Daily Monitoring Reduces Cost of Production in Marginal Wells

Abstract

The economics of a marginal well is highly sensitive to the price of oil and cost of production. Without improvements to production efficiency, marginal wells often must be shut down or risk operating at a loss. Because rod-pumped wells correspond to this pattern, with many of the wells producing less than 10 BOPD, a 4-year system-development effort was undertaken by Petrolects, a California-based engineering consulting firm, and Bakersfield-based independent producer Vaquero Energy to improve production efficiency. The Marginal Expense Oil Well Wireless Surveillance (MEOWWS) oil-production monitoring system is the result of this development effort, primarily funded by the U.S. Dept. of Energy. The system allows marginal wells to be economically monitored daily, allowing operation with near-optimal efficiency. Detection Methods During the first 2 years of the study, small, self-contained, wireless vibration sensors were attached to different sections of rod pump units. Signals induced by vibration of the pumping unit during fluid pounding were transmitted to a base-station computer in the field office. The operator could then identify problem wells by reviewing transmitted data. Statistical analysis of the vibration data was performed, demonstrating that acceleration sensors were able to detect fluid pound when the well was pumped off. Problems encountered during testing of the vibration-detection system included high power usage, which led to short battery life, and the high cost of the sensors. In the third and fourth years of the MEOWWS project, the method used to detect the pump-off condition was re-evaluated in an attempt to overcome the most serious problems encountered during the first phase. Three methods to determine the operating condition of the pumping unit in real time were tested and compared—vibration measurement, acoustic emissions from surface equipment, and flow measurements of produced fluids. Flow measurement was determined to hold the greatest promise for a reliable, economical, easily installed well-operation sensor and was chosen for further investigation. System Development A proprietary method of detecting outflow from a beam pump was conceived by the investigators. The method involves a simple and direct detection of flow through surface piping. A surveillance system was designed to suit the advantages of the flow-detection method: simplicity, reliability, direct monitoring of production, ease of installation, and low cost. The flow sensors are integrated into a well pump surveillance unit (WPSU). Each WPSU contains an inexpensive low-power microcontroller and a 900-MHz spread-spectrum radio modem. The microcontroller interprets readings from the flow sensor, using proprietary software to measure the well’s state of health and the volumetric pumping efficiency. Readings are saved over a period of hours or days. The power requirements of the WPSU are low enough to permit practical battery-powered operation over a period of years without an external electrical supply, eliminating the need for installation of expensive alternating-current power lines or costly and vulnerable solar-power arrays. The WPSU transmits data to a base station located in the field operations office as frequently as is required by the customer’s needs. The system is designed to transmit information on a daily basis, minimizing its contribution to the problem of radio frequency congestion that is increasingly troubling users of supervisory-control and data-acquisition systems. At the base station, readings are compiled by software to a tabular or graphical format that is easily interpreted by operations personnel. Base-station data are made available through a local area network, or across the Internet, by an integrated Web server. Data are also archived for future reference.