Poroelastoplasticidad en Sistemas Geotérmicos y Desequilibrio Térmico

摘要

Poroelastoplasticity is important in geothermal reservoirs because the irreversible deformation in the rock produce fissures, geological faults and ground subsidence; it reduces the reservoir storage capacity, by the compaction of pores and fractures, and the total or partial collapse of wells in extreme cases. The discussion presented herein is based on the plastic flow equations, outlining the most important aspects of the current additive theory, which is illustrated with two practical examples, one radial, and the other in 3D. Geomechanics is coupled to thermal disequilibrium processes, through poroelastic deformations due to a temperature change. The variation of the fluid contained in the pores in this process is generally very small. Yet the fluid pressure is considerably increased by thermal stresses, when the temperature of the fluid changes abruptly. This variation in pressure occurs, for example, when cold water is injected into a high temperature reservoir, producing local thermal non- equilibrium. This phenomenon is coupled to the thermo-poroelastoplastic deformation of the rock, which can result in fractures. In this work the conservation of geothermal energy is used in local thermal non-equilibrium conditions. The heat transfer from the matrix to the fluid at different temperatures is modelled for various velocities and different amounts of global heat flow. Numerical experiments allow estimate the unknown heat transfer coefficients. Special attention is given to the process of cold water at 50°C, injected into a reservoir at 350°C. When the fluid moves at constant speed from the injection point to the area of production, the fluid temperature profile can be estimated. Two additional objectives are achieved in this work: estimation of the volumetric coefficients of heat transfer and the exploration of the validity of the thermal equilibrium hypothesis during reinjection of cold water into a high temperature reservoir in local thermal non-equilibrium.