Gas Well Deliquification Assessment and Nag-To-AG Compression Opportunity – Resolving Liquid Loading Issues in Gas Cap Blow Down Development and Salvaging Value via Second Stage Compression
Authors: Ogbunude Basil , Udobata Uchenna , Muzan Eelah , Maxwell-Amgbaduba Sunday , Okereke Onyedikachi , Alaka Olanrewaju , Barka Chiroma , Nanpan Monday , Laoye Abiodun 
Published: July 2023

A hallmark of the optimal development of hydrocarbon fields is sustenance of production plateau over the life of the wells. This becomes challenging as wells approach terminal production stages due to high water production, reservoir pressure decline, high gas or condensate production, etc. These issues are relatively easier to resolve for oil wells with typical WRFM activities such as water shut offs and reperforations. WRFM activities for gas wells at late life production are more challenging and typically involves resolution of liquid loading issues and reservoir pressure decline.

Gas reservoirs typically experience significant reservoir pressure decline over time (up to 75% observed in the study field) in the absence of an energy recharge system. Water-drive gas reservoirs benefit from sustained reservoir pressure, but they are more susceptible to early water breakthrough which negatively impacts overall recovery. In most cases, the combination of liquid loading and reservoir pressure decline negatively impact the wells, leading to a more complex production challenge requiring detailed assessments and solutions. The liquid loading effects in gas wells reduces the overall recoverable volumes due to early liquid breakthrough which leaves some bypassed gas behind. In many cases, the liquid loaded wells become more difficult to lift as the wellhead pressures drop below the facility inlet pressures, rendering the impacted wells unable to flow.

Komu field has been in production for over 20 years, with &gt;3.5Tscf of gas already recovered from a gas-cap blow down project, including 7 years of compression. Gas production decline and liquid loading necessitated a full well Deliquification study to assess the performance improvement options for these late-life gas wells. This includes velocity strings, foam lifts, gas lift, pumping, water shut-off, intermittent production & compression, with the ultimate aim of achieving reduced tubing head pressure and/or critical rate and increasing well capacity. The assessment and selection of optimal solutions were based on reservoir & well parameters and ease of execution. Subsurface modeling indicated second stage compression, via a lower inlet-pressure nodal compressor or wellhead compressors, presented the best option for additional gas recovery, though at potentially prohibitive costs. Further inventory review presented the opportunity to revamp two existing Associated Gas (AG) compressors in Komu field and convert them to NAG compressors, significantly reducing the cost implications of the option. This paper details the integrated evaluation carried out to select the optimal solutions in the development of an AG-to-NAG solution in Komu field and prescribes the opportunity realization strategy for maximum value addition to the asset.