FACTORS AFFECTING THE THERMAL RESPONSE OF NATURALLY FRACTURED RESERVOIRS

An analysis of the response of naturally fractured reservoirs to thermal recovery processes is presented, utilizing a suite of dual continuum reservoir simulation models (dual porosity. multiple interacting continua, vertical matrix refinement and dual permeability). The effects of the different models as well as many fracture and matrix properties on aspects of steam cycling, steam drive and gravity drainage processes are discussed in some detail. While some factors are consistent with the isothermal response of naturally fractured reservoirs (in particular fracture spacing and the primary effect of matrix permeability), thermal phase behavior and heat flow effects in these reservoirs impart significantly different, more complex behavior. Most of the naturally fractured reservoirs which are produced by using thermal processes contain very low mobility oil and therefore heat conduction plays a very important role at the initial stages of production. With increasing oil mobility, convective, gravity and capillary forces take over if the matrix permeability is fairly high or the reservoir is fractured extensively. During a production cycle in a steam stimulation process, heat is conducted from matrix rock to fracture fluid which can increase the fluid's energy tremendously. Depending on the fracture fluid (water/oil) volatility, the additional energy can cause different phase behavior responses.