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SPE 094

Stress Regime at Acid-Gas Injection Operations in Western Canada

Abstract: Acid gas, a mixture of CO2 and H2S produced from sour gas reservoirs in Western Canada, has been injected into deep geological formations for close to 15 years with a good safety record. Injection currently takes place at 41 locations into depleted oil and gas reservoirs, and deep saline aquifers. From this point of view, the acid-gas injection operations in Western Canada constitute a commercial-scale analogue for CO2 geological storage. A major issue in geological injection of fluids is the integrity of the injection unit; i.e., avoidance of leakage through natural or induced fractures. Regulatory agencies in Western Canada impose safe limits on the injection pressure to maintain the pressure around the injection well below the fracturing threshold of the rocks. An evaluation of the stress regime at the acid-gas injection sites in Western Canada was performed to assess the relationship between the maximum allowed wellhead injection-pressures and the rock-fracturing thresholds.The stress regime in the Alberta Basin has been established in this study on the basis of 1446 hydraulic tests and on density logs in selected wells. On this basis, the minimum horizontal stress and the vertical stress have been estimated at all acid-gas injection sites. Minimum horizontal stresses increase with depth with a basin-wide average gradient of 16.6 kPa/m. Maximum vertical stresses increase with depth with a basin-wide gradient of 23.8 kPa/m. Fracture pressures increase with depth with an average gradient of 19 kPa/m, and are at all the sites greater than the minimum horizontal stress, but smaller than the vertical stress. Maximum bottom hole injection pressures are safely below the minimum horizontal stress, hence lower than the fracture pressure. Thus, there is no danger of opening existing fractures, neither, obviously, of inducing new ones. The study has also shown that, in the case of acid or greenhouse gas injection, prescribing the maximum wellhead injection pressure, according to general values established for water disposal, is not sufficient because the gas most likely will not have enough bottom-hole pressure to overcome the formation pressure and enter the injection unit. Thus, for acid and greenhouse gas injection in geological media, there is need to establish the maximum bottom hole and wellhead injection pressures on the basis of minimum horizontal stress to avoid opening of potential pre-existing fractures, and on the basis of gas properties at reservoir and wellhead conditions (pressure and temperature). The current acid-gas injection operations in Western Canada meet the safety criteria imposed by the need to maintain the integrity of the injection unit. However, the wide range of variability in the ratio between minimum horizontal stresses and fracturing pressures points out to the need to perform hydraulic tests at each site, rather than estimate the fracturing pressure from basin-wide fracturing gradients or numerical models. Performing carefully conducted tests will also allow site-specific determination of the minimum horizontal stress, hence of a better upper limit for the bottom hole injection pressure, to ensure that pre-existing fractures, if present, will not be opened. Place Keywords 72e 72l 72m 73d 73e 73l 73m 74d 74e 74l 74m 82g 82h 82i 82j 82n 82o 82p 83a 83b 83c 83d 83e 83f 83g 83h 83i 83j 83k 83l 83m 83n 83o 83p 84a 84b 84c 84d 84e 84f 84g 84h 84i 84j 84k 84l 84m 84n 84o 84p alberta alberta basin british columbia canada western c Theme Keywords acid gas co2 engineering fractures geology injection

Bachu, S.  Haug, K.  Michael, K.  2008-04-14

SPE 007

Regional Evaluation of the Coal Bed Methane Potential in the Plains and Foothills of Alberta, Stratigraphy and Rank Study

Regional Evaluation of the Coal Bed Methane Potential in the Plains and Foothills of Alberta, Stratigraphy and Rank Study The coal resource in place in Alberta is tremendous by whichever estimate is used. The geologic model developed for the ... Show Abstract

Rottenfusser, B.  Langenberg, C.W.  Mandryk, G.B.  Richardson, R.J.H.  Fildes, B.J.  Olic, J.  Stewart, S.A.  Eccles, D.R.  Evans, C.  Spelrem, M.  Sprecher, B.  Brulotte, M.  Gentzis, T.  Wynne, D.A.  Yuan, L.P.  1999-02-01

SPE 078

Preliminary Release of Kimberlite Indicator Mineral Data from National Geochemical Reconnaissance Stream Sediment Samples in the Jackpine Lake Area (NTS 84C/15, 84C/16, 84F/01, 84F/02), Southwest Buffalo Head Hills, Alberta

Preliminary Release of Kimberlite Indicator Mineral Data from National Geochemical Reconnaissance Stream Sediment Samples in the Jackpine Lake Area (NTS 84C/15, 84C/16, 84F/01, 84F/02), Southwest Buffalo Head Hills, Alberta The Geological Survey of ... Show Abstract

Prior, G.J.  McCurdy, M.W.  Friske, P.W.B.  Pawlowicz, J.G.  Day, S.J.A.  McNeil, R.J.  2006-01-01

SPE 009

The Geological and Geochemical Setting of the Mid-Cretaceous Shaftesbury Formation and Other Colorado Group Sedimentary Units in Northern Alberta

The Geological and Geochemical Setting of the Mid-Cretaceous Shaftesbury Formation and Other Colorado Group Sedimentary Units in Northern Alberta The geological setting of the mid-Cretaceous Shaftesbury Formation and other Colorado Group ... Show Abstract

Dufresne, M.B.  Eccles, D.R.  Leckie, D.A.  2001-06-01

SPE 056

Catalogue of Selected Regional Gravity and Magnetic Maps of Northern Alberta

A practical tool for identifying brittle basement faults in northern Alberta was created by detailed processing of public-domain gravity and magnetic data to highlight subtle linear features. Lineaments can be gradient zones, alignments of separate ... Show Abstract

Lyatsky, H.V.  Pana, D.I.  2003-08-01

SPE 054

An Investigation of Geological Applications of Archival Lightning Strike Data in the Province of Alberta (North of Latitude 54° North)

Lightning detection instruments were initially deployed to protect aerospace launch vehicles and solid-state electronics. [...]because of the large area involved in the study, interpretation of possible lightning strike linears was focused on the ... Show Abstract

Robertson, K.  2003-11-01

SPE 020

A Guide to Kimberlite-Indicator Mineral Trends in Alberta Including Observations from Recently Compiled Indicator Mineral Data

A Guide to Kimberlite-Indicator Mineral Trends in Alberta Including Observations from Recently Compiled Indicator Mineral Data Since 1990, diamond exploration in Alberta has resulted in the discovery of 48 kimberlitic pipes and the recovery of more ... Show Abstract

Eccles, D.R.  2005-03-01

SPE 071

Preliminary Release of Geochemical, Mineralogical and Kimberlite Indicator Mineral Electron Microprobe Data from Silts, Heavy Mineral Concentrates and Waters from a National Geochemical Reconnaissance Stream Sediment and Water Survey

Preliminary Release of Geochemical, Mineralogical and Kimberlite Indicator Mineral Electron Microprobe Data from Silts, Heavy Mineral Concentrates and Waters from a National Geochemical Reconnaissance Stream Sediment and Water Survey A regional ... Show Abstract

McCurdy, M.W.  Prior, G.J.  Friske, P.W.B.  McNeil, R.J.  Weiss, J.A.  Day, S.J.A.  2004-08-01

SPE 005

Investigations of Flare Gas Emissions in Alberta

The research program in the characterization of emissions from flaring in Alberta was designed in conjunction with Government and Industry representatives. The overall terms of reference for the study was to determine experimentally the degree to ... Show Abstract

Strosher, M.  1996-11-01

SPE 012

Alteration Mineralogy of Alberta Kimberlites: PIMA Infrared Spectroscopic Analysis

Alteration Mineralogy of Alberta Kimberlites: PIMA Infrared Spectroscopic Analysis The suite was supplied by the AGS.There were a number of objectives for the work. The Short Wave Infrared (SWIR) technique is extremely sensitive to alteration ... Show Abstract

Hauff, P.L.  Eccles, D.R.  Grunsky, E.  2001-07-01