Enhancing acid fracture design in carbonate formation using a dynamic up-scaling procedure to convert discrete fracture network to dual continuum

For a low-permeability carbonate formation, the acid fracture process is simulated through coupling a commercial acid fracture simulator (GOHFER) to a finite volume reservoir simulator (IMEX). Unlike LGR (Local grid refinement) approach that suffers from severe convergence problems, a dynamic up-scaling procedure is employed to convert the discrete fracture network (DFN) model into a dual continuum model for our simulation. In this paper, multiple simulations are used to optimize the acid fracture schedule parameters, such as fluid volume, flow rate, perforation location, number of injection steps, and acid type, in order to maximize the effective fracture length. For four points perforation as the relevant operation case in this work, acid fracturing consumes 44 Mgal acid volume at a rate of 25 bpm at a 20 ft interval, resulting in a 3.5-fold increase in well productivity index (PI). Based on experimental relative permeability data, two models of fine and medium grid sizes are employed to be compared with the LGR method. The results have shown that these models are 22 and 54 times faster than LGR, however, the latter has a deviation of less than 5% which is quite acceptable.