缝洞型油藏三维离散缝洞数值试井模型

THREE DIMENSIONAL DISCRETE-FRACTURE-CAVITY NUMERICAL WELL TEST MODEL FOR FRACTURED-CAVITY RESERVOIR

缝洞型碳酸盐岩油藏发育着大尺度的溶洞和裂缝,非均质性极强,缝洞型碳酸盐岩油藏问题的研究成为了世界级难题之一.由于大尺度溶洞和裂缝对储层的流体流动起主导作用,因此,基于连续介质理论的双重介质或三重介质模型已不适合其中流体流动的描述.根据大型缝洞分布地质特征,探索性地提出了一种板块组合的复合架构离散缝洞模型描述该类油藏中的流体流动,将三维空间大裂缝用板块描述,溶洞用高渗透率和高孔隙度不规则多面体团块描述.将裂缝面用二维三角形单元离散,溶洞和基质用三维四面体离散,利用三维混合单元有限元法对建立的不定常渗流模型进行求解,得到了三维渗流条件下的试井理论曲线及压力场分布.通过对试井理论曲线特征的分析,获得了各敏感参数对试井曲线的影响规律.通过对1口井的实际测试资料解释结果的分析,并与实际地震反射资料及生产实际资料的对比,发现本文所建立的模型可以较好地反映裂缝和溶洞的地质动态状况,并与实际生产状况具有较好的一致性.这一结果说明了所建模型的正确性以及测试资料分析结果的可靠性.

The fracture-cavity carbonate reservoir is developed with fractures and cavity in large scale and strongly heterogeneous. The fractures and cavity of large scale play a dominant role in reservoir fluid flow. Therefore, the multimedium models based on continuum theory are not suitable for the description of fluid flow. According to the geological features of the large-scale distribution of fracture and cavity, this paper presents a composite architecture of discretefracture-cavity model to describe the fluid flow in the reservoir. This model describes the fractures with plates, the cavity with irregular polyhedrons of large permeability and high porosity. Then, the fracture faces are discretized with triangle elements of two dimensions, and the cavity and matrix are discretized with tetrahedron of three dimensions. The seepage model of discrete-fracture-cavity is solved by mixed finite element method. The wellbore pressure response curve and pressure fields in three dimensions are obtained. The analysis of log-log type curve of wellbore pressure and pressure fields shows that six flow regimes may appear in the model. The effects of the different parameters to log-log type curve are analyzed. A filed data example is analyzed by the present model.