Characterization of the Pliocene Gas Reservoir Aquifers for Predicting Subsidence on the Ravenna Coast

摘要

The Pliocene reservoirs of the North Adriatic have produced gas since 1972. Several studies using reservoir and geomechanical models have been undertaken to quantify the surface land subsidence that may be attributed to pressure depletion resulting from gas production. Subsidence may continue after production ceases, as water influx repressures the depleted gas reservoirs, reduces the aquifer pressure, and causes the subsidence bowl to expand. Therefore, characterization of the Pliocene aquifers and water influx functions is important for long-term prediction of subsidence. An aquifer model was developed by integrating geological/geophysical interpretations, petrophysical data, and pressure/production data to describe the limited water influx observed in these reservoirs. The mechanism restricting water influx in the Pliocene gas reservoirs was found to be a combination of low effective permeability to water in the presence of clays and trapped gas saturation. The final aquifer model, which was validated with field pressure data, was used to predict long-term pressure drop in the aquifer for subsidence predictions.