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Seepage pathway assessment for natural gas to shallow groundwater during well stimulation, in production, and after abandonment

Maurice Dusseault and Richard Jackson
Seepage pathway assessment for natural gas to shallow groundwater during well stimulation, in production, and after abandonment
Environmental Geosciences (September 2014) 21 (3): 107-126

Abstract

Hydraulic fracture stimulation (HFS) of unconventional oil and gas reservoirs is of public concern with respect to fugitive gas emissions, fracture height growth, induced seismicity, and groundwater quality changes. We evaluate the potential pathways of fugitive gas seepage during stimulation, in production, and after abandonment; we conclude that the quality of the casing installations is the major concern with respect to future gas migration. The pathway outside the casing is of particular concern as it likely leads to many wells leaking natural gas from thin intermediate-depth gas zones rather than from the deeper target reservoirs. These paths must be understood, likely cases identified, and the probability of leakage mitigated by methods such as casing perforation and squeeze, expanding packers of long life, and induced leakoff into saline aquifers. HFS itself appears not to be a significant risk, with two exceptions. These occur during the high-pressure stage of HFS when (1) legacy well casings are intersected by fracturing fluids and when (2) these fluids pressurize nearby offset wells that have not been shut in, particularly offset wells in the same formation that are surrounded by a region of pressure depletion in which the horizontal stresses are also diminished. This paper focuses on the issue of gas migration from deeper than the surface casing that occurs outside the casing caused by geomechanical processes associated with cement shrinkage, and we review the origin of the gas pulses recorded in noise logs, landowner wells, and surface-casing vents.


ISSN: 1075-9565
EISSN: 1526-0984
Serial Title: Environmental Geosciences
Serial Volume: 21
Serial Issue: 3
Title: Seepage pathway assessment for natural gas to shallow groundwater during well stimulation, in production, and after abandonment
Affiliation: University of Waterloo, Department of Earth & Environmental Sciences, Waterloo, ON, Canada
Pages: 107-126
Published: 201409
Text Language: English
Publisher: American Association of Petroleum Geologists (AAPG), Division of Environmental Geosciences, Tulsa, OK, United States
References: 95
Accession Number: 2014-104794
Categories: Economic geology, geology of energy sourcesEnvironmental geology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus.
N39°43'00" - N42°17'60", W80°31'60" - W74°40'00"
N48°25'00" - N60°00'00", W139°00'00" - W114°00'00"
Secondary Affiliation: Geofirma Engineering, CAN, Canada
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by American Association of Petroleum Geologists, Tulsa, OK, United States
Update Code: 201452
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