疏松砂岩油藏压裂裂缝延伸规律数值模拟

Numerical simulation of hydraulic fracture propagation characteristics in weakly consolidated sandstone reservoir

范白涛 邓金根 林海 吴锐 刘伟 谭强

FAN Baitao DENG Jingen LIN Hai WU Rui LIU Wei TAN Qiang

中国石油大学(北京)油气资源与探测国家重点实验室 中海石油(中国)有限公司天津分公司 & 海洋石油高效开发国家重点实验室

State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing 102249, China State Key Laboratory Offshore Oil Exploitation, CNOOC China Limited, Tianjin Branch, Tianjin, 300459, China

压裂充填防砂可实现增产与防砂双重目的，是疏松砂岩油藏的一种重要完井方式。疏松砂岩具有高孔、高渗特点，且强度低、塑性强，裂缝起裂与延伸机理较为复杂。为研究疏松砂岩储层压裂裂缝延伸机理，揭示压裂工艺参数对裂缝形态的影响，建立了考虑储层岩石弹塑性变形、裂缝起裂与延伸、压裂液流动与滤失以及储层孔隙流体渗流复杂耦合作用的流固耦合有限元数值模型，针对渤海油田绥中36-1区块典型疏松砂岩储层，开展了压裂裂缝延伸规律数值模拟计算，并重点分析了压裂液效率、排量对于裂缝延伸规律的影响。结果表明：低效率压裂液在疏松砂岩中仅形成极短而窄的裂缝，裂缝两侧伴随着一定范围的剪胀高渗带，难以容纳支撑剂，无法实现充填防砂目的；效率高压裂液可在疏松砂岩中形成压裂充填防砂工艺所需的短宽裂缝，裂缝壁面两侧存在轻微压实现象，对渗透率的影响较小；提高压裂液排量，裂缝长度减小，裂缝宽度增加。研究结果可为疏松砂岩压裂充填设计提供一定理论参考。

Frac-packing and sand control technology can realize the double targets of stimulation and sand control, and it is one important well completion method for unconsolidated sandstone oil reservoirs. Unconsolidated sandstone is characterized by high porosity, high permeability, low strength and strong plasticity, so its fracture initiation and propagation mechanisms are more complicated. In order to study the propagation mechanisms of hydraulic fractures in unconsolidated sandstone reservoirs and reveal the effects of fracturing technologies on fracture morphologies, a finite-element numerical model of fluid-solid coupling was established in this paper. In this numerical model, the elastic plastic deformation of rock, the initiation and propagation of fracture, the flowing and filtration of fracturing fluid and the complex coupling effect of fluid flow through porous medium are taken into consideration. Then, a case study was conducted on the typical unconsolidated sandstone reservoir in Suizhong 36-1 Block of Bohai Oilfield. Its propagation law of hydraulic fractures was numerically simulated and calculated. In addition, the effects of the efficiency and displacement of fracturing fluid on the fracture propagation law were mainly analyzed. It is indicated that the fractures initiated by low-efficiency fracturing fluid in unconsolidated sandstone are quite short and narrow, and they are accompanied with high-permeability dilation zones on both sides, so proppant can be hardly held and consequently sand control cannot be realized. The high-efficiency fracturing fluid can create the short and wide fractures in unconsolidated sandstone that are needed in frac-packing and sand control technology. There are phenomena of slight compaction on both sides of the fracture wall surface, and they have less effect on the permeability. As the displacement of fracturing fluid is increased, the fracture length is decreased and the fracture width is increased. The research results can be used as the theoretical reference for the design of unconsolidated sandstone frac-packing.

10.13639/j.odpt.2018.05.015