A Prefabricated And Automated Offshore Gas Production And Dehydration Facility
Authors: Hicks R.H. , McDonald W.M. , Staffel E.O. 
Published: October 2008

Humble Oil & Refining Company has installed its first completely prefabricated and automated production facility in the Gulf of Mexico. An orderly and planned program from design through implementation was employed to achieve an early completion of the project. The 24-well, 120 MMscfd primary gas production and dehydration facility contains certain unusual processing equipment features. O£ special interest are the facility's automated flow control, gas and liquid measurement, and safety limits monitoring.

Designation of single party responsibility, modular construction, and onshore checkout with simultaneous training of design and field personnel resulted in a relatively trouble-free system, saving in offshore installation, start-up time, and costs. With production automation being a relatively new concept, experience indicates that stringent factory testing and close attention to installation and wiring practices be given to automation components.

Introduction

Development of its South Timbalier Block 172 gas field afforded Humble Oil & Refining Company the opportunity to install its first completely prefabricated production facility in the Gulf of Mexico. Also, due to the remote location of the field and the concurrent expansion of Humble's Computer Production Control (CPC) program into all of its operating Divisions, the facility is Humble's first major offshore unit to be equipped for unattended operation. Planned and coordinated efforts of design, contracting, shop inspection, factory testing, personnel training, onshore system checkout, and offshore construction methods were followed to minimize installation and start-up time.

Humble's South Timbalier Block 172 gas field (Figure 1) is located 57 miles southwest from Humble's nearest land base at Grand Isle, Louisiana, 35 miles from the nearest shore, and 22 miles from Humble's closest other operations in the South Timbalier Block 54 field. In final form, the field facility (Figures 2 and 3) consists of a 70 ft. × 150 ft., two-deck drilling platform and a 60 ft. × 60 ft., two-deck production equipment platform joined by a 100 ft. long bridge and served by a 1000 ft. long, 12 in. diameter emergency flare system. Two 8 ft. × 32 ft. wellhead skid units containing individual well stream heat exchange, flow control, and header equipment and a skid-mounted control building are located on the cellar deck of the drilling platform. The facility is served by an 18-in. diameter gas transmission pipeline and a leased telephone circuit to Humble’s CPC computer center in New Orleans, Louisiana.

Nominal design capacity of the production facility is 120 MMscfd. Gas production is from 24 well completions producing from reservoir sands between 4,000 and 7,000 feet in depth. Low hydrocarbon liquid production averages only about 3.5 Bbls/MMscf with total platform condensate being recombined with the gas in the transmission pipeline. Platform operating pressure is 1200 psig with gas dried to a dewpoint of 25° F and condensate water content maintained to less than 0.1 percent. Recent peak gas sales rates have been 150 MMscfd. In addition to certain unusual processing equipment features, of special interest are the facility's automated flow control, gas and liquid measurement, and safety limits monitoring.