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MDT Permeability Anisotropy Measurements

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Vertical interference testing for permeability and anisotropy away from the wellbore

Information about permeability in the near-wellbore area is typically obtained from core data, nuclear magnetic resonance (NMR) logs, and pretest buildup investigations conducted with a wireline formation testing tool. Although these data, which reflect reservoir conditions within a few inches of the wellbore, are useful and typically confirm each other, permeability values on a much larger scale are needed to represent reservoir heterogeneity. Reservoir modeling studies, geostatistical models, and reservoir simulation grid blocks require horizontal permeability (kh) measurements from tens to hundreds of feet into the formation. Corresponding vertical permeability (kv) values are also needed. A lack of reliable vertical values often results in adjustment of the grid block vertical permeabilities used as history-matching parameters during reservoir simulation.

To perform these critical kv and kh measurements, the flow control module of the MDT modular formation dynamics tester is used to produce a 1,000-cm³ volume of formation fluid. The precise surface-controlled flow rate is recorded for interpretation of pressure data. For tests requiring larger volumes, a pumpout module or sample chamber may be needed.

Optimizing pretests with NMR permeability—and confirming with interference tests

The depth of investigation of pretests conducted with the MDT tester is almost always within the invaded zone, reflecting a limited volume near the wellbore. Thus, pretest mobility values typically agree with core plug data and NMR log-derived permeability values. By running combined surveys with the MDT tester and a CMR-Plus combinable magnetic resonance tool or MR Scanner expert magnetic resonance service, continuous NMR permeability information can be used on site to select the optimal locations for pressure measurement, sampling, and interference tests with the MDT tester.

Although core, NMR measurements, and pretest permeability values may be in good agreement across an entire reservoir section, interference tests can indicate different values. For example, differences in vertical communication could indicate a permeability barrier. The increased depth of investigation of interference testing using the MDT tester and the resulting determination of permeability anisotropy provide a valuable perspective for reservoir characterization.

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Increasing the Length Scale for Permeability Answers

MDT multiprobe and packer-probe configurations offer options for vertical interference testing.Comparison of CMR-derived permeability, core and MDT pretest values. The interference test locations are shown on the formation image.Mini-DST analysis of Test 1. The probe did not show any response during the test, suggesting a possible barrier. Analysis indicates spherical and radial flow.
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