UIC Mechanical Integrity Test (MIT) Overview

The following overview of mechanical integrity testing is excerpted from U.S. EPA Region V's Regional Guidance #5, Determination of the Mechanical Integrity of Injection Wells (Revised June 11, 1998).  While this material was prepared by EPA and contains some biased elements (and a few outright mistakes, especially, but not exclusively, where noted below), it is nevertheless a decent overview of underground injection control (UIC) program MIT technology.  Conspicuously absent below is any discussion of the method for demonstrating mechanical integrity pursuant to 40 CFR 146.8(a)(1) described at 40 CFR 146.8(b)(3).  But fear not, you can see what AnaLog has to say about that particular MIT at 40 CFR 146.8(b)(3) Records of Monitoring MIT (Retest).

A. Mechanical Integrity Pursuant to 40 CFR 146.8(a)(1)
There are a limited number of means by which part 1 of MI (the absence of significant leaks in tubing, casing, and packer) may be demonstrated.  Therefore, little discussion of the relative merits of the various tests is necessary.

1. The Standard Annulus Pressure Test (SAPT)    [See AnaLog's SAPT / Cement Records MITs.]
The SAPT is the most common means used to demonstrate part 1 of MI.  This test is based on the principle that a pressure applied to fluids filling a sealed vessel will persist.  A well's annulus system, though closed to transfer of matter, is not closed to energy transfer because it is not isolated from transfer of heat from its surroundings, therefore an allowance for small pressure changes is necessary.  The test provides an immediate demonstration of whether or not leaks, detectable by these means, exist.  A discussion of and procedures for the SAPT are outlined in Attachment 1.

2. The Standard Annulus Monitoring Test (SAMT)    [See AnaLog's MAP, APM, SAMT MIT.]
Pursuant to 40 CFR 146.8(b), monitoring of the annulus pressure is an approved method for establishing part 1 of MI for all wells.  Annulus pressure monitoring for Class I wells required at 146.13(b)(2) to verify the maintenance of a minimum pressure differential is not the SAMT, because changes in pressure due to loss of annulus liquid are attenuated by the presence of a gas blanket which is replenished as pressure decreases.  If annulus monitoring is used to demonstrate MI, an initial SAPT is required.  Annulus monitoring may continue throughout the life of the well or the operator may choose, at any time, to conduct a SAPT every five years and after well reworks (on rule authorized Class II wells and on permitted wells if the particular UIC permit allows it), thereby discontinuing the SAMT.  A discussion of the merits and procedures for the SAMT is provided in Attachment 2.

3. The Radioactive Tracer Survey (RTS)    [See AnaLog's RTS or RATS Overview.]
On September 18, 1987, the USEPA published a Federal Register (FR) notice at 35324 et seq. FR 52, No. 181, giving interim approval for the use of the RTS as an alternative MIT.  In a FR Notice at 46837 et seq. FR 52, No. 237 on December 10, 1987, the USEPA announced final approval of the RTS as a demonstration of part 1 and 2 (as limited), and provided clarifications and additional information based on comments received and the use of the test during the interim approval period.  A discussion of and procedures for conducting the RTS as a demonstration of part 1 of MI in Region 5 are outlined in Attachment 3[Contains several mistakes.]

4. Water-Brine Interface Test (W-BIT)
On January 10, 1992, approval of the W-BIT was announced in the Federal Register at 1109 et seq FR 57, No. 7.  The test is valid only for Class III wells and only when construction and operating conditions make testing with the SAPT impractical.  Although there are no special recommendations applicable in Region 5, additional explanation of the basis for the test is provided in Attachment 4, and a full description of the procedures for conducting the W-BIT is available in the above referenced FR Notice.

5. Ada Pressure Test    [See AnaLog's "ADA" Pressure MIT.]
The Ada test is a variant of the SAPT.  It is used to test wells which have perforations above the injection zone.  It can be used to test the integrity of the casing above the perforations.  To conduct the test gas pressure is used to depress the liquid level to a point just above the perforations.  The pressure is measured over a period of time.  If the pressure change is less than the established limit, the well has mechanical integrity.

6. Water-in-Annulus Test (WIAT)
The WIAT was announced at 14678 et seq 54 FR No. 19 on April 12, 1989, for existing Class II wells for enhanced oil recovery in the counties in which the Bradford oil field is located in New York and Pennsylvania.  Approval of the test was extended to similar wells in the Redhaw oil field in Ashland County, Ohio. The test is used for wells which are constructed without long string casing.  The level of water near the top of the annulus between the surface casing, which protects all USDWs, and the injection tubing which is set on a formation packer and may have some cement on the top of the packer, is observed under specified conditions.  The presence and nature of relatively small leaks can be determined.

7. Casing Cementing Pressure/Single Point Resistivity Test (SPRT)
The SPRT for Class III uranium mining wells using in situ solution cased with nonconducting PVC or fiberglass casing was announced at 4903 et seq 54 FR No. 19 on January 31, 1989.  The test consists of two parts.  The first part uses an observation of the pressure required to circulate cement during setting of the casing to evaluate cement placement and casing leaks.  If the cement placement is acceptable the casing is tested by measurement of total electrical resistance between the logging tool's location in the well and a grounding rod at the surface near the well head.  Leaks are indicated as low resistance spikes.  There are no wells in Region 5 for which this test is approved.

8. Dual Completion Monitoring Test (DCMT)
The DCMT is used to test wells which produce oil from perforations above an injection zone.  The method was proposed on October 29, 1987, at 41591 et seq 52 FR No. 209.  Final approval has not yet been granted for the test.  Several wells in Indiana and Michigan are tested by this method.  The test includes monitoring of oil and water production, periodic liquid level measurements while producing and while not producing.  The procedures for this test are being re-examined.  When finalized, an attachment describing the test in detail will be added.

B. Mechanical Integrity Pursuant to 40 CFR 146.8(a)(2)
Owner/operators have a choice of a number of methods for demonstrating that wells have part 2 of MI (no significant fluid movement into a USDW through vertical channels adjacent to the injection well bore).  The conditions under which these tests can be used to best effect differ significantly; therefore, a listing of relative advantages and disadvantages of the various options is provided in the attachments concerning each of the approved methods for demonstrating part 2 of MI.

1. Temperature Logs (TL)    [See AnaLog's Temperature Log External MIT.]
Temperature logs are a very versatile and sensitive means of identifying fluids which have moved along channels adjacent to the well bore.  In addition to demonstrations of part 2 of MI, temperature logs can be used to monitor fluid movement through the confining zone adjacent to the well bore and can often locate small casing leaks.  To be effective for demonstrations of MI, there must be adequate time available for short-term temperature effects along the well bore to dissipate.  Background information and general procedures for running temperature logs are provided in Attachment 5.

2. Noise Logs (NL)    [See AnaLog's Noise Log External MIT.]
The use of noise logs is based on the observation that flow behind the casing in the well bore will, at some points, be turbulent.  Turbulent flow causes noise which may travel for significant distances along the well bore.  Noise logs are appropriate where it is impractical for injection operations to be suspended for the length of time needed to allow temperature stabilization to proceed to the point at which a temperature log can be run with good results.  They can also be used to locate some tubing or casing leaks.  Background information and procedures for using noise logs to demonstrate part 2 of MI are found in Attachment 6.

3. Oxygen Activation Method (OAL)
On February 1, 1991, the USEPA published a FR Notice granting final approval, effective March 4, 1991, for use of the oxygen activation method or log (OAL) as a means of demonstrating part 2 of MI.  Details of the operation and conditions under which the OAL can be used can be found at 4063 et seq. FR 56, No. 22 which is included in this guidance as Attachment 7.

4. Radioactive Tracer Survey    [See AnaLog's RTS or RATS Overview.]
The same FRNs which describe how the RTS can be used for demonstrating part 1 of MI also describe its use for demonstrating part 2 of MI.  This method may be used only where there is only a single confining formation separating the lowermost USDW from the injection zone with no aquifers within it.  Additional requirements and limitations of the RTS are described in the previously mentioned FR Notices (See III.C.).  The use of the RTS as a means of demonstrating part 2 of MI is described in Attachment 8.

5. Cement Records    [See SAPT / Cement Records MITs and Cement Bond Log MIT?.]
The most common demonstration of part 2 of MI for Class II wells is based on cementing records.  Demonstrations of MI for Class III wells can also be based on cementing records if the configuration of wells prevents the use of logging methods.  If records show that casings are cemented in a way which will prevent the movement of liquids into or between USDWs, the well has part 2 of MI.  A discussion of the use of cementing records is provided in Attachment 9[The discussion on cement bond logs contains several mistakes.]

C. Additional Mechanical Integrity Tests
Other alternative MITs will be added to this guidance if approved by the Administrator of the EPA for use in Region 5.  In order for a test to be approved, it must be submitted to the Water Division Director in Region 5 with all supporting evidence.  If the proposal is approved by the Director, then it will be submitted to the Administrator, and will be evaluated by the national UIC Technical Workgroup which will evaluate its effectiveness.  If approved by the Administrator, the approval and any limitations placed on the test will be promulgated in the Federal Register.  In addition, specific procedures outlined in this guidance may be modified after additional data are obtained or to accommodate a particular type of well construction.  National UIC Guidances #15 and #34 include information relating to approval of alternate methods of testing mechanical integrity.

D. Tests which are not MI Tests but are Specifically Required by Regulation
1. Radioactive Tracer Survey    [See AnaLog's RTS or RATS Overview.]
The regulations at 40 CFR 146.68(d)(2) require annual demonstrations of the integrity of cement at the top of the injection interval in Class I hazardous-waste injection wells.  The RTS is more often used for that purpose than to demonstrate either part 1 or 2 of MI.  The procedures for demonstrating cement integrity using the RTS are presented in Attachment 10.

2. Casing Inspection Logs (CIL)
The regulations at 40 CFR 146.68(d)(4)require periodic monitoring of change in casing thickness for Class I wells injecting hazardous wastes.  The procedures for running the logs and presentation of the results are set by the logging company.  Because the standards adopted by the logging companies are appropriate, no additional information is provided for running casing inspection logs.

See also AnaLog's The Self Evident MIT.

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