Numerical Simulation of Hydraulic Fracturing in Weakly Consolidated Sandstone

摘要

The article presents a detailed finite-element model for investigating hydraulic fracture propagation in weakly consolidated sandstone. Elastoplastic deformation of the rock matrix, pore fluid flow, initiation and propagation of hydraulic fractures as well as flow of fracturing fluid within a fracture and leakoff into the formation are considered interdependently. The extended Cam-Clay model is used to achieve a more precise assessment of the mechanical behavior of weakly consolidated sandstone. Parametric studies are performed to investigate the effect of the fracturing parameters on the fracture patterns. The numerical results show that extremely short and narrow fractures are formed if low-efficiency fracturing fluid is used to initiate fractures in weakly consolidated sandstone with a zone of shear dilation formed on both faces of the fracture. In contrast, longer and wider fractures initiation of which is desirable in frac-pack (hydraulic fracturing) operations with the use of proppant may be obtained with the use of high- efficiency fracturing fluid and more compact zones are created near the fracture. However, the structure of the compaction zone produces an insignificant decrease in permeability. It is also shown that plastic deformation of the rock matrix has a significant impact on the geometry of a fracture, and this must be taken into account in the design of frac-pack operations with the use of proppant in weakly consolidated sandstone reservoirs.