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Abstract

The first objective of Canadian Hunter in drilling is to obtain complete open-hole evaluation including drill cutting samples, cores, drill-stem tests, and logs. The second objective is to install and adequately cement a high-quality production casing that will allow successful completion and stimulation treatments. Predominant field characteristics in the Deep basin which complicate the task are sloughing uphole shales, underpressured formations, and multiple pay zones stacked in each well.

The loss of open-hole data due to severe shale sloughing was a serious problem at one point in our development. We tried different drilling techniques to get around this problem, including the use of intermediate casing to shut off uphole sloughing. Finally, we used oil-based drilling fluid, and this now has become a common practice. This fluid almost totally eliminates shale sloughing, and substantially improves the reliability of all open-hole evaluation operations. An important additional benefit is that we achieve faster penetration rates through these generally underpressured formations due to the lighter mud weights that are used. Greater reliability of primary cementing also results from having in-gauge holes and a light thin mud. However, there are still a number of drawbacks in attempting to evaluate too many zones with one wellbore and a single productive target now appears prudent in some well designs.

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