Optimizing Gas Lift Performance in Mature Brown Fields

Abstract

The introduction and optimization of gas lift systems is a critical intervention for enhancing hydrocarbon recovery and extending well life, particularly in brownfield and late-life assets. Within the context of Wells, Reservoir, and Facilities Management (WRFM), gas lift systems have consistently demonstrated value beyond marginal gains. Sustaining enhanced recovery from mature wells is strongly influenced by key design parameters such as injection pressure, injection depth, gas rate, valve type, and valve sizing. In the Niger Delta, many development and producer wells are in brownfield assets that have produced for over forty years. Over extended production periods, increasing water cut and reservoir pressure depletion commonly lead to vertical lift challenges and eventual productivity decline. In several such wells, gas lift implementation has proven effective in mitigating these declines. The scalability of gas lift systems from manually operated facilities to fully automated configurations with real-time monitoring and autonomous gas metering allows optimization of cost versus benefit on a well-by-well basis. Field QT is an onshore oil producing asset in the Niger Delta discovered in the 1960s, with production commencing in the early 1970s. The producing reservoirs exhibit strong aquifer support and permeabilities ranging from 200 to 2000 mD. Routine well testing identified eight wells producing below potential, comprising five gas lifted wells and three naturally flowing wells. In the gas-lifted wells, gas recycling occurred due to injection points being shallower than the dynamic fluid level. Conversely, the naturally flowing wells experienced increasing water cut, presenting an opportunity for productivity improvement through gas lift deployment. Nodal inflow and outflow performance analysis was used to optimize gas lift design, including valve sizing, injection rates, and depths. Surface gas lift line repairs were identified where required. Gas lift valve changeouts, orifice deepening, and Venturi orifice installations were executed via wireline on all eight wells. Testing of four wells delivered approximately 1,100 bopd incremental oil, generating approximately USD $13 million in free cash flow. This paper demonstrates the value of targeted gas lift optimization in arresting productivity decline in brownfield assets.