Wettability Alteration in Gas-Condensate Reservoirs To Mitigate Well Deliverability Loss by Water Blocking

Abstract

Liquid blocking in some gas-condensate reservoirs is a serious problem when the permeability is low (for example, of the order of 10 md or less). The current practice centers mainly on hydraulic fracturing to improve gas flow. In most cases, the frequency of application results in high costs. An alternative is the permanent alteration of wettability from liquid-wetting to preferentially gas-wetting. In this work, we present an experimental study of wettability alteration to preferential gas-wetting using a multifunctional surfactant and polymer synthesized for this particular application. The treatments are performed with an alcohol-based-surfactant/polymer solution. We treat Berea cores and reservoir-rock samples from two gas-condensate reservoirs. In one of the reservoirs, water blocking has resulted in a significant reduction of well deliverability. The treatment provides significant improvement on the phase mobility. In this study, our focus is the investigation of water/gas two-phase flow at high temperatures (80 and 140°C). Basic measurements such as contact angle, spontaneous imbibition, and the effect on the absolute permeability are discussed. The initial liquid saturation at the time of treatment may have an influence on the wettability alteration. The results of the treatment on oil-saturated and water-saturated cores are presented. The treatment by alcohol without using the polymer is compared and discussed. Two-phase-flow tests in single-phase and two-phase injections are performed before and after the treatment using brine and gas. Relative permeabilities of gas and water are measured, and the improvement after the treatment is presented. Various measurements in our work show that water and gas relative permeability increase significantly in a wide range, especially at high liquid saturation. The exploitation of low-permeability gas-condensate reservoirs has received increased emphasis in recent years. Liquid trapping (water or condensate blocking) around a wellbore is one of the major causes of reduced productivity in low-permeability gas-condensate reservoirs. Formation damage by the loss of aqueous fluids by operations such as drilling, fracturing, or acidizing is a potential source of reduced productivity of gas reservoirs because it causes water accumulation (water blocking) near the wellbore. Water blocking is caused by capillary pressure, which tends to imbibe and hold the liquid phase, resulting in a reduction of gas mobility. The decrease in water saturation from hydraulic fracturing around the wellbore is a slow process when the permeability is low and the capillary forces are high. The investigation of the gas/water relative permeabilities can determine the gas-mobility loss associated with the change of water saturation.