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

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.