Modeling of Near-Well Matrix Acidization

Abstract

The growing global energy consumption and drive for cleaner energy have generated an immense interest in low enthalpy geothermal energy resources (LEGERs) as an alternative and readily available resource. The LEGERs, albeit under 100 oC, can be harvested to provide heating and power generation from household to industrial scale. One of the challenges encountered during the exploration of such geothermal reservoirs is a poor hydraulic connectivity between the wells. Another challenge is the natural precipitation of solids which leads to an additional permeability reduction, i.e. formation damage. While these problems can be solved by a hydraulic stimulation, the application of chemical stimulation is another clear alternative. In our study, we model an acid stimulation in the near-well region at a high resolution and directly resolve the shape of wormholes associated with matrix dissolution. Since this region has a significant impact on the efficiency of the entire stimulation job, it is of great importance to capture this phenomenon accurately. In the high-resolution simulation study, the solid matrix in some control volumes can be fully dissolved by acid. Since the canonical Darcy’s law cannot be applied when the porosity is near unity, a single, unified continuum approach namely the Darcy-Brinkman-Stokes (DBS) equation is employed and compared with Darcy model. The simulations are done using the Automatic Differentiation General Purpose Research Simulator (AD-GPRS). A convergence analysis and sensitivity studies are performed for key parameters to fully describe and understand the behavior. The shape of wormholes is studied for different flow rates and is validated against a published work for both Darcy and DBS models. The wormholes characteristics, obtained in these two models, are defined by breakthrough parameters and dimensionless variables. Convergence analysis and sensitivity studies were performed for several parameters to fully describe and understand the differences in 2D systems.