Abstract
Horizontal wells drilled in deep coal (deeper than 4000ft) must be hydrofracked for commercial gas production. Loss of permeability with increasing depth is discussed. Prior to hydrofracking, a “mini frac” is done to recover many reservoir data that help design a good hydrofracking. The use of a “self-powered intelligent data retriever (SPIDR)” is discussed. Currently available three techniques of creating openings in the casing are presented. They are (a) pump down P-n-P process, (b) balls and frac sleeves method, and (c) coiled tubing frac sleeves technique. Finally, frac-fluid and proppants are discussed with their merits and demerits. Typically, slick water is the favorite fluid and coated sand or manmade proppants are recommended where closure pressure may exceed 8000psi. The frac fluid rate is usually high (about 100bpm). A typical stage (there are many stages in horizontal lateral spaced at 250–1000ft interval) may consume 300,000gal of fluid with 300,000lb of sand.
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