Simulating pressure changes and production processes in natural fractured formations has been commonly performed by the classic dual-porosity model. Geomechanics factors can be crucial for pressure change and production as both formation deformation and locally induced stresses can contribute to the pressure change thus production significantly, particularly in low-permeability and fractured formations. Multiphase flow in both the matrix and fractured system can significantly affect the production and pressure results, particularly near a wellbore or a hydraulic fracture. The key parts on developing this model are to come up an efficient algorithm and define the parameters characterizing the geomechanics coupling to the flow on top of the explicit coupling to the saturation, where upstream weighting is applied. The proposed algorithm coupled the pressures from both system with the corresponding volumetric strain and subsequently explicitly coupled to the saturation. Petrov-Galerkin finite methods are used where a parabolic approximation verse a linear one is implemented respectively for the displacement and pressures/saturation.
Flow in naturally fractured reservoirs is normally characterized and modelled by the well-known sugar cubic model initiated by Barenblatt et al, (1960) and proposed by Warren and Root (1963). Extensive studies follow by mixture theory focusing on stress-sensitivity and loosely geomechanics coupling (Wilson and Aifantis 1982; Beskos and Aifantis, 1986; Huyakorn and Pinder, 1983; Elworth and Bai, 1992; Bai, Meng, and Roegiers, 1999) and by an alternatively conventional reservoir-geomechanics coupling model following Biot's theory (Biot, 1941; Duguid and Lee, 1977; Vallianppan and Khalili- Naghadeh, 1990; Khalili-Naghadh and Valianppan, 1996, 1997; Chen and Teufel, 1997). Following Vallianppan and Khalili-Naghadeh (1996) and Chen and Teufel (1997), an extended Biot theory coupling the fluid flow to deformation is proposed and implemented. Those critical parameters between stresses and pore pressure and the deformation coupled between pore volume, bulk volume, porous matrix, solid particle, and fractured volume are highlighted. Studies on dual porosity model have been extended into two phase flows (Nair, Absouleimen, and Zaman, 2005; Bai, Meng, and Roegiers, 1999) by a mixture theory. Following Wang and Chen (2001), in which only a single poroelastic model is proposed, a two-phase flow model with extended Biot formulation will be the focus in this paper.
