#DRAWDOWN TEST PROCEDURE SKIN#
#DRAWDOWN TEST PROCEDURE SIMULATOR#
#DRAWDOWN TEST PROCEDURE FREE#

A suite of four problems is presented to illustrate these results. Several more » calculations were performed which demonstrate these errors in interpretation. This assumption can lead to dramatic errors in the permeability data if, in fact, there is multiphase flow during the test. Classical well-test interpretation assumes that only a single phase is flowing during the test. Pressure drawdown and build-up well-tests are performed to acquire permeability data for the reservoir. The computer model is capable of handling a single-phase liquid-water system or a multiphase liquid/vapor system. QUAGMR solves the equations of heat flow and unsteady Darcian fluid flow in one, two, or three space dimensions.

#DRAWDOWN TEST PROCEDURE SIMULATOR#

« lessĬlassical well analyses were performed using Systems, Science and Software's Quasi-Active Geothermal Reservoir simulator (QUAGMR). However, if the well is strongly influenced by cleanup effects, either gradual or abrupt, then this is more likely to be recognized in well-test data. Such a reduction can also produce a constant or nearly constant bottomhole pressure during a period of constant-rate production, thus giving the impression of a steady-state or nearly steady-state condition in the reservoir.

#DRAWDOWN TEST PROCEDURE SKIN#

An important observation in this paper, is that a small gradual reduction in the effective skin factor during a drawdown period, if interpreted as part of the reservoir response, can lead to a gross overestimation of flow capacity and skin.

#DRAWDOWN TEST PROCEDURE FREE#

Moreover, if buildup data, or other well-test data free of cleanup effects, are not available, then repetitions of such segments can be used to estimate the flow capacity of the formation and the rate of well cleanup. It is also shown that if the skin effect stabilizes at constant values within the general more » trend during a drawdown period, then segments of pressure data consistent with buildup data should be detectable. It is shown that data influenced by a stable cleanup trend can be modelled by including a simple hyperbolic expression for the skin factor in solutions for wells with constant skin.

The methods are based on both analytical and empirical observations, with field cases included to verify the applicability of the results. Methods are introduced to analyze well-test data influenced by variable skin and cleanup effects, with emphasis on problems concerning verifications of consistency in the wellbore pressure behavior during drawdown and buildup periods. In all cases, we have shown the synergy between the results of the two tests. These examples include a short-duration onshore DST, a gas-lift well-test involving a gas vent period, a long-duration production test with a suspected pressure-sensitive rock properties, and a slug/closed-chamber test. We present field examples from various scenarios to show the usefulness of this approach. Third, the new rate history is used to reinterpret buildup data. The reconstructed rate history is then used to perform the variable-rate (convolution) analysis of drawdown data. From this study, it is concluded for the types of production rate declines most likely to be encountered during gas-well pressure drawdown testing, the Winestock and Colpitts procedure for analysis leads to acceptable estimates of reservoir and well = model. Their proposed method and the reason for the method were reviewed. The purpose of these investigations was to find the limits of applicability of the Winestock and Colpitts method.

Winestock and Colpitts showed that both problems could be avoided if gas-well drawdown tests were run with a fixed choke. However, in practice, the theoretical requirement that flow rates must be maintained strictly constant during the test has led to 2 major problems: (1) the constant flow rate requirement is frequently ignored, and use of conventional analysis on such tests has led to serious error in many cases, leading to a loss of confidence in drawdown testing or (2) the constant flow rate is maintained, but only with great difficulty. Use of pressure drawdown tests to characterize gas wells has long been accepted, in principle, to be an excellent formation evaluation technique.

Drawdown test procedure