致密油水平井体积压裂产能影响因素

Influencing factors on the productivity of the volume-fractured horizontal well in the tight oil reservoir

为了分析水力裂缝与天然裂缝对致密油储层体积改造后产能的影响,以新疆S油田储层物性、原油物性以及天然裂缝走向和密度等为基础,利用COMSOL with MATLAB混合编程建立了致密油水平井体积压裂后的复杂缝网模型;考虑基质与裂缝的应力敏感,模拟了致密油在储层基质、裂缝和水平井筒的全耦合流动,分析了不同裂缝长度80~140 m、不同裂缝间距10~40 m、不同天然裂缝密度0.5~2.5条/m条件下压后致密油储层产能的变化。通过与矿场数据对比,该模型准确性较高。同时,模拟发现压裂后储层中压力波及区域的扩展过程表现出较强的非均质性,分布在压裂区周围的天然裂缝有助于扩大储层改造体积;增加裂缝长度,减小裂缝间距,较高的天然裂缝密度均能提高油井日产量峰值和累计产量,模拟得到该区块的最优裂缝长度和裂缝间距分别为140 m和10 m左右。油井日产量提高的同时衰减速度加快,特别是较高天然裂缝密度的衰减速度约为较低天然裂缝密度时的4倍,天然裂缝密度和裂缝间距对产能的影响程度较裂缝长度更为显著。

In order to analyze the effects of the hydraulic and natural fractures on the productivity after the volume fracturing of tight oil reservoirs, based on the reservoir and oil physical properties and natural fracture orientation & density in Xinjiang Oilfield S, the combined compiling-COMSOL with MATLAB was used to build a model of the complex fracture network after volume fracturing of the horizontal well in tight oil reservoir;taking the stress sensitivities of the matrix and fractures into consideration, the total coupling flow of the tight oil in the reservoir matrix, fracture and horizontal borehole was stimulated, the changes of the tight oil reservoir productivity after the fracturing were analyzed for different fracture lengths(80-140 m), fracture intervals(10-40 m) and natural fracture densities(0.5-2.5 fractures/m). Comparing with the field data, the model accuracy is pretty higher. At the same time, rather stronger heterogeneity is found by the model in the spread process of the pressure wave swept area in the reservoir after the fracturing, the natural fractures around the stimulated area are helpful to increase the stimulated volume;Increasing the fracture length, decreasing the fracture spacing and possessing much higher density of the natural fracture are all beneficial to enhance the daily and cumulative productions, the optimal fracture length and fracture spacing in the block obtained by the model are 140 m and about 10 m respectively. At the time of enhancing the daily production, its decline speed is rather higher, especially for the production decline rate with rather higher natural fracture intensity i.e. 4 times that of the lower natural fracture intensity, the influenced degrees of the natural fracture density and the fracture spacing on the productivity are more obvious than that of the fracture length.