致密油藏多级压裂水平裂缝井不稳态产能分析

Rate transient analysis of multistage fractured wells with horizontal fractures in tight oil reservoirs

新疆准噶尔盆地克拉玛依油田吉木萨尔(JMSE)凹陷二叠系芦草沟组(P2l)是致密油储层主要层位。为提高单井产能,目前多采用多级分段压裂技术。以往对于水力压裂的研究多集中于压裂缝为垂直裂缝的情况,但目前已认识的垂直裂缝模型不能解释该区块实际资料,且通过理论及实验研究表明,由于天然裂缝方位与地应力的匹配关系,该区块在实际压裂过程中易产生水平裂缝。因此,目前的研究导致该储层在实施压裂生产而形成水平裂缝时缺乏理论指导。文中基于质量守恒定律,在同时考虑启动压力梯度、压力敏感性及有限导流压裂缝的情况下,建立了双孔单渗油藏中多级压裂水平裂缝井的无因次数学模型,采用隐式差分法和共轭梯度算法对无因次模型进行求解。通过数值模拟的方法依次研究了启动压力梯度、地层非均质系数、窜流系数、压力敏感系数、压裂缝导流能力、压裂缝条数对不稳态产能的影响。研究结果表明,裂缝参数及地层参数均对产能曲线有影响,故而在优选该类油藏的压裂方案时不仅要考虑裂缝参数,还要考虑到在地层压力降落时地层参数所带来的影响。

Permian Lucaogou Formation （ P2 l ） in Jimusaer （ JMSE ） sag of Karamay oilfield is a typical representative of tight oil reservoirs in Junggar Basin .Staged fracturing technology is commonly used to improve the productivity of single well .While previous researches were more concentrated on the cases of vertical fractures ,the vertical fracture model could not explain the actual data in the blocks .At the same time,the theoretical and experimental studies show that horizontal cracks are easy to form during the process of fracturing according to the matching relationship between natural fracture azimuth and geostress .Therefore there is a lack of theoretical guidance in study area .Based on the law of conservation of mass and considerations of starting pressure gradient ,pressure sensitivity and finite conductivity fractures ,a dimensionless mathematical model has been set up to study the flow in the multistage horizontal fracturing fractured well in dual porosity and single permeability reservoir in this paper .And numerical solutions of the model are obtained by using implicit diffe-rence method and conjugate gradient algorithms .The effects on unsteady productivity of starting pressure gradient ,forma-tion heterogeneity coefficient ,interporosity flow coefficient ,pressure sensitive coefficient ,conductivity and the number of cracks are studied through numerical simulation in turn .Research results show that the fracture parameters and formation parameters affect the productivity curves .So it is necessary to consider both fracture parameters and the pressure decline reasonably ,as choosing an appropriate fracturing scheme to obtain maximum productivity .