The goal is to help to improve the deliverability of existing underground storage wells and reservoirs by developing and testing sonication cleaning as a potential remediation technique for removing inorganic precipitates.
There are more than 14,000 storage wells in the United States and according to a 1993 study conducted by the Gas Technology Institute, these wells are losing an average of 5.2 percent of their capability to inject and withdraw natural gas annually. Thus, there is a need to reduce the cost of deliverability enhancement by developing lower cost alternatives. To gain a better understanding of the types of damage that affect gas storage wells, the National Energy Technology Laboratory (NETL) co funded research with the Gas Technology Institute (GTI). The GTI/DOE co funded project completed research on 33 wells in 12 gas storage fields to identify the mechanisms responsible for losses in well deliverability, and established guidelines for use by storage field operators. The major causes of damage were inorganic precipitates (more commonly known as scale), hydrocarbons, organic residues, production chemicals, bacterial fouling, and particulate plugging. This project is designed to test sonic-based mechanisms which employ sound waves to dislodge scale and plugging material within the near-wellbore formation, improving the injectability and producibility of the well. The sound waves are created by a magnetostrictive transducer that quickly converts a changing magnetic field into mechanical energy.
Furness-Newburge, Inc. (FNI) – project management and research and design of prototype
Argonne National Laboratory (ANL) – laboratory testing of prototype and field coordination
Nicor Gas – field testing of prototype
Versailles, Kentucky 40383
The Sonic Tool was successfully operated in two injection/withdrawal wells for more than 20 hours and 28 hours, respectively, without failure. The tool removed damage in one well, as evidenced by its negative mechanical skin, and improved deliverability by 30 percent. It has an added advantage over some conventional technologies in that the production tubing does not need to be removed, saving $10,000 -$15,000 to the gas storage operator. The Sonic Tool could be used in thousands of wells to restore lost deliverability.
At the start the project was separated into two parallel paths. Path One was related to development and testing of a low frequency sonic tool and Path Two to an underwater plasma discharge tool. The initial laboratory configuration of the low frequency sonic tool yielded a substantially higher rust removal rate when operated in the sonic range rather than in the originally proposed ultrasonic range. Commercially available off-the-shelf audio power supplies greatly reduced the time needed to prepare this tool for downhole (in-well) testing. Thus, the low frequency sonic tool was designed to be a relatively low cost instrument with the potential to be left in the well as a long term “preventive maintenance” tool. The underwater plasma discharge tool, although much more powerful than the low frequency sonic tool, will require much more time to develop into a field ready device. Compared to the low frequency sonic tool, the rust removal rate for the plasma tool was greater and the power consumption at least 80 percent lower per unit volume of rust removed.
The first field test was conducted in August 2001 at Nicor Gas' underground aquifer storage facility located near Pontiac, Illinois. The well chosen for the demonstration was the Bashore #1 observation well. Since a prototype-laboratory sonic tool was available, it was modified for the field test. Comparison of pre- and post-sonication water chemistry data indicate that the sonic tool is removing scale. The post-sonication segmented bond log showed that operating the sonic tool caused no damage to the cement bond in the well.
A successful field test of the low frequency sonic tool was conducted in November 2002 in a pressurized injection-withdrawal well at Nicor Gas' storage field near Pontiac, IL. The tool was operated at 1,200 watts of power in a frequency range of 800-1,000 hertz, using two different operating modes (sine and pulsed sine waves). Tests were conducted in a perforated zone 3,200 to 3,300 feet below ground. The tool was run for 45 minutes at a given depth and then moved further down-hole in 5-foot increments. After 2 days of testing, the “horn” (used to distribute energy) showed signs of pitting due to the high power levels being employed. After a new horn was installed, an additional day of testing was completed. A suite of diagnostic tools and tests were run prior to the sonic tool test to collect background information. Following testing, a complete field evaluation of the sonic tool's ability to remove scale damage was conducted. Analysis of the well test data indicated that no improvement to the well's deliverability was obtained. However, the analysis also indicates that the well was a poor choice since it was already in a “stimulated” condition.
In August, 2004, the Sonic Tool was run (without pulling the production tubing) in a second Nicor gas storage well. Pre-sonication well tests were run to ensure that the well was in a damaged state. Over a four day period, the sonic tool was operated for over 28 hours without failure. Recent well test analysis and results have clearly shown that the tool removed damage, decreasing the mechanical skin from +2.5 to -1.3, and increased the flow potential of the well by roughly 30%.
The project has been completed.