Advanced Dual Probe Formation Tester with Transient, Harmonic, and Pulsed Time-Delay Testing Methods Determines Permeability, Skin, and Anisotropy

摘要

Three new pressure-transient testing methods are employed torndetermine horizontal and vertical permeability using a dualrnprobe formation tester. Real-time interpretation duringrnacquisition of pressure data, is the focus of all three newrnpressure-testing techniques. In the first, a new spherical flowrnmodel with anisotropy, storage, and skin is developed fromrnfirst principles for dual probe analysis. Historically, pressurerntransient solutions are presented as Laplace transforms andrnapproximated in the time domain using numerical techniques.rnTypically, early, intermediate and late time periods arernidentified using derivative plots; but very often, the selectionrnof appropriate data results in confusion. Here, the Laplacerntransform is inverted to yield a single, exact, closed form,rnanalytical, time domain solution valid for all times, makingrnreal-time parameter matching possible with high accuracy.rnThe second technique uses an oscillatory displacementrnsource at the piston face, and the phase delay of the pressurernpulse between the probes is used to determine permeabilityrnand anisotropic index. This technique is particularly usefulrnwhen the second monitoring probe signal is weak (as in highrnpermeability zones) or where there is large spacing betweenrnthe probes. Pulse timing can usually be detected morernaccurately than its magnitude, thus extending the range ofrnpermeability and anisotropic measurements. Thisrnmethodology, which is based on a derived relationshiprnbetween wave phase and permeability, was developed byrnmathematical analogy with resistivity determination methodsrnused in induction logging.rnIn the above method, it is often possible to encounterrn“phase wrapping” for excessively tight formations, leaving anrnindeterminate permeability. To circumvent this problem, in thernthird method, a short, abrupt “pulse” having a well-definedrn“center frequency” is produced at the piston face, and its travelrntime is measured until arrival at the receiver probes. Thernharmonic, closed form expression is then used to translate thisrntravel time to permeability. This new method is analogous tornsonic wave models; although, of course, “waveforms” arernoften smeared due to the diffusive nature of the problem.rnSimulation results using a detailed finite element, dualrnprobe model are compared against the above analyticalrnmethods to assess the effects of near wellbore parameters suchrnas mudcake effectiveness, probe, and packer size. Field-testrnresults are shown to demonstrate the successfulrnimplementation of these new testing methods. The threernmethods described above provide a practical level ofrnredundancy in permeability prediction. Also, monitoringrnpermeability and anisotropy changes while sampling arernshown to be beneficial in identifying fluid type changes.