A water-base drilling fluid treated with a special additive has successfully replaced the diesel oil base muds (DOBM) on a series of wells drilled in the South Texas Lower Wilcox formation. Until recently, a relaxed fluid loss DOBM mud was used in this hole interval because It provided improved hole stability and higher penetration rates at favorable economics. The only problem the DOBM mud did not solve was environmental. The cuttings were coated with oil and high salinity brine and therefore had to be treated before they could be disposed of locally. Efforts to find an environmentally safe DOBM mud replacement have resulted in the development of a special additive for water base muds. It offers a significant reduction in total well cost by increasing the rate of penetration and reducing the mud and cuttings disposal costs.

This paper will discuss the field development and use of this special drilling fluid additive that provides improved performance characteristics when compared to traditional, economic, environmentally safe water-based mud systems. Over 45 wells have been drilled with this new water-base drilling fluid additive. In some areas, the average rate of penetration, including connection time, has increased 30% over the DOBM average. The rotating hours required to drill an interval from 1500 - 3000 feet in length with 14.0 - 16.0 ppg mud have been reduced accordingly. Total well costs have been reduced by 20 percent. The authors provide data on how to optimize water-base mud formulations, special additive maintenance treatments, mud solids management and bit performance utilized on this successful South Texas drilling program.

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