In multifractured horizontal wells producing from unconventional reservoirs, linear flow is commonly observed to be the dominant flow regime during early production. This linear flow regime may remain infinite-acting for a long stretch of time because of the ultralow permeability character of these formations. In this study, we first analytically corroborate that constant gas/oil ratio (GOR) should be expected in unconventional multiphase reservoirs (gas condensates and volatile oils below saturation conditions) exhibiting linear flow under constant-bottomhole-pressure (BHP) production constraint during infinite-acting periods (i.e., before pressure transient reaching the reservoir boundary). We propose a semianalytical solution to the multiphase governing partial-differential equations (PDEs) by applying the similarity method-also referred to as the Boltzmann transformation-to transform the system of PDEs to ordinary-differential-equation (ODE) form. The transformed system of ODEs and boundary conditions are solved by means of Runge-Kutta integration. By solving the equations for pressure and saturation, the GOR trend and value can be fully predicted before availability of production data. The results show that a constant GOR effect could be maintained as long as the flow regime remains infinite-acting and its value varies with BHP specifications for a given reservoir and fluid system.
All Science Journal Classification (ASJC) codes
- Energy Engineering and Power Technology
- Geotechnical Engineering and Engineering Geology