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.

Automated summary

Low permeability oil reservoirs have low porosity and low permeability characteristics. The physical mechanism of refracturing to improve recovery in these reservoirs lacks systematic research. This paper clarifies the refracturing effect of low permeability reservoirs under a five point well pattern, reveals the refracturing mechanism of vertical-horizontal well combination, and analyzes reservoir production performance characteristics under different soak time conditions. It is found that there is high residual oil between fractures after initial fracturing, which serves as the material basis for refracturing. Refracturing creates secondary fractures that connect to the main fractures, effectively reducing oil saturation between them. The influence of soak time on cumulative oil production is significant, with longer soak times leading to increased production.