Robust and simple graphical solution for wireline formation tests: Combined drawdown and buildup analyses
- and others
Wireline Formation Testers (WFT) can provide valuable, cost-effective information on undisturbed reservoir pressure (P*), vertical pressure gradients, in addition to formation fluid samples, and an estimate of near-wellbore permeability. Various analysis techniques have been borrowed from the well testing studies and adapted to analyze WFT-measured drawdown and buildup data. Spherical-flow analysis utilizes early-time data and usually gives a reliable estimate of permeability. For P* determination, cylindrical-flow analysis is preferred because it focuses on late-time buildup data. However, the cylindrical-flow analysis has its drawbacks. Late-time data crucial for cylindrical-flow analysis, especially in low-permeability formations, but long testing periods are not desirable because of potential tool {open_quotes}sticking{close_quotes} problems. Even on long tests, the cylindrical-flow period may not occur or may not be detectable on WFT. When it does occur, permeability estimates derived from the cylindrical-flow period may be incorrect and their validity is difficult to judge. We introduce a new analysis technique that simplifies the interpretation of WFT pressure-transient data. The theory is based on the geometric factor concept, which is equally valid for drawdown, stabilized flowrate, and buildup data. The technique is less sensitive to data quality than other methods, does not require long buildup periods for low-permeability formation testing, and can be implemented with a simple graph of pressure vs. formation flowrate, from which both near-wellbore permeability and P* are readily determined. Three numerical simulation cases are set to test the theories of spherical, cylindrical, stabilized drawdown and the newly introduced pressure vs. flowrate analysis techniques. Occurrence of these flow regimes are tested by comparing their predicted slopes with the slopes of simulation run data.
- OSTI ID:
- 471908
- Report Number(s):
- CONF-961003--
- Country of Publication:
- United States
- Language:
- English
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