743/ogg20160209

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Due to wide application of horizontal well fracturing technology in the Ordovician weathering crust reservoirs of Daniudi gasfield, Ordos Basin, karst reservoirs exhibit its great potential of gas production, regardless of its low porosity, permeability and strong heterogeneity.However, development pattern of reservoir is the key of gas accumulation in karst reservoirs.Karst cycles and reservoirs distribution are studied by using lithofacies based on core observation and well-logging interpretation.The following results were obtained.(1) Three Karst cycles can be identified in the Ordovician Majiagou Formation.The upper two karst cycles formed in the earlier time and are larger in scale than the lower one; therefore the development of karst reservoirs are mainly related to the upper two karst cycles.(2) The long-term dissolution of gypsiferous dolostone and muddy dolostone layers produces fractures in cave-roof zone and finally led to the collapse of overlying strata, forming a thick layer of breccias.(3) Reservoirs are mainly developed in areas with relatively weak karst intensity.Laterally, they mainly occur in monadnock of palaeogeomorphology slope, while vertically, they are distributed in the intact vadose zones of upper two karst cycles.The lithofacies are dominated by crackle-mosaic breccias lithofacies.The research on karst cycles and lithofacies will play significant roles in the reservoir predication for the following gas exploration.

Gas reservoir types in Shiguhao area of the Yimeng Uplift,Ordos Basin

Qi Rong

2016, 37(2):  218-223.  doi:10.11743/ogg20160210

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Lithologic and anticlinal gas reservoirs were developed in the Lower Permian Shanxi Formation and Lower Shihezi Formation in Shiguhao area of Yimeng Uplift, Ordos Basin.In order to study the hydrocarbon accumulation rules and optimize emplacement of horizontal wells, it is essential to analyze the geometries and types of the gas reservoirs.Based on drilling and seismic data in combination with identification of gas and water layers and test results, this paper analyzed the geometries on plane and sectional views of typical gas reservoir and researched the mainly factors that influence the sealing of gas reservoirs.Five types of gas reservoirs are recognized in the study area.In vertical, lithologic gas reservoirs are mainly developed in the P₁x² and the P₁x³, anticlinal gas reservoirs are mainly developed in the P₁x¹, stratigraphic overlapping gas reservoirs and structural-lithologic gas reservoirs are the predominant types in the Shanxi Formation.On the plane, lithologic and stratigraphic overlapping gas reservoirs are mainly developed in the slope belt of western Shiguhao area; anticlinal and structural-lithologic gas reservoirs are mainly developed in uplift belt of eastern Shiguhao area.Meanwhile, interlayer faults are well developed in Shiguhao area.In addition to small scale fault block gas reservoirs, some lithologic and anticlinal gas reservoirs are cut by interlayer faults, changing their geometries.By using three-dimensional seismic data, the geometries of gas reservoirs can be depicted accurately.

Sedimentary environment and tectonic backgrounds of the Wangquankou Formation carbonate rock sequences in southwestern Ordos Basin

Song Lijun, Liu Chiyang, Li Guangxiang, Zhao Hongge, Wang Jianqiang, Zhang Xiaolong, Wang Yuping

2016, 37(2):  224-237.  doi:10.11743/ogg20160211

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A very thick Middle Proterozoic carbonate strata represented by the Wangquankou Formation is distributed in the southwestern Ordos basin.In order to forecast its petroleum exploration prospects, major and trace elements were measured on samples to reveal the rock characteristics, sedimentary environment, tectonic settings and origin of siliceous rocks of the Wangquankou Formation.The Wangquankou Formation mainly consists of dolomites, siliceous dolomites and silicalites, with minor quartz sandstones.Geochemical features of siliceous materials in silicalites and siliceous dolomites clearly show a biochemical origin, with almost no influences from epicontinental clastic input.Discrimination diagrams of redox environment, such as V/Cr, Ni/Co, V/(V+Ni) and Ce/La, indicate that the Wangquankou Formation was deposited in aerobic or transitional dysaerobic shallow water.Paleo-temperature data, in good agreement with Sr/Cu values, suggest that regional temperatures were highest during deposition of the Wangquankou Formation, further indicating an arid and scorching climate background.Sr/Ba and CaO/(CaO+MgO) environment discriminant graphs, Y abnormity and (La/Nd)_pass ratio show that the carbonate rocks formed in marine saltwater or transitional semi-saltwater environment.A comprehensive analysis of various diagrams, such as La-Th-Sc，Th-Co-Zr/10 and 100Eu/∑REE- LREE/HREE graphs, indicates that carbonate samples from the Wangquankou Formation carry information of active continental margin, continental island arc and middle continent-shallow water sedimentary system.Samples from regions of Long Country Guguan, Tanshan, and Zhuozishan located at the basin margin are all characterized by high REEs, indicating a tectonic background of continental back-arc depression during the Wangquankou Stage.In conclusion, siliceous rocks and carbonate rocks of biochemical origin in this region were deposited in mild-oxidizing, marine-continental transition environment, with the backgrounds of desiccation and torridness with the tectonic settings of epicontinental back-arc depression.

Comprehensive evaluation of effectiveness of dual-porosity sandstone reservoir:A case study from Chang 8¹ reservoir in Honghe oilfield in southwest of the Ordos Basin

Jia Jun, Sima Liqiang, Meng Juntian, Meng Yuntao

2016, 37(2):  238-244.  doi:10.11743/ogg20160212

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Chang8¹ reservoir in Honghe oilfield is a tight sandstone reservoir with dual porosity consisting of pores and fractures.Due to various interstitial material component, fine grain size, complex pore structure, poor physical condition and strong heterogeneity, effective reservoir characteristics are inconspicuous and production is generally low.In addition, production capacities among wells are significantly different owing to varying degrees of reservoir permeability improvement by fractures with different occurrences, openess and filling degree.Based on core analysis, experimental test and production data, five evaluation index, including logging facies, pore throat structure, physical property, permeability and fracture effectiveness, were selected to evaluate dual-porosity Chang8¹ reservoir and establish evaluation standards.Verified by 31 wells in Honghe oilfield, the evaluation results are consistent with production conditions.

Study on diagenetic facies of the Donghetang tight sandstone reservoirs in Bachu area

Peng Jun, Wu Huiming, Han Haodong, Yang Suju, Zhang Hanbing, Liu Lu

2016, 37(2):  245-255.  doi:10.11743/ogg20160213

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Sedimentological principles and investigation approaches were combined with thin sections, scanning electron microscope data on the study of tight sandstone reservoir diagenetic facies in Donghetang formation, Bachu area.The result dictates that reservoirs of the formation were shaped by 6 diagenesis effects but only three of which, namely compaction, cementation and dissolution, had played most part.The Formation was determined to be in an A-B stage of middle diagenesis phase.Based on four parameters (apparent compaction rate, apparent cementation rate, apparent dissolution rate, amount of dissolution) and asphalt-filling of the formation, we recognized seven kinds of diagenetic facies in the formation contains, including medium compaction and cementation with strong dissolution facies (Ⅰ), medium compaction and cementation with medium dissolution facies (Ⅱ), medium compaction and cementation with weak dissolution facies (Ⅲ) and etc., among which, type I to Ⅲ are considered facies with exploration potentials.Relevant log data and the k-nearest neighbor classification method were also used to differentiate continuously and automatically the diagenetic facies of layers penetrated by 17 wells in the research area.The result shows that the upper Formation is dominated by type Ⅵ facies, with the most favorable facies occurring in Ga2-Yu2-Ba5 and Qun6-Bakai8-Batan4-Kangtan1 wellblocks, and the lower part is more developed than the upper one and dominated by type Ⅱ facies, with the most favorable facies occurring in Ga2-Qun6-Bakai8-Ba2-Kang1 wellblock.The study may serve as a geological basis for high-quality reservoir prediction.

Evaluation of development effect of cluster horizontal wells in Daniudi gas field,Ordos Basin

Wu Jianbiao, Liu Xugang, Bai Xiaoxia, Yu Yaonan, Gao Peng

2016, 37(2):  256-260.  doi:10.11743/ogg20160214

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Almost all the quality gas reserves of Daniudi gas field have been produced.The remaining gas reserves are low in quality, thus cannot be developed efficiently with vertical wells.Considering the strong heterogeneity, limited sizes of effective sandbodies, low reserves abundance and low single well production rate of the tight sandstone layers, horizontal wells are preferred for the development of the remaining gas reserves.Cluster horizontal well group plays a key role in the practical production.Numerical simulation and dynamic evaluation are integrated to evaluate the exploitation performance of Daniudi gas field with different patterns of cluster horizontal well groups by comparing the pressure drawdown rate and gas production per pressure drop unit.The results demonstrate that the angle between the laterals and maximum principal stress should be larger than 60 degrees, and the minimum distance between these wells should be greater than 500 meter when using horizontal wells cluster group as the development strategy.These understandings will provide a useful reference for the exploitation of similar tight marginal gas fields in Ordos Basin and other basins.

Engineering optimization technique of horizontal well development for Daniudi tight sandstone gas field in Ordos Basin

Liu Zhongqun

2016, 37(2):  261-266.  doi:10.11743/ogg20160215

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Daniudi gas field is a typical tight sandstone gas reservoir.The remaining non-produced reserves are charac-terized by poor quality, thin net pay thickness and poor vertical superimposition of pay zones.For these types of reservoirs, it is critical to optimize technical policy of horizontal well development and perfect gas reservoir engineering technique series.Empirical formula, dynamic performance analysis, numerical simulation and economic evaluation were used to optimize technical policies including productivity evaluation, single well design, well pattern and spacing and other aspects regarding horizontal well development.We defined the principles of strata series classification and selected mutiple methods of productivity evaluation.The study shows that the gas production should be proportionally 1/5~1/3 of open-flow capacity, and the lateral should be 1 000~1 200 meter long.The well trajectory should be perpendicular to the maximum principal stress and be located as close as possible to the center part of the reservoir.The fracturing design should refer to the quantitative calculation model.The well pattern should be staggered line-drive with a well spacing of 800~1 200 meter.The abandonment formation pressure should be 8 MPa.All these factors would finally yield a recovery factor of 40%.The optimized parameters have been applied to the Daniudi gas field, and they provided a strong technical foundation for the successful implementation of the development plan in this tight sandstone gas reservoir.

Stress sensitivity of the 1^st Member of Xiashihezi Formation and its influences on horizontal well development of Daniudi gas field,Ordos Basin

Chen Kui, Ren Guanglei, Yang Wenjuan, Yu Yaonan

2016, 37(2):  267-271.  doi:10.11743/ogg20160216

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The 1^st Member of Xiashihezi Formation(H1)of Daniudi gas field is a typical low permeability reservoir in Ordos Basin.In order to clearly understand the stress sensitivity of H1, 13 core samples of different types were chosen for stress sensitivity tests.The experimental results show that the core samples from H1 commonly show stress sensitivity and permeability hysteresis, indicating that the cores experience plastic deformation with the increasing of net stress.Analysis of the experimental data with internal stress sensitivity index method shows that the type Ⅰ reservoirs with better physical properties has a relatively low stress sensitivity, while the type Ⅱ and Ⅲ reservoirs have low to moderate stress sensitivity.The averaged internal stress sensitivity index of these 13 core samples is 0.086, indicating that the overall stress sensitivity is low.We built numerical simulation models of multi-stage fracturing of horizontal wells for Ⅰ-Ⅲ type reservoirs, into which the relationship between dimensionless permeability and the formation pressure was incorporated.Under a constant gas production rate scheme in the numerical model, the effects of stress sensitivity on horizontal well performance were investigated.The numerical simulation results show that the stress sensitivity has very little effect on gas rate during stable production period for type Ⅰ reservoir, which only decreased by 1.6% in comparison with that without stress sensitivity case.For type Ⅱ and Ⅲ reservoirs, the gas rate during stable production period decreased by 11.2% and 23.6%, respectively.Therefore, production allocation and management should be strengthened for type Ⅱ and Ⅲ reservoirs to guarantee well performance.

CO₂-EOR in Chang 8 tight sandstone reservoir of Honghe oilfield in Ordos Basin

Zhang Benyan, Dang Wenbin, Wang Shaopeng, He Xuewen

2016, 37(2):  272-275.  doi:10.11743/ogg20160217

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The Honghe oilfield in Ordos Basin has difficulty achieving effective development due to low formation pressure, quick production decline and low recovery efficiency during natural depletion.In addition, natural fractures are well developed in Chang 8 tight sandstone reservoir, making it difficult to carry out waterflooding due to serious water channeling and low efficiency.Various CO₂-EOR experiments including PVT, minimum miscible pressure and CO₂ flooding in fractured cores were performed to determine the feasibility of maintaining reservoir pressure via CO₂ injection.The performance of CO₂ puff-huff was also eveluated.The results show that the crude oil of Honghe oilfield swells significantly after CO₂ injection.The diffusion between crude oil and CO₂ gradually increased as the pressure grows.The measured miscible pressure of crude oil and CO₂ is 17.34 MPa, lower than the initial formation pressure of Honghe oilfield, indicating that miscible flooding of CO₂ is feasible.Multi-cycle CO₂ huff-puff experiments show that an additional oil recovery factor of 3.14% can be achieved on the basis of 4.04% of natural depletion.A comprehensive evaluation of the experiment results indicates that CO₂ injection is feasible in Chang 8 reservoir of Honghe oilfield.

Application of SEC dynamic reserves evaluation method in extra-low permeability and tight gas reservoir:A case from Daniudi gasfield,Ordos Basin

Luo Xiaomin

2016, 37(2):  276-279.  doi:10.11743/ogg20160218

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SEC dynamic reserves evaluation is one of the important methods of listed reserves evaluation.In practical application, the parameters and calculation results are various.SEC dynamic reserves evaluation is closely related to evaluation method, understanding of geological conditions and familiarity with production situation of the assessment staff.There are many convenient practical evaluation methods for the SEC reserves evaluation of Daniudi gasfield, the Ordos Basin，and these methods play an important role in summarizing the declining pattern and determining the parameters.The stripping of effects of new wells and normalization of production rate can objectively and rationally reveal the production declining pattern of the Daniudi gasfield; Exponential decline, hyperbolic decline, harmonic decline are integrated to establish single well declining model for the calculation of single well reserves and for verification of the reserves evaluation results.

Method of horizontal logging virtual well co-simulated inversion in depth domain and its application in Daniudi gasfield,Ordos Basin

Qin Xuefei

2016, 37(2):  280-285.  doi:10.11743/ogg20160219

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Aiming at horizontal well development of complex reservoir with strong heterogeneity, logging data of the lateral can be discretized in the form of virtual vertical wells, and further to carry out lithology stochastic simulation inversion in depth domain.It not only can effectively use the horizontal well logging data, but also can realize quantitative prediction of the laterals through the updating of logging while drilling in the laterals.Its application in Daniudi gasfield shows that significant improvement of prediction accuracy is achieved in respect of top and bottom structural framework of the single sand body and the barriers and baffles within the reservoir, and the reservoir penetrating ratio of horizontal wells is significantly increased.

Application of 90° phase rotation technique in reservoir prediction:A case study from the Chang8¹ reservoir in Binchang block,Ordos Basin

Fan Jiuxiao, Li Xiaowei, Yuan Chunyan, Wang Shanming

2016, 37(2):  286-290.  doi:10.11743/ogg20160220

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Chang8¹ reservoir in Binchang block is one of the main targets for petroleum exploration and development at the southern margin of the Ordos Basin.Because of the strong reflector resulted from the Zhangjiatan shale at the bottom of the overlying Chang 7³ and the small thickness of the Chang8¹ reservoir, non-uniqueness exists when performing reservoir prediction by using conventional seismic data.On the basis of comparison and analysis of velocity and reflection intensity of the Zhangjiatan shale and the Chang8¹ reservoir and their combination patterns, reservoir prediction based on the 90 degree phase rotation technology of 3D seismic attribute is put forward for Chang8¹ reservoir in Binchang block.The main events of seismic reflection are well correlated with geological reservoirs by using the 90 degree phase rotation technology, so as to make the seismic phase having lithologic stratigraphic significance.Reservoir prediction was performed on the basis of the forward modeling, reflection structure comparison and multiple-window attribute optimization.It is believed that the reflection intensity and amplitude attribute within a certain time window under the 90 degree phase rotation can be used to more effectively predict Chang8¹ reservoir.