In 1999, C-FER completed a project, on behalf of Chevron, that showed that a GL-JP system can achieve measurable increases in production rates, compared to conventional continuous gas lift, when conditions are favorable. The Inflow/Outflow Performance Relationship (IPR/OPR) curves show how this is possible. The top OPR curve indicates the tubing pressure, at the gas injection location, for a continuous gas lift (GL) system. It also indicates the discharge pressure (Pd) for the jet pump in a GL-JP system operating with the same gas injection rate. The lower OPR curve indicates the suction pressure (Ps) for the jet pump in a GL-JP system under these conditions. While the operating point for a continuous gas lift system is indicated by the intersection of the IPR with the top OPR, the operating point for the GL-JP system is indicated by the intersection of the IPR with the lower OPR.

The primary objective of the project was to assess the feasibility of this GL-JP technology on the basis of theoretical analyses of equipment performance for varying well conditions. The work scope included developing a representative system model for a GL-JP system and completing sensitivity analyses, using the model, to bracket system performance as a function of: (1) jet pump efficiency; (2) lift gas injection pressure; (3) reservoir pressure; (4) productivity index; (5) water cut; and (6) GOR.

The results were presented at the 2000 Gas-Lift Workshop, which was held in New Orleans, LA, February 15-16, 2000. A good match between the system model predictions and reported production data for select Chevron wells was achieved.

In general, the following reservoir and gas lift system characteristics were found to be favorable for achieving incremental production with a GL-JP system: low reservoir pressure, the ability to increase lift gas injection pressure above current injection pressures, the ability to inject at higher gas lift rates, and moderate GOR.

As such, the system was found to be advantageous in mature field applications where the original reservoir pressure has declined and the available lift gas injection pressure is higher than the one required to inject at the bottom of the well.

Sensitivity analyses also showed that variations in jet pump efficiency have a large affect on production potential. Thus, to be able to benefit from this technology in a particular application, it is important to ensure that the maximum possible efficiency is achieved, through optimum selection of the jet-pump geometry. However, a method to accurately estimate the pump efficiency as a function of pump geometry and operational conditions is not available yet. Therefore, it appears that the GL-JP technology has sufficient merit to warrant further investigation.

Contact: Kelly Piers, Manager, Production Operations

Tel: 780.450.8989 x246