Restriction of Water Production in Gas Wells by Induced Phase Inversion: Field Case Studies

摘要

Water shutoff treatments need different approach and chemicals in gas and oil fields due to the inverse mobility ratio. Therefore, the primary aim of the research project was to develop special treating solution, which may form barrier phase against the flow of water by in-situ mixing of the treating fluid with formation water. As a novelty, water sensitive petroleum- based solutions were developed, which are stable until they are contacted with water. The induced phase inversion of such metastable systems restricts the water flow by 80-90% in sandstone cores through evolving extremely high viscosity in the mixing zones. Optimizing the composition of the treating fluid containing environmentally friendly chemicals the method was qualified as matured for field pilot tests. Evaluating the production history of possible alternatives, two gas producing wells were selected for the pilot. The wells are operating in different layers of the largest, stacked Hungarian oil and gas field. Prior to treatment, in both cases, the gas rate dropped significantly; meanwhile the water production rapidly increased to 120 and 150 BPD, respectively. The injection protocol started with partial reduction of water saturation in the nearby zone of wells by injection of water-miscible organic solvent driven deeply into the reservoir with N2. Afterwards, the petroleum bulk solution containing tenside and fatty acid ester in appropriate concentration was injected. Injecting 40-50 m3 treating solution, nitrogen drive served again to reach deep penetration of treating solution. Monitoring the wellhead pressure it was clearly indicated when the induced phase inversion started to build-up resistance against the water flow. Applying short shut-in time, transient production period was observed, which was followed by gradually increasing gas production with water-free and reduced water influx. The preliminary data firmly proved that the unique water shutoff technology might open new vistas reservoir conformance control in gas fields.