Transient Pressure Analysis for a Vertical Gas Well Intersected by a Finite-onductivity Fracture

摘要

Pressure-transient analysis for gas wells has a greatimportance in the oil and gas Industry. Transient pressureresponses of unfractured and hydraulically fractured gas wellsmay be affected by non-Darcy flow near the wellbore, suchimportant effect needs to be taken into account whenestimating reservoir and well parameters. An additionalproblem encountered in gas wells test analysis is the presenceof the rate-dependent skin, which requires a search for anotherparameter (non-Darcy flow coefficient).Several tests are performed in order to measure thedeliverability of gas wells and to describe reservoirperformance. Such specific tests as flow after flow, isochronaland modified isochronal were initially designed to obtain theabsolute open flow potential of a well, however, the use ofthese tests has been extended to obtain additional informationfrom the reservoir. Drawdown tests are focused in obtainingsuch data as wellbore storage, reservoir transmissivity, skinfactor, flow efficiency and system geometry. Buildup testslead us to the average pressure of the reservoir, however,proper analysis of buildup test provides values ofpermeability, wellbore storage and apparent skin factor.Buildup and drawdown tests are currently analyzed usingtype-curve matching procedures, which involves trial anderror and conventional techniques.Pseudopressure concept, which was used in this study, hasshown to provide sufficient engineering accuracy in dealingwith gas well test data. This study utilizes characteristicpoints, intersection and lines found on the pseudopressure andpseudopressure derivative plot to obtain fracture length,fracture conductivity, skin factor and reservoir permeability.It was found that changing the non-Darcy factor, D, theshape of the pseudo-pressure curve varies from the originalgas curve shape at D=0, which implies that an additional skin effect is added at high rates. On the other hand, the pseudopressurederivative curve remains on its original shape, then,in spite of increasing non-Darcy effect factor, D, the pseudopressurederivative curve is not affected by this additional skineffect added to the system because of the non-Darcy floweffect. The interpretation technique was successfully testedwith simulated and field examples.