The primary objective of this study was to improve deliverability in gas storage wells by better understanding when damage develops, and, with this knowledge, identify the most likely source(s) of damage and the changes necessary to prevent damage from occurring.
Specifically, project goals are threefold:
Schlumberger Technology Corporation – project management and research product
Columbia Gas/NICOR – use of storage wells for testing
Maintenance of deliverability is one of the primary concerns of the gas storage operator, since most gas storage wells suffer loss of deliverability over time. The cause of this loss of deliverability is often unknown. An aid to identifying the cause (or causes) of the damage would include knowledge of when the damage develops. Unfortunately, monitoring and quantifying wellbore damage over time with conventional buildup and falloff tests would be prohibitively expensive.
Many gas storage operators use electronic flow measurement (EFM) systems capable of collecting high-frequency (10 to 15 second intervals) wellhead pressure and flow rate data. In the normal course of storage operations, wells will often be shut in for short periods of time. With data collected by the EFM system, these routine shut-in periods may be analyzed as buildup or falloff tests to provide insights into the onset of wellbore damage.
This project is developing analysis modules to process, analyze, and interpret the EFM data, in such a manner that the damage timing can be identified. These modules currently do not exist in the industry. They will be provided and are applicable to any U.S. storage operator who collects EFM data.
The modules were developed by obtaining the EFM data for one of the Columbia’s storage fields, and then building processing, filtering, extracting, and analysis algorithms to process this data in a manner that would result in a plot of the degree of damage over time. The modules provide a quick method for storage companies to process and analyze EFM data. The modules will track both the mechanical and non-darcy flow damage at very frequent intervals (i.e., daily, weekly, or at the very least, monthly).
Widespread adoption of EFM systems and the proper analysis of the resulting data will ultimately result in improved storage field performance at reduced costs.
A tool has been developed to automatically filter high-frequency EFM data from gas storage wells to identify shut-in periods that can be analyzed as buildup or falloff tests, and to perform a preliminary analysis of the test data so collected. The tool automatically generates semilog and log-log plots for analyzing each test, as well as composite graphs of apparent skin (s') vs. flow rate and s' vs. date. The tool allows the user to manually review and fine-tune the test analyses.
To date the system has been used to analyze data from 20 wells in a major gas storage field for the period December 2003 through May 2005. Since wellhead pressure and flowrate data are recorded for each well at 15-second intervals, the system had to be able to process large amounts of data. A total of 357 shut-in periods were identified, 207 of which were analyzable.Three wells had no interpretable tests, while eleven of the wells had 8 or more analyzable tests. The final report for this project has been received and approved.
$56,975 (20% of total)