Distribution of Heavy Metals in Waste Drilling Fluids Under Conditions of Changing pH

Abstract

A laboratory study was conducted to determine the influence of pH on the distribution of arsenic (As), barium (Ba), chromium (Cr), and lead (Pb) in three different oil and gas well drilling fluid wastes. Samples were obtained from disposal pits and equilibrated in the laboratory under controlled conditions of pH. A sequential extraction procedure was then used to fractionate the selected elements into the fractions of aqueous, KNO3‐extractable, H2O‐extractable, NaOH‐extractable, EDTA‐extractable, and HNO3‐extractable phases. The chemical fractions present at each pH were then compared, thus providing insight into the potential of mobilization of As, Ba, Cr, and Pb into ground‐ or surface waters. The majority of each of the elements studied was found in the NaOH‐extractable, EDTA‐extractable or HNO3‐extractable fractions except for one waste which contained a major portion of the total barium in the KNO3‐extractable fraction. Generally, decreasing pH caused a shift from the more stable HNO3‐extractable fraction toward less stable EDTA‐extractable, NaOH‐extractable, or KNO3‐extractable fractions. In no case was there a substantial release to the aqueous phase with changing pH. The significance of these results is that with pH changes to be expected in the natural environment there is not likely to be a major release of As, Ba, Cr, and Pb from drilling fluid waste disposal pits. The lower pH values (< 4) which might produce some impact are unlikely to occur in the environment because the wastes themselves have a large neutralizing capacity.

Soil Properties Affecting Wheat Yields following Drilling‐Fluid Application

“…The fate of trace metals in soil following drilling‐fluid application has also been investigated. Some workers (Deeley and Canter, 1986) conducted fractionation studies that suggested trace metals would not be significantly released while others (Bates, 1988) found increases in plant available forms of trace metals and movement in a column study.…”

Heavy Metals Uptake by Aerial Biomass and Grain of Soybean

“…The problem of increased concentrations of some heavy metals caused by the application of crude oil-based fluids was pointed out by Nelson et al, 1984. When crude oil-based fluids were used as liming material, the expected positive changes in soil pH occurred (Deeley & Canter, 1986). As optimum soil reaction for the majority of cultivated plants is around the neutral pH value, liming is a desirable practice because under neutral to weakly alkaline conditions bioavailability of some heavy metals (except As, V, Mo, Co and Cr) decreases (Mathur et al, 1991;Dermatas & Meng, 2003).…”

Revegetation of Oil Well Reserve Pits in West Texas

“…Both organic and inorganic constituents were identified as potential contaminants. However, low pH values (<4.0) sufficient to result in significant release to trace elements from drilling fluids are unlikely due to their great neutralizing capacity (Deeley and Canter 1986). Plant uptake of Zn, Cu, Cd, Pb, and As was directly related to the concentrations of these trace elements added to soils by drilling fluids (Nelson et al 1984).…”