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Oil, Gas & Geothermal - Inje n Wells Page 2 of 3 <br />injection wells in the Underground Injection Control (UIC) program. <br />Where Are They? <br />Injection wells are found in many oil and gas fields located in the <br />counties where oil and gas are produced. <br />What Are They For? <br />Class II injection wells are used to safely dispose of the salt and fresh <br />water produced with oil and gas. Injection is often accomplished in a <br />manner that will increase oil and gas production. About 6 times more <br />water than oil is produced from California's oil and gas fields. <br />Does Injected Water Serve a Useful Purpose? <br />Yes. In about 90 percent of the Class II injection wells, water is <br />injected into petroleum reservoirs to increase oil production. About 60 <br />percent of California's oil production is a result of Class II injection <br />wells. <br />Is Anything Besides Water Injected? <br />Current state and federal regulations allow nonhazardous fluids <br />produced from oil or gas wells and several other nonhazardous fluids <br />associated with the production process to be injected into a Class II <br />well. These other fluids include diatomaceous earth -filter backwash, <br />thermally enhanced oil recovery cogeneration plant fluid, water - <br />softener regeneration brine, air scrubber waste, drilling mud filtrate, <br />naturally occurring radioactive materials (NORM), and tank bottoms. <br />What Is An Injection Well Like? <br />After a well is drilled, often to depths over 5,000 feet, steel pipe called <br />casing is cemented in the hole. The casing and cement prevent fluids <br />in different zones from mixing with each other or with injected fluids. <br />The casing and cement are perforated opposite the injection zone. To <br />provide an extra layer of protection, tubing is placed in the well to a <br />point just above the perforations and a packer is used near the bottom <br />of the tubing to seal it against the casing. The packer prevents water <br />from entering the space between the tubing and casing when water is <br />injected down the tubing. Several tests are run to make sure the well is <br />operating properly and the injected fluids are confined to the intended <br />injection zone. <br />What Is An Injection Zone Like? <br />An injection zone is usually sandstone, a rock porous and permeable <br />enough to accept injected fluids. Rock beds chosen for injection zones <br />are covered by impermeable beds, like shale, that act as cap rocks, <br />confining injected liquids in the porous beds. <br />How Is Produced Water Handled? <br />After oil and gas are separated from the produced water at the <br />producing well, the water is piped or trucked to the injection site. <br />There, the water is transferred to holding tanks and pumped down a <br />Class II injection well. <br />How Often Are Injection Wells Checked? <br />All injection wells are monitored by Division engineers to ensure the <br />wells are operated properly and have mechanical integrity. Monitoring <br />includes reviewing operational data and running tests like Mechanical <br />Integrity Tests (i.e., spinner, temperature, and pressure tests and <br />tracer surveys). In addition, most well sites are inspected annually by <br />Division engineers. Samples of the injected fluids may be taken at any <br />time to confirm compliance. <br />How Are Injection Wells Permitted? <br />Operators of Class II injection wells must file for a permit with the <br />http://www.conservation.ca.gov/dog/general_informationIPageslclass_injection_wells.aspx 6/29/2009 <br />