Estimation of the current stress field and fault reactivation analysis in the Asmari reservoir, SW Iran

Knowing the current condition of the faults and fractures in a reservoir is crucial for production and injection activities.A good estimation of the fault reactivation potential in the current stress field is a useful tool for locating the appropriate spot to drill injection wells and to calculate the maximum sustainable pore pressure in enhanced oil recovery and geosequestration projects.In this study,after specifying the current stress state in the Gachsaran oilfield based on Anderson’s faulting theory,the reactivation tendency of four faults(F1,F2,F3,and F4)in the Asmari reservoir is analyzed using 3D Mohr diagrams and slip tendency factors.Results showed that all the faults are stable in the current stress state,and F2 has the potential to undergo the highest pore pressure build-up in the field.On the other hand,F3 has the proper conditions(i.e.,strike and dip referring to σHmax orientation)for reactivation.Stress polygons were also applied to show the effect of the pore pressure increase on fault stability,in a graphical manner.According to the results,the best location for drilling a new injection well in this part of the field is the NW side of F2,due to the lower risk of reactivation.It was found that both methods of 3D Mohr diagrams and slip tendency factors predict similar results,and with the lack of image logs for stress orientation determination,the slip tendency method can be applied.The results of such studies can also be used for locating safe injection points and determining the injection pressure prior to numerical modeling in further geomechanical studies.

The productivity evaluation model and its application for finite conductivity horizontal wells in fault block reservoirs

It is very difficult to evaluate the productivity of horizontal wells in fault block reservoirs due to the influence of fault sealing.On the basis of the method of images and source-sink theory,a semianalytical model coupling reservoir and finite conductivity horizontal wellbore flow dynamics was built,in which the influence of fault sealing was taken into account.The distribution of wellbore flow and radial inflow profiles along the horizontal interval were also obtained.The impact of the distance between the horizontal well and the fault on the well productivity was quantitatively analyzed.Based on this analysis,the optimal distance between the horizontal well and the fault in banded fault block reservoirs could be determined.According to the field application,the relative error calculated by the model proposed in this paper is within ±15%.It is an effective evaluation method for the productivity of horizontal wells in fault block reservoirs.The productivity of the horizontal well increases logarithmically as the distance between the horizontal well and the fault increases.The optimal distance between the horizontal well and the fault is 0.25-0.3 times the horizontal well length.

Multi-parameter quantitative assessment of 3D geological models for complex fault-block oil reservoirs

In the field of 3 D geologic modeling, researchers often pay more attention to modeling methods and workflows, but neglect the quantitative evaluation of models. If the evaluation is narrowed to the same reservoir type, the comparability and practicality of quantitative assessment will be emerging. The evaluation system should include three parts: data verification, geological understanding and process check. Data verification mainly involves testing the accuracy of local prediction with actual data, and geological understanding is to examine whether the global estimation honors geological principles and prior insights. Process check is also indispensable to avoid occasionality. To this end, we produced a set of assessment criteria, taking complex fault-block sandstone oil reservoir as an example. To be specific, thirteen characteristic parameters were totally selected, setting weights according to their rated importance, formulating three-level evaluation standards in a centesimal system for each characteristic parameter, and obtaining the final assessment based on the cumulative score. The results indicate that such evaluation can not only access the quality of the model objectively and comprehensively, but also identify the aspects in need of improvement through the deduction items.

Three-dimensional analysis of a faulted CO2 reservoir using an Eshelby-Mori-Tanaka approach to rock elastic properties and fault permeability

This work develops a three-dimensional(3D) multiscale model to analyze a complex carbon dioxide(CO_2) faulted reservoir that includes some key geologic features of the San Andreas and nearby faults southwest of the Kimberlina site.The model uses the STOMP-CO2 code for flow modeling that is coupled to the ABAQUS~ finite element package for geomechanical analysis.A 3D ABAQUS~ finite element model is developed that contains a large number of 3D solid elements with two nearly parallel faults whose damage zones and cores are discretized using the same continuum elements.Five zones with different mineral compositions are considered:shale,sandstone,fault damaged sandstone,fault damaged shale,and fault core.Rocks' elastic properties that govern their poroelastic behavior are modeled by an Eshelby-Mori-Tanaka approach(EMTA).which can account for up to 15 mineral phases.The permeability of fault damage zones affected by crack density and orientations is also predicted by an EMTA formulation.A STOMP-CO2 grid that exactly maps the ABAQUS~ finite element model is built for coupled hydromechanical analyses.Simulations of the reservoir assuming three different crack pattern situations(including crack volume fraction and orientation) for the fault damage zones are performed to predict the potential leakage of CO_2 due to cracks that enhance the permeability of the fault damage zones.The results illustrate the important effect of the crack orientation on fault permeability that can lead to substantial leakage along the fault attained by the expansion of the CO_2 plume.Potential hydraulic fracture and tendency for the faults to slip are also examined and discussed in terms of stress distributions and geomechanical properties.

深层断溶体油气藏钻完井储层保护技术挑战与对策

深层断溶体油气藏储层裂缝发育,易导致大量工作液漏失,造成严重储层损害。以顺北区块奥陶系碳酸盐岩储层为例,考虑储层超深、超高压、超高温与断裂带特点,综合工区钻井液漏失情况、储层物性特征、矿物组成和裂缝发育情况,结合流体敏感性、应力敏感性与储层润湿性评价,揭示了深层断溶体油气藏储层损害机理。钻井液漏失是深层断溶体油气藏最重要的储层损害方式,岩体结构破碎、储层非均质性强、走滑断层裂缝缝面光滑及高温长井段循环进一步加大了储层保护的难度;通过采用控压钻井技术,结合抗高温高酸溶屏蔽暂堵技术与抗高温强滞留堵漏技术,可以达到较好的储层保护效果;根据深层断溶体碳酸盐岩油气藏裂缝发育特征,钻进全程加入高强度架桥材料,利用鳞片状岩屑作为填充材料,达到钻井过程防漏与开发过程预防裂缝应力敏感性的效果,实现漏失控制—储层保护—增产增渗的一体化目标。

Study on Injection-Production System Adjustment of Fault Block Reservoir Based on Equilibrium Displacement

This paper proposed a method of injection-production system adjustment to solve the problem that the water flooding effect was restricted because of the horizontal and vertical contradictions during the development process of fault block reservoirs. Considering the heterogeneity of reservoir, the Buckley-Leverett water flooding theory was applied to establish the relationship between the recovery and cumulative water injection. In order to achieve the goal of vertically balanced recovery of each section, the calculation method of vertical sectional injection allocation was proposed. The planar triangular seepage unit was assumed and sweep coefficients of different oil-water distribution patterns were characterized using multi-flow tube method. In order to balance and maximize the plane sweep coefficient, the calculation method of plane production system optimization was obtained. Then the injection-production system stereoscopic adjustment method based on equilibrium displacement was proposed with vertical sectional injection allocation and plane production system optimization. This method was applied to injection and production adjustment of BZ oilfield in southern Bohai. The effect of water control and oil increase was obvious. This method can greatly improve the effect of water flooding of offshore fault block reservoirs with the adjustment of injection-production system.

Study on Fault Lateral Sealing Based on SGR Method

Bozhong A Oilfield is located in the northeast of Huanghekou Sag in the Bohai Bay Basin, and is a complex fault block oilfield. The main oil bearing horizon is the lower Minghuazhen Member, belonging to shallow water delta sedimentation. For the rolling exploration and evaluation of adjacent fault blocks, this paper uses the mudstone smear method to analyze and accurately characterize the lithological contact relationship between the two walls of the fault. Based on the establishment of different reservoir docking modes on the two walls of the fault, the sealing parameters are calculated to evaluate the sealing ability of the fault, thereby evaluating its reservoir formation characteristics, and predicting the height of the oil column. The above methods provide geological basis for further rolling expansion and potential tapping in the study area and surrounding areas, and have guiding significance for exploration and rolling potential tapping in similar blocks in the Bohai Sea.

超深断控碳酸盐岩油藏空间结构表征技术与工程实践

在积极推进深地工程的背景下,超深断控缝洞型碳酸盐岩成为油气勘探开发的重点领域,而超深走滑断裂精准解译、缝洞体内部构型建模、断控油气藏储量雕刻评估、高效井位部署及提高采收率等是制约超深领域“增储上产”的重要科学问题与技术挑战。本文基于区域应力场研究、露头剖析、三维地震解译、物模数模,全面构建了涵盖动力学、运动学、几何学,分期、分级、分性质、分带、分层的“三学五分”断裂构造解析技术,据此阐明了走滑断裂纵向分层、横向差异分段特征,揭示了走滑断裂控储、控藏、控油气富集等地质规律,发现了超深断控缝洞型10亿吨级大油田。依据动/静态资料,精细刻画了断控缝洞体内部构型,通过“井震”结合实现了断控缝洞型油气藏量化表征,形成了相应的高效井位部署、油气储量雕刻评估等技术系列,支撑了富满油田10亿吨级油气储量的发现与落实。依据断控油气藏的定量刻画结果,针对性提出了提高采收率技术对策,推动了富满5×106t大油田的高效建设,形成了超深断控碳酸盐岩“增储上产”范例,可为我国类似油气藏的开发“上产”提供借鉴。

基岩油气成藏特征与中国陆上深层基岩油气勘探方向

基于全球基岩油气藏数据库和中国基岩油气藏解剖,深入分析基岩油气成藏特征,探讨深层基岩油气成藏的有利条件和勘探方向。研究表明:全球已发现的基岩油气田主要分布在埋深小于4500 m的中浅层,层位以太古宇和前寒武系为主,储集层岩性以花岗岩和变质岩为主;规模较大的基岩油气田主要分布在中新生代构造运动活跃的裂谷盆地、弧后盆地和前陆盆地。基岩油气成藏特征主要表现为:(1)以孔隙-裂缝型低孔特低渗储集层为主,非均质性强,强抗压实作用导致储集层物性不受埋深控制,规模成储期为盆地基底风化剥蚀期及后期构造改造期;(2)他源供烃,成藏组合可划分为烃源岩-基岩接触型和烃源岩-基岩分离型两大类;(3)烃源岩异常高压和基岩储集层常压-低压,导致烃源岩与储集层之间存在较大的压力差,有利于深层基岩抽吸成藏。基底构造活动性、成藏组合关系、深大断裂(尤其走滑断裂)发育程度及区域性盖层等是深层基岩选区评价的主要参数;古老克拉通盆地陆内裂谷边缘的前寒武系结晶基底、紧邻生烃凹陷的古生代褶皱基底和中新生代块断基底,均具有较好的成藏条件,是未来深层基岩油气勘探的主要方向。

塔里木盆地富满断控破碎体油藏储集类型特征与注水替油效果

塔里木盆地走滑断裂控制的超深油气藏是近年来中国油气勘探开发最重要领域之一,但目前该类型油藏的储集空间类型并不清楚,不同储集空间类型与注水效果关系不明确,严重制约了富满油田的高效开发。在充分分析野外露头、岩心、成像测井以及动态监测资料的基础上,系统剖析了断控破碎体的3种主要储集空间类型及其与注水效果的关系。提出了断控破碎体的概念,指出富满油田主要为断控破碎体油藏,研究结果表明:①断裂空腔型储集体主要分布在断裂带的核部,由断层滑动面产状变化引发内部体积调整形成了“空腔”型洞穴。埋藏条件下的储集空间相对较为封闭,内部孔隙空间较大,注水后原油置换率较高,部分油井动用储量的注水采收率可高达93%。②角砾间孔隙型储集体主要分布在断裂带的核部,由相邻的角砾相互支撑而形成角砾间不规则储集空间类型。该类储集体分布较为均匀,孔隙度中等,单位压降下的产液量较高,但是由于储集空间内部连接并不通畅,注水后置换率较低,需要研究探索构建立体结构井网来提高开发效果。③构造裂缝型储集体主要分布在断裂带的损伤带和过程带,在断层带的两侧和端部发育形成一定宽度的裂缝带。裂缝带周边也会发育少量孔隙,部分区域会形成一定的渗流优势通道,因此注入水的流失量较大,注水效果相对于断裂空腔型储集体较差。研究成果支撑了富满油田上产原油350×10^(4) t,可助推注水开发方案和提高采收率方案的优化,对同类型油藏高效开发具有重要的借鉴意义。

塔里木盆地北部奥陶系海相碳酸盐岩断溶体油藏成因类型及特征再认识

前人提出的“断溶体”油藏概念,现已成为海相碳酸盐岩油气藏勘探开发的新目标、新类型。但断溶体油藏与传统的风化壳型喀斯特油藏有显著差别,断溶体储集体类型、结构特点也存在差异。研究断溶体溶蚀作用和构造破裂作用的差异性,将断溶体划分为过溶蚀残留型、破碎+强溶蚀型和强破碎+弱溶蚀型3种类型。研究表明不同成因类型的断溶体油藏,其溶蚀程度、缝洞规模、累产油量、地层能量和缝洞间连通性差异明显。过溶蚀残留型油藏的分布受风化壳不整合面及断裂带的纵向溶蚀作用控制。破碎+强溶蚀型及强破碎+弱溶蚀型油藏的形成和分布与不整合面的发育和构造位置关系不大,主要受溶蚀断裂带“破碎+溶蚀程度”控制,在溶蚀断裂带核部发育规模较大的洞穴,向两侧逐步发育裂缝-孔洞型、裂缝型储层。

顺北超深断溶体储层典型试井曲线特征及类别

顺北地区超深断溶体储层主要发育有裂缝及片状洞穴,采用可横向穿越缝洞储集体的水平井进行开发,其试井曲线形态特征复杂多变。依据井筒和表皮效应结束后的中期试井曲线的典型特征,将顺北地区实测试井曲线分成了3个大类。该3大类试井曲线特征直接反映了井与缝洞储集体的不同接触关系。再根据后期的试井形态特征,将顺北地区实测试井曲线细分成了9个亚类,不同的亚类试井曲线特征明显不同,是井外围缝洞发育状况变化的试井曲线响应。最后,提出了与试井曲线特征相对应的3大类9个亚类的试井解释评价物理模型。本文研究成果可用于指导顺北地区的试井分析与试井研究工作,亦可为其他深层断溶体储层的试井研究提供借鉴与参考。

新疆克拉玛依乌尔禾张扭性走滑断裂特征及其控藏作用研究

乌尔禾沥青矿断裂带位于准噶尔盆地西北缘乌夏断裂带乌尔禾鼻隆之上,是一个小型左旋走滑断裂带。断裂带形成后未发生强烈改造,断裂带内发育沥青矿脉,露头地质条件好,且有三维地震覆盖,是研究走滑断裂特征和控藏作用的天然实验室。本文采用无人机三维立体建模技术,结合野外剖面实测,对乌尔禾沥青矿走滑断裂带野外剖面露头进行定量分析和解剖。结果表明,沥青矿断裂带共发育17条断层,主断层西北侧断层呈雁列状分布,东南侧断层呈马尾状,断裂带纵向呈负花状。研究表明,断层形成于燕山期左旋剪切应力场,受拉张应力影响,整体处于张扭环境,形成张扭性走滑断裂带。断层发育空腔和诱导裂缝,尤其主动盘裂缝更为发育,空腔的开度与油气侵染宽度呈正相关。结合塔里木盆地张扭性走滑断裂与油气藏关系分析,本文认为张扭性走滑断裂是良好的垂向油气运移通道,主动盘具有侧向输导作用,被动盘具有封堵作用,走滑断裂主动盘一侧圈闭是良好的油气聚集区域。

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。

Fault－weakening effect of reservoir temperature of hot spring and its influence on seismic activities

In this paper, the reservoir temperatures of 14 hot spring samples collected from the northern segment of theRed River Fault are calculated by using the mixing-model of SiO2-geothermometer. Based on the features ofreservoir temperatures and densities of hot springs, the northern segment of the Red River Fault is furtherdivided into 4 sub-segments. The influence of weakening effect of water on seismic activities is discussed fromthe view point of fault-weakening effect of water. It is suggested that the difference in seismic activity between various sub-segments is principally caused by the difference in intensity of the fault-weakening effect ofwater of these sub-segments. The Eryuan sub-segment where the reservoir temperatures are high and the hotsprings are dense corresponds to a slipped region, however, the Jianchuan and Midu sub-segments where thereservoir temperatures are lower and the hot springs are fewer as well as the Dan sub-segment where the hotspring are very few all correspond to locked regions. It is suggested that Dan sub-segment is the riskiest region for strong earthquake preparation, while the possibility for strong earthquake preparation is very little inthe Eryuan sub-segment.

Integrated Modelling and Reservoir Characterization of Ataga Field, Niger Delta Basin, Nigeria

Integrated modelling, well correlation and petrophysical analysis were performed to characterize the reservoirs for optimum hydrocarbon correlation using 3-D seismic reflection data and suites of well logs from Ataga 5, 7, 10 and 11 wells respectively in Ataga field, shallow offshore, Niger Delta Basin, Nigeria. The study revealed the presence of two viable hydrocarbon bearing reservoirs, AT1 and AT2 and the average values of porosity, permeability, water saturation, hydrocarbon saturation, Net to Gross (NTG) and volume of shale are in the ranges of 15% - 77%, 44.5% - 75.5%, 25.5% - 85%, 15% - 75.5%, 0.70 - 0.88 and 0.11 - 0.38 respectively which goes further to show that the both reservoirs have fair characteristics that are suggestive of the presence of hydrocarbon accumulation. It can therefore be deduced that the permeability values are reflective of fair interconnectivity of pore spaces of sands within the well areas and their ability to transmit fluids, the depth and depth structural map generated for the horizons and structures shows that the most dominant trapping mechanism in the area under study is the crescentic growth fault and the rollover anticlines trending in the Northwest-Southeast direction and from the volumetric analysis. It can be deduced that the recoverable gas for AT1 and AT2 reservoirs is 2 × 106 mscf and 6 × 106 mscf respectively.

塔里木盆地超深层走滑断控油气藏研究进展与趋势

在塔里木盆地开辟了超深层走滑断控油气藏勘探开发领域,但断控油气藏极为复杂,难以效益开发,亟需加强油气藏基础地质研究。走滑断控油气藏具有非均质性强、储集层与流体分布复杂、油气产量变化大及采收率低的共性,不同地区走滑断控油气藏的断裂、储集层、成藏与流体存在较大的差异,面临一系列勘探开发难题。建立了差异成因的走滑断裂破碎带及其控储模型,揭示了沿走滑断裂带“相-断-溶”三元复合控储、连片差异规模发育的成储机制;构建了“源-断-储-盖”四元耦合成藏、“小藏大田”的走滑断控油藏模型,揭示了超深层走滑断控油藏的形成与保存机理。突破了克拉通盆地弱走滑断裂难以形成走滑断控大规模储集层与大油气田的理论认识局限,明确了克拉通盆地走滑断裂系统大规模发育的成因机制、走滑断裂破碎带差异成储成藏机理与油气富集规律。

塔里木盆地顺北地区顺北84X井超千米含油气重大发现及其意义

塔里木盆地顺北中部北东向走滑断裂带长期处于油气运聚富集的优势区,顺北8号走滑断裂带实钻揭示沿断裂带发育断控缝洞型油气藏,顺北84X井纵向上沿断裂带含油气高度高达1088 m,揭示断控缝洞型油气藏含油气高度大、不受现今构造高低控制。为查明断控缝洞型油气藏含油气高度的主控因素,立足顺北中部奥陶系碳酸盐岩油气藏的成藏地质条件和钻探成果,开展顺北84X井的储层、圈闭及成藏特征等石油地质条件分析,为深化断控缝洞型油气藏认识和向深层评价拓展提供支撑。研究表明:①走滑构造破碎是致密碳酸盐岩成储的关键,其储层发育深度不受碳酸盐岩地层埋深的控制,在近9000 m的埋深条件下仍发育断控缝洞型储集体;②上覆巨厚泥岩盖层顶封、两侧致密灰岩侧封、走滑断裂平面分段和纵向分层变形是形成断控缝洞型圈闭的关键;③油-源对比分析表明油气来自寒武系玉尔吐斯组烃源岩,证实了前期顺北中、东部“寒武多期供烃、构造破裂成储、原地垂向输导、晚期成藏为主、走滑断裂控富”的成藏模式的合理性。顺北84X井的发现揭示塔里木盆地超深层致密碳酸盐岩发育受走滑断裂控制,储层纵向深度大,油气充注足,超深层勘探潜力巨大。

基于深度残差网络的走滑断层智能识别方法——以塔里木盆地富满油田为例

走滑断层精细识别是断控缝洞型碳酸盐岩油气藏勘探开发的关键环节之一,但走滑断层的水平位移在垂直断层走向的地震剖面上不易识别,为此,提出了一种基于深度残差网络的走滑断层智能识别方法。该方法的网络模型由特征提取子网络、结构提取子网络和去噪卷积子网络3个子网络构成。特征提取子网络提取地震与断层预测映射的残差特征,结构提取子网络提取边界结构的残差映射实现断层解释的目标,去噪卷积子网络去除网络累计生成的噪声。网络在预测时采用了多层输出融合技术和迁移学习的方式,能有效避免高频特征信息的丢失,增强对不同规模断层分类解释的鲁棒性和泛化力。通过对合成记录验证分析可知,该方法对低信噪比地震资料情况下的小断距、弱走滑断层的识别精度高,预测的损失率低,预测断层连续性好,断层边界清晰,且抗噪性较好。塔里木盆地富满地区果勒西区块实际地震资料的应用结果表明,该方法对线性走滑断层、压扭辫状走滑断层和拉张辫状走滑断层等不同性质的走滑断层均有较好的识别效果。