Enhancing oil extraction from oilsand by hydraulic fracturing technique hasbeen widely used in practice. Due to the complexity of the actual process. Modeling of hydraulic fracturing is far behind its application. Effects of highpore pressure and high temperature combined with complex stress changes in theai/sand reservoir requires a comprehensive numerical model which is capable ofsimulating the fracturing phenomenon. To capture all of these aspects in theproblem three partial differential equations. i.e. equilibrium. flow and heattransfer should be solved simultaneously in a fully implicit (coupled) manner.
A fully coupled thermo-hydro-mechanical fracture finite element model isdeveloped to incorporate all of the above features. The model is capable ofanalyzing hydraulic fracture problems in axisymmetric or plane strainconditions with any desired boundary conditions, e.g constant rate of fluidinjection, pressure, temperature and fluid flow/thermal flux. Fractures can beinitiated either by excessive tensile stress or shear stress. The fractureprocess is simulated using node splitting technique. Once a fracture is formed, special fracture elements are introduced to provide in-plane transmissivity offluid. Effectiveness of the model is evaluated by solving simple examples andcomparing the numerical results to analytical solutions. The model is also usedto simulate large scale laboratory hydraulic fracturing experiments.
Hydraulic fracturing technique has been a fast growing technology since itsfirst application in 1947. By 1988 more than one million hydraulic fracturingtreatment had been performed[1], and today this technique is one of the mostimportant methods in enhancing oil extraction from wells. Hydraulic fracturingin oilsand reservoirs plays an even more important role. Due to low temperatureand low permeability of oilsand deposits and high viscosity of bitumen, oil isvirtually immobile[2]; hence any attempt for in-situ oil extraction shouldemploy one of the techniques such as cyclic steam stimulation, in-situcombustion or hydraulic fracturing.
Despite the fact that hydraulic fracturing technology has advancedsignificantly over the past fifty years, our ability to design the process hasnot change rapidly. As a matter of fact this technique has been so successfulthat in the past designing the treatment with a high degree of precision wasnot of interest. But as the industry moved towards applications of very highvolume/rate and highly engineered and sophisticated hydraulic fracturingtreatments, the demand for more rigorous designs in order to optimize theprocedure have become more important. On the other hand without a thoroughunderstanding of the physical process and the factors that are involved, ourability for an optimal design is limited. Modeling of fluid flow combined withheat transfer in the reservoir has been used by the industry for a long timeand fracturing process often was designed based on two dimensional closed formsolutions such as Geertsma-deKlerk[3] or GdK in brief and Perkins-Kern[4] and Nordgren[5] or PKN. Most of the flow and heat transfer models are based on thefinite difference method and effects of stresses and deformations in theground, if not totally ignored, is solved in a decoupled or partially coupledmanner with other elements.
