A new approach for evaluating well deliverability in ultra-thick gas reservoirs

• We derived a pressure drop formula with varying mass flows in wellbore.
• We proposed a new set of deliverability equations for gas wells in ultra-thick layers.
• The impact of varying mass flow along wellbore is incorporated in the proposed deliverability equations.
• We derived testing methods suitable to gas wells in ultra-thick gas reservoir.
• We validated deliverability equations and testing method with case study.

Despite the recent activities in ultra-thick gas reservoirs worldwide, accurate evaluation of gas wells deliverability remains technically challenging. The success of such evaluation efforts relies heavily on proper consideration of the impact of ultra-thick pay zones. Deliverability equations and corresponding test methods are necessary to predict the deliverability of gas wells in ultra-thick gas reservoirs. In this paper, we develop a new model for calculating the pressure drop along the wellbore with varying mass flow rates from gas production profile testing. A new set of deliverability equations is proposed for gas wells in ultra-thick reservoirs. The new equations incorporate production testing data and are applicable to a wide reservoir pressure range. Correspondingly the deliverability test method for ultra-thick gas reservoirs was proposed. The integrated approach of utilizing deliverability equations and the proposed test method were validated against reservoir simulations that incorporate wellbore pressure drop. Good agreements between simulation and current analytical results were obtained for both low-pressure and high-pressure gas reservoirs. It is appropriate to apply the proposed deliverability equations and the corresponding test method to predict the deliverability of ultra-thick gas reservoirs. Further, validations using field data are in progress.