Design of a High-Pressure Research Flow Loop for the Experimental Investigation of Liquid Loading in Gas Wells

Abstract

Existing models to predict and analyze liquid loading in gas wells are based on steady-state flow. Even when transient-multiphase-wellbore models are employed, steady-state or pseudosteady-state inflow-performance relationships are used to characterize the reservoir. A more-reliable approach consists of modeling the dynamics in the near-wellbore region with its transient boundary conditions for the wellbore. The development of new models to mimic the dynamic interaction between reservoir and wellbore requires a purpose-built flow loop. We have developed a design to construct such a facility. This new facility will be the first to integrate pipe representing the wellbore with a porous medium that will fully mimic the formation surrounding the wellbore. This design will account not only for flow into the wellbore, but also for any reverse flow from the pipe into the medium. We used integrated wellbore/reservoir system analysis to screen the parameters required to recreate liquid loading under laboratory conditions. Our results suggested using a compressed-air system with a discharge pressure between 470 and 650 psi with gas rates of 400 to 650 scf/min along with water injected at a rate of 100 gal/min. Once the range in operating conditions was defined, the equipment and mechanical components for the facility were selected and designed. Our results showed that three reciprocating compressors working in parallel provide the smallest, most economic, and most flexible configuration for the TowerLab facility at Texas A and M University (TAMU). The design of the pressure vessel hosting the porous medium will require a cylindrical body with top- and bottom-welded flathead covers with multiple openings to minimize weight. The required superficial velocities for air and water indicate the system will need independent injection into the porous medium through two manifolds. Optimally, the system will use digital pressure gauges, coriolis or vortex technology to measure air flow, and turbine meters for water flow. A joint-industry project (JIP) on liquid loading in gas wells was initiated in January 2009, which includes the implementation of the proposed design for the TowerLab facility to generate experimental data that will significantly improve our ability to mimic the physics of multiphase flow, and so develop and validate flow models for the characterization of liquid loading in gas wells. It is anticipated that a preliminary version of the new loop, including an inlet multiphase-flow pump, has been assembled and will be operational early in Fall 2010, with plans for the full design to be implemented in 2010-11.