Volume 42: Energy Transitions toward Carbon Neutrality: Part V

Pressure Calculation Method and Mechanism of Advance Water Injection in Ultra-low Permeability Reservoirs Jinchong Zhou, Renyi Cao, Meng Zhang, Jian Liu, Dong Sun, Bingchen Lyu, Yongjian Feng

Abstract

Advance water injection is one of the effective methods to alleviate the rapid decline of formation pressure in ultra-low permeability reservoirs, to establish an effective displacement system between oil and water wells, and to increase the production of wells. In order to make up for the influence of threshold pressure gradient and stress sensitivity which are not fully considered in the traditional advance water injection pressure calculation model, based on the material balance method, threshold pressure gradient and stress sensitivity equations are introduced, a nonlinear flow model of the relationship between the advance water injection volume and formation pressure is established, and an iterative solution calculation program is compiled. Taking Y2 ultra-low permeability reservoir in Changqing Oilfield, China, as an example, the formation pressure values under different amounts of advance water injection in the well group of this block are calculated and compared with the numerical simulation results, which are basically in agreement with each other, proving that the model for calculating the advance water injection pressure established in this paper has a high calculation accuracy. The pressure and pressure gradient distribution law in the reservoir under different advance water injection volume is further revealed. When the advance water injection volume of the well group is greater than 10,000m3, the pressure lift becomes slower, and the pressure gradient between the oil and water wells is higher than the threshold pressure gradient, which forms an effective displacement system. The study results can provide theoretical guidance for the development of advance water injection technical programs for ultra-low permeability reservoirs.

Keywords Advance water injection, threshold pressure gradient, stress sensitivity, calculation model, pressure distribution, mechanism