Water availability footprint of shale gas production in Sichuan Basin, China

China has been optimistic by setting its shale gas production goal, in the newly released 13th Five-Year National Shale Gas Development Plan, to reach 30 billion m3 by 2020, which is anticipated to be a seven-fold increase of... [ view full abstract ]

China has been optimistic by setting its shale gas production goal, in the newly released 13th Five-Year National Shale Gas Development Plan, to reach 30 billion m³ by 2020, which is anticipated to be a seven-fold increase of 2015. Sichuan Basin, possessing the highest technically recoverable shale gas reserves and most pilot regions for commercial production in China, is the most promising area for developing shale gas to realise China’s national strategy of increasing nature gas in primary energy consumption.

Shale-gas production potential is constrained by water availability in terms of both consumptive water use (related to the mixture of freshwater and chemicals used in the hydraulic fracturing process) and degradative water use (related to wastewater generated by the well). No study of water availability of shale gas production so far has addressed both via a single indicator; most studies have focused on consumptive water use. Besides, the current critical dilution approach to assessing degradative water use distorts the fact that the positive/negative sign of indicator score is the same as that of the emission load, and ignores the contribution of any water purifying process. This study aims at assessing the water availability footprint of shale gas production by using a new single stand-alone indicator.

The water availability footprint indicator (WAF), at the unit-process level, is defined as the sum of results for consumptive water use (V_con) and degradative water use (V_deg). V_con equals the volumetric change between water extraction and wastewater effluent. V_deg for a certain type of emission is defined by the emission load and the reference emission concentration in a water quality standard. V_con and V_deg for background processes are calculated based on specific assumptions for processing data from existing databases. The WAF is then multiplied by the water stress index (WSI) of the region where the process occurs to get a weighted indicator WSAF, followed by aggregating every WSAF into a life-cycle score.

The case study is a cradle-to-gate analysis of the shale gas production in all the four pilot regions in Sichuan Basin, China. The functional unit is defined as 1 MJ of natural gas at plant ready for further application (e.g. electricity production/heating/transport fuels/etc.). Inventory data for foreground unit processes (viz. well site investigation, well pad and road construction, well drilling, hydraulic fracturing, well completion including wastewater treatment and re-fracturing, gas production and cleaning, and well closure) are collected through site surveys and literature. Background data are from databases CLCD-China and ecoinvent. Emission of total dissolved solids is assessed regarding consumptive water use. WSIs of various regions in Sichuan Basin are adopted from literature. Computations are with the software eBalance.

By presenting the water availability footprint of shale gas production in Sichuan Basin, China, we anticipate to show that the primary benefit added by WASF to product water availability footprint assessment lies in its ability to distinguish water purifying processes (e.g. wastewater treatment) from water degradative processes and its operability with existing LCA database support.