A Numerical Model for Simulating Solid Waste Injection in Soft Rock Reservoirs

Abstract

Abstract This paper describes the development, validation, and application of a numerical model that simulates solids injection operations for soft rock reservoirs. There exist many classical fracturing models that are good tools for evaluating solids injection operations in formations with competent rocks. However, when evaluating solids injection operations in soft rock formations such as unconsolidated sand, these classical fracturing models generally fail to provide reliable evaluations. In this paper, a solids injection model was specifically formulated and developed for solids injection in soft rock formations. The development of the proposed model for soft rock formations is based on the Biot's self-consistent theory, plasticity theory, and fracturing and liquefaction criteria for rock. The predictive capability of the developed model was verified against field data from waste injection wells in soft rock formations. The validated model was used to evaluate solid waste disposal for cases of various injection operation conditions in a soft rock reservoir. Results show that the solids injection model provides an effective tool to assess the maximum injection volume allowed per well, the area of influence of injection, the bottom-hole injection pressure, and the vertical containment of the injected fluids and solids. Simulation results for representative cases are presented. The model can also be useful for quantitatively assist in identifying feasible solids injection mechanisms in soft rock reservoirs.