Characterization of in-situ stresses and its implications for production and reservoir stability in the depleted El Morgan hydrocarbon field, Gulf of Suez rift basin, Egypt

摘要

A comprehensive reservoir geomechanical analysis has been performed in the matured giant El Morgan field, Gulf of Suez to assess the effect of hydrocarbon production on stress magnitudes, reservoir stability, and fault slip potentiality. The average vertical stress (sigma v) gradient of the field is found to be around 22.93 MPa/km. Based on the rock properties and downhole measurements, virgin pore pressure (PP) and minimum horizontal stress (sigma hmin) gradients within the Middle Miocene Hammam Faraun and Kareem reservoirs are interpreted as 11.10-11.25 and 15.88-16.65 MPa/km, respectively. The latest measurements indicate 6-6.5 MPa pressure drop in the Hammam Faraun reservoirs, while Upper and Lower Kareem Formations are depleted by 8-9.5 and 10-11.75 MPa, respectively. The effect of depletion on sigma hmin is modeled using rock linear poroelastic approach. The Middle Miocene reservoirs exhibited average stress path values of 0.61-0.66, respectively. The study infers that the Kareem Formation has more chances of production-induced normal faulting at the present rate of depletion, as the reservoir stress path value is very close to its critical faulting limit. To maintain the production and minimize the bypassed oil, infill injector wells are commonly utilized in the El Morgan field. The reservoir stability threshold was evaluated by appraising critical pore pressure build up limits (PPc) during fluid injection at the present-day depletion level in various PP-stress coupling scenarios. A maximum pressurization window of 10 MPa and 8 MPa are interpreted in the Hammam Faraun and Kareem reservoirs (PPc of 23.33 MPa and 20.31 MPa) respectively, which are well below the fracturing limit of the overlying caprocks, thus ensuring seal integrity. This geomechanical study provided critical insights regarding the optimization of production and repressurization by the infill injector wells by minimizing the risk of subsurface instabilities.