Water-gas mixtures injection into a reservoir by pump-ejector system using fresh and highly mineralized formation water

For the operating conditions of the Romashkinskoye field, a comprehensive technology of simultaneous water and gas (SWAG) injection with the extraction of associated gas from the annular spaces of producing wells was proposed. Fresh and salty highly mineralized water was used when pumping water-gas mixtures (WGM) by the pump-ejector system. Experiments on WGM injection started using fresh water from the reservoir pressure maintenance (RPM) system and associated petroleum gas (APG) from producing wells. The pump-ejector system operated stably, without supply disruptions, and provided a WGM injection pressure of at least 20 MPa. But in the case of APG injection with fresh water, the injection pressure of the mixture steadily increased over time and reached limiting values for the ground equipment of the RPM system and injection wells, then it was necessary to turn off the pump-ejector system. When using salt water, the injection pressure of the mixture first increased, then, having passed through a maximum (10,7-10,8 MPa), 40 hours after the start of the pump-ejector system it was about 9 MPa. Field tests confirmed the operability and stable operation of the pump-ejector system at WGM injection pressures of up to 20 MPa and a decrease in the annular pressure from 3 MPa to atmospheric, revealed the problem of hydrate formation when using fresh water with Devonian associated petroleum gas, and enabled to establish that the use of salty highly mineralized water completely solves the problem of hydrate formation and a decrease in the injectivity of injection wells during SWAG treatment of the formation. © 2025 Elsevier B.V., All rights reserved.