Nano-Silica Gel for Water Shut-Off in Fractured Reservoirs: Experimental Insights and Promising Results

Abstract In the oil industry, the pervasive challenge of water production during hydrocarbon extraction presents operational and environmental complexities, impacting costs, oil recovery efficiency, and environmental sustainability. Over the last decade, many chemical systems were developed to mitigate this problem. As the nanomaterials showed its capability to add improvement in EOR and drilling applications, it becomes a demanding to incorporate such materials in water shut-off applications. This paper delves into examining the potential of nano-silica gel to prevent water flow in fractures. While prior research has explored its utility in high permeable matrix, this study extends the investigation to fractures that contribute to unproductive water production. In this study, a fractured limestone sample featuring a groove (middle) with a depth of 0.5 to 0.7 mm was created intentionally to simulate reservoir fractures. Nano-silica gel was injected using a core flooding system to ensure precise gel placement. The core flooding experiment was implemented at 200° F and involved three stages: 1) a pre-treatment stage for evaluating initial permeability, 2) an injection stage for the gel solution, and 3) a post-treatment stage for the constant pressure endurance test. Subsequently, the sample underwent a 3-month aging process in formation water at 167° F. Endurance tests were conducted in both the first and third months to reevaluate the plugging efficiency at 200° F. The experimental findings demonstrated the gel's effectiveness in plugging water flow in both the fracture path and matrix, achieving initially a 100% plugging efficiency. The gel was durable to high differential pressure up to 1500 with minimal leak-off rate of 0.09 ml/min. There was a substantial reduction in the average permeability across the sample, decreasing from 37.19 mD to 0.0012 mD. Analysis of the pore system through CT scans before and after treatment confirmed successful gel placement in the inlet and outlet fracture sections, as well as an invasion into the matrix. The CT scans also verified the uniform distribution of the gel along the sample length. Additionally, the gel was capable of maintaining exceptional plugging efficiency of 99.98% after 3 months from the initial treatment.