Injection Well

The Safe Drinking Water Act, administered by the U.S. Environmental Protection Agency (EPA), provides authorities for regulating underground injection of fluids and serves as the framework for regulation of geologic sequestration of CO₂ and enhanced oil recovery (EOR). The major purpose of the act’s Underground Injection Control (UIC) provisions is to prevent endangerment of underground sources of drinking water from injection activities. EPA has put regulations into effect with minimum federal requirements for six classes of injection wells. In 2010, EPA put regulations into effect for the underground injection of CO₂ for long-term storage and established UIC Class VI, a new class of wells solely for geologic sequestration (storage) of CO₂. The well performance standards and other requirements established in the Class VI rule are based on the distinctive features of CO₂ injection compared to other types of injection.

CO₂ injection for EOR is conducted using Class II wells (those associated with oil and gas production). The Safe Drinking Water Act also authorizes states to administer UIC programs in lieu of EPA, known as primacy. For Class VI CO₂ geologic sequestration wells, only a few states have primacy. Most oil and gas producing states have primacy for Class II wells and regulate these wells under their own state programs.¹

Application

Like the design and construction of all wells, injection wells for a carbon storage project must be carefully thought out and planned considering the overall, long term goals of the project. Those goals include operation as well as monitoring, verification and accounting throughout the life of the project. As an example, we will look at the injection well designed for the Aquistore Project in Saskatchewan, Canada as compiled in a report by the Global CCS Institute.²

Injection well design for the Aquistore Project in Canada. The deep saline system targeted for the Aquistore project comprises the Deadwood and Black Island Formations at a depth of ~ 3,150 m in the well. The Ice Box Shale / Winnipeg Shale constitute the primary sealing unit. Notice that the Prairie Evaporite, higher up in the well, is considered a secondary sealing unit.³

The injection well was specially designed to be CO₂ resistant.
- Chromium casing was used, along with a special blend of designed CO₂ -resistant cement system. This CO₂ resistant cement is in place to a depth of 2600 meters.
- Down the well, the instrumentation consists of a CO₂ resistant packer and a corrosion inhibitor between the well casing and tubing. The tubing itself is 4 ½ inch carbon steel.
The injection well is equipped with a ‘down-hole’ pressure and temperature gauges.
- These tubing-conveyed gauges were installed on the 4 ½ inch tubing.
- These gauges will provide real-time data on downhole pressure (injection and/or shut in) for the well and measure internal tubing pressure (the CO₂ injection pressure) and the pressure between the casing and the tubing (the inhibited fluid above the packer).
Additionally, a fiber optic Distributed Temperature System (DTS) and a Distributed Acoustic System (DAS) were installed on the 7 5/8 inch casing of the injection well. These systems enable monitoring of pressure, temperature and sound in multiple geologic intervals to provide evidence of containment of injected CO₂.
The well itself is topped by surface equipment including a 34.5 MPa wellhead.
In addition, a full suite of well logs were run on the well.