鄂尔多斯盆地南缘过渡带致密-低渗油藏断缝体的识别与描述

Identification and description of fault-fracture bodies in tight and low permeability reservoirs in transitional zone at the south margin of Ordos Basin

鄂尔多斯盆地南缘过渡带构造复杂,成藏条件与盆内不同,断裂、裂缝的发育为致密-低渗储层提供了重要的渗流通道和优质储集空间。在明确区域构造应力特征和断裂、裂缝发育特征的基础上,利用岩心、钻井资料、测井资料,结合三维地震的精细相干、振幅变化、曲率属性等技术,开展了断裂、裂缝的识别技术研究。裂缝型储层在鄂尔多斯盆地南缘过渡带是一种较为常见的储层类型,针对这种储层提出了断缝体的概念,认为断缝体是由断裂、伴生脆性破碎带及被其改造过的致密低渗砂岩共同构成的储集体,其上部及侧面均有非渗透泥质岩、致密层等封挡。目前已在断缝体中发现多个油藏,开发效果良好,意义重大。通过对断缝体的识别与描述,明确了大-中尺度裂缝的组合展布决定断缝体的骨架形态,小-微尺度裂缝发育边界与砂体发育边界叠合决定断缝体的边界,并形成了一套较为完整的断缝体识别与描述流程,阐述了断缝体油藏的基本地质特征。实践证实,断缝体的识别与描述技术对于盆缘构造带低丰度致密-低渗油藏的勘探开发具有重要的指导作用。

The transitional zone at the south margin of Ordos Basin is structurally complicated and unique in terms of reservoiring conditions with its well-developed faults and fractures serving as better channels for hydrocarbon seepage and providing more space for hydrocarbon accumulation in tight and low permeability layers.Based on the determination of regional structural stress and fault-fracture evolving characteristics in the zone,technologies for identifying and characterizing these faults and fractures are developed through a combination of core,drilling and logging data with 3 D seismic analysis of fine coherence,amplitude change,curvature attributes and etc.Considering the fact that fractured reservoirs are widely distributed in the zone,the study proposes the concept of fault-fracture bodies to describe the reservoirs.The fault-fracture bodies are defined as composite reservoirs composed of faults,associated brittle fractured belts and low-permeability sandstone layers modified by the belts.They are usually capped or flanked by impermeable argillaceous rocks or tight layers.The discovery of several oil reservoirs in the bodies of the zone has already verified their exploration value.The identification and description of the bodies indicates that the distribution of large-to-medium-scale fracture assemblages determine the skeletal morphology of the bodies,and the superimposition of small-to-micro-scale fracture and sand body boundaries determines the ranges of the bodies.Meanwhile,a set of identification and description procedures is formed to characterize the geology of the bodies.Practices have proven that the procedures are of guiding value to the exploration and development of low abundance and low permeability reservoirs in the zone.