A 3D analysis of interference testing in anisotropic composite reservoirs

A composite reservoir is one with multiple compartments, each having distinct rock and (or) fluid properties separated by geologic discontinuities; these discontinuities regulate the degree of compartment distinctiveness depending on the amount of leakage involved. This reservoir system is encountered often in fields due to the geologic interplay between depositional and tectonic forces.Using transform methods, a general three dimensional point source solution for the drawdown response in composite clastic systems separated by a leaky fault is developed. This semi-analytical solution is converted to line source for horizontal wells by integrating along the producing well length while treating the leaky fault as a thin finite conductivity fracture separating two reservoirs with different properties. An arbitrary well orientation to principal permeability direction is adopted to obtain a general solution in the anisotropic system.Sensitivity analysis conducted on generated interference responses with respect to areal permeability anisotropy, well position, reservoir dimensions, dimensionless fault conductivity and mobility ratios in composite clastic reservoir systems reveals that the response is a convoluted function of reservoir properties from both compartments and the separating semi-permeable medium.For the first time, it is observed that the intersection time between the long-time approximation of the pressure drawdown and pressure derivative signature of an observer is unique for every boundary condition—from which producer hydraulic diffusivity is obtained through Tiab direct synthesis (TDS). From resulting type curves, there exists a limiting fault conductivity, compartment-permeability contrast and well-fault distance among other reservoir parameters that could register on the drawdown response signature.

► Three dimensional interference analysis of observer in composite reservoirs.
► Sensitivity of horizontal well pressure drawdown with reservoir parameters.
► Unique points of intersection observed from generated type curves.
► Tiab Direct synthesis of reservoir parameters is obtained from unique points.
► Sensitivity of type curves is limited to a certain range of reservoir parameters.