Impact of pressure drawndown on the coning process during the development of bottom water gas reservoirs

Abstract

Currently, the development of gas and gas-condensate reservoirs with bottom water remains insufficiently effective, while the phenomenon of coning is a fundamental problem in petroleum engineering. To develop methods for slowing down or preventing bottom water breakthrough into production wells and extending the production period of hydrocarbon reservoirs, additional research was conducted using hydrodynamic modeling tools. Based on 3D models, a study was performed to assess the impact of different pressure drawdown on the coning process during reservoir development. The consi­dered pressure drawdown levels were 5%, 7.5%, 10%, 20%, 30%, 40%, and 50% of the initial reservoir pressure. The results indicate that increasing pressure drawdown leads to a decrease in gas and condensate recovery factors. This is due to the rapid breakthrough of bottom water into the perforation interval of the production well. The greater the pressure drawdown, the shorter the operational period of the well. According to the simulation results, the most significant impact on recovery factors occurs within the pressure drawdown level not exceeding 20% of the initial reservoir pressure. Further increases in pressure drawdown have a less critical effect on recovery factor. In a specific case, increasing pressure drawdown from 5% to 20% resulted in a reduction of the gas recovery factor from 7.02% to 6.58%, which corresponds to a loss of 0.44% of the initial gas reserves. However, increasing pressure drawdown from 20% to 50% led to a gas recovery factor decrease from 6.58% to 6.5%, with a difference of only 0.08%. Additionally, analysis of water saturation distribution at the moment of bottom water breakthrough revealed that increasing pressure drawdown does not affect the shape or size of the bottom water cone. The base length and cone height remain unchanged at pressure drawdown levels of 5% and 50%. However, the water saturation of the outermost grid cells at the base of the cone varies slightly. Based on the statistical analysis of the modeling results, the optimal pressure drawdown level for a partially penetrated reservoir (with 60% of the total gas-saturated thickness) is determined to be 15% of the initial reservoir pressure.

Keywords

• 3d modeling
• gas condensate reservoir
• water flooding
• bottom water
• cone formation
• penetration ratio
• pressure drawdown
• increase in hydrocarbon recovery