基于岩相-断层破碎带耦合约束的构造裂缝预测研究——以博兴洼陷大芦湖油田沙三中亚段为例

Tectonic fracture prediction based on the coupling constraint of lithofacies and fault damage zone:A case study of the 2nd sand group of middle Es3 member in Daluhu oilfield,Boxing subsag

致密砂岩储层广泛发育构造裂缝,严重影响储层非均质性与后期井位部署.本文以博兴洼陷大芦湖油田樊162、樊3区块沙三中亚段致密砂岩储层为例,从影响构造应力的地质材料体不均一性与构造强度的差异性入手,将沉积相控制下的岩相展布模型与断层内部结构模型进行耦合,进行岩相-断层破碎带耦合约束下的构造应力场数值模拟,通过建立应力场与裂缝参数间关系,构建裂缝密度空间展布模型进行裂缝分布预测,认为构造裂缝的发育受断层结构和岩相差异的耦合控制.研究结果表明:研究区断层核部最大主应力在50~60 MPa之间,水平应力差在58~79 MPa之间,属应力中低值区域,裂缝密度集中在1.2~2.7条/m.在断层上盘的砂砾岩相部位最大主应力在41~52 MPa,水平应力差在78~91 MPa,属应力低值区域,裂缝密度集中在1.0~1.7条/m;在断层上盘的细砂岩相部位,最大主应力在73~76 MPa,水平应力差在90~95 MPa,属应力中高值区域,裂缝密度在3.5~4.0条/m.在断层破碎带上盘部位、河道前缘砂坝的中粗砂岩相与朵叶体的粉砂岩相交互处,最大主应力在73~80 MPa之间,水平应力差在106~110 MPa,属应力高值区域,裂缝密度集中在3.5~5.0条/m.总体呈现出伴随距断层核部距离的增加,裂缝密度先增加后减小的规律;距断层越近,构造应力对裂缝发育影响权重越大,距断层越远,岩相类型对裂缝发育影响权重越大.

Tectonic fractures are widely developed in tight sandstone reservoir,which greatly affect reservoir heterogeneity and well deployment.In this paper,taking middle Es3 member of the Paleogene Shahejie formation as a case study,starting with the heterogeneity of geological materials and the difference of tectonic strength which affect tectonic stress,the lithofacies distribution model controlled by sedimentary facies is coupled with the fault internal structure model.And the numerical simulation of tectonic stress field under the coupled constraints of lithofacies-fault damage zone is carried out.By establishing the relationship between stress field and fracture parameters,the spatial distribution model of fracture density is constructed.It is considered that the development of tectonic fracture is controlled by the coupling of fault and difference of lithofacies.The prediction results of tectonic stress field and fracture distribution showed that the maximum principal stress of fault core zone was between 50-60 MPa,and the difference of horizontal stress was between 58-79 MPa.The fault core zone belonged to the area with low stress.And the fracture density was concentrated in 1.2-2.7 fractures/m.The stress of sand conglomerate in the hanging wall was middle-low,the maximum principle stress was between 41-52 MPa,the difference of horizontal stress was between 78-91 MPa,and the fracture density was 1.0-1.7 fractures/m.The stress of fine sandstone in the hanging wall was high,the maximum principle stress was between 73-76 MPa,the difference of horizontal stress was between 90-95 MPa,and the fracture density was 3.5-4.0 fractures/m.On the hanging wall of the fault damage zone and the interaction area between coarse sandstone of channel leading sand dams and siltstone of lobes microfacies,the maximum principle stress was between 73-80 MPa,the difference of horizontal stress was between 106-110 MPa,and the fracture density was 3.5-5.0 fractures/m.The development of natural fractures is obviously controlled by the coupling of lithofacies and fault damage zone.With the increase of the distance from fault slip plane,the fracture density increases rapidly firstly and decreases slowly.The closer it is to the fault core zone,the greater the weight of structural stress on fracture development can be;the further away it is from the fault core zone,the greater the weight of lithofacies type on fracture development can be.