Gas Migration Behind Cased Energy Wellbores as a Transient Process
Thursday, November 13, 2014: 9:30 a.m.
Richard Jackson, Ph.D., P.Eng.
,
Geofirma Engineering Ltd., Heidelberg, ON, Canada
Maurice Dusseault, Ph.D., P.Eng.
,
Earth & Environmental Sciences, University of Waterloo, Waterloo, ON, Canada
Because of autogenous shrinkage of cement and the subsequent reduction in radial contact stress between the borehole wall and the cement, a micro-annulus may develop that creates a pathway by which natural gas may rise outside the casing. This gas may become evident as sustained casing pressure (SCP) in the U.S., or in Canada as surface casing vent flow (SCVF) or as gas migration (GM), i.e., that which occurs outside the casing strings. GM may emit at ground surface as a greenhouse gas or penetrate shallow aquifers, causing groundwater contamination. Gas emissions recorded as surface casing vent releases frequently display a pulsing or periodic nature. These gas slugs are well known to those using noise logs to detect annular cement pathways. We hypothesize that these pulses or slugs are due to the formation of Taylor bubbles, which are created by the coalescence of small bubbles and their buoyant ascension behind the casing. Their displacement pressure is sufficient to overcome the capillary entry pressure posed by shallow aquifers and thus cause groundwater contamination. The periodic nature of these gas slugs is of consequence if such emissions are to be fully accounted for during monitoring by hydrogeologists in water wells.
Richard Jackson, Ph.D., P.Eng., Geofirma Engineering Ltd., Heidelberg, ON, Canada
Dick Jackson is a registered Professional Engineer in both Ontario and British Columbia and has worked as a hydrogeologist since the early 1970s. In 1986, he became Chief of the Ground-Water Contamination Project at the National Water Research Institute. He joined INTERA in 1989 and his group modified petroleum-engineering methods and applied them to the characterization and remediation of NAPLs. He is now a Principal with Geofirma Engineering Ltd. of Ottawa, Ontario, and received the Farvolden Award in 2013 from the Canadian National Chapter of the IAH. He is an Adjunct Professor at the University of Waterloo where he received his PhD.
Maurice Dusseault, Ph.D., P.Eng., Earth & Environmental Sciences, University of Waterloo, Waterloo, ON, Canada
Maurice Dusseault has taught rock mechanics and petroleum geomechanics at the University of Waterloo since 1982. He has been advisor to the Alberta Government and its policy and regulatory agencies for many years and has given numerous short courses to the petroleum and mining industry. All three of his degrees are from the University of Alberta.
