A Novel Water Shut-Off Technology, Lab and Field Application, Using Sized Calcium Carbonate Particles in Safah Field, Oman

Using Calcium Carbonate to improve waterflood conformance is a new concept borrowed from drilling operations in which sized Calcium Carbonate particles are routinely used to prevent lost circulation. The application for water shut-off is to inject a pre-designed volume of Calcium Carbonate particles to reduce the permeability contrast between the fractures and the matrix, thereby improving the injection conformance to achieve better waterflood sweep efficiency. The journey of developing this new conformance technology started in early 2021 by working with a vendor to redesign a bridging agent used for drilling fluid losses into a simpler, less expensive recipe comprising Calcium Carbonate particles with different sizes and a friction reducer to suspend and carry the particles deep into the formation. This technology features several key advantages: low-cost rigless operation, a flexible recipe for materials of different sizes, the volumes and pumping schedule can be adjusted, and the treatment is reversible in case of a screen-out. The first campaign of implementing this technology was successfully completed in January 2022. Three water injectors were treated in the Safah field in Oman, a mature waterflood with an area of high-water cuts and low recovery factors. A drop in injectivity was seen after pumping a total of 300 bbl of the two sizes of Calcium Carbonate particles, indicating that the treatment achieved the objective. After logging one of the injectors and comparing the injection profile before and after the treatment, found a clear improvement at the heel section of the openhole horizontal lateral and improved injectivity at the middle of the lateral by 38%. A coreflooding lab experiment was conducted to simulate the treatment in a core scale with induced fracture, and to witness the nature of the material if packed well in the fractures. The procedure in the lab mimicked the actual field operation regarding the material size used of 600,150 and 50 microns, and as well with same pumping sequence. At the end of experiment the core was opened, and the material was very well consolidated and sorted. Moreover, permeability test pre and post the treatment explaining the actual observed field results with fracture permeability reduced from 7 Darcy to 15 md. To date, three campaigns of this new injection treatment targeting 16 water injectors achieved an excellent success rate of 93%, with a significant drop in injectivity in nine wells after treatment. Three of those injectors were logged afterwards to confirm the improvement in conformance profiles. Moreover, a 20% oil gain observed from one of the treated patterns, which proves the improvement in waterflood sweep. To our knowledge, this is the first application of Calcium Carbonate particles for water injection conformance purposes. Based on the results obtained thus far, there are plans to expand its use to other parts of the field and to other fields in northern Oman.