Access recently became available to a web site that can assist oil and gas field operators in sorting out the many available methods for handling water production.
Argonne National Laboratory developed the Produced Water Management Information System, http://web.evs.anl.gov/pwmis, through funding from the US Department of Energy.
The web site includes three modules:
- A technology description module containing basic information on current practices for managing produced water. The module includes fact sheets describing technologies and providing references for additional information.
- A regulatory module summarizing state and federal regulations or guidelines on produced-water management. It also contains hot links to the relevant US Environmental Protection Agency, US Bureau of Land Management, US Minerals Management Service, and state regulatory agency web pages.
- A technology identification module containing a series of questions, mostly answered with “yes” or “no.” These questions lead the user through a decision tree that suggests the most appropriate option for a given location as a function of such factors as location, regulatory acceptance of the practice, technical feasibility, cost, and availability of infrastructure and equipment.
In June 2004, Argonne launched a similar web site, the Drilling Waste Management Information System (DWMIS), http://web.ead.anl.gov/dwm/, which has similar modules (OGJ, Aug. 2, 2004, p. 31). Argonne says that in 3 years DWMIS has received more than 1.7 million hits and nearly 120,000 visitor sessions representing 57,000 unique visitors.
Water production
Water is the largest waste stream by volume generated by oil and gas producers. Some estimates place worldwide water production at more that 77 billion bbl/year. Argonne estimates that onshore oil wells in the US alone produce about 14 billion bbl/year of water. Total US water production increases to 15-20 billion bbl/year when the estimate includes water from natural gas wells, coalbed methane wells, and offshore wells.
These volumes compare with 30 billion bbl/year of oil produced in the world.
Argonne notes that a complicating factor for handling produced water is the water’s variability. Physical and chemical properties depend on geographic location, geological formation, and hydrocarbon produced. Water quality also may change during the producing life of a reservoir.
Water handling
Argonne lists water minimization as an effective way operators can save money and protect the environment. This can be done either with mechanical (packers, plugs, and cement) or chemical (polymer gels) means that prevent water from entering the wellbore. Operators also can reduce water coming to surface through downhole oil-water and gas-water separators as well as seafloor separation modules.
Although looked at mostly as a waste, produced water may have uses. It can enhance oil recovery when reinjected into a producing formation. Argonne notes that tens of thousands of injection wells exist throughout the US and elsewhere for enhancing oil production.
Other uses of water include storage in aquifers for future use and for hydrological purposes such as subsidence control and stream flow augmentation.
In the case of water from coalbed methane wells, the water may have low enough salinity for use without treatment in irrigation, water for livestock and wildlife watering, and wetland management. Argonne also notes that produced water has found industrial uses such as for dust control, make-up water for drilling fluids, and water supply for power generation boilers and cooling units. If treated, the water also can add to drinking water supplies.
If no use is found, operators may also choose to dispose of the water, although this usually requires them to treat the water before disposal. Some disposal technologies that Argonne lists include discharging into a larger body of water, underground injection, evaporation, and offsite commercial disposal.
Argonne says the parameters of greatest concern in disposal are the organic content (oil and grease) and the salt content (salinity, conductivity).
It notes that in some cases the salinity of discharged water such as to the Gulf of Mexico is not a concern, but oil and grease concentration regulations need to be met.
Different technologies can treat the water. Operators can remove salts with membrane processes, including reverse osmosis, filtration, and electrodialysis. Other technologies for removing salts are ion exchange, capacitive deionization, and thermal distillation.
Oil and grease removal technologies include physical separation with hydrocyclones, centrifuges, and filtration. Other options include coalesors, flotation cells, combined physical and extraction process, solvent extraction, and adsorption.
