Abstract
Finding a suitable in-depth water control and conformance strategy was the key objective of the study presented in this paper. Carbonate reservoirs with complex lithology (Carbonate/Dolomite) presenting structural features such as fractures, high permeability streaks and karsts are known to lead to low waterflood recovery factors and early water production. Chemical Polymer Gels studies were carried out by ADNOC Onshore in 2021-2022 to select an appropriate product for Field Conditions. The objective was to identify a robust gel system that could be placed in-depth for a more durable effect. Laboratory studies were carried out including Gel rheology measurements, bottle tests for gelation time and gel stability assessments and Corefloods using an artificially fractured core from the pilot area. This coreflood was conducted to measure gellant injectivity, gel parting pressure, permeability reduction (Rk) and pore volume reduction obtained by gel placement. Two Gel Systems were investigated: Gelix and a SAV10 Chromium acetate gel.
Based on the study results, Gelix system was selected and qualified to be used in the In-Depth water control and conformance pilot. Results showed that Gelix technology had the lowest viscosity meeting the maximum viscosity requirement of 200cP.Best gel consistency results were obtained using a 2%KCl brine and Mix Water, leading to a rigid gel. It was in addition possible to delay gelation for several days depending on the concentrations of the products and brine salinity. Accelerated ageing tests confirmed the excellent gel stability of Gelix in 2%KCl, maintaining Gel consistency whatever temperature and ageing time.
Two corefloods in artificially fractured cores showed that in-situ performance of Gelix was far above those of SAV10 / CrAc. Gelix gel retained a gel parting pressure of 1 bar/ft and a residual permeability reduction (RRF) between 16000 and 196000 making it suitable formulation to block fractures and/or high permeability streaks for in-depth water control. Finally, in order to protect the oil-bearing matrix from a hybrid gel placement injection strategy will be used with pre-injection of Small calibrated Microgels (SMGs). Field trials are now planned in two horizontal production wells.
