Life cycle toxicity assessment on deep-brine well drilling

Abstract

The features of a life cycle toxicity assessment (LCTA) model include regionalization, uncertainties, and geographical variability. This study provides a simplified and regionalized LCTA to improve the evaluation of regional toxicity impact based on a case study of deep-brine well drilling in China. Uncertainty analysis was conducted using Taylor series expansions. The proposed LCTA can efficiently quantify the toxicity impact and identify its key contributing factors. Results show that the key factors contributing to the toxicity impact of deep-brine well drilling are steel, electricity, and direct pollutant emissions generated from fluid loss and waste (i.e., waste drilling fluid and drilling cuttings) disposal during drilling. The most significant substances are mercury and arsenic to water, copper and barium to soil, and vanadium to air. Selecting a drilling fluid with low heavy metals, decreasing the consumption of energy and raw materials, reducing the drilling fluid loss, and optimizing the waste disposal are effective approaches to reduce the overall toxicity impact of deep-brine well drilling.

Introduction

Life cycle assessment (LCA) is a scientific method for evaluating the environmental impact of a product, activity, or process from cradle to grave. Features of LCA include regionalization and geography data, specifically for toxicity impact category (i.e., life cycle toxicity assessment (LCTA)). To date, although regionalized LCA models have been established in Europe, America, Canada, and Japan, no models are available for other areas. The present study proposes a simplified LCTA approach based on regional information (i.e., population, environment and geography) to address the gap. A deep-brine well drilling in China is used as an example for the application of the proposed LCTA in a particular region.

Deep-brine is an important mineral resource that contains abundant chemical elements (e.g., Na, Mg, Ca, and I) (Nguyen et al., 2012) that are commonly used in chemical production industry (e.g., sodium chloride, sodium sulfate, barium chloride, and caustic soda production) (Lin et al., 2013). However, drilling deep-brine wells has led to serious environmental problems (e.g., drilling waste production and drilling fluid leakage) (Hong et al., 2014, Ghazi et al., 2011). Disposal of waste drilling fluid is considered one of the most serious environmental problems worldwide (Zou et al., 2011) because drilling fluid contains heavy metals (e.g., Cd, Hg, and Pb (Alimohammadi et al., 2013, Hong et al., 2014) and organic pollutants (e.g., acrylamide and poly vinyl pyrrolidone, Chu et al., 2013, Zhao et al., 2015). LCTA on industrial activities, including cement (Li et al., 2015), aluminum (Hong et al., 2012), copper (Memary et al., 2012), and caustic soda production (Hong et al., 2014) has been widely conducted. Although several LCA studies have been conducted to analyze the impact of well drilling (Hong et al., 2014, Ecoinvent centre, 2010, Stamford and Azapagic, 2014), only one study has involved China (Hong et al., 2014). Hong et al. (2014) evaluated the toxicity impact of deep-brine well drilling by using a European model (ReCiPe) because no regionalized LCTA model has been developed in China. A previous study (Hong and Li, 2010) reported that adopting European data for Chinese research is inappropriate because LCTA involves regional information. Considering the importance of brine in the chemical manufacturing industry and the serious environmental burden caused by well drilling, this case study focuses on deep-brine well drilling in Dongying City.

This study aims to develop and apply an easy and useful regionalized LCTA approach to quantify the toxicity impact of deep-brine well drilling, identify key factors, and explore potential approaches to reduce toxicity impact.