压裂水平井裂缝分布对产能影响的电模拟实验

The impact of fracture distribution on the productivity of a fractured horizontal well:A study based on electrolytic analogy experiments

水平井压裂是开发页岩储层、致密砂岩储层等难动用储层的有效方法,但其渗流机理非常复杂,而水电模拟实验则是研究压裂水平井储层流体渗流规律直观有效的方法。根据水电相似原理,利用电模拟实验装置,分单因素和多因素分别考察了裂缝位置、分布、条数、长度等影响压裂水平井产能的因素,绘制了各种裂缝分布情况下的储层压力场分布图,并综合采用正交试验设计和灰色关联分析方法分析压裂参数对压裂后水平井产能影响的重要程度。结果表明:①压裂水平井控制的储层有效生产区域存在差异,垂直缝控制储层有效生产区最大,水平缝次之,然后是30°、60°、75°斜交缝;②压裂裂缝有效缓解了近井筒区域的应力集中现象;③水平井筒长度与裂缝长度存在产量变化临界点,该临界点随井筒长度变化而变化。压裂裂缝参数对水平井产能影响程度依次为:裂缝长度、裂缝条数、裂缝间距、裂缝与水平井井筒之间的夹角。

Horizontal well fracturing is an effective means to tap and unlock difficulttoproduce hydrocarbon reserves from such reservoirs as shales, tight sandstones, etc. Actually, their percolation mechanism is very complex. The electrolytic analogy experiment is the intuitive and effective method to study the permeability rule of formation fluids of fractured horizontal wells. Based on the similitude principle, univariate and multivariate analyses were made to decide the influence of the fracture position, distribution, number, and length by an electrolytic analogy apparatus. Besides, the pressure distribution maps under different fracturing conditions were drawn. Then based on the orthogonal experimental design and the grey relational analysis, the importance of the fracturing parameters on well performance was analyzed. The following results were achieved. a. The effective drainage area of a fractured horizontal well varies with different fractures. To be specific, the vertical fractures produce the largest effective drainage area, followed by the horizontal fractures, then 30°, 60° and 75° inclined fractures. b. The artificial fractures effectively alleviate the stress concentration near wellbore regions; c. Between the length of the crack and length of the horizontal wellbore there exists a critical point of output change, which varies with the wellbore length. In conclusion, the productivity of a horizontal well is affected by the following fracturing parameters in a descending order： fracture length, number of fractures, fracture spacing, and the angle between the fracture and the horizontal wellbore.