泥质疏松砂岩水力压裂裂缝形态与有效加砂机理研究

Domestic and foreign laboratory experiments and field tests showed that the formation mechanism of unconsolidated sandstone induced fracture contain both tensile failure and shear failure, and the fracture morphology is complex; sand plugging often occur during shaly loose sandstone reservoir fracturing, and to achieve effective sand input is the key issues of the shaly loose sandstone reservoir reconstruction. According to shaly loose sandstone sampling difficult, the research route of this study intends to combine the indoor experiment and theoretical modeling, firstly, through the investigation，make a formation of argillaceous loose sand index evaluation system, and explore the suitable material formula and process production to simulate shaly loose sand. On this basis make a study of mechanical parameter ,physical parameters of shaly loose sandstone, and establish physical model of shaly loose sand. Using big core hydraulic fracturing equipment to do hydraulic fracturing test without sand .The aim is to study the fracture morphology of shaly loose sandstone, and to predict the fracture patterns of different shaly loose sandstone by modeling and fitting. Using big cores hydraulic fracturing equipment for sand-carrying hydraulic fracturing test to study the parameters of sand effect to the fracture morphology, effective sand mechanism; Ultimately through the muddy effect to the unconsolidated sandstone fracture morphology, effective sand-input, post-flush production, we established a shaly loose sandstone fracturing feasibility evaluation system, in order to lay the theoretical foundation for the effective development of the shaly loose sandstone reservoir.

国内外室内实验和现场试验表明，疏松砂岩压裂裂缝的形成机理既有拉伸破坏又有剪切破坏，裂缝形态比较复杂，而泥质疏松砂岩储层压裂还面临砂堵问题，实现水力压裂的有效加砂是泥质疏松砂岩储层改造的关键问题。针对泥质疏松砂岩取样困难的现状，本项研究拟采用室内实验与理论分析模拟相结合的方法，首先建立起泥质疏松砂岩评价指标体系，研究形成在实验室制作仿真泥质疏松砂岩的工艺技术；通过对泥质疏松砂岩的储层物性和力学参数的实验研究，建立泥质疏松砂岩物理模型；利用大岩心水力压裂设备进行不携砂水力压裂试验，研究泥质疏松砂岩压裂裂缝形态并进行建模拟合来预测不同泥质疏松砂岩压裂的裂缝形态；利用大岩心水力压裂设备进行携砂水力压裂试验，研究加砂参数对裂缝形态的影响，研究有效加砂机理；最终通过泥质对疏松砂岩裂缝形态、有效加砂、压裂产量的影响分析建立起泥质疏松砂岩水力压裂可行性评价体系，为泥质疏松砂岩储层有效开发奠定理论基础。

目前赋存在地层浅部泥质疏松砂岩储层的大量油气无法得到有效动用，探索采用压裂方法开采成为一条可行的道路。通过对泥质疏松砂岩岩心制作技术和泥质疏松砂岩储层物性与岩石力学特性研究，形成了仿真泥质疏松砂岩制作配方和制作工艺，建立起泥质疏松砂岩岩石物理模型，可用于诊断岩石微结构。通过对泥质疏松砂岩压裂实验研究，得到泥质疏松砂岩压裂裂缝形态具有宽短缝、多分支缝的特点。利用UDEC和PFC软件研究了泥质疏松砂岩压裂裂缝形态形成机制，实现了对泥质疏松砂岩压裂裂缝形态的预测。通过支撑剂嵌入实验和泥质堵塞实验，获得压裂支撑剂随时间的嵌入规律和泥质颗粒浓度变化对渗透率影响的规律。泥质疏松砂岩压裂后经支撑剂充填、裂缝闭合后支撑剂不断嵌入、油气生产时泥质堵塞导致部分裂缝失效，只有压裂砂形成的裂缝没有遭受泥质堵塞的部分才会是有效裂缝。在以上泥质疏松砂岩压裂有效加砂机理研究的基础上，形成泥质疏松砂岩可压裂性的评价指标体系。通过泥质对压裂裂缝和油气井产量的影响分析，建立泥质疏松砂岩压裂可行性评价方法。泥质疏松砂岩压裂的特殊性导致目前压裂井的产量偏低，泥质堵塞是影响产量的关键因素，压开剪切缝输送压裂砂形成有效分支缝是提高油气井产量的理想路径。