Abstract
Unlike most other conventional petroleum products that are derived from crude oil, gas‐to‐liquids (GTLs) are petroleum products that are synthesized from natural gas (methane). This process results in GTL products having no sulfur and low aromatic content, so they should have less impact on human health and the environment compared with crude oil–derived products. The GTLs have been registered for use as nonaqueous base fluids (NABFs) in drilling muds, which aid in the process of drilling wells for oil and gas extraction; it is through these uses and others that they enter terrestrial environments. The primary objective of the present study was to determine whether GTLs were less toxic to terrestrial soil biota than conventional NABFs used for land‐based drilling, such as diesel and low‐toxicity mineral oil (LTMO). A second objective was to understand the fate and impact of these fluids under more realistic soil and aging conditions of a common west Texas (USA) oil‐producing region (i.e., sandy loam soil with low organic matter and a hot arid climate). Acute terrestrial toxicity studies were conducted on the soft‐bodied terrestrial invertebrate earthworm (Eisenia fetida) along with 3 plant species—alfalfa (Medicago stavia), thickspike wheatgrass (Elymus lanceolatus), and fourwing saltbrush (Atriplex canescens). We also assessed changes in microbial community structure of the soils following additions of NABF. Overall, the GTL NABFs had lower toxicity compared with conventional NABFs like diesel and LTMO, as measured by invertebrate toxicity, plant seed germination, and impact on the microbial community. Environ Toxicol Chem 2020;39:721–730. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.
Highlights
Gas‐to‐liquids (GTLs) are hydrocarbon liquids that are synthesized from natural gas, unlike most other conventional petroleum liquids that are derived from crude oil
The 2 GTL nonaqueous base fluids (NABFs) had a similar composition; GTL with a carbon chain length ranging from C10 to C22 was referred to as GTL10–22, and GTL with a carbon chain length ranging from C11 to C24 was referred to as GTL11–24
Dissipation of NABFs from sandy loam soil during the 90‐d aging period at either 10 or 30 °C was assessed from the GC–flame ionization detector (FID) and 2D GC data
Summary
Gas‐to‐liquids (GTLs) are hydrocarbon liquids that are synthesized from natural gas (methane), unlike most other conventional petroleum liquids that are derived from crude oil. The technology to produce GTL products was first developed in 1926 but was not considered economically feasible for commercial‐scale use. It is economically feasible to produce GTLs, and they are entering the market in a variety of products including fuels, base oils, solvents, naphtha, waxes, and drilling base fluids. The GTLs are being used as nonaqueous base fluids (NABFs) in drilling muds both onshore and offshore (International Association of Oil & Gas Producers 2016). The drilling mud mixes with material from the borehole and carries it up to the surface. This mixture, termed drill cuttings, is often saturated with drilling mud and is treated using various physical separation methods to recover the drilling mud for recycling. The treated cuttings can be further processed to remove more of the wileyonlinelibrary.com/ETC
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