摘要
断层破碎带是由断面附近派生裂缝和断面充填物组成的地质体,在地表露头容易识别,但在地下油田的鉴别还是一个难题。因而,人们对断层破碎带地下结构及性质认识比较局限,无法建立真实的断块油藏地质模型,导致断块油田深入挖潜难以进行。
本文在认识断层破碎带露头特征的基础上,利用测井信息及相关地质资料对东辛断块油田断层破碎带进行识别。通过测井曲线对比,提出用裂缝发育系数识别派生裂缝(Fdr>0.35)和断面充填物(Fdr<0.35),并发现了5种结构的断层破碎带:①派生裂缝-断面充填物-派生裂缝的对称结构断层破碎带,②派生裂缝-断面充填物组成的非对称断层破碎带,③不完整的断层破碎带,包括无断面充填物只有派生裂缝的和无派生裂缝只有断面充填物的两种,④结构复杂的断层破碎带。研究还发现了断层破碎带厚度与断距之间存在1:10-1:20的关系。
评价了永3断块不同级别断层破碎带物性特征和排替压力,发现该断块断层破碎带有较好的封闭性,且断面充填物的封闭性强于派生裂缝,由于断层破碎带的结构差异,造成同一断层不同部位的封闭性不同。
永3和辛109断块剩余油大多临近断层破碎带,但由于物性条件差,设计水平井时还要避免钻遇断层破碎带,因此根据断层破碎带的空间展布特征,对该断块设计了水平井轨迹,以达到对断块油田剩余油进一步挖潜的目的。
A fault broken zone is defined as a geological body which is composed of fractures derived by fault movement and fragments filled between two walls of the fault, and is easily identified from outcrop, but difficultly to recognize subsurface. Therefore, people have known little about the structure and properties of fault broken zone, and can not establish real fault-block reservoir geological model. So it is hard to have an in-depth study in fault-block oilfield.
The paper conducted the investigation in the Dongxin Oilfield in the Jiyang Depression, and identified 5 types of fault broken zones, i.e. (1) symmetrical fault broken zone with configuration of derived fractures– filled fragments– derived fractures, (2) unsymmetrical fault broken zone with of derived fractures– filled fragments, (3) two kinds of imperfect fault broken zone with only derived fractures or with only filled fragments, and (4) complex fault broken zone without fixed derived fractures or filled fragments. The identification is based on repeated comparisons of well loggings and related geological data. A key coefficient (Fdr) is used successfully in identification, if Fdr>0.35 being derived fractures and if Fdr<0.35 being filled fragments. It was found that fault displacement is ten to twenty times than the thickness of fault broken zone.
As an example, petrophysics and displacement pressures of the derived fractures and filled fragments of fault broken zones with different sizes in the Yong-3 fault-block, and are believed as key factors for the fault sealing properties. The sealing of filled fragments is better than the derived fractures; it caused that different part of the same fault express different sealing characteristics because of different structure of fault broken zone.
Remaining oil mostly close to the fault broken zones in Yong-3 and Xin-109 fault-blocks. The distribution of the fault broken zones are mapped and applied in designing horizontal wells to produce efficiently the remaining oil in the fault blocks.
引文
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