Lost Circulation Specialists, Inc.

Case History

Karr Area Seepage Loss

Gulf has drilled 7 wells in the Karr field since July 1987. These wells were all drilled using an I.D.F. maintained 80/20 invert diesel oil mud to an average T.D of 2,390 m. Invert losses have averaged 82 m3 per well.

Invert losses can be separated into drill solid losses and seepage losses. Drill solid losses account for invert lost on surface as a fine invert coating on the drilled solids. This loss should correlate directly to cuttings volume and be relatively constant n the Karr area assuming constant physical down hole parameters. Seepage losses account for whole mud lost into permeable parameters. Seepage losses account for whole mud lost into permeable formations, fractures and coal seams. In the Karr area, invert losses increase substantially when porous intervals are penetrated.

Karr seepage losses were formerly controlled by additions of bridging solids such as mica, ground walnut, venfiber and ground calcium carbonate throughout the mud system. However, losses were still substantial (82 m3) and the high surface area of some additives (Mica) may even have increased surface losses. Inverseal was used on 12-29 resulting in 86 m3 of invert losses. Magma Fiber, a relatively new product, was utilized on the most recently drilled well, Karr 16-25-65-4W6. The improved seepage control was apparent.

Magma Fiber Description

Magma Fiber is a fluid loss additive composed of lumps of long Fibers manufactured from spun molten mineral. The mineral composition is largely composed of Ca0 and SiO2 and despite this composition is practically 100% soluble in 7.5% HCl. Magma Fiber readily dissociates into individual fibers when mixed in either water or oil-based muds. These fibers form a fluid suspended mat that can effectively bridge off formation permeability.

Magma Fiber Application at Karr 16-25-65-4W6

A 10 m3 invert pill with 35 kg/m3 Magma Fiber addition was mixed and isolated in one of the suction tanks. This pill was circulated around the hole once daily. The pill returns were diverted to by pass the shaker to prevent it from screening off and returned to the isolation tank. The Magma Fiber pill became strung out or diluted with each circulation. This can be controlled by treatment of the excess diluted pill with a centrifuge. Contamination of the entire mud system with Magma Fiber is undesirable due to increased invert losses over the shaker screen.

Two Magma Fiber pills were utilized at Karr 16-25 at a cost of approx. $1,500. The invert losses for this well were 54 m3 as compared to the average Karr area loss of 82 m3. The mud bill for 16-25 was $42K as compared to an average of $72K for the previous 6 Karr wells.

Recommendations

1. Continue to use Magma Fiber as a seepage loss additive in the Karr area as per the attached Recommended Procedure.
2. Discontinue use of other seepage loss additives such as ground walnut, mica, venfiber, etc. when utilizing Magma Fiber.
3. Consider Magma Fiber for seepage loss control in all invert-drilled wells.

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