Annular Gas Migration as a Result of Poor Cement Jobs

United States Department of the Interior

Content:
Kumkum Ray
703-787-1604

Pagemasters:
OMM Web Team

National Safety Alert No. 2
February 2, 2000

Annular Gas Migration as a Result of Poor Cement Jobs

During calendar year 2000 there have been two separate incidents involving gas migration through annuli due to poor cement jobs in the Gulf of Mexico. This is not a new problem for the OCS as MMS has already issued two Gulf of Mexico Safety Alerts on this subject:

Notice No. 066, September 26, 1977, "Blowouts from Surface Casing – Conductor Casing Annulus"

Notice No. 165, April 3, 1995, "Shallow Gas Flows While Cementing Surface Casing"

The two annular flow incidents this year, one of which led to a blowout, are the result of poor cement jobs.

The first incident happened on January 5^th, 2000. It was a result of a poor cement job in the 26" / 18" x 13 3/8" annulus. Two successive cement bond logs were run on the well both showing a poor cement job. The first one was run at normal pressure and the second one was run under pressure. The well flowed for a week before it was successfully capped. The operator performed remedial cement work on the 13 3/8" casing to reduce the pressure on the annulus. They are continuing to monitor the pressure in the annulus.

The second incident occurred on January 12^th, 2000. It was a result of a poor cement job in the 20" x 13 5/8" annulus. There was evidence of cement channeling during the cement job and cement bond logs showed that the cement was possibly contaminated with mud. As a result of cement channeling the 20" x 13 5/8" annulus had to be washed out using a 1¼" tubing string with 13.9 ppg mud. The well began flowing up the annulus and was shut in to allow the cement to set up. Dry gas and mud were bled off through the choke line in an attempt to reduce the pressure on the annular blowout preventer. The operator nippled up a snubbing unit and conducted a remedial cement job on the 20" x 13 5/8" annulus to kill the annular pressure. They are continuing to monitor the annulus for pressure.

MMS regulations at 30 CFR 250.404 (a)(2) require "…. Cement composition, placement techniques and waiting time shall be designed and conducted so that the cement in place behind the bottom 500 feet of casing or total length of annular cement fill, if less, attains a minimum compressive strength of 500 pounds per square inch (psi)…." MMS regulations at 30 CFR 250.405 (d) state "After cementing any string of casing other than the structural casing string, drilling shall not be resumed until there has been a time lapse of 8 hours under pressure for the conductor casing string and 12 hours under pressure for all other casing strings. Cement is considered under pressure if one or more float valves are shown to be holding the cement in place or when other means of holding pressure are used."

Current MMS drilling requirements do not address the methods operators must use to cement casing strings or liners. MMS has allowed operators to use judgment in selecting the proper method and practices for the cementing of casing and liners. It is recommended that lessees and operators have procedures in place to assure that adequate wait on cement time is determined and appropriate cement compressive strength is achieved.

MMS has formed a team to analyze the data from these two incidents and other incidents over the past few years. This team will address issues involving the cementing of casing. Some of the possible outcomes of this investigation could include workshops on cementing practices, regulatory review, additional research on cementing practices, and adopting standards on cementing.

If you have any questions, please contact Joe Levine, (703) 787-1033 or Joe Gordon, (504) 736-2923.

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Last Updated: 02/01/2006, 12:48 PM