Abstract
PetroChina’s Xinjiang oilfield has a large quantity of tight oil reserves and hydraulic fracturing technology has been widely used to achieve commercial production. Some parts of this tight glutenite formation are laumontite-rich and the actual productivity of the hydraulically fractured wells is less than expected. To figure out the ways that laumontite affects tight glutenite well productivity, comprehensive experimental and numerical simulation studies have been conducted to investigate the rock mechanical properties, fluid flow behaviors and the major controlling factor of productivity. Laboratory results indicate that the tight glutenite formation with higher laumontite content has higher initial porosity, permeability but lower yield strength and more severe stress sensitivity in both permeability and fracture conductivity. For laumontite-rich glutenite rocks, there are commonly three types of rock deformation during the loading process: elastic compression, shear dilation and shear enhanced compaction. Both elastic compression and shear enhanced compaction will cause the reduction on rock porosity and permeability. A fully coupled finite element model (FEM) considering stress-induced permeability evolution was introduced to simulate the production process. Permeability evolution models of three different deformation stages were presented, respectively. Simulation results showed that our model is in good agreements with the well testing data. The simulated oil production characteristics for permeability evolution coupled and uncoupled models were discussed. Results showed the strong stress-induced permeability reduction is the major factor that laumontite causing the low and quickly declining oil rates. Initial permeability has a positive effect on productivity and stress-induced fracture conductivity reduction has slight influence on productivity. The results of this paper indicate that the stress-induced permeability evolution in the oil production process must be considered to accurately evaluating reservoirs in the studied area.