Array Formation Testing with Multiple Azimuthal and Axial Pressure Transducers

Abstract

An early formation tester operating a “sink probe” that extracts fluids from the borehole, also measures pressures at its location; pressures are additionally collected at two passive sensors, one situated 180 deg away and the second about meter axially. These positions are not conducive to accurate permeability predictions, since pressure transient signals used for inverse analysis attenuate very rapidly. Closer probe spacings offer formation evaluation advantages at low mobilities because Darcy pressure dissipation is reduced. Logging applications for such testing tools include heterogeneity, anisotropy and layer characterization. Multiprobe tools with smaller transducer separations are ideal, but at present, analytically based hardware design and software interpretation methods are not available. Two design approaches are described in this paper, namely, testers with multiple probes that are displaced azimuthally, and those with axially displaced probes. For the former, we describe a new triple-probe array tester and related software models that support pressure transient analysis in transversely isotropic media. The numerical approach supports independently operable probes with different nozzle shapes, flow rates and start and stop times. This flexibility supports anisotropy and heterogeneity mapping ‘’circumferentially about the borehole. The latter class of tools, those formed by axial pressure arrays, extend conventional “dual probe tools” by including additional pressure probes axially along the same azimuth. These support improved pressure gradient analysis and detection of isolated zones in vertical wireline applications. Taken together, both array methods and their computational models support more effective job planning and inverse properties analysis. Comments are also offered on “hybrid multiprobe tools” consisting of both azimuthal and axial arrays. These math formulations and computing methods for both tool classes not only support pressure analysis, but also, for more effective hardware design. For example, what pump flow rates are required to provide a given depth of investigation? Analogous questions can be answered “on paper” prior to prototype building. Representative computed examples are presented demonstrating the versatility and capabilities of the new models. This article introduces techniques focusing on single-phase flow fundamentals. Applications to other multiprobe tools, together with multiphase extensions, dealing with coupled pressure and contamination models, nonlinear gas pumping, convergence acceleration, and in addition, inverse approaches and “big data” support, will be presented in a forthcoming 2024 book.