Preparations for Foam Gas Shut off in Carbonate Reservoirs

Abstract

Abstract High GOR is a constraint for many production wells. Foam has been proved able to reduce GOR in several field production well treatments. The primary goal of this study is to qualify foams for use at reservoir conditions (280 bars, 103 °C). Foam will block gas and thereby reduce Gas-Oil Ratio (GOR) and improve field oil production. Bulk foam experiments and dynamic foam core flooding experiments have been performed to qualify foam for gas shut off at reservoir condition. Foam has been studied in static foam tests using different surfactants, and in limestone core flood experiments at reduced conditions 30 bars and 50 °C. Further foam generation and gas blocking test at reservoir conditions have been conducted both in outcrop and in reservoir material. Dynamic core flooding experiments at 30 barg and 50 °C have shown generation of moderate to strong foams in carbonate limestone core material both with Nitrogen and Methane as the gas phase. Strong foam with mobility reduction factors around 65-70 have been generated in reservoir core material at reservoir conditions. The presence of oil in the carbonate material is a challenge for in-situ foam generation. One solution to the problem has been identified by use of a pre-flush with FS-500 (fluorinated surfactant), prior to alpha olefin sulfonate (AOS). CO2-foamers such as Duomeen has been tested, but gave no foam with Nitrogen as gas phase. Higher concentration of AOS surfactant was able to generate in-situ foam without assistance of fluorinated surfactant. The generated foam is stable also with lower surfactant concentration after first generation. The mobility reduction factor is constant for a range of surfactant concentrations. Strong foam has been generated in carbonate reservoir core material at reservoir conditions. The presence of oil in carbonate material prevents in-situ foam generation at low surfactant concentration, but gives strong foam at higher surfactant concentration.