Optimization of the transition timing from natural flow to artificial lift in Jimusar shale oil wells

To mitigate the matrix stress-sensitive damage induced by gradual reservoir pressure depletion during the late production stage of shale oil wells, and to optimize the post-fracturing development strategy for horizontal wells transitioning from natural flow to artificial lift, a numerical simulation approach was employed to maximize the development potential of matrix oil in Jimsar shale oil reservoir. The entire production process including hydraulic fracturing, well shut-in, natural flowing production, and the transition to artificial lift was simulated. The pressure and permeability evolution at different time points during the natural flowing stage were quantitatively characterized. Results indicate that when the wellhead pressure of an oil well declines to 10.0 MPa, severe stress-sensitive permeability damage occurs in both the upper and lower sweet spot reservoirs. Specifically, the average permeability of the substrate within the stimulated reservoir volume of the upper sweet spot reservoir decreases by 62.5%, while the lower sweet spot reservoir experiences more pronounced damage, with an average permeability reduction of 76%. Increasing the wellhead pressure at the transition point and reducing the pumping rate during the transition are both effective in alleviating reservoir damage and enhancing the estimated ultimate recovery (EUR) of a single well. Wellhead pressure is selected as the key indicator for determining the optimal transition timing, and the post-transition production rate. For wells targeting the upper sweet spot, artificial lift is recommended when the wellhead pressure declines to 4.0–6.0 MPa, with a pumping rate of 15–25 m3/d. For wells targeting the lower sweet spot, the transition should occur at a wellhead pressure of 2.0–4.0 MPa, with a pumping rate of 20–25 m3/d. The findings provide practical guidance for optimizing the transition from natural flow to artificial lift in shale oil wells in the Jimusar area and similar reservoirs.