Formation Testing in the Dynamic Drilling Environment
Formation testing objectives have changed little since their introduction in the early 1950''s. A formation test is used to determine the formation pressure, obtain fluid samples, estimate formation rock properties, and, ultimately, evaluate reservoir producbilty. Wireline formation testers (WFT) were introduced soon after drill stem testing (DST), but they have now nearly replaced DST through a succession of technical innovations. More recently, formation testing while drilling (FTWD) has been introduced. FTWD tools introduce new capabilities that address the drilling environment.
The drilling environment truly offers challenges for testing because mud column pressures are indeed dynamic, and invasion while drilling is in its early stages of progression. Dynamic changes typically introduce pressure transients that are not detected in other forms of testing. New pressure-transient analysis techniques have therefore been developed and introduced to analyze these changes. The advantages in analyzing pressure transients are that they can determine properties of interest to drilling, such as filtrate loss rate and depth of invasion. Traditionally, it had been assumed that measured pressures only reflect formation pressures, an assumption that is not always valid.
FTWD testing is still in its infancy; and if history repeats itself, this form of testing will take a larger role in formation evaluation in the future. Some applications have already been developed, applied, and successfully demonstrated. Highlights of these developments will be emphasized in this talk. New applications very likely will be developed as this testing technology evolves.
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