Identification and characterization of a proper gel system for large-volume conformance control treatments in a fractured tight reservoir: From lab to field

Abstract

The existence of fractures in petroleum reservoirs can greatly reduce the sweep efficiency and subsequently limit the oil recovery during water flooding. Gel treatment is widely known as a cost-effective method for conformance control and water shutoff during water flooding in fractured reservoirs. In this study, we discuss the feasibility of three types of gel systems for conformance control in fractured reservoirs, aiming to select a proper one for field pilot applications in Huabei oilfield (China). Based on the gelation time and the gel strength, the water-soluble phenolic resin (WSPR) gel was chosen for field applications. This silica nanoparticle strengthened WSPR gel demonstrated high gel strength and long-term thermal stability in the lab. Furthermore, its plugging capability was studied by determining the rupture pressure of the gel-filled tubes. The results indicate that the plugging ability of WSPR gel is enhanced with increasing the polymer concentrations and decreasing the size of apertures. Besides, the WSPR gel exhibits high rupture pressure under low brine injection rate. For field applications, the pressure transient tests, tracer tests and the injection-production data were used collaboratively to determine the volume of the fractures in the reservoir. A large volume of gelant was designed for well treatment, and multiple gel slugs with different polymer concentrations were tailored to meet the operational conditions. After the gel treatments, the bottom hole pressure for each injector was significantly increased, indicating that the fractures were effectively plugged. Moreover, the oil production rates were notably increased, accompanied by a prominent decrease in water cut after the gel treatment. To date, the oil production rates of two well-connected production wells, HH55P56 and HH55P58, have been increased from 0.36 t/d to 0.9 t/d and from 0.19 t/d to 0.48 t/d, respectively. The oil production rate of well HH55P24 has been increased by 0.5 t/d.