Evaluating In-Situ Gelation Property for Conformance Improvement

Abstract

Gel-based deep conformance control is a potential method for improving sweep efficiency and facilitating contact with the remaining oil in heterogeneous reservoirs. When using an in-situ gelling system for in-depth treatment, gel strength gradually increases during and after the gel placement in reservoir. Understanding the in-situ gelation properties is essential for screening reliable gelling systems to achieve successful field treatment results. In this study, we performed in-situ gelation evaluations on an organically crosslinked polymer gel system at 95°C. The gel consisted of a low molecular weight polyacrylamide polymer and a polyethylenimine (PEI) crosslinker. Bulk gel properties were assessed through bottle tests and rheological measurements. Results showed that the gelation time of the studied gel system can reach up to 10 days at 95°C. The oscillatory measurements demonstrated the dominance of its elastic nature and remarkable stretch ability. This indicated the potential of the studied organically cross-linked gel for deep conformance improvement applications. Coreflooding experiments of both the bidirectional displacement and continuous injection were conducted for in-situ gelation assessment. In the bidirectional displacement test, the polymer solution was alternately injected from both ends of a three-plug composite core with gel pre-placed in the middle plug. In the continuous injection test, a slug of gel was kept at dynamic flow condition in a slim tube by continuously injecting the polymer solution. The pressure responses from these displacement tests were used to assess the in-situ gelation behavior. Results showed that the in-situ gelation times from both tests were almost the same for a same gel. The in-situ gelation time from the displacement tests also corresponded very well with the transition time from moderately flowing gel to strong gel observed in the bottle test. This demonstrates that both displacement methods can be used to effectively evaluate the in-situ gelation property, and the conventional bottle test can be calibrated as a very efficient way to assess in situ gel performance.