Identification And Description Of Typical Fault Broken Zones In Dongxin Oilfield

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.