A Coupled Fluid Flow - Geomechanical Approach for Subsidence Numerical Simulation

This paper investigates the effect on compaction and subsidence induced by gas production using two techniques for coupling fluid-flow and geomechanics. To this end, a synthetic case representing a typical, shallow, weakly compacted, multi-layered, off-shore gas reservoir in the Adriatic Sea was set up and its dynamic and mechanic behavior during gas production was analyzed. Three numerical models (i.e., geological; fluid-flow and geomechanical) were built using high quality data set from an existing gas-bearing formation (off-shore Croatia). The laboratory analyses for deformation and strength parameters determination were conducted together with tests to define the coupling law required by the adopted coupling technique. Experimental data showed strong permeability stress-dependent behavior of core samples retrieved from gas bearing layers. Nevertheless, the results showed that the system stress-strain evolution always remains in the elastic domain and the deformation magnitude is extremely narrow (104 m/m) due to the limited net effective stress variation induced by the stressed production scenarios. The difference between the coupling techniques is negligible in terms of subsidence evolution at ground level but not in terms of compaction at reservoir level. Furthermore, the two-way coupled technique could be used for better development planning by integrating reservoir, drilling and completion management.