Gas-Lift Design: Importance of Well/Reservoir Full Life Cycle Consideration and Analysis

This paper discusses how production rates can be sustained and further increased from an indepth gas-lift design that considers the holistic properties associated oil and gas Well production lifecycles. An example is shown of a Well 58 in a field onshore Nigeria which was shut-in for 2-days as part of scheduled Field shut-down. After several failed attempts to restart the Well post shut-down period, lessons learnt analysis indicated that while the affected Well had all the required gas-lift system installed, it's inability to flow may have been due to inadequate gas-lift design that did not account for the full life cycle of the reservoir, Well and surface facilities. A major re-analysis is carried out on the gas-lift design technique, this time capturing key requirements and the resultant proposal is discussed in detail. The proposed gaslift design optimizes the depth of gas injection with consideration given to the latter production phase of the the Well. Through the example of Well 58, this paper outlines and proposes a checklist of recommendations for gas lift design for new Wells and re-working or workover of existing gas-lift installations from which Well performance can be sustained and optimized. Even if quality gaslift-production results can be achieved through a wide range of other activities such as; special training for production operators, optimizing gas injection rates, modifying surface piping systems, identifying and replacing defective wireline-retrievable gas-lift valves, the most important variable that will ensure the full benefit of the above listed range of activities is the improved gas-lift design technique. Although Well 58 was revived via unconventional methods, the recorded 3-week downtime and the associated financial losses could have been avoided if an adequate gas lift design as proposed in this paper was explored during the Well planning and completion.