玛湖砾岩油藏油水分布状态与压裂模拟裂缝扩展研究

Study on oil-water distribution state and fracture extension of fracture simulation in Mahu conglomerate reservoirs

为解决新疆玛湖致密砾岩油藏非均质性强、单井产量影响因素不明确等问题,通过超真空扫描电镜、XRD、CT扫描等实验手段表征微观尺度孔喉及油水分布状态,利用全直径岩心尺度压裂物理模拟实验探究储层条件下的裂缝扩展规律.实验结果表明微纳米空间的原油赋存非常有限,分布成大孔道的可动油和黏土矿物中的束缚油,原油经二次运移后无法在微纳米空间形成有效聚集.致密砾岩储层中沸石类胶结物约占30 wt.%~40 wt.%,后期溶蚀产生溶蚀孔喉.砾岩储层内部不同成分砾石和填隙物岩石强度差异大,压裂过程中易产生环砾石微裂缝,储层微结构面较发育,破压点明显,由压裂曲线可以看出裂缝呈现以1~2条主裂缝为主,多条微裂缝为辅的体积压裂模式.通过韧性剪切压裂工艺形成微裂缝体积压裂,改善近裂缝地带基质导流能力,避免大排量、大砂量产生单一长裂缝,砾岩油藏压裂液滤失快,净压力低,两向应力差大,难以暂堵转向;通过加入破压剂可以提高转向成功率.

In order to solve the problems of strong non-homogeneity and unclear factors influencing the production of a single well in the dense conglomerate reservoir of Mahu,Xinjiang,we characterised the micro-scale pore throats and the state of oil-water distribution by means of experimental methods such as ultra-vacuum scanning electron microscopy,XRD,CT scanning,etc.,and used full-diameter core-scale fracture physical simulation experiments to explore the fracture extension law under the reservoir conditions.The experimental results show that the crude oil fugacity in micro-and nanospace is very limited,distributed into movable oil in large pores and bound oil in clay minerals,and the crude oil is unable to form effective aggregation in micro-and nanospace after secondary transport.Dense conglomerate reservoirs contain about 30 wt.%~40 wt.%zeolite-like colluvium,and later dissolution produces dissolution pore throats.There is a big difference in the rock strength of gravels and fillers of different compositions inside the conglomerate reservoir,which is easy to produce ring gravel microfractures during fracturing,and the microstructural surface of the reservoir is more developed,with obvious pressure-breaking points,which can be seen from the fracturing curves that the fracture shows a volumetric fracturing pattern with 1~2 main cracks as the main cracks,supplemented by multiple microfractures.Through the toughness shear fracturing process to form micro-fracture volume fracturing,improve the matrix conductivity in the near-fracture zone,to avoid large displacement,large sand volume to produce a single long fracture,conglomerate reservoir fracturing fluid filtration loss is fast,the net pressure is low,and the stress difference in both directions is large,it is difficult to temporarily block the steering;through the addition of the pressure-breaking agent can improve the success rate of the steering.