Application of Drag Reducing Agent in Pipeline handling High Water Cut Fluid - Case Study from a Mature Field in Mumbai Offshore Region

Abstract

Pipelines are usually considered the most effective and economical means for transporting fluids from satellite wellhead platforms to central processing platforms. However, the actual production from the reservoir during field life could be different than expected due to associated uncertainties in various production phases. As a result, pipeline flow assurance issues are the most common challenges faced in mid-to-late life phase of an oil field. In mature oil fields, water cut increases with time. The total fluid flow through a pipeline may also increase due to better reservoir deliverability than expected, infill wells opportunity, workovers, zone change, gas lift deepening, etc. An increase in total fluid content causes a higher frictional pressure drop in the pipeline and increases the backpressure on flowing wells. This detrimentally affects well deliverability at declining reservoir pressure in mature fields. A traditional approach to reduce backpressure on flowing wells is to flow the selective wells in a satellite platform. In short, the risk of increased backpressure can prevent the opening of additional available wells, thereby significantly limiting the production from a satellite platform. Another approach is to lay a new pipeline, but this is capital-intensive and time-consuming option that is often uneconomical in the late-life phase of an oil field. This paper explores a chemical route, the application of drag-reducing agent (DRA), to address the issue of high frictional pressure drops in pipelines. DRAs have traditionally been used in pipelines handling fluid with low-to-moderate water cuts (<50%). However, their application in high water situations (fluid having water cut higher than 80%) have been rare and met with limited success. A trial of a new DRA was carried out in a mature oil field in the Mumbai offshore region. A pipeline handling high water cut fluid (>80%) was selected for this application. This DRA is a long-chain polymer that attaches to water molecules, thereby streamlining the flow. The DRA reduces the frictional pressure by acting as a buffer along the pipe wall to decrease the amount of energy lost in turbulent flow. Application of this DRA in high water cut pipeline lowers the pressure drop with a given fluid flow, enabling the operator to flow additional wells into the same pipeline. This paper discusses the rationale behind the identification of a problem using pipeline flow modeling (using water cut, production rates) and the selection of the appropriate chemical (considering water chemistry), along with the results from a successful field trial. In the future, many mature oil fields will deal with issues like higher water cut fluid flow in a smaller diameter pipeline. In these situations, a drag-reducing chemical can significantly improve overall recovery.