Microprocessors Play a Major Role in Optimizing the Intermittent Gas Lift System in the Ventura Avenue Field

Abstract

Summary Microprocessor-assisted programmable controllers have been installed as time-cycle control devices in Getty Oil Co.'s intermittent gas lift operation in the Ventura Avenue field. Electric clock intermitters located at each well site were replaced by centralized programmable controllers. intermittent gas lift cycles for 125 wells are now controlled by nine programmable controllers that use microprocessors as the timekeeping mechanism. With accurate control by the programmable controllers and the use of a specially designed computer program. individual well gas lift cycles are scheduled so that the demand for compressed gas at the compressor station is constant. A constant demand for compressed gas has eliminated compressor discharge rate and pressure fluctuations, therefore providing more efficient gas lift operations. In addition to accurate control of gas lift cycle timing, the centralized programmable controllers offer a much faster method of changing cycle length and cycle frequency. It is now more feasible to experiment with combinations of cycle length and frequency for each well to achieve the optimum gas-liquid ratio (GLR). As a result of more efficient well operations, the total system efficiency has improved, and compressor fuel gas requirements have dropped significantly. Introduction The Ventura Avenue field is located in southern California approximately two miles north of the city of Ventura in Ventura County (Fig. 1). Getty Oil Co. operates that portion of the field located at the east of the riverbottom area portion of the field located at the east of the riverbottom area of the Ventura River. The Ventura Avenue field produces from two major zones or "blocks"-C Block and D Block. Wells completed in C Block produce from depths between 5,000 and 8,000 ft [ 1.5 and 2.4 km]. D Block wells produce from 8,000 to 13,000 ft [2.4 to 4.0 km). The development of the D Block zones began in 193 1. Early development was rather slow owing to deep drilling problems, but active development continued into the early 1960's. Wells usually came in flowing at 200 to 900 BFPD [32 to 143 m3/d fluid] and continued to flow for 7 to 10 years. It was for these D Block wells that the current gas lift system originally was developed. Not only was there plenty of produced gas to be processed as fuel for the gas-fired compressor engines, but there was also plenty to be used in the compressors as recycle gas. The plenty to be used in the compressors as recycle gas. The wells were produced originally on continuous lift. but as production rates declined, intermittent lift proved to be production rates declined, intermittent lift proved to be more economic. D Block currently produces approximately 9,000 BFPD [ 1431 M3 /d fluid], 5,800 BFPD [922 m 3/d fluid] by rod pump and 3.200 BFPD [509 M3 /d fluid] by intermittent gas lift. Waterflood operations recently were initiated in D Block, although approximately 72 % of the current D Block production is still considered primary production. Many waterfloods ultimately will be primary production. Many waterfloods ultimately will be required to develop D Block because of numerous fault blocks and massive zone thickness (greater than 1,000 ft [300 m] in some wells) of D Block. The first D Block waterflood was initiated in Jan. 1980. injection into the second and third waterfloods began in Jan. 1983 and Dec. 1983, respectively. Eleven more potential D Block waterflood projects have been identified potential D Block waterflood projects have been identified for future consideration. A major impact of the waterflooding operations is the expected increase in fluid production and the corresponding decrease in gas production. An analysis was made to estimate the remaining effective life of the gas lift system operation in conjunction with the waterflooding operation. The analysis projected that the fuel gas and recycle gas required to lift the expected fluid volumes will be greater than the produced gas volumes within the next five years. Intermittent gas lift can be less expensive than rod pumping, especially at depths associated with D Block. pumping, especially at depths associated with D Block. For this reason, an investigation was conducted into ways to improve the efficiency of the current gas lift system operation, thus extending the remaining life of the system. The recommendations from the investigation were as follows.Conduct a diligent search for gas line leaks and repair immediately.optimize single-well GLR'S. Recycle gas requirements will be minimized, thus reducing fuel gas usage.Minimize compressor discharge pressure and rate fluctuations. A balanced system must be achieved for maximum system efficiency. On the basis of these recommendations, a search for gas line leaks was carried out. All lines were pressure tested and leaks repaired. Because of the age of the gas JPT P. 696