Computer Control of High-Pressure Sour Gas Wells, Kaybob South BHL Gas Unit No: 3

Abstract

Abstract This paper describes the computer- controlled supervisory and control system which was installed to measure and control production tram and injection into the gas wells of the Kaybob South Beaverhill Lake Gas Unit No. 3. Items to be covered include: reasons for installation of an automation, scheme in this field, initial configuration of the system, field installation and start-up, changes that have been made and an assessment of the systems performance after one year of operation. Introduction THE KAYBOB SOUTH BEAVERHILL LAKE GAS UNIT No. 3 is located approximately 130 miles west of Edmonton. The plant, which is one of the largest gas plants in North America, is located centrally in the 12- by 6-mile field. The terrain in this area is heavily wooded and has high relief, with ground elevations ranging from 2600 to 4150 feet above sea level. Temperatures at the Kaybob plant range from -50 °F in the inter to +80 °F in the summer. Precipitation averages 75 inches of snow in the winter and 30 inches of rain in the summer. The plant was designed for an inlet rate of 445 MMcf/D of very rich, sour gas, yielding a daily output of 3,065 long tons of elemental sulphur, 32,720 barrels of pentanes plus, 17,950 barrels of LPG's and 284 MMcf of dry residue gas. Of the residue gas, 54 MMcf is sold and the remaining 230 MMcf is re-injected into the formation in a recycling scheme designed to enhance the recovery of pentanes plus and sulphur. Prior to plant start-up, the well count was 37 producing wells, 11 injection wells and one well that could be used as either an injector or a producer. The effluent from the producing wells is carried as two-phase flow through lateralpipelines to one of the three-trunk lines feeding the plant. These gathering lines operate at pressures of 1200 to 1500 psig and temperatures of 90 °F to 150 °F. At these conditions, the liquid hydrocarbon ratio is as high as 150 barrels per MMcf of gas. The residue gas from the plant to the reinjection wells is carried in a three-trunk line to lateral sy.3terns operating- at a maximum discharge pressure of 4700 psig at the plant. Reasons for Automation At Kaybob South Operating problems within the gas plant make frequent cuts in plant inlet rate necessary. This could be accomplished by reducing the producing flow rates or diverting part of the inlet gas to flare. If consideration is given to pollution of the environment and conservation of energy resources, it is obvious that flaring of inlet gas is not acceptable. A method of reducing well flow rates that is used by many gas plants is to increase the, back pressure that the plant exerts on the gathering system. Two-phase flow in pipelines installed in hilly terrain produces liquid heads wherever the flow is uphill. The amount of liquid build-up increases as the flow rate is reduced, up to the point at which the liquid starts to move as a slug.