23 April 2020, Volume 47 Issue 2
    

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    PETROLEUM EXPLORATION
  • Differences and controlling factors of composite hydrocarbon accumulations in the Tazhong uplift, Tarim Basin, NW China
    JIANG Tongwen, HAN Jianfa, WU Guanghui, YU Hongfeng, SU Zhou, XIONG Chang, CHEN Jun, ZHANG Huifang
    Petroleum Exploration and Development, 2020, 47(2): 213-224. https://doi.org/10.11698/PED.2020.02.01
    Abstract ( ) Download PDF ( ) Rich HTML   Knowledge map Save
    Based on three-dimensional seismic interpretation, structural and sedimentary feature analysis, and examination of fluid properties and production dynamics, the regularity and main controlling factors of hydrocarbon accumulation in the Tazhong uplift, Tarim Basin are investigated. The results show that the oil and gas in the Tazhong uplift has the characteristics of complex accumulation mainly controlled by faults, and more than 80% of the oil and gas reserves are enriched along fault zones. There are large thrust and strike-slip faults in the Tazhong uplift, and the coupling relationship between the formation and evolution of the faults and accumulation determine the difference in complex oil and gas accumulations. The active scale and stage of faults determine the fullness of the traps and the balance of the phase, that is, the blocking of the transport system, the insufficient filling of oil and gas, and the unsteady state of fluid accumulation are dependent on the faults. The multi-period tectonic sedimentary evolution controls the differences of trap conditions in the fault zones, and the multi-phase hydrocarbon migration and accumulation causes the differences of fluid distribution in the fault zones. The theory of differential oil and gas accumulation controlled by fault is the key to the overall evaluation, three-dimensional development and discovery of new reserves in the Tazhong uplift.
  • Enrichment rules and exploration practices of Paleogene shale oil in Jiyang Depression, Bohai Bay Basin, China
    SONG Mingshui, LIU Huimin, WANG Yong, LIU Yali
    Petroleum Exploration and Development, 2020, 47(2): 225-235. https://doi.org/10.11698/PED.2020.02.02
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    Based on formation testing data of more than 40 wells with industrial oil flow, systematic observation of 1 010.26 m long cores taken from 4 wells and test data of over 10 000 core samples combining with drilling and pilot fracturing data of multiple wells, the geological characteristics of the upper submember of the Sha 4 Member to the lower submember of the Sha 3 Member of Paleogene (Es4s-Es3x) in Jiyang Depression were investigated to find out factors controlling the enrichment of shale oil and the accumulation model of shale oil, and a comprehensive evaluation method for shale oil sweet spots was established. It is found through the study that the target shale layer is characterized by strong heterogeneity, weak diagenesis, low thermal evolution and high content of clay and carbonate minerals. Shale lithofacies, microcrack, thin interlayer and abnormal pressure are the main factors affecting enrichment and stable production of shale oil, the organic rich laminar shale has the best storage and oil-bearing capacity, microcrack network system improve the storage capacity and permeability of the shale, the thin interlayer is the main flow channel for stable shale oil production, and the abnormal high pressure layer is rich in free state shale oil and high in oil content. The shale oil layers in the target section were divided into three types: matrix, interlayer and fracture ones. According to the occurrence state and exploration practice of shale oil at home and abroad, it is concluded that the interlayer shale oil is the most profitable type at present. The selection parameters for the different types of shale oil were determined, and accordingly the favorable areas were pointed out by comprehensive evaluation of multiple factors. Vertical wells in the interlayer shale oil reservoir, such as Fan 159, Fan 143 and GX 26, were stimulated by volume fracturing and high conductivity channel fracturing jointly. After fracturing, they had a daily oil production of over 6 t, up to 44 t, and stable productivity. Shale oil is expected to become an important replacement energy resource in Jiyang Depression.
  • Accumulation and exploration of petroleum reservoirs in west slope of northern Songliao Basin, China
    MENG Qi’an, BAI Xuefeng, ZHANG Wenjing, FU Li, XUE Tao, BAO Li
    Petroleum Exploration and Development, 2020, 47(2): 236-246. https://doi.org/10.11698/PED.2020.02.03
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    On the basis of the present situation of oil and gas exploration and geological research of the west slope in the northern Songliao Basin, the factors controlling reservoir formation, oil and gas migration and accumulation, have been re-examined from the aspects of structure, deposition and reservoir formation. The results show that: (1) The west slope is a gentle slope overlapping to the west on the oil and gas migration path, where there develop nose structures on the side near the hydrocarbon generation sag and a series of NE structural belts, which are favorable places for oil and gas accumulation. (2) The west slope can be further divided into the upper slope and the lower slope, and there are many kinds of oil and gas reservoirs, including structural, structural-lithologic and lithologic ones. In the upper slope, the major oil layer is Saertu controlled by structure; in the lower slope, multi-layers are oil-bearing, and the oil reservoirs are mostly composite ones. (3) Faults, unconformity surfaces and continuous sand bodies are the main channels of oil and gas migration; structure, sand body and fault jointly control the oil and gas enrichment in the slope; and the matching relationship between micro-amplitude and sand body, small fault and sand body control the oil and gas accumulation. On the basis of the above research, fine identification and effectiveness evaluation technology of composite trap has been developed through extensive study. Combination traps were identified by combining multiple technologies, including fault classification, micro-amplitude structure identification, fine sedimentation research, and lithologic trap identification by waveform indication inversion; and then the relationship between fault and sand body, structural amplitude and sand body configuration were analyzed to set up the evaluation criteria of effective trap. According to the criteria, the traps were selected to enhance the exploration success rate.
  • Formation conditions and exploration direction of large and medium gas reservoirs in the Junggar Basin, NW China
    HU Suyun, WANG Xiaojun, CAO Zhenglin, LI Jianzhong, GONG Deyu, XU Yang
    Petroleum Exploration and Development, 2020, 47(2): 247-259. https://doi.org/10.11698/PED.2020.02.04
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    The Junggar Basin is rich in oil but lacks natural gas, which is inconsistent with its geological background of natural gas. Based on the analysis of main source kitchens, and the evaluation of geological setting and controlling factors of gas accumulation, it is proposed that three significant fields for gas exploration should be emphasized. The first field is the Carboniferous volcanic rocks. The Carboniferous residual sags and large-scale reservoirs were developed in three active continental margins, i.e., the southeastern, northeastern and northwestern active continental margins. Gas accumulation is controlled by the favorable reservoir-caprock combinations composed of volcanic rocks and their superimposed lacustrine mudstones in the Upper Wuerhe Formation. Dinan, Eastern and Zhongguai uplifts are three favorable directions for natural gas exploration. The second field is the Lower combinations in the southern margin of Junggar Basin. Rows of structural traps were developed in this area with ideal preservation conditions and space-time configuration for trap-source combinations. Sets of clastic reservoirs and overpressured mudstones formed perfect reservoir-caprock combinations which are the main exploration direction for Jurassic coal-type gas reservoirs in this area. The seven large structural traps in the middle-east section are recently the most significant targets. The last field is the Central Depression. Large hydrocarbon generating centers, i.e., Mahu, Fukang and Shawan sags, were developed in this area, their source rocks were deeply buried and at highly-mature stage. Thus the Central Depression is a favorable exploration direction for Permian high-over mature gas fields (reservoirs). Great attentions should be paid to two types of targets, the deeply-buried structures and structural-lithologic traps. Based on three main gas systems, gas exploration is suggested be strengthened within three fields and on three levels.
  • Formation conditions and exploration direction of large natural gas reservoirs in the oil-prone Bohai Bay Basin, East China
    XUE Yong’an, WANG Deying
    Petroleum Exploration and Development, 2020, 47(2): 260-271. https://doi.org/10.11698/PED.2020.02.05
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    The Bohai Bay Basin is a typical oil-prone basin, in which natural gas geological reserves have a small proportion. In this basin, the gas source rock is largely medium-deep lake mudstone with oil-prone type II2-II1 kerogens, and natural gas preservation conditions are poor due to active late tectonic movements. The formation conditions of large natural gas fields in the Bohai Bay Basin have been elusive. Based on the exploration results of Bohai Bay Basin and comparison with large gas fields in China and abroad, the formation conditions of conventional large-scale natural gas reservoirs in the Bohai Bay Basin were examined from accumulation dynamics, structure and sedimentation. The results show that the formation conditions of conventional large natural gas reservoirs in Bohai Bay Basin mainly include one core element and two key elements. The core factor is the strong sealing of Paleogene "quilt-like" overpressure mudstone. The two key factors include the rapid maturation and high-intensity gas generation of source rock in the late stage and large scale reservoir. On this basis, large-scale nature gas accumulation models in the Bohai Bay Basin have been worked out, including regional overpressure mudstone enriching model, local overpressure mudstone depleting model, sand-rich sedimentary subsag depleting model and late strongly-developed fault depleting model. It is found that Bozhong sag, northern Liaozhong sag and Banqiao sag have favorable conditions for the formation of large-scale natural gas reservoirs, and are worth exploring. The study results have important guidance for exploration of large scale natural gas reservoirs in the Bohai Bay Basin.
  • Origin and depositional characteristics of supported conglomerates
    ZHANG Changmin, SONG Xinmin, WANG Xiaojun, WANG Xulong, ZHAO Kang, SHUANG Qi, LI Shaohua
    Petroleum Exploration and Development, 2020, 47(2): 272-285. https://doi.org/10.11698/PED.2020.02.06
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    The origin and depositional characteristics of supported conglomerates in the Mahu Sag, Junggar Basin, Xinjiang, China, are examined. Based on the terminological comparison, modern sedimentary survey and core description, the initial connotation and similarities and differences in definition between supported conglomerates and other similar concepts are discussed, the modern sedimentary environment in which supported conglomerates develop is analyzed, and the sedimentological characteristics of supported conglomerates formed in different depositional environments revealed by the cores description of Mahu conglomerate oil field in the Junggar Basin are described. The supported conglomerate is similar in texture to grain supported conglomerate and openwork conglomerate but has differences from them, so it is suggested to keep the term "supported conglomerate", but the formation mechanism of supported conglomerate needs to be re-examined. Through field survey of modern sediments in Baiyanghe alluvial fan, Huangyangquan alluvial fan, and Wulungu Lake in Xinjiang, it is found that supported gravels not only formed by flooding events but also by sieving, avalanching, fluvial sorting as well as wind and wave reworking in the depositional environments such as inter-mountain creek, colluvium fan, gravel channel on gobi and the fan surface, lake beach, delta front, subaerial debris flow and subwater grain-flow etc. Supported gravels could form supported conglomerate after being buried. Supported conglomerates of seven different origins have been recognized in the cores of the Triassic and Permian stratum of Mahu Depression, Junggar Basin, namely, supported conglomerates in gravel channel deposits, in wind reworked channel deposits, in gravel beach bar deposits, in wave reworked delta front deposits, in mouth bar deposits and in debris flow deposits respectly. The study shows the supported conglomerates may be formed by a single depositional event or by multi-events during the post-depositional sedimentary reworking and even in diagenesis stage. Through flume experiment, numerical simulation, empirical model and modern sediment survey, infiltration process of gravelly channel can be reconstructed and the primary pore structure of supported gravel can be estimated. Statistics on physical properties of various types of reservoirs in Triassic Baikouquan Formation of Mahu oilfield show that granule conglomerate and pebbly conglomerate have higher porosity and permeability, while the cobble and coarse pebble conglomerate have lower permeability, which indicates that the supported gravels are easy to be reworked by post depositional filtration and diagenesis, and thus decrease in porosity and permeability.
  • Origin, hydrocarbon accumulation and oil-gas enrichment of fault-karst carbonate reservoirs: A case study of Ordovician carbonate reservoirs in South Tahe area of Halahatang oilfield, Tarim Basin
    DING Zhiwen, WANG Rujun, CHEN Fangfang, YANG Jianping, ZHU Zhongqian, YANG Zhimin, SUN Xiaohui, XIAN Bo, LI Erpeng, SHI Tao, ZUO Chao, LI Yang
    Petroleum Exploration and Development, 2020, 47(2): 286-296. https://doi.org/10.11698/PED.2020.02.07
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    Based on comprehensive analysis of tectonic and fault evolution, core, well logging, seismic, drilling, and production data, the reservoir space characteristic, distribution, origin of fault-karst carbonate reservoir in Yueman block of South Tahe area, Halahatang oilfield, Tarim Basin, were studied systematically. And the regular pattern of hydrocarbon accumulation and enrichment was analyzed systematically based on development practice of the reservoirs. The results show that fault-karst carbonate reservoirs are distributed in the form of "body by body" discontinuously, heterogeneously and irregularly, which are controlled by the development of faults. Three formation models of fault-karst carbonate reservoirs, namely, the models controlled by deep major connecting oil source fault, secondary connecting oil source fault and secondary fault inside formation, are built. The hydrocarbon accumulation and enrichment of fault-karst carbonate reservoirs is controlled by the spatiotemporal matching relation between hydrocarbon generation period and fault activity, and the size and segmentation of fault. The study results can effectively guide the well deployment in Ordovician carbonate reservoir of South Tahe area, Halahatang oilfield and help the efficient development of fault-karst carbonate reservoirs.
  • Pliocene hyperpycnal flow and its sedimentary pattern in D block of Rakhine Basin in Bay of Bengal
    ZHOU Lihong, SUN Zhihua, TANG Ge, XIAO Dunqing, CAI Zheng, WANG Haiqiang, SU Junqing, HUA Shuangjun, GE Wei, CHEN Changwei
    Petroleum Exploration and Development, 2020, 47(2): 297-308. https://doi.org/10.11698/PED.2020.02.08
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    Based on core, logging, lab test and seismic data, sedimentary characteristics and pattern of marine hyperpycnal flow, the distribution rules of hyperpycnal flow reservoir, prediction method of favorable hyperpycnal flow reservoir zones, hydrocarbon accumulation model in hyperpycnal flow reservoir in D block of Bay of Bengal were investigated, and the favorable exploration zone and well sites were predicted. Pliocene in D block has typical hyperpycnal flow sediment, which is a set of fine-medium sandstone held between thick layers of marine mudstone and features a series of reverse grading unit and normal grading unit pairs. The hyperpycnal flow sediment appears as heavily jagged box shape, bell shape and tongue shape facies on log curves with linear gradient, and corresponds to multiple phases of deep channels on the seismic section and high sinuous channel on stratal slices. The sedimentary bodies formed by a single phase hyperpycnal flow which include five types of microfacies, namely, supply channel (valley), channel complex, branch channel, levee and sheet sand. The hyperpycnal flow sediments appear in multiple branches, multiple generations and stages in space, forming high-quality reservoirs in strips on the plane and superposition vertically, with fairly good physical properties. The channel complex sandstone, with large thickness, coarse particle size and good physical properties, is the most favorable exploration facies. Based on the guidance of the sedimentary model, distribution of the channel complex microfacies was delineated in detail by seismic reflection structure analysis, spectrum waveform characteristic analysis, slice and attribute fusion, and combined with the structural feature analysis, the favorable drilling zone was sorted out, effectively guiding the exploration deployment of the block.
  • Numerical modeling of stress perturbations caused by geometric changes of salt bodies
    WANG Mingwen, LUO Gang, SUN Yunqiang, CHANG Cheng
    Petroleum Exploration and Development, 2020, 47(2): 309-320. https://doi.org/10.11698/PED.2020.02.09
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    By building a static salt structure model under compression stress background, the stress changes around salt basin were simulated to find out the stress perturbations caused by different shapes of salt bodies and test the effect of amplitude of salt body on stress perturbation. A two-layer salt model with 3 bulges and sags was designed with finite element method to calculate the stress perturbation around the salt. The results show that the shape of the salt is closely related to the stress perturbation in the sediments around the salt, and the fluctuations of the bulge and sag (smooth or steep) can also affect the magnitude of the stress perturbation. Extrusion horizontal stress, normal stress and vertical stress on the plane would occur near the salt uplift under compressive tectonic stress environment. In contrast, tensile horizontal stress, normal stress and vertical stress would occur near the salt subsag. In addition, the smoother the bulge, the smaller the stress perturbation produced will be; the steeper the subsag, the more reduction of stress perturbation in the sediment will be. The stress of salt structure in the western of Kelasu of Kuqa depression was simulated, which proves that the previous conclusions are applicable to this salt structure. These conclusions provide scientific basis for the prediction of stress disturbance around the salt basin system.
  • Diagenetic evolution and formation mechanisms of middle to deep clastic reservoirs in the Nanpu sag, Bohai Bay Basin, East China
    WANG Enze, LIU Guoyong, PANG Xiongqi, LI Changrong, WU Zhuoya
    Petroleum Exploration and Development, 2020, 47(2): 321-333. https://doi.org/10.11698/PED.2020.02.10
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    The reservoir properties, diagenetic features and evolution of the Paleogene Shahejie Formation (Es) in the Nanpu sag, Bohai Bay Basin were analyzed based on mineralogical and petrological data, and the main controlling factors and formation mechanisms of medium to deep high-quality reservoir were revealed by multiple regression analysis. The results show that the sedimentary microfacies, rigid grains content, and dissolution process are the key factors controlling the formation of high-quality clastic reservoir in middle to deep depth in the Nanpu sag. The formation mechanisms of middle to deep sandstones of the Es in different structural belts differ widely in formation mechanism. The Es1 (uppermost member of Es) sandstone reservoirs in the Nanpu No.3 structural belt is low porosity, moderate to high permeability reservoir in the middle diagenesis A2 stage on the whole, and the formation of high-quality reservoirs is mainly attributed to strong compaction resistance ability primarily, and dissolution process secondarily. The Es3 (third member of Es) sandstones in Gaoshangpu structural belt is classified as tight sandstones in the middle diagenesis A1 stage, in which the development of favorable reservoirs is primarily controlled by dissolution. This study provides references for reservoir evaluation of deep clastic reservoirs and exploration deployment in the Bohai Bay rift basin. As there are high-quality reservoirs, it is believed that the deep clastic reservoirs in the east part of Bohai Bay Basin still have significant exploration potential.
    • OIL AND GAS FIELD DEVELOPMENT
  • Oil oxidation in the whole temperature regions during oil reservoir air injection and development methods
    LIAO Guangzhi, WANG Hongzhuang, WANG Zhengmao, TANG Junshi, WANG Bojun, PAN Jingjun, YANG Huaijun, LIU Weidong, SONG Qiang, PU Wanfen
    Petroleum Exploration and Development, 2020, 47(2): 334-340. https://doi.org/10.11698/PED.2020.02.11
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    The oil oxidation characteristics of the whole temperature regions from 30 ℃ to 600 ℃ during oil reservoir air injection were revealed by experiments. The whole oil oxidation temperature regions were divided into four different parts: dissolving and inflation region, low temperature oxidation region, medium temperature oxidation region and high temperature oxidation region. The reaction mechanisms of different regions were explained. Based on the oil oxidation characteristics and filed tests results, light oil reservoirs air injection development methods were divided into two types: oxygen-reducing air flooding and air flooding; heavy oil reservoirs air injection in-situ combustion development methods were divided into two types: medium temperature in-situ combustion and high temperature in-situ combustion. When the reservoir temperature is lower than 120 ℃, oxygen-reducing air flooding should be used for light oil reservoir development. When the reservoir temperature is higher than 120 ℃, air flooding method should be used for light oil reservoir development. For a normal heavy oil reservoir, when the combustion front temperature is lower than 400 ℃, the development method is medium temperature in-situ combustion. For a heavy oil reservoir with high oil resin and asphalting contents, when the combustion front temperature is higher than 450 ℃, the development method at this condition is high temperature in-situ combustion. Ten years field tests of air injection carried out by PetroChina proved that air has advantages in technical, economical and gas source aspects compared with other gas agents for oilfield gas injection development. Air injection development can be used in low/super-low permeability light oil reservoirs, medium and high permeability light oil reservoirs and heavy oil reservoirs. Air is a very promising gas flooding agent.
  • Productivity simulation of hydraulically fractured wells based on hybrid local grid refinement and embedded discrete fracture model
    ZHU Dawei, HU Yongle, CUI Mingyue, CHEN Yandong, LIANG Chong, CAI Wenxin, HE Yanhui, WANG Xiaoyong, CHEN Hui, LI Xiang
    Petroleum Exploration and Development, 2020, 47(2): 341-348. https://doi.org/10.11698/PED.2020.02.12
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    Using current Embedded Discrete Fracture Models (EDFM) to predict the productivity of fractured wells has some drawbacks, such as not supporting corner grid, low precision in the near wellbore zone, and disregarding the heterogeneity of conductivity brought by non-uniform sand concentration. An EDFM is developed based on the corner grid, which enables high efficient calculation of the transmissibility between the embedded fractures and matrix grids, and calculation of the permeability of each polygon in the embedded fractures by the lattice data of the artificial fracture aperture. On this basis, a coupling method of local grid refinement (LGR) and embedded discrete fracture model is designed, which is verified by comparing the calculation results with the Discrete Fracture Network (DFN) method and fitting the actual production data of the first hydraulically fractured well in Iraq. By using this method and orthogonal experimental design, the optimization of the parameters of the first multi-stage fractured horizontal well in the same block is completed. The results show the proposed method has theoretical and practical significance for improving the adaptability of EDFM and the accuracy of productivity prediction of fractured wells, and enables the coupling of fracture modeling and numerical productivity simulation at reservoir scale.
  • Permeability damage micro-mechanisms and stimulation of low-permeability sandstone reservoirs: A case study from Jiyang Depression, Bohai Bay Basin, China
    ZHANG Shoupeng, FANG Zhengwei
    Petroleum Exploration and Development, 2020, 47(2): 349-356. https://doi.org/10.11698/PED.2020.02.13
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    According to the characteristics of "structural elements" (framework grain, interstitial material and pore throat structure) of low-permeability sandstone reservoir, the "step by step dissolution and separation" acidification and acid fracturing technology has been developed and tested in field. There are three main mechanisms affecting permeability of low-permeability sandstone reservoir: (1) The mud fillings between the framework grains block the seepage channels. (2) In the process of burial, the products from crystallization caused by changes in salinity and solubility and uneven migration and variation of the syn-sedimentary formation water occupy the pores and throat between grains. (3) Under the action of gradual increase of overburden pressure, the framework grains of the rock is compacted tighter, making the seepage channels turn narrower. The "step by step dissolution and separation" acidification (acid fracturing) technology uses sustained release acid as main acidizing fluid, supramolecular solvent instead of hydrochloric acid to dissolve carbonate, and a composite system of ammonium hydrogen fluoride, fluoroboric acid, and fluorophosphoric acid to dissolve silicate, and dissolving and implementing step by step, finally reaching the goal of increasing porosity and permeability. By using the technology, the main blocking interstitial material can be dissolved effectively and the dissolution residual can be removed from the rock frame, thus expanding the effective drainage radius and increasing production and injection of single well. This technology has been proved effective by field test.
  • Artificial neural network based production forecasting for a hydrocarbon reservoir under water injection
    NEGASH Berihun Mamo, YAW Atta Dennis
    Petroleum Exploration and Development, 2020, 47(2): 357-365. https://doi.org/10.11698/PED.2020.02.14
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    As the conventional prediction methods for production of waterflooding reservoirs have some drawbacks, a production forecasting model based on artificial neural network was proposed, the simulation process by this method was presented, and some examples were illustrated. A workflow that involves a physics-based extraction of features was proposed for fluid production forecasting to improve the prediction effect. The Bayesian regularization algorithm was selected as the training algorithm of the model. This algorithm, although taking longer time, can better generalize oil, gas and water production data sets. The model was evaluated by calculating mean square error and determination coefficient, drawing error distribution histogram and the cross-plot between simulation data and verification data etc. The model structure was trained, validated and tested with 90% of the historical data, and blindly evaluated using the remaining. The predictive model consumes minimal information and computational cost and is capable of predicting fluid production rate with a coefficient of determination of more than 0.9, which has the simulation results consistent with the practical data.
  • Predictive data analytics application for enhanced oil recovery in a mature field in the Middle East
    YOUSEF Alklih Mohamad, KAVOUSI Ghahfarokhi Payam, ALNUAIMI Marwan, ALATRACH Yara
    Petroleum Exploration and Development, 2020, 47(2): 366-371. https://doi.org/10.11698/PED.2020.02.15
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    Top-Down Modeling (TDM) was developed through four main steps of data gathering and preparation, model build-up, model training and validation, and model prediction, based on more than 8 years of development and production/injection data and well tests and log data from more than 37 wells in a carbonate reservoir of onshore Middle-East. The model was used for production prediction and sensitivity analysis. The TDM involves 5 inter-connected data-driven models, and the output of one model is input for the next model. The developed TDM history matched the blind dataset with a high accuracy, it was validated spatially and applied on a temporal blind test, the results show that the developed TDM is capable of generalization when applied to new dataset and can accurately predict reservoir performance for 3 months in future. Production forecasting by the validated history matched TDM model suggest that the water production increases while oil production decreases under the given operation condition. The injection analysis of the history matched model is also examined by varying injection amounts and injection period for water and gas (WAG) process. Results reveal that higher injection volume does not necessarily translate to higher oil production in this field. Moreover, we show that a WAG process with 3 months period would result in higher oil production and lower water production and gas production than a 6 months process. The developed TDM provides a fast and robust alternative to WAG parameters, and optimizes infill well location and its corresponding true vertical depth (TVD).
  • Applications of smart proxies for subsurface modeling
    SHAHKARAMI Alireza, MOHAGHEGH Shahab
    Petroleum Exploration and Development, 2020, 47(2): 372-382. https://doi.org/10.11698/PED.2020.02.16
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    Using artificial intelligence (AI) and machine learning (ML) techniques, we developed and validated the smart proxy models for history matching of reservoir simulation, sensitivity analysis, and uncertainty assessment by artificial neural network (ANN). The smart proxy models were applied on two cases, the first case study investigated the application of a proxy model for calibrating a reservoir simulation model based on historical data and predicting well production while the second case study investigated the application of an ANN-based proxy model for fast-track modeling of CO2 enhanced oil recovery, aiming at the prediction of the reservoir pressure and phase saturation distribution at injection stage and post-injection stage. The prediction effects for both cases are great. While a single run of basic numerical simulation model takes hours to days, the smart proxy model runs in a matter of seconds, saving 98.9% of calculating time. The results of these case studies demonstrate the advantage of the proposed workflow for addressing the high run-time, computational time and computational cost of numerical simulation models. In addition, these proxy models predict the outputs of reservoir simulation models with high accuracy.
    • PETROLEUM ENGINEERING
  • Selection of candidate wells for re-fracturing in tight gas sand reservoirs using fuzzy inference
    ARTUN Emre, KULGA Burak
    Petroleum Exploration and Development, 2020, 47(2): 383-389. https://doi.org/10.11698/PED.2020.02.17
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    An artificial-intelligence based decision-making protocol is developed for tight gas sands to identify re-fracturing wells and used in case studies. The methodology is based on fuzzy logic to deal with imprecision and subjectivity through mathematical representations of linguistic vagueness, and is a computing system based on the concepts of fuzzy set theory, fuzzy if-then rules, and fuzzy reasoning. Five indexes are used to characterize hydraulic fracture quality, reservoir characteristics, operational parameters, initial conditions, and production related to the selection of re-fracturing well, and each index includes 3 related parameters. The value of each index/parameter is grouped into low, medium and high 3 categories. For each category, a trapezoidal membership function all related rules are defined. The related parameters of an index are input into the rule-based fuzzy-inference system to output value of the index. Another fuzzy-inference system is built with the reservoir index, operational index, initial condition index and production index as input parameters and re-fracturing potential index as output parameter to screen out re-fracturing wells. This approach was successfully validated using published data.
  • Super-amphiphobic, strong self-cleaning and high-efficiency water-based drilling fluids
    JIANG Guancheng, NI Xiaoxiao, LI Wuquan, QUAN Xiaohu, LUO Xuwu
    Petroleum Exploration and Development, 2020, 47(2): 390-398. https://doi.org/10.11698/PED.2020.02.18
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    Based on the amphiphobic theory on underground rock surface, a super-amphiphobic agent is developed and evaluated which can form nano-micro papilla structure on rock, filter cake and metal surface, reduce surface free energy, prevent collapse, protect reservoir, lubricate and increase drilling speed. With this super-amphiphobic agent as the core agent, a super-amphiphobic, strong self-cleaning and high-performance water-based drilling fluid system has been developed by combining with other agents based on drilled formation, and compared with high-performance water-based drilling fluid and typical oil based drilling fluid commonly used in oilfields. The results show that the super-amphiphobic, strong self-cleaning and high-performance water-based drilling fluid has better rheology, and high temperature and high pressure filtration similar with that of oil-based drilling fluid, inhibiting and lubricating properties close to oil based drilling fluid. Besides, the super-amphiphobic system is non-toxic, safe and environmentally friendly. Field tests show this newly developed drilling fluid system can prevent wellbore collapse, reservoir damage and pipe-sticking, increase drilling speed and lower drilling cost, meeting the requirement of safe, high efficient, economic and environmentally friendly drilling. Compared with other drilling fluids, this new drilling fluid system can reduce downhole complexities by 82.9%, enhance the drilling speed by about 18.5%, lower drilling fluid cost by 39.3%, and increase the daily oil output by more than 1.5 times in the same block.
  • Structural failure mechanism and strengthening method of plugging zone in deep naturally fractured reservoirs
    XU Chengyuan, YAN Xiaopeng, KANG Yili, YOU Lijun, ZHANG Jingyi
    Petroleum Exploration and Development, 2020, 47(2): 399-408. https://doi.org/10.11698/PED.2020.02.19
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    Focused on the lost circulation control in deep naturally fractured reservoirs, the multiscale structure of fracture plugging zone is proposed based on the theory of granular matter mechanics, and the structural failure pattern of plugging zone is developed to reveal the plugging zone failure mechanisms in deep, high temperature, high pressure, and high in-situ stress environment. Based on the fracture plugging zone strength model, key performance parameters are determined for the optimal selection of loss control material (LCM). Laboratory fracture plugging experiments with new LCM are carried out to evaluate the effect of the key performance parameters of LCM on fracture plugging quality. LCM selection strategy for fractured reservoirs is developed. The results show that the force chain formed by LCMs determines the pressure stabilization of macro-scale fracture plugging zone. Friction failure and shear failure are the two major failure patterns of fracture plugging zone. The strength of force chain depends on the performance of micro-scale LCM, and the LCM key performance parameters include particle size distribution, fiber aspect ratio, friction coefficient, compressive strength, soluble ability and high temperature resistance. Results of lab experiments and field test show that lost circulation control quality can be effectively improved with the optimal material selection based on the extracted key performance parameters of LCMs.
  • An evaluation method of volume fracturing effects for vertical wells in low permeability reservoirs
    ZHANG Anshun, YANG Zhengming, LI Xiaoshan, XIA Debin, ZHANG Yapu, LUO Yutian, HE Ying, CHEN Ting, ZHAO Xinli
    Petroleum Exploration and Development, 2020, 47(2): 409-415. https://doi.org/10.11698/PED.2020.02.20
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    To evaluate the fracturing effect and dynamic change process after volume fracturing with vertical wells in low permeability oil reservoirs, an oil-water two-phase flow model and a well model are built. On this basis, an evaluation method of fracturing effect based on production data and fracturing fluid backflow data is established, and the method is used to analyze some field cases. The vicinity area of main fracture after fracturing is divided into different stimulated regions. The permeability and area of different regions are used to characterize the stimulation strength and scale of the fracture network. The conductivity of stimulated region is defined as the product of the permeability and area of the stimulated region. Through parameter sensitivity analysis, it is found that half-length of the fracture and the permeability of the core area mainly affect the flow law near the well, that is, the early stage of production; while matrix permeability mainly affects the flow law at the far end of the fracture. Taking a typical old well in Changqing Oilfield as an example, the fracturing effect and its changes after two rounds of volume fracturing in this well are evaluated. It is found that with the increase of production time after the first volume fracturing, the permeability and conductivity of stimulated area gradually decreased, and the fracturing effect gradually decreased until disappeared; after the second volume fracturing, the permeability and conductivity of stimulated area increased significantly again.
    • NEW ENERGY AND EMERGING FIELD
  • On the connotation, challenge and significance of China’s "energy independence" strategy
    ZOU Caineng, PAN Songqi, ZHAO Qun
    Petroleum Exploration and Development, 2020, 47(2): 416-426. https://doi.org/10.11698/PED.2020.02.21
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    The world’s energy is in the "third major transformation period" from fossil energy to new energy, and all countries in the world have formulated energy development strategies. Through advanced deployment, the United States is about to achieve "energy independence" relying on "unconventional oil and gas revolution". China’s energy development is faced with four challenges: (1) The population base and economic development scale determine the "totally huge amount" of energy consumption; (2) the "coal rich but oil and gas insufficient" resource structure determines the "unclean" energy consuming structure; (3) the increasing dependence on imported oil and gas determines the "unsafe" energy supply; and (4) the unconventional oil and gas endowment makes it impossible to achieve energy independence by copying the American model. From the perspective of the world energy trend and the unique situation of China’s energy, we put forward a "three-step" strategy for China to achieve "energy independence": From 2020 to 2035, "energy supply security" will be addressed by "cleaning coal, stabilizing oil and gas production and vigorously developing new alternative energy"; from 2035 to 2050, the vision of "production independence" will be realized by relying on "domestic production and overseas oil and gas mining rights"; from 2050 to 2100, "intelligent energy and new energy" will help China realize "energy independence". The two important signs of China’s "energy independence" are that domestic production accounts for more than 90% of the domestic consumption and clean energy production accounts for more than 70%, and energy security realizes "independence and self-control" and "long-term security". The strategic significance of "energy independence" is to ensure national energy security, drive the development of relevant major industries, achieve energy management reform, and implement the environmental protection goal of zero carbon emissions. The "energy independence" of China is a strategic mission, it might be fulfilled in the future with the growth of the state’s power, even when the domestic energy production does not catch up with the domestic consumption. Perhaps the world’s new technological revolution will exceed expectations, and China’s "energy independence" dream will eventually come true.
  • Anisotropy interpretation and the coherence research between resistivity and acoustic anisotropy in tight sands
    LI Chaoliu, YUAN Chao, LI Xia, FENG Zhou, SONG Lianteng, WANG Lei
    Petroleum Exploration and Development, 2020, 47(2): 427-434. https://doi.org/10.11698/PED.2020.02.22
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    Aiming at the problem of anisotropy inversion of tight sands, a new method for extracting resistivity anisotropy from array laterolog and micro-resistivity scanning imaging logging is proposed, and also the consistency of electric and acoustic anisotropy is discussed. Array laterolog includes resistivity anisotropy information, but numerical simulation shows that drilling fluid invasion has the greatest influence on the response, followed by the relative dip angle θ and electrical anisotropy coefficient λ. A new inversion method to determine ri, Rxo, Rt and λ is developed with the given θ and initial values of invasion radius ri, flushed zone resistivity Rxo, in-situ formation resistivity Rt. Micro-resistivity image can describe the resistivity distribution information in different directions, and the resistivity from micro-resistivity log in different azimuths, lateral and vertical directions can be compared to extract electric anisotropy information. Directional arrangement of mineral particles in tight sands and fracture development are the intrinsic causes of anisotropy, which in turn brings about anisotropy in resistivity and acoustic velocity, so the resistivity anisotropy and acoustic velocity anisotropy are consistent in magnitude. Analysis of log data of several wells show that the electrical anisotropy and acoustic anisotropy extracted from array laterolog, micro-resistivity imaging and cross-dipole acoustic logs are consistent in magnitude, proving the inversion method is accurate and the anisotropies of different formation physical parameters caused by the intrinsic structure of tight sand reservoir are consistent. This research provides a new idea for evaluating anisotropy of tight sands.
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