Title : An Integrated Interpretation of Pressure Transient Tests from the Fractured North Galio Reservoir
Natural fractures are mechanical breaks in igneous, metamorphic, and sedimentary rocks, involving discontinuities in displacement across their planes. Fracture networks can be continuously or discretely distributed, have a dominant or arbitrary strike and/or dip directions. They often act as conduits or baffles to oil, gas and water production. That is why natural fractures have significant impact on hydrocarbon reservoirs performance and management from drilling to EOR. Static and dynamic data are used by geo-modelers to build 3D models for Naturally Fractured Reservoirs (NFR).
It was observed that pressure transient data obtained from most NFR tend not to exhibit the well-known characteristic behavior, including pressure derivative, of the Warren and Root dual-porosity reservoir model. These field data illustrate diverse pressure behaviors of discretely and continuously NFR. Unlike the single derivative shape of the Warren and Root model, the derivatives of these examples exhibit many different flow regimes depending on fracture distribution, intensity, and conductivity. We use recently published solutions for the pressure transient behavior of continuously and discretely NFR that contain finite- and/or infinite-conductivity fractures with different lengths, densities, and orientations. In the solutions, fractures, matrix elements, and the wellbore are treated explicitly, where the well intersects one or more fractures, or is located in the matrix blocks with wellbore storage and skin effects. These solutions are a part of an integrated geologically model-driven methodology for the characterization of NFR.
We apply the recent solutions and methodology to an appraisal well in X field in North Africa. The reservoir consists of the Upper and Lower naturally fractured sandstone Nubian formations. Open and closed fractures intersecting the wellbore are dipping between 50 and 80 degrees, and striking respectively in the NE-SW and NNW-SSE directions. A fault intersects also the vertical well. Hydraulic fracturing and well tests were performed in both formations.
Audience Take Away:
These field data illustrate diverse pressure behaviors of discretely and continuously NFR. Unlike the single derivative shape of the Warren and Root model, the derivatives of these examples exhibit many different flow regimes depending on fracture distribution, intensity, and conductivity.