Design, Installation, and Operation of a Large Offshore Production Complex
Authors: Frankenberg W.G. , Allred J.H. 
Published: October 2008

Humble Oil & Refining Company has made operational a high volume oil and gas production system in the Grand Isle area, Offshore Louisiana. The system processes approximately 50,000 barrels per day and has a capacity of 90,000 barrels per day. Gas facilities provide fuel gas for two offshore sulfur mines and compress gas for sales and injection into underground reservoirs.

Notable features of this system include:desanding and associated sand cleaning equipment,a pneumatic control system for gas distribution and failsafe operation,capacitance probes and turbine meters for computerized net oil measurement,check valve system for compounding pumps during production surges,measurement and pumping of gas-saturated crude at 55 psi, anduse of engine waste heat for gas dehydration.

This paper reviews the design concept, process flow, control system, packaging, installation, and operating experience of the facility.

INTRODUCTION

Grand Isle Block 16 is Humble's largest offshore field and in cumulative production is the sixth largest oil field in Offshore Louisiana. This field produces approximately 50,000 barrels of oil and 60 million cubic feet of casinghead gas per day. Secondary recovery projects utilize both water and gas injection. In addition to the oil and casinghead gas, 760 long tons of sulfur per day are extracted by the Freeport Sulphur Company Caminada Mine. Fig. 1 shows the location of the field, about 10 miles south of the Grand Isle base

Until recently, well-head pressures were utilized to flow field production via pipeline to onshore treating facilities. However, increasing producing rates brought on by additional development, reservoir unitization, and higher allowables imposed excessive back pressure on flowing wells through pipeline pressure losses. It became apparent that oil rates would exceed capacity of the two-phase line to shore.

FIELD OPERATIONS

Grand Isle Block 16 Field was discovered in 1948 and has twenty producing platforms, one quarters platform, and one compressor platform in water depths ranging from 40 to 65 feet. The field, which is associated with a piercement type salt dome, produces from approximately 200 active completions, ranging in depth from 6,000 to 13,000 feet. Flowing tubing pressures range from 25 to about 2,500 psi with most being between 500 and 1,500 psi.

Prior to 1968, oil and gas flowed two phase to the centrally located "L" Platform for separation. You will note in Fig. 2 the gathering system to the central facility. Separator oil with its gas in solution then flowed directly to a 12-inch pipeline to Grand Isle. Approximately 8-10 million cubic feet of separator gas provided primary fuel supply to Freeport Sulphur Company's Grand Isle Mine in the adjacent Block 18 Field. The remainder of the separator gas was either injected into reservoirs or compressed and transported via gas pipeline to a Gas Plant at Grand Isle for processing and subsequent sales. By mid-1966, with a field oil rate of 32,000 barrels per day, producing well back pressures were "550 psi at the central gathering platform and 800 psi at remote outlying platforms.