Hydraulic Seam Fracturing

the creation of cracks in rock adjacent to a well by means of pressure on the face and as a result of the injection of viscous liquid into the rock.

Hydraulic seam fracturing is utilized for increasing the productivity of petroleum, natural-gas, and pressurized wells; for forming impermeable screens in rocks; and for improving the conditions for degassing coal seams. The equipment for hydraulic seam fracturing includes pumping units, which develop pressures of up to 50-70 meganewtons per sq m and a production capacity of approximately 10 l/sec; pump-compressor pipes; packers, which allow the insulation of the well face from the tubing space; sand-mixing units; and chambers for the liquids, solid material, and measuring apparatus.

During the process of hydraulic seam fracturing, a viscous liquid is pumped into the well at a rate that ensures the creation at the face of sufficient pressure to form cracks. These cracks are both vertical and horizontal. The cracks may be as much as several dozen meters long and several millimeters or centimeters wide. After the formation of the cracks, a mixture of viscous liquid with solid particles (usually coarse and medium sand, with a grain diameter of about 0.5-1.0 mm) is pumped into the well to prevent the cracks from closing under the effect of the mine pressure. In hydraulic seam fracturing a sand concentration of 100-200 g/l in the liquid and an, amount of sand of up to several dozen tons are used; there are even instances of hydraulic seam fracturing with the injection of hundreds of tons of sand into the cracks. The selection of a liquid depends on the type of seam: in seams that are saturated with petroleum, hydrocarbon liquids are generally used (mineral oils, high-viscosity petroleums, petroleums with asphalt additives, and so on); in water-saturated seams, liquids with a water base are used (products of the pulp-and-paper industry, emulsions, and so on). To increase the length of the cracks, additives are used in the working liquid to decrease its filterability. A combination of hydraulic seam fracturing and treatment of the wells with hydrochloric and hydrofluoric acids is also used. If the seam subjected to hydraulic fracturing consists of a number of intercalations, interval methods of hydraulic seam fracturing are utilized, allowing cracks to be formed in each of the intercalations. In the USSR the method of hydraulic seam fracturing has markedly increased the productivity of oil wells (in certain instances several times over), as well as the intake capacity of pumped wells that are utilized for flooding petroleum seams.