Critical Evaluation of Existing Methods for Accounting for Multiphase Effects AroundProducers in Depleting Gas/Condensate Reservoirs

摘要

Well test analysis techniques use variations of thepseudopressure concept to account for multiphase effects dueto condensate drop-out in near-well regions (e.g. Jones andRaghavan 1 approach). In this work, an evaluation of theaccuracy and applicability of these techniques was carried outusing data from the discovery well of the Cupiagua field,including well testing, relative permeabilities (Kr) measured atlow capillary number and a tuned PREOS.Henderson et al’s capillary number dependent relativepermeability and effective inertial resistance correlations 2 , asimplemented in a commercial simulator, were used to historymatch the well test data. To investigate the assumptions in theanalytical models, numerical simulations were run, first withconstant Kr, and then with the effect of capillary number andinertial resistance.The main conclusions are:1. For the constant Kr simulation, a constant compositionexpansion (CCE) data of the flowing compositionaccurately reproduces the pressure-saturation relationshipin the region where both oil and gas are mobile. However,contrary to Fevang and Whitson’s assumption 3 , theconstant volume depletion (CVD) data did not match thesaturation distribution of the region where only gas flows.2. When Kr dependence on capillary number and inertialresistance was considered, the immobile oil regionpractically disappeared. In consequence, the CCE data ofthe original fluid composition can reproduce the pressure-saturationrelationship in the two phase region.3. Al-Hussainy et al’s total skin versus rate plots 4 to obtainmechanical skin figures were found to give results similarto those obtained by numerical simulation.In summary, this work identifies clearly the conditionsunder which the analytical models are not correct, which data should be used for analysis, and when the numerical instead ofan analytical approach is required.