A NEW MODEL PREDICTING WATER BREAKTHROUGH TIME IN BOTTOM-WATER DRIVE GAS RESERVOIR BASED ON CAPILLARY PRESSURE AND BUCKLEY-LEVERETT EQUATION

摘要

To develop a bottom-water drive gas reservoir, it is very important to predict bottom-water advancement, calculate water breakthrough time, and provide mitigation for early water invasion. Existing methods often deal with activities after a certain amount of water invasion or water breakthrough in a gas well, and it is difficult to accurately predict the water breakthrough time. In this paper, we calculated the water saturation front in a bottom-water-invaded region using the Buckley-Leverett (BL) equation, in which multiple factors were considered such as the gas-water velocity difference in the water-invaded region, non-piston advancement of bottom water, seepage pattern changes in both perforated and non-perforated intervals, as well as gas and water flow rates in the bottom-water-invaded region based on the capillary pressure. Integration of a capillary pressure model, the BL equation, and a coning model of the bottomwater gas reservoir yielded a new method for calculating the water breakthrough time in a bottom-water gas reservoir and its corresponding analytical equation. The results from the analytical and numerical simulation methods were close to the actual water breakthrough time of a bottom-water gas reservoir. Our model provides a theoretical basis for predicting the water breakthrough time of a bottom-water gas reservoir.