Technology Update: Rethinking Gas Lift Intervention

Abstract

Technology Update Gas lift is an artificial lift technique used in wells in which the natural reservoir pressure is insufficient to deliver fluids to the surface in the initial production stage or has depleted to the point of being incapable of bringing fluids to the surface. Gas is delivered from surface-based compressors by way of the annulus between the casing and production tubing to a series of gas lift mandrels (conduits), which are positioned at strategic points within the production tubing string. When a predetermined gas pressure is reached, valves that are set within the mandrels open, causing gas to be “injected” into the production tubing, thus reducing the density of produced fluid and enabling flowback to the surface. Various types of valves are used in gas lift mandrels, depending on the need of the well. These valves are typically preinstalled and deployed with the production tubing string during well completion and may need replacement later in the life of the well. This will require an intervention. When designing a gas lift completion, engineers must consider a range of factors such as the availability of gas and the infrastructure on surface to process and deliver the gas into the well. Placement of the mandrel within the completion string is also critical when planning for production optimization and future intervention strategy. The industry remains cautious when designing gas lift completions, tending to place gas lift mandrels in areas of the well that are considered accessible when using standard slickline techniques. Most operators, if possible, place mandrels at no more than a 60° deviation within the completion string. However, this approach can lead to a suboptimal gas lift completion, with the benefit of optimizing production rates, by placing mandrels at greater true vertical depth, sacrificed for ensuring the ease of intervention access. Effective gas lift remediation has been a major challenge for the well intervention service industry and has not advanced significantly in terms of technique or operational efficiency. Slickline tools and methods are generally the same as those used when gas lift was introduced to the market about 40 years ago. Kickover tools deployed by slickline are used to undertake the vast majority of gas lift valve maintenance. The kickover tool is attached to the bottom of a standard tool string, which includes stem (mass) and mechanical jars that are positioned just above the tool. The mechanical jars deliver a critical upward and downward shock load during valve setting and retrieval. The tool string may also include power jars to deliver a significant upward jarring force when retrieving valves, if required.