Margaret C. Waid, Mark A. Proett, Rafael Vasquez
Halliburton Logging Services
Chih C. Chen
Halliburton Reservoir Services
Wayne T. Ford
Texas Tech University
ABSTRACT
Wireline sequential formation test tools (SFTT) typically perform short duration well tests, drawing formation fluid samples which are relatively small compared with traditional drill stem or production testing. Techniques for interpretation of the pressure response which correct for fluid compressibility in the flowline and chambers, mud invasion effects, and higher formation pressures due to supercharging are investigated in this paper. In previous publications some of these effects have been calculated independently using analytical methods, but the combined effects have not yet been determined due to the complexity of the analytical problem. By combining a finite element Near Wellbore Simulator (NEWS) with analytical techniques, it is now possible to simulate these effects in combination.
By combining NEWS and time-step integration techniques to adjust the flow parameters, these effects are simulated in a three dimensional near-wellbore model, This model includes anisotropic permeabilities, bed boundaries, dip angles and other physical constraints encountered in well testing. The entire near-wellbore flow pattern can be visualized with three dimensional contour plots of formation pressure profiles.
Results in the paper indicate that, in many instances, classical interpretation techniques for formation testers produce uncorrected values for formation pressure and permeability which may differ significantly from actual values. The questions of how long the SFTT should remain in place during the buildup phase of the test and how points are chosen in the test interpretation are the outstanding questions in formation tester applications. These practical issues are resolved and sample correction charts are presented which give actual formation pressure and permeability from formation tester logs.