青西油田裂缝特征及其对开发过程的影响

【作者】 刘战君；

【导师】 李允； 孔繁瑾；

【作者基本信息】 西南石油学院 ， 油气田开发工程， 2003， 博士

【摘要】 青西油田各储层段裂缝广泛发育，裂缝在青西油田既是重要的储集空间，又是油气主要的渗滤通道，因此，裂缝的研究对于青西油田的储量评价、产能建设和采收率提高都尤为重要。 本文将分形分维技术与测井解释相结合，建立了基于分形分维的裂缝性地层裂缝孔隙度的测井定量计算方法。该方法为确定裂缝孔隙结构指数提供了一条新途径，使该参数的确定不再唯一地依赖于室内岩心实验，缓解了裂缝性地层由于不易取得包含天然裂缝的岩心，进而导致其孔隙结构指数难以获得的矛盾。该方法也可以应用于非裂缝性储集层确定孔隙结构指数。 以现代岩石力学的研究成果为依据，将裂缝空间展布规律预测建立在原地水平应力预测的基础上，综合利用成像测井、双井径测井曲线等资料，通过对青西油田原地水平应力方向的预测实现了青西油田裂缝延伸方向和井间裂缝发育带的预测。青西油田地层中裂缝孔洞均有发育，层间缝特别发育。窟窿山地区裂缝分布主方向与原地最大水平主应力的方向趋于一致，原地应力对构造成因裂缝的发育起着主导作用。 应力敏感性实验研究表明青西油田基质岩块应力敏感性较弱，裂缝应力敏感性很强，因此，在油田开发初期必须进行地层保压生产，严格控制产量。 利用接触理论的弹、塑性有限元，计算分析了不同产状裂缝在油田开采过程中的闭合规律。结果表明，在青西油田发育的不同产状的裂缝中，低角度缝，尤其是水平层间缝极易受到裂缝内流体压力降低的影响而闭合，闭合压力高。有限元方法虽可以逐步逼近计算得到临界闭合压力点，但计算复杂，不便于现场操作；室内实验可能会因为岩样受压破坏而无法得到临界流体压力。因此，本论文最后就利用解析法求取临界闭合流体压力的方法进行了探讨，基于简化的弹塑性模型，建立了裂缝弹塑性接触解析模型。裂缝临界闭合压力的确定，对指导油田开发，提高油藏的采收率具有重要的指导性意义。 对青西裂缝性储层裂缝的发育和分布规律、裂缝的空间延伸、裂缝孔隙度的定量计算及储层裂缝应力敏感性等方面的分析研究，将为青西油田今后的开发方案部署与实施提供重要的理论参考。更多还原

【Abstract】 Fracture in the reservoir of QingXi oil field grows widely. It is not only the important storage space, but also the main flow passage for the oil and gas. For this reason, the research on fractures is of significance for the reserve estimation, the productivity to achieve and recovery in QingXi oil field.A method which is based on the technology of fractal and fractal dimension and well logging data has been developed and been used to calculate pore structure index and the fracture porosity in the fractured reservoir quantitatively in this paper. The method has provided another way for obtaining formation pore structure index. So the pore structure index is no longer only relied on core test in lab. The method above can also be used to calculate the pore structure index of non-fractured reservoir.Based on the achievements of the modern rock mechanics, by using of image logs dual caliper logs and so on comprehensively, the fracture extended direction and fracture area around borehole and in-situ horizontal stress direction have been obtained in the Qingxi .On the basis of the prediction of in-situ horizontal stress direction, the fracture areas of inter-well could be obtained. The results also show that In the reservoir of Qingxi oil field, both the fracture and the vug have grown; especial the interlayer fracture is in well growth. In Kulong mountain area in Qingxi oil field, the main direction of fracture distribution tends to the same as the direction of the in-situ maximum horizontal stress. The primary earth stress controls the growth of the fracture.The results of stress sensitivity experiment show that matrix rock of Qingxi oil field is weak stress sensitivity, but for the fracture, it’s very strong. So, at the beginning of production in this field, Keeping reservoir pressure and limiting production are important and essential.The closure rules of fracture in different occurrence are also calculated and analyzed during production by using elastic-plastic finite element method of contact theory. The results show that fractures with low dip angle in Qingxi, especial horizontal interlayer fractures, tend to close easily due to inside fracture pressure dropping down. The closure pressure of fractures with low dip angle is relative high. By using of finite element method can achieved the critical closure pressure step by step, but the work is very complex and it is not convenient for the well-site operation. It is possible that the critical closure pressure couldn’t be obtained because of rock sample failure during lab test and no rock sample with natural fracture for test. So At the end of this paper, base on simplified elastic-plastic constitutive model ,a elastic-plastic contact analytic model to calculate the critical fracture closure pressure has been established and discussed.更多还原