Experimental study on the mechanism of five point pattern refracturing for vertical & horizontal wells in low permeability and tight oil reservoirs

Low permeability oil reservoir has the characteristics of low porosity and low permeability. The initial fracturing can effectively improve the recovery of the reservoir, but the physical mechanism of refracturing to improve the recovery is still lack of systematic research. In this paper, the refracturing effect of low permeability reservoirs under the condition of five point well pattern is clarified; the refracturing mechanism of vertical-horizontal well combination is revealed; the reservoir production performance characteristics under different soak time conditions are analyzed. It is found that: (a) after 1st fracturing, the area between the two fractures still has a high residual oil, which is the material basis for refracturing. (b) After refracturing, there are secondary fractures connecting the main fractures. The crude oil in the low permeability reservoir can flow not only to the main fracture and horizontal wellbore, but also to the secondary fractures. This leads to the effective reduction of oil saturation between the main fractures. (c) The influence of soak time on cumulative oil production is obvious. With the increase of soak time, the cumulative oil production increases significantly.