Candidate Selection And Optimization For Refracturing In Low Permeability Reservoir

Influenced by geological and technical factors, flow conductivity of initial fracture of wells in low permeability reservoir is tapered which leads to drop of well productivity, so restimulated treatments need to be done to regain or enhance production. Candidate selection is the key factor that determines design and productivity of refracturing work. This paper screened and obtained sample database of the chief factors that influenced effect of refracturing and proposed a dimensionless parameters method for candidate selection in fracturing work based on data of oilfield. Firstly, dimensionless parameters that influenced the effect of refracturing work were defined including poroelastic and mechanical stress reorientation parameter, well completion parameter, reservoir depletion parameter and production decline parameter, then proper criterion of these parameters were identified according to the evaluative model of candidate selection effect and finally applied the criterion on candidate selection work. Typical conceptual models considered time variation of flow conductivity using numerical simulation were built to identify the proper limit of some element in fracturing work. Based on the method above, potential well group was selected to optimize the fracture parameters using numerical simulation. The results show that, the dimensionless parameters method of candidate selection can take into account of the influence of geological and fluid character, fracturing work and production performance in selecting work, and this method can be applied in different reservoirs thanks to the dimensionless advantage of the parameters. Research shows that there exists a best range of the dimensionless parameters in which economical profile will be obtained, practiced in the researching oilfield, it must be satisfied that: with the well completion parameter smaller than 0.15 and initial production decrement smaller than 0.15, or with the well completion parameter bigger than 0.15, combination parameter of well completion parameter and production decline parameter smaller than 0.12 and reservoir depletion parameter smaller than 0.15 in wells that fracture is easy to reoriented; with the well completion parameter smaller than 0.1 and initial production decrement smaller than 0.2, or with the well completion parameter bigger than 0.1, combination parameter of well completion parameter and production decline parameter smaller than 0.06 and reservoir depletion parameter smaller than 0.2 in wells that fracture is hard to reoriented. In rhombic inverted nine-spot well network, the most proper limits for production enhancement are wells with thickness of 15 m, permeability of 0.3×10-3μm2, water cut smaller than 20% and pressure coefficient bigger than 1. Regular-crossed trials of the chosen well group show that the best refracturing time of corner and edge wells is in water free oil production period, with a half fracture length of 190 m and fracture flow conductivity of 300×10-3μm2·m after refracturing; and the best angle of reoriented fracture of corner wells is 23° whose value intends to be +90°and-90°of edge wells located in different edge of the well group. The research can provide theoretical guide for fracturing work in the oilfield.