基于声波远探测和岩石力学分析的井旁裂缝有效性评价方法

储层中裂缝有效性的定性判断对实际生产具有十分重要的意义,特别对于以裂缝为主要储集空间的致密储层。目前,偶极横波远探测技术在井外裂缝的成像和识别方面已经成熟应用,但仍需要对其探测到的井旁地层裂缝开展有效性（流体输导性能）评价研究。研究提出了利用岩石力学中常用的三维莫尔圆分析来评价井旁裂缝有效性的新方法,利用偶极横波远探测成像获得的裂缝走向、倾角及地应力信息计算裂缝在平面上的应力状态,结合莫尔-库仑破裂准则,可获悉裂缝是否处于开启的临界应力状态并以此来判断裂缝的渗透性。分析表明,偶极横波远探测对裂缝倾向识别的180°不确定性问题并不影响莫尔圆方法对缝面上应力状态的确定,从而使得这2种方法可以综合起来形成一种裂缝有效性的评价方法。对不同地区碳酸盐岩储层裂缝的有效性分析表明,该研究可以有效地评价裂缝的流体输导性能,评价结果可为现场试油和开采方案的确定提供合理的依据。

Fracture characterization combining acoustic reflection imaging and rock mechanics

Qualitative evaluation of the fracture effectiveness in reservoir is of great significance to actual production, especially for tight reservoirs with fractures as the main reserving space. At present, the dipole acoustic remote detection technology has been maturely applied in the imaging and identification of fractures outside the borehole, but it still needs to carry out evaluation research on the effectiveness (fluid conductivity) of the near-borehole fractures detected. The research puts forward a new method to evaluate the effectiveness of near-borehole fractures, i.e., to analyze using the three-dimensional Mohr’s circle commonly applied in rock mechanics. The paper calculates the plane stress state of fractures using the fracture strike, dip angle and geostress information obtained by the dipole acoustic reflection imaging. Combined with the Mohr-Coulomb failure criterion, it can be learned whether the fracture is in the critical stress state of opening to judge the fracture permeability. The analysis shows that the 180° ambiguity in the identification of fracture dip by dipole acoustic reflection imaging does not affect the determination of stress state on the fracture surface by the Mohr’s circle method, so the two methods can be combined to form an evaluation method for fracture effectiveness. The analysis of fracture effectiveness of carbonate reservoirs in different regions shows that this method can effectively evaluate the fluid conductivity of fractures, and the evaluation results can provide a reasonable basis for the determination of on-site oil testing and production plans.