Water-Lift and Disposal Operations in Low-Pressure Shallow Gas Wells

Abstract

Abstract Salt-water removal and disposal from shallow gas wells in the Hugoton and Greenwood gas fields have become an increasingly serious problem. Panhandle Eastern Pipe Line Co. initiated a program to determine the optimum methods for removing and disposing of the salt water. Field test results on gas-lift valves, pumping units, pneumatic pumping units and a differential pressure controller indicated that the pumping unit is the most efficient and economical method for removing the water. Different methods of water disposal have been tried, such as evaporative salt-water ponds lined with vinyl plastic, reinforced concrete or tetra-sodium pyrophosphate for wells producing up to 300 bbl/month. For wells which produce more than this, slim-hole disposal wells are used. Economics of the various systems as well as the efficiency, are discussed. Introduction For the past several years operators have been confronted with ever increasing problems of salt-water removal and disposal from shallow gas wells located in southwestern Kansas, and in the Oklahoma and Texas Panhandles. These low-pressure, shallow gas wells are principally located in the Hugoton and Greenwood gas fields. Several methods of salt-water removal have been investigated through field installations and their results evaluated. Great strides have been made in recent years, and periodically new water-lift methods are recommended and investigated. So far, the pumping unit has proved the most efficient as well as an economical method of removing large quantities of salt water. As more and more water is produced the problem of disposing of the water at the surface becomes more apparent. Panhandle Eastern Pipe Line Co. has several methods of disposal in service at the present time. The evaporative salt-water pond which can be lined with vinyl plastic, reinforced concrete, or chemically treated with tetra-sodium pyrophosphate is satisfactory in this area for wells producing up to 300 bbl water/month. The salt water from wells producing in excess of this quantity is usually disposed of in a slim-hole disposal well. Field Test Results As the reservoir pressure declines, water in the formation encroaches into and near the wellbore. If this water is not removed the gas production will decline to the point where the well "logs off", and has to be blown frequently and for long periods of time to remove the water. This waste of gas is expensive, but new techniques and tools will enable us to eventually prevent this waste. Some four years ago the company began an intense study of all water-lift methods in use at that time. The principal purpose of the study was to determine the efficiency of existing water-lift methods and to investigate all conceivable means of improving the water-lift ratio, which is expressed as the number of cubic feet of gas required to lift 1 bbl of water. A test-separator unit was designed to test problem wells, most of which were equipped with gas-lift installations operated by time-cycle intermitters. The test-separator is connected to the vent line running from the tubing to the disposal pit. When the intermitter opens the tubing at a designated time, the lift gas and water are directed through the test unit where they are separated. The water is measured into a test tank and the gas volume is measured by an orifice well tester and recorded on a 24-hour chart. All wells are tested for a period of from 24 to 72 hours so an accurate and representative water-lift ratio can be determined. After the initial water-lift ratio is determined, the time cycle is changed and a new water-lift-ratio test is run. Several tests are conducted on each well to determine the optimum cycle which results in the highest water-lift efficiency, i.e., the lowest volume of gas required to lift each barrel of water. Currently two test-separators are operating full time on the testing program. Gas technicians are placed in charge of these units and instructed to test all problem wells that are producing substantial quantities of salt water. Monthly reports of hard-to-produce wells are reviewed and each well appearing on this report investigated. Those wells with a water-production problem are scheduled for water-lift-ratio tests. JPT P. 619ˆ