This paper presents a new method, successfully implemented in March 1990, of operating Gonelle field wells in Gabon. Permanent actions of a programmable logic controller in Permanent actions of a programmable logic controller in respect to an expert logic ensure continuous production of the wells with a minimum gas injection rate.
A sharp production increase has been possible despite a simultaneous decrease in gas consumption.
Gonelle is an offshore gas-lifted Gaboneese field. Wells are located on 2 platforms. The main 12-well platform is close to the treatment platform; The complementary 6-well platform is about 2 km (1 mile) away. Living quarters are more than 10 km (6 miles) away from the field. Gas-lift gas comes from another field through a sea-line.
The reservoir is water driven and has been producing since 1976 from unconsolidated sands. Sand control is used on each well and any risk of high instantaneous production rate must be prevented. This risk leads to a permanent choking of the wells that strongly reduces gas-lift efficiency.
Productivity of the wells is declining as the field becomes Productivity of the wells is declining as the field becomes older. The production rate is difficult to maintain even with increased gas consumption. At the same time, available gas is decreasing.
The content of CO2 in the fluid is high and a corrosion inhibitor is injected into the gas-lift gas. Sea temperature is close to hydrates formation point. The additive in the gas and the gas quality plug partially or even fully the gas chokes. Their geometry emphasizes this plugging when the injected gas rate is decreased.
Trouble on the wells and production losses are frequent. Increasing field production therefore requires:* effective control over gas injection on each well;* opening of chokes while limiting instantaneous production rate.
The gas-lifted well operation is based on adjustments that are achieved from the surface. Injected gas is the main adjustment, production choke at tubing head is sometimes also used. production choke at tubing head is sometimes also used. These adjustments have two main purposes: to steady conditions and afterwards to obtain the production target. Steady conditions are the result of two steps - start-up and stabilization.
Well start-up is a transitional phase; production rate irregularities occur and injected gas needs are specific.