安塞致密砂岩油藏单砂体刻画与压裂改造

安塞油田多期河道叠加致密砂岩油藏开发中后期, 油井含水量升高, 油层有效动用不均, 整体压裂易出现水窜、水淹现象, 已不适应油田现今的生产状况。针对这一问题, 通过对油水井单砂体进行细分和对比, 建立岩体力学模型和三维应力场分布模型, 结合现场压裂施工参数, 开展单砂体全缝长压裂数值模拟。结果表明, 安塞油田多期河道叠加致密砂岩油藏侧向复合砂体内部单砂体间泥质、钙质物性夹层发育, 形成的应力夹层对压裂裂缝的展布有较好的封隔作用, 即使压裂施工过程中隔夹层产生裂缝, 但随着泵压的降低, 张开的裂缝会随之闭合, 支撑剂并没有进入隔夹层中产生有效裂缝, 油层单砂体间有效动用不均, 60%的层有效动用程度较低。由此提出针对小层内动用程度不高的11 口井的单砂体补孔、重复压裂、堵水、隔采等措施, 经过现场实施, 增产效果明显, 平均日增油1.2 t 以上, 最终形成多期河道叠加致密砂岩单砂体细分与压裂改造的技术方法体系, 对今后类似油藏的开发有借鉴意义。

Characterization and Fracturing Stimulation on Single Sand Body of Tight Sandstone Oil Reservoir in Ansai Oilfield

In the middle and late stage of oilfield exploitation of multi-period superimposed channel tight sandstone oil reservoir in Ansai oilfield, water content of the well is increasing and the effective production of the reservoir is uneven. The breakthrough and water-flooding occur easily during the integral fracturing, which can’t be adapted to the oilfield production situation today. In order to solve this problem, rock mechanics model and triaxial stress field distribution model are built by subdivision and correlation of single sand body between oil and water wells, full-length fracturing numerical simulation are carried out by combining with fracturing parameters design, stress intercalations were formed, which could constrain the distribution of fracturing fracture. Although fractures in the intercalations are formed during fracture operation, gaping fissures are closed with the decrease of pump pressure so that propping agents can’t enter into the intercalations to cause effective fractures, effective production of single sand body in the reservoirs is uneven, and effective producing degree of 60% of layers is relatively low. Thus for the 11 wells which have a low producing degree in the small layer, measures of additional perforation, multiple fracturing, shutting off water and exploitation when separated with other pay zone are proposed, which have an apparent stimulation effect after site implementation. Average daily increase of production is more than 1.2 t. In summary, the technique approach system of subdivision and fracturing treatment of multi-period superimposed channel tight single sand body is formed, which could guide the future development of the similar reservoirs.