Classification of Complex Reservoirs in Superimposed Basins of Western China

Many of the sedimentary basins in western China were formed through the superposition and compounding of at least two previously developed sedimentary basins and in general they can be termed as complex superimposed basins. The distinct differences between these basins and monotype basins are their discontinuous stratigraphic sedimentation, stratigraphic structure and stratigraphic stress-strain action over geological history. Based on the correlation of chronological age on structural sections, superimposed basins can be divided into five types in this study： （1） continuous sedimentation type superimposed basins, （2） middle and late stratigraphic superimposed basins, （3） early and late stratigraphic superimposed basins, （4） early and middle stratigraphic superimposed basins, and （5） long-term exposed superimposed basins. Multiple source-reservoir-caprock assemblages have developed in such basins. In addition, multi-stage hydrocarbon generation and expulsion, multiple sources, polycyclic hydrocarbon accumulation and multiple-type hydrocarbon reservoirs adjustment, reformation and destruction have occurred in these basins. The complex reservoirs that have been discovered widely in the superimposed basins to date have remarkably different geologic features from primary reservoirs, and the root causes of this are folding, denudation and the fracture effect caused by multiphase tectonic events in the superimposed basins as well as associated seepage, diffusion, spilling, oxidation, degradation and cracking. Based on their genesis characteristics, complex reservoirs are divided into five categories： （1） primary reservoirs, （2） trap adjustment type reservoirs, （3） component variant reservoirs, （4） phase conversion type reservoirs and （5） scale-reformed reservoirs.

Application of fluid modulus inversion to complex lithology reservoirs in deep-water areas

It has been a challenge to distinguish between seismic anomalies caused by complex lithology and hydrocarbon reservoirs using conventional fluid identification techniques,leading to difficulties in accurately predicting hydrocarbon-bearing properties and determining oil-water contacts in reservoirs.In this study,we built a petrophysical model tailored to the deep-water area of the Baiyun Sag in the eastern South China Sea based on seismic data and explored the feasibility of the tri-parameter direct inversion method in the fluid identification of complex lithology reservoirs,offering a more precise alternative to conventional techniques.Our research found that the fluid modulus can successfully eliminate seismic amplitude anomalies caused by lithological variations.Furthermore,the seismic databased direct inversion for fluid modulus can remove the cumulative errors caused by indirect inversion and the influence of porosity.We discovered that traditional methods using seismic amplitude anomalies were ineffective in detecting fluids,determining gas-water contacts,or delineating high-quality reservoirs.However,the fluid factor Kf,derived from solid-liquid decoupling,proved to be sensitive to the identification of hydrocarbon-bearing properties,distinguishing between high-quality and poor-quality gas zones.Our findings confirm the value of the fluid modulus in fluid identification and demonstrate that the tri-parameter direct inversion method can significantly enhance hydrocarbon exploration in deep-water areas,reducing associated risks.

The influence of pore structure on P-& S-wave velocities in complex carbonate reservoirs with secondary storage space

Secondary storage spaces with very complex geometries are well developed in Ordovician carbonate reservoirs in the Tarim Basin,which is taken as a study case in this paper.It is still not clear how the secondary storage space shape influences the P-＆ S-wave velocities （or elastic properties） in complex carbonate reservoirs.In this paper,three classical rock physics models （Wyllie timeaverage equation,Gassmann equation and the Kuster-Toks z model） are comparably analyzed for their construction principles and actual velocity prediction results,aiming at determining the most favourable rock physics model to consider the influence of secondary storage space shape.Then relationships between the P-＆ S-wave velocities in carbonate reservoirs and geometric shapes of secondary storage spaces are discussed from different aspects based on actual well data by employing the favourable rock physics model.To explain the influence of secondary storage space shape on V P-V S relationship,it is analyzed for the differences of S-wave velocities between derived from common empirical relationships （including Castagna＇s mud rock line and Greenberg-Castagna V P-V S relationship） and predicted by the rock physics model.We advocate that V P-V S relationship for complex carbonate reservoirs should be built for different storage space types.For the carbonate reservoirs in the Tarim Basin,the V P-V S relationships for fractured,fractured-cavernous,and fractured-hole-vuggy reservoirs are respectively built on the basis of velocity prediction and secondary storage space type determination.Through the discussion above,it is expected that the velocity prediction and the V P-V S relationships for complex carbonate reservoirs should fully consider the influence of secondary storage space shape,thus providing more reasonable constraints for prestack inversion,further building a foundation for realizing carbonate reservoir prediction and fluid prediction.

Analysis of Channeling-Path Phenomena in a Complex Fault-Block Reservoir with Low Recovery Factor and High Water-Cut Ratio

Current methods for the analysis of channeling-path phenomena in reservoirs cannot account for the influence of time and space on the actual seepage behavior.In the present study,this problem is addressed considering actual production data and dynamic characteristic parameters quantitatively determined in the near wellbore area by fitting the water-cut curve of the well.Starting from the dynamic relationship between injection and production data,the average permeability is determined and used to obtain a real-time quantitative characterization of the seepage behavior of the channeling-path in the far wellbore area.For the considered case study(Jidong oilfield),it is found that the seepage capacity of the channeling-path in the far wellbore area is far less(10 times smaller)than that of the channeling-path in the near wellbore area.The present study and the proposed model(combining near wellbore area and far wellbore area real-time data)have been implemented to support the definition of relevant adjustment measures to ultimately improve oil recovery.

Exploration Technology for Complex Sandstone Reservoirs in the Developed Area of Shengli Oilfield

Jiyang depression, which is the main oil productive area of Shengli oil field, is located at the southeast part of the Bohai Bay Basin and is a terrestrial lacustrine rift subsidence basin formed in the late Mesozoic with fully developed fault system. The main hydrocarbon productive formations of this depression are the terrestrial clastic rocks of the Tertiary, which are of strong lateral variation. The complex fault reservoirs and subtle lithological reservoirs distributed extensively and are becoming the main exploration targets in recent years. The exploration and development practice in these years has formed the exploration technologies, mainly including detailed study and description of low grade faults, delineation of microstructures, facies constrained formation description and prediction and low resistivity oil bearing formation’s identification. These exploration technologies have resulted in remarkable effectiveness on the reserve and oil production increments.

Shuffled complex evolution coupled with stochastic ranking for reservoir scheduling problems

This paper introduces an optimization method(SCE-SR)that combines shuffled complex evolution(SCE)and stochastic ranking(SR)to solve constrained reservoir scheduling problems,ranking individuals with both objectives and constrains considered.A specialized strategy is used in the evolution process to ensure that the optimal results are feasible individuals.This method is suitable for handling multiple conflicting constraints,and is easy to implement,requiring little parameter tuning.The search properties of the method are ensured through the combination of deterministic and probabilistic approaches.The proposed SCE-SR was tested against hydropower scheduling problems of a single reservoir and a multi-reservoir system,and its performance is compared with that of two classical methods(the dynamic programming and genetic algorithm).The results show that the SCE-SR method is an effective and efficient method for optimizing hydropower generation and locating feasible regions quickly,with sufficient global convergence properties and robustness.The operation schedules obtained satisfy the basic scheduling requirements of reservoirs.

Multiple-Element Matching Reservoir Formation and Quantitative Prediction of Favorable Areas in Superimposed Basins

Superimposed basins in West China have experienced multi-stage tectonic events and multicycle hydrocarbon reservoir formation, and complex hydrocarbon reservoirs have been discovered widely in basins of this kind. Most of the complex hydrocarbon reservoirs are characterized by relocation, scale re-construction, component variation and phase state transformation, and their distributions are very difficult to predict. Research shows that regional caprock （C）, high-quality sedimentary facies （Deposits, D）, paleohighs （Mountain, M） and source rock （S） are four geologic elements contributing to complex hydrocarbon reservoir formation and distribution of western superimposed basins. Longitudinal sequential combinations of the four elements control the strata of hydrocarbon reservoir formation, and planar superimpositions and combinations control the range of hydrocarbon reservoir and their simultaneous joint effects in geohistory determine the time of hydrocarbon reservoir formation. Multiple-element matching reservoir formation presents a basic mode of reservoir formation in superimposed basins, and we recommend it is expressed as T-CDMS. Based on the multiple-element matching reservoir formation mode, a comprehensive reservoir formation index （Tcdms） is developed in this paper to characterize reservoir formation conditions, and a method is presented to predict reservoir formation range and probability of occurrence in superimposed basins. Through application of new theory, methods and technology, the favorable reservoir formation range and probability of occurrence in the Ordovician target zone in Tarim Basin in four different reservoir formation periods are predicted. Results show that central Tarim, Yinmaili and Lunnan are the three most favorable regions where Ordovician oil and gas fields may have formed. The coincidence of prediction results with currently discovered hydrocarbon reservoirs reaches 97 %. This reflects the effectiveness and reliability of the new theory, methods and technology.

“中国西南储气能力”建设的技术基础与发展思考

为保障国家天然气安全平稳供应,2019年国家能源局启动了川渝天然气千亿立方米级“气大庆”的建设项目,将四川盆地天然气储气调峰和战略应急保供能力建设提升至国家战略安全高度。此外,中国石油在“十四五”期间确立了打造“西南储气中心”的战略目标,积极攻关各项地下储气库(以下简称储气库)建库技术难题,已初步形成“西南储气中心”建设格局。为此,在分析四川盆地建设储气库面临的挑战基础上,系统梳理总结了中国石油近17年在四川盆地的发展规划、建设现状、技术进展等方面的成果,并对打造“中国西南储气能力”提出了具体的攻关方向。研究结果表明:(1)四川盆地天然气资源丰富且拥有与全国天然气管网互连互通的完善管网设施,能够为盆地储气库建设提供坚实基础;(2)提出了复杂盆地气藏的“十指标”选址体系,建立了完善的储气库库址优选技术;(3)形成了储气库建库运行七大特色技术,健全了碳酸盐岩气藏建库主体技术系列;(4)构建了国内首个储气库地质体、井、地面完整性管理评价技术体系,保障了储气库安全稳定运行。结论认为,为支撑国家天然气千亿立方米级“气大庆”建设,提出了“中国西南储气能力”建设的概念,其核心是以中国石油初步建成的企业级“西南储气中心”为基础,走出单一油公司储气库建设模式,建立政府主导协调、跨企业的储气库协同共建共享共营机制,全面推动四川盆地整体储气能力建设,保障国家天然气能源安全。

Reservoir characteristics and genetic differences between the second and fourth members of Sinian Dengying Formation in northern Sichuan Basin and its surrounding areas

This study investigated the characteristics and genesis of reservoirs in the 2^(nd) and 4^(th) members of Sinian Dengying Formation in northern Sichuan and its surrounding areas, on the basis of outcrop, drilling cores and thin section observation and geochemical analysis. The reservoirs of 2^(nd) member are distributed in the middle part of the stratum. The reservoir quality is controlled by supergene karst and the distribution of mound-shoal complex. The bedded elongated isolated algal framework solution-cave and the residual "grape-lace" cave, which are partially filled with multi-stage dolosparite, constituted the main reservoir space of the 2^(nd) member. There is no asphalt distribution in the pores. The pore connectivity is poor, and the porosity and permeability of the reservoir is relatively low. The reservoirs of 4^(th) member were distributed in the upper and top part of the stratum. The reservoir quality is controlled by burial dissolution and the distribution of mound-shoal complex. The bedded algal framework solution-pores or caves, intercrystalline pores and intercrystalline dissolved pores constituted the main reservoir space of the 4^(th) member. It's partially filled with asphalt and quartz, without any dolosparite fillings in the pores and caves. The pore connectivity is good. Most of the 4^(th) member reservoirs had medium-low porosity and low permeability, and, locally, medium-high porosity and medium permeability. Affected by the development of mound-shoal complex and heterogeneous dissolution, the platform margin along Ningqiang, Guangyuan, Jiange and Langzhong is the most favorable region for reservoir development. Deep buried Dengying Formation in the guangyuan and langzhong areas should be the most important hydrocarbon target for the future exploration.

高含水复杂断块油藏单层系边外注水开发模式

复杂断块油藏在开发后期面临综合含水率高、地层能量不足、剩余油分布复杂、井网适应性差等问题。以济阳坳陷沾化凹陷中部垦71断块油藏为例,基于水驱油藏的油包水和水包油2种油水分布状态,利用理论模型推导和数值模拟方法,开展了单层系边外注水开发模式研究。结果表明:从采液端和注水端的受力分析可获得单层系开发的合理注水量、合理采液量和合理注采井距,单层系开发的合理注水压差、合理注水量、合理采液量是影响其剩余油饱和度、含水饱和度的关键因素,对油层合理地层压力水平及剩余油二次富集起主要控制作用。通过加大注采井距至油水边界外围,以2.9倍含油条带宽度为合理注采井距的临界值,采用短注长静置的非对称周期注采方式,建立单层系边外注水开发模式,有利于保持单层系的压力系统稳定和提高剩余油波及率,从而提高原油采收率。矿场实践表明,采用单层系边外注水开发模式后,垦71断块油藏日产油量提高至254 t/d,含水率控制在93.7%,采收率提高至31.53%,采油速率提高4.9%,显示出良好的增产效果。单层系边外注水开发模式解决了高含水复杂断块油藏开发中的剩余油分布分散、水驱波及率低和井网适应性差等难题,可为复杂断块油藏开发提供指导和借鉴。

深层页岩气储层水力压裂裂缝扩展影响机理

现有中浅层页岩气压裂取得的认识难以解释深层页岩气储层压裂过程中水力裂缝扩展的影响机理。为了研究四川盆地深层页岩气储层水力压裂裂缝扩展机理,文中以泸州深层页岩气区LS1平台为研究对象,进行基于地质-工程一体化的水力压裂裂缝扩展数值模拟与分析。首先,根据泸州区块目标井区储层的地质概况,建立地质模型,明确地质力学属性;然后,基于微地震和蚂蚁体数据,建立符合真实储层构造特性的离散天然裂缝网络;在此基础上,根据现场实际施工数据,建立了基于DFN的水力压裂复杂裂缝扩展模型,并基于微地震监测结果对模型进行了验证;最后,还研究了4个单因素对储层改造体积的影响特点。研究结果对深层页岩气储层水力压裂复杂缝网研究有一定的指导作用。

复杂压力系统薄互层致密油藏水平井钻井关键技术

南堡凹陷高柳区块沙三3段V油组属于典型的砂泥薄互层致密油藏,因多年压裂注水开发导致地层压力系统复杂、人工缝网分布密集,水平井钻井过程中井漏、油水侵与井壁垮塌复杂情况同时存在、矛盾突出。结合高柳区块地层特征阐述了水平井安全钻井技术难点,明确了钻井液漏失、井壁垮塌原因,优选纳微米级乳化防塌剂、石墨微球与微米级柔性封堵剂、超细钙构建了封堵承压井壁稳定油基钻井液体系,该体系有效降低滤液对泥岩地层的侵入,对泥岩强度保持能力提高5倍以上,使中高渗砂岩封堵承压能力达到18 MPa;针对油基钻井液漏失问题提出了油基桥接堵漏技术与油基固化堵漏技术。现场试验解决了高柳区块复杂压力系统致密油藏水平井安全钻井难题,十余口应用井无井壁垮塌情况发生,漏失井堵漏后漏失层承压能力提高5.4 MPa,满足后续钻井施工要求。

基于地震相识别的相控储层预测技术及应用——以魏岗-张店结合部为例

随着勘探开发不断深入,南阳凹陷的勘探开发方向由魏岗、张店主体区逐渐向背斜翼部转移,滚动勘探目标也由构造油藏向复杂岩性油藏转变。由于魏岗-张店结合部构造较为复杂且地震资料分辨率较低,导致储层预测多解性强,为了准确识别不同岩性体和进行储层预测,以核桃园组核二Ⅱ亚段为例,通过开展地震相识别及多属性融合分析,指出魏岗-张店结合部由北向南发育的水下分流河道是储层发育的有利相带;并在此基础上,通过岩性反演提高了地震分辨率,实现了5 m以下厚度砂体的精细刻画。可为魏岗-张店结合部勘探开发的深化提供技术支撑。

非电阻率测井流体识别研究现状及展望

电阻率测井是目前流体识别的主要手段,但其在具有低孔隙度低渗透率、非均质性较强、特殊矿物发育等特点的储层中不易准确判别流体性质。为解决复杂储层流体识别问题,基于非电阻率测井技术衍生出了一系列方法,该文分别阐述其判别流体性质的原理、应用实例以及适应条件。针对非电阻率测井流体识别方法的发展方向提出:二维核磁共振可结合实验室刻度进行流体识别图版优化,并且在数据采集质量及处理效果提升的基础上发展三维核磁共振流体识别方法。利用斯通利波直接反演流体表征参数,并开展大量实验、模拟完善氯元素产额校正理论以形成稳定氯离子流体识别法,尝试基于岩性扫描测井仪器Litho Scanner等提取快中子截面进行流体识别;结合机器学习算法进行图谱流体信息提取及性质区分。开展多测井技术联合识别流体性质方法研究,并形成具有推广价值的工作流程。

复杂断块油藏井震联合建模数模一体化技术研究

【目的】为解决复杂断块油藏面临的油藏构造碎小、低序级断层数量多、准确识别难度大和油藏描述效率低等问题。【方法】充分应用地震资料、测井数据等储层信息,开展井震联合建模数模一体化技术研究,利用三维地震资料,结合现场生产动态响应情况开展断层精细解释、断裂系统精细刻画,准确落实低序级断层发育及组合方式,在精细地层对比研究的基础上,建立三维地质模型,利用数值模拟与模型互检,迭代修正更新模型,尽可能保证模型精准,以便厘清剩余油分布规律,指导后期开发。【结果】该技术在胜利油田复杂断块区D块、L块等多个区块先后进行了应用,结果显示,断点吻合率均达到100%,数模含水拟合率达到90%以上。【结论】该技术能够实现复杂断块构造的精细描述,对特高含水期自然断块剩余油潜力认识、提高老区采收率具有重要意义,对其他同类型油藏的剩余油挖潜具有指导意义和良好的推广价值。

中上扬子区海相页岩复电阻率响应特征及总有机碳含量预测

页岩的电性响应特征是评价页岩气储层总有机碳含量(TOC)的重要技术指标,而现有的TOC评价模型仅利用电阻率一个电性参数,不能满足储层评价的需要,复电阻率为此提供了新途径. 本文采用实验分析和理论建模的方法,以中上扬子区海相页岩为研究对象,通过对不同地区、不同地层及页岩气井的页岩进行复电阻率实验与模型研究,反演提取页岩的激发极化(IP)参数,揭示页岩有机质富集与复电阻率响应的内在联系及规律. 结合TOC测试结果,建立电阻率、极化率与TOC评价关系模型,发掘有利于页岩气储层评价的电性敏感参数,并应用于实际勘探试验区的储层TOC预测. 形成了一套以复电阻率参数测试为主的页岩储层岩石物性测试与分析的方法和技术,为应用电磁勘探方法进行页岩气储层TOC评价提供了理论基础和物性数据.

鄂尔多斯盆地东北部奥陶系马四段白云岩储层特征及主控因素

米探1井等多口探井在鄂尔多斯盆地东北部奥陶系马四段白云岩中获得高产天然气流,展示出该区域马四段具有良好的勘探前景。然而对盆地东北部马四段是否发育规模白云岩储层还存在争议,白云岩储层分布不清制约了下一步勘探部署。基于岩心、薄片、场发射扫描电镜及地球化学特征等资料,对盆地东北部奥陶系马四段白云岩储层特征及其发育控制因素开展了系统研究,并预测了盆地东北部奥陶系马四段白云岩储层分布。研究结果表明:(1)盆地东北部奥陶系马四段白云岩发育潮坪型白云岩储层、丘滩型白云岩储层和生物扰动型白云岩储层,3类白云岩储层储集空间主要为晶间孔,含少量微裂缝,平均孔隙度分别为4.77%、5.12%和2.52%。(2)白云岩储层的形成与丘滩体、生物扰动作用和白云石化作用相关。白云石化作用是潮坪型白云岩储层晶间孔形成的关键,丘滩体和白云石化作用控制了丘滩型白云岩储层发育,生物扰动作用和白云石化作用控制了生物扰动型白云岩储层发育。(3)盆地东北部神木—靖边地区在奥陶纪马四期位于低隆起带上,有利于丘滩体发育和生物扰动作用、白云石化作用的发生,形成的白云岩储层可为天然气富集提供规模储集空间。

复杂油气藏储层预测方法综述

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