An Analytical Model of Temperature and Stress Fields During Cold-Water Injection Into an Oil Reservoir

Abstract

Summary A new transient analytical model has been developed to study the temperature and stress distribution induced by nonisothermal fluid injection, particularly conventional waterflooding. In the model, the transient pressure, temperature, and stress fields are computed consecutively. The pressure field has been computed by using either the exponential integral solution for a unit mobility ratio displacement or Ramey's composite reservoir model for a nonunit mobility ratio pistonlike displacement. The transient temperature field has been computed by using a model that can account for both the overburden heat losses and transversal heat dispersion within the reservoir. The stress distribution has been calculated with a method presented for a plane strain in a hollow cylinder. The results implied that the thermoelastic changes in the cooled zone could affect the surrounding stress fields in a profound manner. For instance, for a porous medium with stiff material (such as carbonate reservoirs) owing to cooling by the injected cold water, large-scale tensile stresses arise and may induce new fractures (or propagate existing ones) far into the reservoir. In addition, a major tangential stress concentration develops just in front of the cooled zone; hence, shear yield is highly likely to occur ahead of the thermal front. The 2D treatment of the temperature field makes the new method superior to the previous analytical models where only a 1D field has been used.