With proper engineering, liquid nitrogen can be used safely as a hydraulicfracturing fluid. The fluid's extremely cold temperature (-300 to -320°F) willinduce thermal tensile stresses in the fracture face. These stresses exceed thetensile strength of the Devonian shale, causing the fracture face to fragment.Because of the extreme temperatures, treated water can be used as a diverterbetween fracturing stages. This water freezes instantly when it contacts thefirst treatment zone. This paper discusses the successful application of thistechnology to stimulate the Devonian shale in Eastern Kentucky.
Liquid nitrogen has been applied in coal seams and sandstone reservoirs forthe stimulation of gas production in the San Juan Basin of New Mexico. Fornitrogen to be pumped safely into a well, the entire surface manifold andwellhead must be made of stainless steel. In some cases, operators may usefree-hanging fiberglass tubing to protect the casing from extremely coldtemperatures.
Using liquid nitrogen as a fracturing fluid is a process that is in an earlystage of development. Theoretically, self-propping fractures can be created bythe thermal shock of an extremely cold liquid contacting a warm formation. Asthe fluid warms to reservoir temperature, its expansion from a gas to a liquidresults in an approximate eightfold flow-rate increase. For example, a12-bbl/min liquid nitrogen flow can result in a flow rate as great as 96bbl/min some distance from the fracture.
The Devonian shale, a thick formation beneath a large portion of EasternKentucky and West Virginia, has been described previously. This Devonian shale has a low permeability, is somewhatwater-sensitive, and typically produces through natural fractures. Operatorshave used a number of different techniques to stimulate wells in the Devonianshale. However, stimulating these wells with a nitrogen-gas fracturingtreatment is currently a common method. Fracturing this type of formation withcold liquid nitrogen rather than warm gas could prop fractures open moreefficiently.
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