Surface heave by steam injection and subsidence by aquifer production- a 2D modeling study with Plaxis

Abstract

Steam injection is an EOR method, which is mostly used for heavy oil production. This viable method is based on increasing the pore pressure in the reservoir and reducing the viscosity of the heavy oil. In particular cases, the increase in pore pressure and thermal expansion related to the steam injection leads to surface deformation – heave. The results show that the level of heave increases when the reservoir thickness is larger. For a 100 m thick reservoir, with a pressure increase of 5 MPa and temperature increase to 570 K, the heave is 80 mm. Increasing the reservoir thickness by a factor of two (200 m) results in an increase of heave by a factor of 1.6 (130 mm). A similar increase in heave results when we increase the pressure increment in the reservoir. In our experiments, pressure and heave are linearly related. Results depends on rock properties, most noticeably the elastic property, Young’s modulus, and thermal expansion factor. An increase in Young’s modulus leads to decrease in level of heave. An increase of thermal expansion factor leads to increase in heave.
When the water required for the steam is extracted from a shallow aquifer, producing this aquifer leads to a reduction of the level of heave that is caused by steam injection. This reduction depends on the pressure reduction in the aquifer and on its thickness. For realistic dimensions and rock properties of the aquifer, this effect appears to be insignificant. Only with very low Young’s modulus (7 GPa) and very thick aquifer, the subsidence due to water depletion can compensate the expansion caused by steam injection.