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One important application of wireline formation tests (WFTs) is the near-wellbore-region formation characterization by way of conducting controlled local drawdown buildup, and interference tests along the wellbore. In this chapter, we present a general interpretation methodology for interval pressure transient tests (IPTTs) after completing geological- and formation-model building, as in the quality assurance/quality control (QA/QC) and data processing presented in the preceding chapter. Here, we cover general principles of pressure transient test interpretation methodology for formation testing. A standard pretest with a probe or a packer creates a localized pressure diffusion (flow) around the wellbore in the formation. The flow regime generally is spherical and occasionally hemispherical, if the probe or packer is located near to a no-flow boundary. The radius of investigation for a probe pretest usually is in the range of 1 to 20 ft, and for a packer pretest, it is in the range of 5 to 50 ft, depending on the formation parameters and, particularly, mobility (kμ). The radius of investigation for a probe IPTT varies from 5 to 40 ft with an appropriate flow rate, which cannot be very large because of a very small production area of the probe. The multiprobe examples in Chapter 14 show that we have an observable pressure change at the vertical probe at 15 ft. Depending on mobility, sometimes we do not have any observable pressure change, even at 5 ft. Of course, mobility or penneability is an important parameter, but pressure-gauge resolution, flow rate, duration of the IPTT, and other formation and fluid properties affect the radius of investigation, provided that the data are valid, as discussed in the QA/QC process section in the preceding chapter.

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