Earlier this year, the World Economic Forum and CERA released a new report, “Thirsty Energy: water and energy in the 21st century.” Given this month’s production focus on water management, it seems an appropriate time to briefly review some of the report’s more salient points as it relates to upstream oil and gas.

Water is an issue of increasing import to the industry, as many of the more promising, remaining fossil fuel reserves are water intensive to produce — including oil sands and unconventional natural gas. The introduction and scale-up of carbon capture and storage also increases the water exposure of the energy sector. As is well known, in older fields, more water is produced than oil. This water is frequently too contaminated to release without proper treatment.

The report asserts that as the industry focuses on advanced and enhanced oil recovery (EOR), it will need to find new water sources for use in production and solve disposal problems related to produced water. The quality of produced water varies widely—some nearly fresh, but the vast majority as salty as seawater.

In 1999 worldwide, the CERA/WEF report stated, “an estimated 210 million barrels of water were produced along with oil. As much as 75% of this produced water was re-injected into the oil reservoirs to enhance oil recovery.”

EOR techniques and unconventional oil resources are often net users of water, sometimes in large quantities. Oil sands are another such consuming resource.When oil sands are mined and oil is removed at the surface, steam is used to strip the bitumen from the surrounding clay and sand. When oil sands are produced in situ, steam is pumped underground to strip the bitumen.

Unconventional natural gas resources are also generally net users of water. Most natural gas resources considered unconventional today involve gas trapped in tight formations underground, including shale or tight sandstone. To produce gas from these reservoirs requires fracturing the underground formation with water to allow gas to flow to the production well. On the other hand, water use is likely to decrease as the well matures, and some older wells will produce water rather than consume it.

The report cites three instances of innovative management of the water produced along with oil. While often a disposal or pollution challenge, the volume of such water is increasing about 10% a year. The ratio of water to oil produced can be as high as 40 to one.

Shell and Petroleum Development Oman are looking to phase out the practice of disposing of produced water into aquifers with salinity lower than seawater. Two preferred methods for disposing of the produced water include: 1) disposal wells to inject the produced water into deep aquifers that contain water unsuitable for human use, and 2) use of produced water in agriculture or forestry near the oil field.

A second example of a better way comes from Chevron’s Kern River oil field in California. There steam is used in the field to lower the viscosity of the oil and allow it to flow to producing wells. Therefore, about nine barrels of water are produced for every barrel of oil. Chevron uses about half this water to generate new steam to enhance oil production.

Because water produced from the field contains minimal dissolved solids and metals, it can, with minimal treatment, be used for agriculture. The excess produced water is treated with an oil-water separator and then processed through large filters filled with, of all things, walnut shells. The water can then be sent through canals for use in local crop irrigation.

Finally, at an oil field near Casper,Wyo., the US Dept. of Energy and Ormat Technologies have been testing use of produced water in geothermal power generation. Hot water from an oil well is moved to a heat exchanger where it vaporizes another liquid with a lower boiling point. The vapor from that liquid turns a turbine, which is connected to a generator. Once the water from the well is cooled, it can be re-injected into the well to enhance oil recovery or released.

As Jeroen Van der Veer, chief executive, Royal Dutch Shell, noted in his contribution to the report, “Availability and access to fresh water have emerged as critical issues, perceived by many as a challenge as pressing as climate change. Analysts estimate that, by 2025, two-thirds of the world’s population could be living in conditions of ‘water stress,’ with a major impact on farming (using 70% of the world’s fresh water), industry (using 22%), and day-to-day living (using 8%)… It is imperative for our industry to improve handling of water-related issues through schemes that reduce freshwater use and maximize treatment and reuse of produced water in our operations.”