Soil properties affecting wheat yields following drilling-fluid application.

crease in waste drilling-fluid production. For example, Colorado drilling permits for oil and gas wells increased Oil and gas drilling operations use drilling fluids (mud) to lubricate by over 100% from 2000 to 2003 (Anonymous, 2004). the drill bit and stem, transport formation cuttings to the surface, and seal off porous geologic formations. Following completion of the well, Few studies have addressed the impact of drillingwaste drilling fluid is often applied to cropland. We studied potential fluid land application on plant growth and soil properchangesinsoilcompactionasindicatedbyconepenetrationresistance, ties. Previous research indicates that the drilling-fluid pH, electrical conductivity (ECe), sodium adsorption ratio (SAR), impact on plant growth is largely negative due to high extractable soil and total straw and grain trace metal and nutrient plant available trace metals and soluble salts (Nelson concentrations, and winter wheat (Triticum aestivum L. ‘TAM 107’) et al., 1984; Miller et al., 1980; McFarland et al., 1992a, grain yield following water-based, bentonitic drilling-fluid application 1992b, 1994; Younken and Johnson, 1980). However, (0–94 Mg ha 1 ) to field test plots. Three methods of application (nor- some researchers (Nelson and Mikesell, 1982) also found mal, splash-plate, and spreader-bar) were used to study compaction positive or no impact from drilling fluids applied at effects. We measured increasing SAR, ECe, and pH with drillinglower rates or drilling fluids produced with more benign fluid rates, but not to levels detrimental to crop production. Field measurements revealed significantly higher compaction within areas materials. Differences between studies have primarily affected by truck travel, but also not enough to affect crop yield. In resulted from the wide range of drilling-fluid compothree of four site years, neither drilling-fluid rate nor application nents and rates used by various investigators. The fate method affected grain yield. Extractions representing plant availabil- of trace metals in soil following drilling-fluid application ity and plant analyses results indicated that drilling fluid did not has also been investigated. Some workers (Deeley and significantly increase most trace elements or nutrient concentrations. Canter, 1986) conducted fractionation studies that sugThese results support land application of water-based bentonitic dril- gested trace metals would not be significantly released ling fluids as an acceptable practice on well-drained soils using con- whileothers(Bates,1988)foundincreasesinplantavailtrolled rates. able forms of trace metals and movement in a column study. Impacts of application on farm land in Colorado are T he oil and gas drilling industry uses drilling fluid primarily anecdotal, with some farmers claiming im(often referred to as drilling mud or muds) to lubri- proved moisture retention on sandysoils (L. Avis, Colocate and cool the drilling apparatus, transport formation rado Oil and Gas Conservation Commission, personal cuttings to the surface, and seal off porous geologic communication, 1995). The Colorado Oil and Gas Conformations. Following completion of a well, spent dril- servation Commission (Anonymous, 2001) lists land apling fluids and formation cuttings are allowed to settle plication of water-based bentonitic fluids disposal as an in a reserve pit before disposal. Waste drilling fluids are acceptable method of disposal with limits on the depth often land-applied following completion of an oil or gas of the drilling fluid. The waste shall be applied to prewell in Colorado and other areas of the Western United vent ponding or erosion and must be incorporated as States. This material usually contains production water, soon as practicable. The regulations also specify limits bentonitic clays, formation cuttings, barite, Na com- following application for concentrations of metals and pounds, and synthetic organic polymers. During the early total petroleum hydrocarbons in soil, and limit soil ECe 1990s, explosive growth in natural gas drilling created to less than 4.0 dS m 1 or two times background, SAR over 800 000 m 3