Effect of $\hbox {CO}_{2}$ Injection on Brine Flow and Salt Precipitation After Gas Field Production

Abstract

This paper reports modeling of gas field production and $\hbox {CO}_{2}$ injection in a theoretical reservoir based on characteristics of the P18 gas field in the Dutch offshore, which consists of four geological deposits with different petrophysical properties. We especially focus on the brine flow during and after exploitation of the reservoir, which affects salt precipitation and dissolution in the near-well area. We first computed the water saturation with depth, in static equilibrium with a free water level at the bottom of the reservoir. We then computed production from the gas field, predicting very low brine production and mobility, without salt precipitation. Subsequently, injection of dry $\hbox {CO}_{2}$ leads to dry-out and salt precipitation in the near-well bore area, resulting in a maximum permeability reduction of 23 %. After abandonment, brine flows toward the well, resulting in redissolution of precipitated salt, leading to salt saturated brine in the near-well bore area. After 1,000 years, it is predicted that supersaturated brine is concentrated in the lower part of the reservoir, where solid salt still remains. The computed long-term effects of brine mobility could influence predictions of well-cement degradation and well-abandonment strategies like intentional clogging.