This paper describes the processes and results of an extensive gas-lift optimization effort executed at the field level in South Pass Block 24 (SP24) of the Gulf of Mexico. The processes described herein include data gathering. problem identification, and problem resolutions which resulted in a 50% reduction in lift gas requirements.
In 1991 SP24 was operating at maximum compression capacity of 105 MMscf/D with numerous wells routinely shut-in due to unavailable lift gas. With the goal of increasing production by reducing shut-ins, a gas-lift optimization effort was initiated to review and modify lift gas allocation. Optimal allocation maximizes profitable utility of available compression capacity.
During the process of obtaining data to optimize allocation, it became evident that most wells were being over-injected mainly to reduce heading problems. At this point the focus shifted away from a constrained allocation problem to the task of eliminating heading problems and minimizing lift gas requirements.
SP24 is located in East Bay along the Mississippi River's Southwest Pass about 80 miles southeast of New Orleans. Initial development of the field began in the early 1950's. About half of SP24 is located in marshlands with the other half of the field in the bay's open, shallow water.
SP24 was developed mostly with single-well jackets tied back to two-phase processing platforms. Gas separated at the processing platforms flows to the Central Facilities located along the river bank where it is dehydrated and compressed for sales and gas-lift needs. Roughly half of the liquids separated at the processing platforms flows to a FWKO platform for water separation; the separated water then flows to a water treating plant at the Central Facilities, and the oil flows to a tank facility for final processing. The other half of the liquids simply flows directly to the tank facility for water separation.
The field has roughly 200 gas-lifted producers averaging 90+% water cut. Most wells have sidepocket gas-lift mandrels spaced down to the packer and are equipped with 1" pressure-operated gas-lift valves with an orifice installed at the point of injection. As a result of being developed from single-well jackets, the majority of wells are near vertical which allows for relatively simple wireline operations.
On the surface, all wells have positive chokes with most bean sizes at or near 64/64". Each well is equipped with a Willis controller to adjust the lift gas rate and a three-pen Barton recorder which measures tubing pressure, casing pressure, and differential for calculating lift gas rates.
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