Tag: solids-removal equipment

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UNDERBALANCED DRILLING SOLIDS-CONTROL POSSIBLE PROBLEMS

Shale

In general, thick shale sections cause problems with UBD. They slough or cave into the hole. This is probably due to thick shale sections having some elements of laminating, geo pressuring, or sensitivity to water. As a general rule, thick shale sections should not be drilled underbalanced. In the special case of air/gas drilling, shale usually remains stable as long as it is kept dry. Even the small amount of water in mist drilling will destabilize most shale. These formations need to be put behind casing within a few days. Watch out for excessive caving and especially long, thin cuttings. Once caving starts, it cannot be controlled with under-balance operations.

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REMOVAL EQUIPMENT EFFICIENCY ON WEIGHTED DRILLING FLUID

After drilling 1000 ft of hole with a 12.5-lb / gal drilling fluid circulated at 25 bbl / min, the hole was circulated clean. This required four hole volumes to eliminate all solids in the discard. Assuming that the formation averaged about 13%vol porosity, a multiarmed caliper indicated
that a volume of 97.3 bbl of new hole was drilled. The drilling fluid was freshwater-based mud weighted with barite and contained 2%vol bentonite, no oil, and 5%vol drilled solids. While drilling this interval, 1350 sacks (sx) of barite (100 lb / sx) were added to the system, and the drilled solids remaining in the system were diluted as required to control their concentration at the targeted 5%vol. Some drilling fluid was pumped to the reserve pits, and all discards of the solids-control equipment were captured in a container to be shipped back to shore. One drilling-fluid technician reported that 200 bbl were hauled to shore, and another reported that 180 bbl were captured.

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SOLIDS REMOVAL EQUIPMENT EFFICIENCY IN AN UNWEIGHTED DRILLING FLUID

Situation: NoProfit Drilling Company is drilling 100 bbl of hole daily in a formation with 15% porosity. For four consecutive days, 400 bbl of discards and fluid were captured each day in discard tanks. The pit levels remained constant, but some drilling fluid was jetted to the reserve pits daily to keep the pits from overflowing. The unweighted drilling fluid weighed 9.4 ppg daily and contained 2%vol bentonite

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OPTIMUM SOLIDS REMOVAL EQUIPMENT EFFICIENCY

For that reason the resulting solids removal equipment efficiency required is called the optimum solids-removal efficiency. It is independent of the volume of drilled solids reaching the surface, or the volume of the drilling-fluid system. Equating the volume of clean drilling fluid needed to the volume of discard results in the minimum volume of clean drilling fluid needed and, as a consequence, the minimum volume of drilling fluid disposal.

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