Managed-Pressure Drilling To Counteract Lost-Circulation and High-Pressure-Gas Zones: South Wapiti Red Rock Field
- Dennis Denney (JPT Senior Technology Editor)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- April 2011
- Document Type
- Journal Paper
- 90 - 92
- 2011. Society of Petroleum Engineers
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- 74 since 2007
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This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 137428, "Successful Use of Managed-Pressure Drilling To Counteract Lost-Circulation and High- Pressure-Gas Zones: A Case Study From the Red Rock South Wapiti Field in Grande Prairie, Alberta, Canada," by Hassan K. Malik, SPE, Raymond J. Litwin, SPE, and Bernard C. Jones, ConocoPhillips Canada, prepared for the 2010 Canadian Unconventional Resources & International Petroleum Conference, Calgary, 19-21 October. The paper has not been peer reviewed.
Use of heavy mud weight (MW) to control high-pressure (HP) -gas and lost-circulation zones at the same time is a challenge. The Red Rock field in the South Wapiti area in Alberta experienced this combination, which resulted in high operational costs, primarily caused by an additional casing string, high MW, and severe mud losses. On average, costs were 20% higher than anticipated, making this drilling program uneconomical.
The Red Rock field is in the Deep basin of western Alberta, where much of the gas is found in low-porosity, low-permeability reservoirs deposited in an epicontinental seaway. The Deep basin is unique in that porous rocks are water saturated updip to the east and gradually become gas saturated and less porous downdip to the west.
The Falher section (overlying the Gething formation) is overpressured in the area, but there is more confidence in predicting the presence on a broad scale. Coals are found throughout the Falher and Gething formations and must be considered. Historically, lost circulation has occurred in the Falher section at elevated MWs, also into several coal seams in a few cases. Recent wells have experienced kicks in the Bluesky, Gething, and Falher zones, which have driven MWs higher to manage risk. Further uphole, the Doe Creek and Dunvegan formations have been pinpointed as a main lost-circulation section in the area. Natural fractures exist in the wider area across this section, which supports the determination that these zones cause lost circulation.
Red Rock Drilling Challenges
Wells in this area are drilled with an invert-oil-based-mud (OBM) system, which is used in the field with consistent success in keeping reactive shales stable. The use of OBM systems, with high oil/water ratios, is costly in lost-circulation situations. Wellbore-strengthening materials have been used to varying degrees to mitigate losses while drilling the usual problem zones. This is seen when drilling into the Doe Creek and Dunvegan formations with low MWs (930–980 kg/m3) and losses are encountered. A regime of adding wellbore-strengthening materials before penetrating these zones helps heal the losses, and in several cases allowed the MW to be increased deeper in the well. This technique is an important tool in this area to drill through loss zones.
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