A technique using interwell connectivity is proposed to characterize complex reservoir systems and provide highly detailed information about permeability trends, channels, and barriers in a reservoir. The technique, which uses constrained multivariate linear regression analysis and pseudosteady-state solutions of pressure distribution in a closed system, requires a system of signal wells and response wells.
Signal wells and response wells can be either producers or injectors. The response well can also be either flowing or shut in. In this study, for consistency, waterflood systems are used in which the signal wells are injectors and the response wells are producers. Different borehole conditions, such as hydraulically fractured vertical wells, horizontal wells, and mixed borehole conditions, are considered.
Multivariate linear regression analysis was used to determine interwell connectivity coeffients from bottomhole pressure data. Pseudosteady-state solutions for a vertical well, a well with fully penetrating vertical fractures, and a horizontal well in a closed rectangular reservoir were used to calculate the relative interwell permeability. The results were then used to obtain information on reservoir anisotropy, high-permeability channels, and transmissibility barriers.
The following are some conclusions drawn from this study: (a) the interwell connectivity determination technique using bottomhole pressure fluctuations can be applied to waterflooded reservoirs that are being depleted by a combination of wells (e.g., hydraulically fractured vertical wells and horizontal wells); (b) wellbore conditions at the observation wells do not affect interwell connectivity results; (c) the complex pressure distribution caused by a horizontal well or a hydraulically fractured vertical well can be diagnosed using the pseudosteady-state solution and, thus, its connectivity with other wells can be interpreted.
Different synthetic reservoir simulation models are analyzed, including homogeneous reservoirs, anisotropic reservoirs, and reservoirs with a high-permeability channel, or a partially sealing barrier, or a sealing barrier.