Validation and Benchmarking of an Inorganic Aluminium-Carbamide Gel System for in-Depth and Near Wellbore Conformance Control

Abstract

Abstract Both Wintershall Dea and Equinor have successfully conducted conformance control pilots previously. Wintershall Dea's past field experience and Equinor's search for an option for a salinity tolerant chemical to prevent pre- and post-flush measures led to further investigation of an inorganic thermotropic Aluminium-Carbamide gel system – GALKA, Kuvshinov et al. (2019). In this paper, we present the steps to validate GALKA and benchmark it against Sodium Silicate with regards to in-depth and near wellbore conformance control. Bulk gelation experiments using bottle tests were performed to monitor and estimate gel strengths according to the gel strength codes outlined by Sydansk et al. (1993). Gelation time, syneresis, gel strength dependency on temperature, salinity and concentration were measured to determine optimized gel formulation. Rheology measurements were performed using both rotational and oscillatory viscometry at different temperatures to measure viscosity variations with the corresponding gelation times. Corefloods performed using 25 cm outcrop cores showed excellent injectivity and in-depth gelation was observed at elevated temperatures. The gelation times were found to be in good agreement with the bulk gelation times. Stable gel formation was witnessed over a wide range of temperatures, ranging from 38 to 100°C and salinities ranging from 0.2 to 186 g/L during the bulk gelation experiments. Investigation of gelation kinetics of GALKA revealed that in-situ gelation can be controlled primarily by varying the temperature and the Carbamide concentration of the system. GALKA compositions containing a constant amount of Aluminium salt (8.8%) with decreasing amounts of Carbamide (from 30 to 1.87) % showed an increase of gelation time (5 to 13 folds) respectively, at different temperatures. Simultaneously, the corresponding viscosity and shear stress of the gels increased with increase in temperature. Corefloods demonstrated excellent injectivity due to the low initial viscosity (∼1.1 cp) of the GALKA system similar to brine viscosity. This was confirmed by the mobility reduction, (RF∼2.1) which was close to the measured relative viscosity value during GALKA injection. Stable gel formation was observed even at pressure gradients exceeding 100 bar/m without any sign of gel destruction. Benchmarking with Sodium Silicate gel revealed slightly faster gelation times for the GALKA system. However, systems with high buffer capacity could be used as additives to retard the GALKA gelation time accordingly. Good solubility in harsh brines, excellent injectivity and strong gel formation capabilities of GALKA over a broad temperature range and at high salinity conditions were confirmed during our investigations. Additionally, high flexibility with regards to adjusting the in-situ gelation times and its environmental-friendly classification validates it and makes it an alternative for potential implementation in both onshore and offshore assets requiring in-depth and near wellbore conformance control.