40 CFR 146.8(b)(1) Monitoring of Annulus Pressure MIT

40 CFR 146.8(b)(1) describes a mechanical integrity test (MIT) referred to by several acronyms; the monitoring of annulus pressure MIT is variously called the MAP, the APM, the SAPM, and the SAMT.  We prefer MAP or APM since EPA has restricted the use of said MIT to the extent there can be nothing "standard" about it ("S" in the remaining two acronyms is of course for "standard").  This provision has not been widely applied to Class II wells; in fact, it has never been allowed in Kentucky by EPA Region IV, not even for a single well.

The original EPA 1976 UIC regulatory proposal contained no specific MITs, although there was a general prohibition against "leaks in the system".  The 1979 reproposal contained eight MITs for the demonstration of internal or Part I (no significant leak in casing, tubing, or packer) mechanical integrity: (a) TV monitoring, (b) monitoring of annulus pressure, (c) radioactive tracer survey, (d) casing cement loss, (e) fluid or gas pressure test, (f) temperature survey, (g) flowmeter survey, or (h) packer test.  EPA's 1980 final regulations retained only two internal MITs, monitoring of annulus pressure and fluid or gas pressure tests (40 CFR 146.8(b)(2)).  A third internal MIT, the records of monitoring retest, was later added at 40 CFR 146.8(b)(3) as a result of the 1981 multi-industry litigation challenging EPA's 1980 final UIC regulations.

The original language at 40 CFR 146.8(b)(1) said only "Monitoring of annulus pressure."  However, the Mid-Course Evaluation workgroup, and others at EPA, decided the MAP had problems.  As a result, EPA proposed changes to said section as part of the 1990 Reg-Fix package.  The final rule revision was published in the Federal Register on December 3, 1993, and 40 CFR 146.8(b)(1) now reads as follows:

"Following an initial pressure test, monitoring of the tubing-casing annulus pressure with sufficient frequency to be representative, as determined by the Director, while maintaining an annulus pressure different from atmospheric pressure measured at the surface."

The MAP can be viewed as a continuing SAPT, though the pressure involved would typically be lower.  The main problem with the MAP, aside from EPA's unwillingness to let anyone use it, has to do with the many factors that complicate interpretation.  While a sealed annulus with no leaks is closed to matter transfer, it is not closed to energy transfer, because it is free to exchange heat with its surroundings.  Heat transfer has not proven to be a major problem with the SAPT, presumably because of the short time duration of said MIT, but it is a major problem with regard to the MAP where huge pressure variations have been demonstrated as a result of temperature changes over time.  For example a temperature change from 65F to just 70F in a 3,000 foot well with 5-1/2 inch casing and 2-3/8 inch tubing will result in a 160 psi increase in annular pressure.  API hired Gruy Engineering to do heat transfer analyses, and they calculated a possible 1,100 psi annular pressure change for a mere 10F change in injection fluid temperature.  Here are some conclusions from various studies:

1. Increases or decreases in injection fluid temperatures result in rapid increases or decreases in annulus pressures.
2. Changes in injection rate, especially commencing or ceasing injection, result in a change in annulus pressure.
3. Changes in injection pressure result in a change in annulus pressure.
4. The change in annular pressure is greatest in the first two hours following a change in injection conditions, but temperatures and pressures within the injection system continue to change and a true steady-state is never attained.
5. Even changes in atmospheric pressure and phases of the moon have been alleged to have observable effects (believe what you will on this one).

The required annulus monitoring for Class I wells required at 40 CFR 146.13(b)(2) is not the MAP.  Further the annulus monitoring requirements imposed on Class II wells (only permitted wells in Region IV) has nothing to do with the MAP.  See Annulus Monitoring - Closed or Open Annulus? for more on how EPA Region IV has disingenuously used the MAP MIT provisions at 40 CFR 146.8(b)(1) to attempt to justify a closed annulus requirement in UIC permits for existing Class IIR injection wells in Kentucky.

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Last 10-20-10