Implementation of Mechanical Earth Model in Predicting the Maximum Water Injection Flow Rate in Mature Field

Abstrak

Fracture can occur at shale zone, when fluid injection pressure to reservoir sand target exceeds fracture pressure. Consequence, fluid injected to reservoir target will not be optimum. Therefore, we must determine the fracture pressure that will apply. This study was performed in order to build fit purpose 1D mechanical earth model which will be used to determine or predict injection pressure and maximum injection flow rate, in order to prevent fracture growth from targeted reservoir sand to the enclosing shale interval. Required data to build 1D mechanical earth model in this study namely gamma ray log, density, sonic compression, sonic shear and repeat formation test (RFT). Then, mohr stress diagram applied to determine the safety factor and reservoir simulation done to predict flow rate maximum of water injection at inverted five spot pattern and inverted seven spot patterns with three scenarios. Based on calculation, then obtained vertical stress (Sv) > Maximum Horizontal Stress (SHmax) > Minimum Horizontal Stress (Shmin), with average value of Sv, SHmax, Shmin is 0.827 psi/ft, 0.731 psi/ft, 0.696 psi/ft, which mean normal stress regime. Fracture pressure that obtained at intact reservoir (cap rock) is 1521.19 psi, and safety factor obtained is 12% or maximum injection pressure is 1460.7 psi. The result of reservoir simulation performed with three scenarios at inverted five spot pattern and inverted seven spot patterns show that second scenario provide the best result with apply flow rate water injection is 53000 STB/D pressure reached is 1453 psiand at inverted seven spot patterns with apply flow rate water injection is 56000 STB/D pressure reached is 1458psi.