USING HORIZONTAL SURFACE DISPLACEMENTS DURING FLUID INJECTION TO CHARACTERIZE THE PERMEABILITY REGIME OF DEEP RESERVOIRS

Land surface deformation resulting from fluid withdrawal or injection has long been observed at the surface above aquifers and oil reservoirs. With the advancement of high resolution ground surface monitoring techniques detailed horizontal surface displacements 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 examining the approaches of taken by each discipline, which shows that these two approaches actually evaluate the same problem from two extreme boundary conditions. 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 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 (20km x 20km) 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 displacements can be used to determine whether the injected fluid is remaining trapped in its desired environment or whether outward migration is occurring.