FACTORS AFFECTING THE THERMAL RESPONSE OF NATURALLY FRACTURED RESERVOIRS

An analysis of the response of naturally fractured reservoirs to therm al recovery processes is presented, utilizing a suite of dual continuu m reservoir simulation models (dual porosity. multiple interacting con tinua, 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 process es are discussed in some detail. While some factors are consistent wit h the isothermal response of naturally fractured reservoirs (in partic ular fracture spacing and the primary effect of matrix permeability), thermal phase behavior and heat flow effects in these reservoirs impar t significantly different, more complex behavior. Most of the naturall y fractured reservoirs which are produced by using thermal processes c ontain very low mobility oil and therefore heat conduction plays a ver y important role at the initial stages of production. With increasing oil mobility, convective, gravity and capillary forces take over if th e matrix permeability is fairly high or the reservoir is fractured ext ensively. During a production cycle in a steam stimulation process, he at is conducted from matrix rock to fracture fluid which can increase the fluid's energy tremendously. Depending on the fracture fluid (wate r/oil) volatility, the additional energy can cause different phase beh avior responses.