As a result of an increasing need for environmental awareness, PanCanadian Petroleum Limited initiated an abandonment program to reduce the backlog ofsuspended wells. Within the Brooks District of Southern Alberta, it becameapparent that 40 to 50% of the wells being abandoned had gas migrationflows.
This paper focuses on the remediation of annular vent flows and migration, outside the surface casing, on we1ls that were originally cemented to surface.Beginning in 1992 the testing a various techniques resulted in the developmentof a system that has significantly improved the success of remedial work. Alongwith the proper system, and a teamwork approach with Dowell Division of Schlumberger Canada Limited, an optimised and efficient operation has reducedcosts associated with annular gas flow remediation. Also included in this paperare statistics from all the techniques attempted and a detailed description ofthe process presently being used.
Gas migration remediation is a subject that has come to the forefront of theoil and gas industry in Alberta as a result of the Energy Resources Conservation Board (ERCB) and Alberta Environment developing a new policy whichis expected to be issued as an informational letter early in 1995. Thefollowing definitions by the ERCB have been paraphrased from a draft version ofthat document. 1
A Vent Flow - Is any flow of gas, water, or hydrocarbon liquids with ameasurable pressure buildup.
Gas Migration - A detectable amount of gas or fluid migration flowing tosurface outside the outermost casing string.
Serious Vent Flow - Any flow where any usable water zone is not covered bycemented surface casing and/or cemented production casing.
With a stabilized gas flow equal to or greater than 300 m 3/day.(and/or)
Shut-in surface pressure greater than or equal to a pressure one-half of theformation leakoff pressure at the surface casing shoe.
Or a pressure greater than 11 kPa/m times the surface casing settingdepth.
Serious Migration - Is any fluid or gas flow that constitutes a fire, publicsafety risk, or is causing off lease environmental damage.
All new wells will require a vent check within 30 days of rig release: if avent leak is detected, a report must be submitted to the ERCB. This report mustinclude a charted stabilized shut-in pressure, a 24-hour pressure buildup rate,a measured flow rate with a description of the equipment used for themeasurement an analysis of the fluid or gas type being produced, and aremedial action plan.
Wells in a special Lloydminister area will require a fluid migration studywhich is described in more detail later in this paper.
Wells which have serious flows will require immediate repair upon approval ofthe action plan; nonserious flows may be monitored and reported to the ERCB attheir discretion and repaired upon abandonment.
The Gas Migration Remediation Process development began three years ago whenPanCanadian Petroleum Limited (PCP) made a corporate decision to reduce itsenvironmental liability by developing a method and process of abandoning thebacklog of suspended wells that had accumulated in the Brooks District.