鄂尔多斯盆地长7致密油体积压裂水平井产能预测研究

致密油储集层致密,孔隙结构复杂,孔隙度小,渗透率低,储集层微裂缝发育,采用体积压裂后形成复杂缝网系统,水平井单井产量大幅提高。目前的水平井产能公式很难适应于体积压裂水平井产能的预测。以鄂尔多斯盆地长7致密油为例,利用体积压裂水平井与直线无限井排直井的相似性,忽略了水平井筒内流体阻力的影响,将各条压裂缝之间的干扰问题转化为直线无限井排直井之间的干扰问题,依据势的叠加原理,推导出体积压裂水平井稳态产能公式。在推导过程中,考虑了储层的有效厚度、压裂改造后油藏等效渗透率、流体的黏度、水平井水平段长度、压裂段数、压裂段间距和井底流压等因素对水平井产能的影响,使水平井产能计算结果更加合理和符合实际。利用所推导的计算公式,结合鄂尔多斯盆地长7致密油特征,分析了影响水平井产能的几个重要因素,得出了水平井最佳压裂段间距和合理流压,其结果对致密油体积压裂水平井的设计具有一定的指导意义。

A Study of Volumetric Fractured Horizontal Well Productivity of Chang7 tight oil in Ordos Basin

Chang7 tight oil is of the characteristics of tight sandstone reservoir, complex pore-throat structures, small porosity, low permeability and micro-fracture development. By the volumetric fracturing, a complex fracture network system is formed, the horizontal well production greatly is improved. The existing horizontal well productivity formulas are very difficult to adapt to the volumetric fracturing horizontal well productivity prediction. Taking Chang7 tight oil in Ordos Basin as an example, based on the comparability of volumetric fracturing horizontal wells and straight infinite vertical wells with certain distance, the effects of fluid resistance in the horizontal well bore can be ignored. So, the interferences with individual hydraulic fractures can be transformed into the inter-well interferences of straight infinite vertical wells. Flow the superposition principle of electric potentials, the steady-state productivity formula of volumetric fracturing horizontal well is developed in this paper. In the developing process, we considerate the impact of formation effective thickness, equivalent formation permeability after fracturing, fluid viscosity, horizontal length, fracturing stages, fracture distance and bottom hole pressure, the calculated horizontal well productivity result can be more reasonable and practical. With the characteristics of C7 tight oil formation in Ordos basin, we analysis several important factors which impact the horizontal productivity result, and optimize the fracture distance and reasonable bottom hole pressure. The results can be use to conduct the designs of volumetric fracturing horizontal wells in tight oil formation with certain guidance.