How Horizontal Surface Deformation during Fluid Injection Correlates to Reservoir Permeability Setting

Abstract

Land surface deformation due to fluid withdrawal and injection has long been observed at the surface above aquifers and oil reservoirs. With the advancement of ground surface monitoring techniques, the detailed land deformation behavior, particularly the horizontal component of deformation, can reveal valuable information about deeply buried host reservoirs. Historically, two analytical approaches describing material deformation have been developed independently in the fields of hydrogeology and petroleum engineering based on different theories. A critical review has been made by crossing the discipline boundary, and shows that these two different approaches are actually handling two extreme conditions of the same problem. The petroleum engineering approach deals with a very sharp permeability boundary, whereas the hydrogeology approach assumes an infinite areal reservoir without a permeability boundary (called the Theis-Thiem confined aquifer). By changing the lateral permeability gradient of the reservoir, a well-confined reservoir as considered in the petroleum engineering can be gradually opened to approximate a Theis-Thiem confined aquifer as considered in hydrogeology. Thus these two approaches can be unified. A large model (20 km × 20 km) was created to simulate ground deformations during fluid injection with different permeability boundary conditions. We found that the maximum horizontal displacement and the migration behavior of its location during fluid injection can yield valuable information about the permeability distribution in deeply buried reservoirs. Thus, horizontal surface deformations can be used to determine whether the injected fluid is remaining trapped in its desired environment or whether outward migration is occurring.