Almost half of our current gas portfolio comes from unconventional resources, including shale gas, tight gas and coalbed methane. We have unconventional gas operations in five US states and in Oman, where we began producing gas in 2017.
The volume of freshwater withdrawn by our unconventional gas operations was 2.1 million m3 in 2017, which represents 0.8% of the group total. We look at ways to reduce freshwater use and support industry efforts to identify new water treatment technologies. For example, we have invested in a water company that manufactures desalination management systems.
We design, operate and decommission our wells in a way that reduces the risk of water contamination. We install multiple layers of steel into each well and cement above and below any freshwater aquifers. We then test the integrity of each well before we begin the fracturing process and again at completion.
We work to reduce our greenhouse gas and other emissions. As an example, in Oman our central processing facility reduces the need for processing equipment at individual well sites, which can be additional sources of methane emissions in gas production.
The water and sand that make up 99.5% of the injection material used in hydraulic fracturing are mixed with chemicals that help reduce friction and bacterial growth in the well. We list the chemicals that we use at each site. We also submit data on their use in our hydraulically fractured wells in the US, to the extent allowed by our suppliers, who own the chemical formulas, at fracfocus.org, or other state-designated websites.
Hydraulic fracturing creates very small earth tremors that are rarely felt at the surface. Before we start work, we assess the likelihood of our operations causing such activity. For example, we identify natural faults in the rock. This analysis informs our development plans for drilling and hydraulic fracturing activity, and we design our operations to mitigate this risk.