Drilling for oil and gas in the Overthrust and Disturbed belts of the Rocky Mountains has received considerable attention in recent years. Zones having low pressure gradients are frequently encountered, when drilling in the mountains. Operating companies and drilling contractors have learned to respect lost circulation problems.

This paper discusses Phillips Petroleum Company's approach for controlling this problem in a well drilled in Gallatin County, Montana. Using compressed air down the drill pipe to lighten the drilling mud's hydrostatic pressure is an accepted method of combating lost circulation. A parasite aerating string is a tubing string attached to the outside of the surface or intermediate casing and is used to inject air into the casing-drill pipe annul us. Reduction in hydrostatic pressure to effective mud weights of 6 ppg (719 kg/m2) or less can be obtained with the proper air/mud ratios and the correct setting depth of the air injection point.

A parasite aerating string offers several advantages over using an air-mud mixture down the drill pipe:

  1. Ease of operation, no special procedure needed for making connections or trips.

  2. No changes in downhole equipment are required.

  3. Conventional bit hydraulics can be used.

  4. Air does not contact the open hole.

  5. Corrosion is limited to the coolest section of the hole and only above the injection point.

Keywords:
drill pipe, injection tie-in, drilling fluid management & disposal, drilling operation, spe 14734, rotary table, diameter, parasite, iadc spe 14734, eccentricity
Subjects:
Drilling Operations, Pressure Management, Drilling Equipment, Drilling Fluids and Materials, Casing and Cementing, Well control, Drilling fluid management & disposal, Casing design
Copyright 1986, IADC/SPE Drilling Conference
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