Publications Details
Hydraulic fracturing in tight, fissured media
There are tremendous resources of natural gas in tight fissured rocks, but these formations require special care for hydraulic fracturing to be successful. Serious problems include leakoff, damage and complex fracturing. Leakoff may be constant, pressure-sensitive, or accelerating. Leakoff becomes most severe when fissures begin to dilate and accept large volumes of fracture fluid, which may rapidly dehydrate a sandladen slurry. Determining values of pressure-sensitive and accelerated leakoff coefficients is difficult, and generally requires both a pressure-decline analysis (after a minifrac) and an analysis of the injection pressure. Fine-mesh sand, often used in fissured reservoirs, will help control leakoff. Damage to the natural fractures, due to leakoff of the fluid and gels and to mechanical types of damage, must be avoided, since the fissures are the production mechanism. It is particularly important to minimize the amount of liquid and gels, since the fissures are narrow and easily blocked. These concepts are also applicable to oil reservoirs.