Wellbore effects on pressure transient analysis

The knowledge of wellbore effects is essential for the proper interpretation of well testing data. This work considers wellbore effects on closed chamber tests and pressure buildup tests.;An analytical expression is derived for the overall wellbore storage coefficient for a closed chamber test (CCT) in an oil well. This allows the correct wellbore boundary condition to be written which suggests that a version of pseudotime can be used to correlate the CCT solution with the corresponding slug test solution. In many realistic cases, the pseudotime correlation is applicable and thus pressure data from a CCT can be analyzed using several available slug test analysis techniques. The new pseudotime is also applicable to analyze slug test data influenced by a step change in the wellbore storage coefficient.;This work also presents new methods for the analysis of gas-well, closed-chamber tests. It is shown that pseudopressure and pseudotime can be used to correlate gas-well, closed-chamber test results with the analogous liquid, slug-test solutions. This allows data from a gas-well CCT to be analyzed using liquid slug-test analysis procedures. Multirate analysis techniques were found to be applicable to gas-well, closed-chamber tests in terms of pseudopressure and time, not pseudotime.;A drift-flux model is formulated to simulate wellbore phase redistribution and to investigate its effect on pressure buildup data. This model rigorously treats well-bore and reservoir flow interaction and accurately handles the effect of interphase mass transfer through the black-oil approach accounting for a variable bubble-point pressure. The investigation reveals that buildup tests influenced by wellbore phase redistribution can show an increasing or a decreasing wellbore storage coefficient. The variation in the wellbore storage coefficient is affected by both phase segregation and gas compression. If the magnitude of afterflow is small after the end of wellbore phase segregation, pressure buildup data will show an increasing wellbore storage coefficient at the end of the test. If afterflow is still large after complete phase segregation, the gas column will be compressed due to afterflow and the pressure buildup data will show a decreasing wellbore storage coefficient.