A Successful Rigless Water Shut Off Solution in an Open Hole Horizontal Water Injection Field in the Sultanate of Oman Using a Water-Swelling Polymer System

Abstract

Abstract Premature water breakthrough between injector and producer wells through natural fractures can be a significant challenge leading to poor waterflooding performance in fractured reservoirs. Thus, applying a cost-effective Water Shut-Off (WSO) technique to stop injected water from flowing into fractured zones has become paramount to increasing production from mature fields and enhancing hydrocarbon recovery from such reservoirs by modifying the injection profile. This paper presents a successful chemical WSO solution designed to help improv injection systems’ sweep efficiency by stopping injected fluids in waterflood fields from flowing into fractured or highly vugular zones, leading to direct communication with the producing wells. Each water injector well supports two to three oil producers forming a horizontal waterflood pattern. Since the early days of injection, water cut has increased dramatically, reaching almost 100% in some producers to indicate direct communication through the fracture network. The treatment consists of bullheading a water-swellable agent into the injection well along with an aqueous solution to swell the agent. The agent is a synthetic polymer capable of absorbing 30 to 400 times its weight in water to seal off the fractures without penetrating most matrix systems. The carrier fluid helps determine the agent's swelling rate, and a shutoff period is required to give enough time for the polymer swelling to take place. After the treatment, the injection pressure response was observed between 200 psi to 600 psi at the same injection rate. Water cut dropped gradually; a drop of 0-15% in water cut was observed in the nearby producers, resulting in an oil gain up to 100 Bbls in some of the oil producers. The result was a cost-effective treatment, producing more bbl. of incremental oil in one year. This paper will discuss the job planning process along with the treatment design. The treatment execution is summarized, followed by the results obtained from the job's realization with key lessons learned and recommendations.