Design and Installation of a High-Pressure Gas Cycling System

Abstract The Gillis-English Bayou field is ahigh pressure gas reservoir locatedapproximately five miles north ofLake Charles, La., in CalcasieuParish. The field was discovered by SunOil Co. with the drilling of the LayneLouisiana Co. Well No. 1 in Dec.,1961. Sun Oil and others have drilleda number of wells in this reservoirin the last four years. Since thereservoir was found to be a gas phaseaccumulation, which had severeretrograde condensation characteristics, a gas cycling program was begun toobtain maximum liquid recovery. Agas cycling unit called the UpperHackberry Unit was established byorder of the Louisiana Department ofConservation in Nov., 1964. The need to inject gas in the wellswhich had tubing pressures of 5,000psi presented mechanical designproblems previously not encountered bySun Oil in the Gulf Coast Division. Extensive investigation revealed threeor four places in the southern UnitedStates where injection compressorswere being operated at the highpressures expected in this project. Production control of the wells, processing of the gas and oil for injectionand sale, respectively, and safe, unattended operation of the entirefacility and associated properties wereall factors considered duringplanning of this program. This paperdescribes design considerations and theparticular items of equipment used toaccomplish the gas cycling programwhich has been in operation forapproximately one year. Introduction The Upper Hackberry reservoir ofthe Gillis-English Bayou field hasfour sands occurring in threelocalities, or a total Of nine sandaccumulations, all in pressure communicationand Comprising a single reservoir. These sands occur between twounconformities and are productive atdepths ranging from approximately9,750 to 10,020 ft (Fig. 1). Bottom-hole pressure data andanalyses of recombined reservoir fluidsamples indicate the reservoir fluid tobe in a vapor phase with a 7,000-psidew point. Further, there is noindication of a significant water drive inthe reservoir. Reservoir fluid analyseshave indicated severe retrogradecondensation. This, in conjunction withthe depletion-type drive mechanism, will result in 84 per cent loss ofinplace reservoir liquids which wouldrepresent a 13 million bbl loss ofliquids if preventive measures were nottaken. To prevent these losses, SunOil decided to instigate a gas cyclingprogram. Parties with an interest inthe reservoir were contacted during1963 and advised of Sun's programand plans to establish a LouisianaDepartment of Conservation unit forthe purpose of gas cycling. A formalhearing was held in Sept., 1964, andthe resultant order was issuedeffective Nov. 1, 1964; gas cycling wasinitiated Jan. 24, 1965. JPT P. 1286ˆ