Abstract: In the later stage of tight sandstone reservoir development, a complex fracture network system, comprising natural fractures, hydraulic fractures, and waterflooding-induced fractures, governs the seepage characteristics and performance of waterflooding development of reservoirs. Constructing a three-dimensional geological model of the complex fracture network system to elucidate its distribution characteristics is crucial for enhancing oil recovery in tight and low-permeability reservoirs. This paper is a case study of the tight sandstone reservoir from the first layer of first submember of Member 8 of Yanchang Formation in Jiyuan oilfield, Ordos Basin. Based on the data from cores, thin sections, well logs, microseismic monitoring, and production dynamics. combined with the analyses of the distribution of natural fractures, the development characteristics of hydraulic fractures, and the distribution of waterflooding-induced fractures, this paper proposes a geological modeling method for the complex fracture network system coupling natural fractures, hydraulic fractures, and waterflooding-induced fractures in tight sandstone reservoirs of the first layer of first submember of Member 8 of Yanchang Formation in the Wellblock L of Jiyuan oilfield. A three-dimensional geological model of the complex fracture network system has been established for the study area, and reservoir numerical simulation results demonstrate the model’s high reliability. The study results show as follows. (1)In tight sandstone reservoirs of the first layer of first submember of Member 8 of Yanchang Formation in Wellblock L of Jiyuan oilfield, natural fractures are predominantly high-angle fractures trending NEE-SWW and nearly EW, with the most developed fractures in the southeast, and less developed fractures in the southwest, parts of the northeast, and some areas in the central region. (2)Waterflooding-induced fractures primarily trend nearly NE-SW and NW-SE, partially trending nearly EW. These fractures are mainly distributed in the central to eastern, northeastern, northwestern, southern, and southeastern parts of the study area. (3)The hydraulic fractures primarily trend between 48° and 71°, with an average fracture length of 204.5 m, an average fracture width of 38.5 m and an average fracture height of 14.7 m. (4)Considering the interactions among natural fractures, hydraulic fractures, and waterflooding-induced fractures, to establish a dynamic complex fracture network system model by coupling these three types of fractures based on their origins, formation time, and other factors is a crucial way for achieving breakthroughs in the modeling of fracture coupling systems in tight sandstone reservoirs.

Key words: natural fracture, hydraulic fracture, waterflooding induced fracture, complex fracture network system, tight sandstone, Jiyuan oilfield

摘要： 在致密砂岩储层开发后期,由天然裂缝、水力压裂缝和注水诱导裂缝耦合的复杂缝网系统控制了注水开发油藏的渗流特征及开发效果,建立复杂缝网系统的三维地质模型,揭示复杂缝网系统的展布特征对致密油藏提高采收率具有重要意义。以鄂尔多斯盆地姬塬油田L井区延长组8段(长8段)1亚段1小层致密砂岩储层为例,基于岩心、岩石薄片、测井、微地震监测和生产动态等资料,在开展天然裂缝分布规律、水力压裂缝发育特征和注水诱导裂缝展布特征研究的基础上,提出了一种适用于姬塬油田L井区长8段1亚段1小层致密砂岩储层天然裂缝、水力压裂缝和注水诱导裂缝耦合的复杂缝网系统地质建模方法,建立了L井区的复杂缝网系统三维地质模型,且油藏数值模拟结果表明该模型具有较强的可靠性。研究结果表明:①姬塬油田L井区长8段1亚段1小层的天然裂缝以NEE—SWW向和近EW向高角度裂缝为主,裂缝在东南部最发育,在西南部、东北部局部和中部局部地区的发育程度较差;②注水诱导裂缝以近NE—SW向和NW—SE向为主,部分为近EW向,主要分布于L井区中部偏东部、东北部、西北部、南部和东南部;③水力压裂缝的走向主要为48°~71°,平均缝长为204.5 m,平均缝宽为38.5 m,平均缝高为14.7 m;④综合考虑天然裂缝、水力压裂缝与注水诱导裂缝之间的相互作用,将3种裂缝按成因、形成时间等要素进行耦合,建立动态的复杂缝网系统模型,是致密砂岩储层天然裂缝、水力压裂缝与注水诱导裂缝耦合的复杂缝网系统建模亟待攻关的方向。

关键词: 天然裂缝, 水力压裂缝, 注水诱导裂缝, 复杂缝网系统, 致密砂岩, 姬塬油田