An injection well bored in a mafic and/or ultramafic rock used for carbon dioxide sequestration and a method of cementing a CO.sub.2 injection well with a formulated cured. The injection well may include a surface casing and an injection casing placed in a drilled borehole. The injection well may have an open interval permitting fluid communication f into the mafic and/or ultramafic rock. A cured cement may be present between the mafic and/or ultramafic rock and the injection casing and may be formed from a cementitious slurry mixture containing a class G cement, fly ash, microsilica, additives, and an epoxy resin blend. An injection tubing is disposed in the interior of the injection casing, having fluid communication with the interior of the injection casing. A packer connected to the injection tubing may be present as a fluid seal within the injection casing.

A downhole tool can include a body within a tubing string, a first component such as an outer mandrel, a detent pin connected to an inside of the first component, wherein the detent pin comprises a pin body and a spring located within the pin body, and a second component such as a sliding sleeve that moves in relation to the first component. The outside of the sliding sleeve includes a channel with a first stop, second stop, and optionally a third stop. When a pressure differential is applied to the tool, the spring can compress and the detent pin moves from the first stop to the second stop, which can open flow ports into a wellbore annulus. The detent pin can traverse again through the channel from the second stop to the third stop, which can close the flow ports.