Hydrofracturing is a well development process that involves injecting water under high pressure into a bedrock formation via the well. This is intended to increase the size and extent of existing bedrock fractures, pumping water into those fractures at pressures as high as 3000 psi and flow rates as high as 85 gallons per minute, this cleans out the fractures and allows them to interconnect with nearby water bearing fractures. Water can then flow back thru these fractures and into the well at a faster rate than before.

Process

The procedure involves the installation of an inflatable packer which is placed in the well bore at least 40 feet below the well casing and drive shoe seal and at least 60 feet below ground surface to insure that the process does not “break” the seal or allow surface water contaminants to enter the well. The packer is inflated or locked into position and water is pumped through the packer under pressure. Most applications require between 500 and 2000 pounds per square inch(psi) pressure and in some cases 3000 psi pressure may be needed in tight rock formations.

If successful, pressure will steadily rise to a maximum level as the rock formation resists flow then will suddenly drop off and stabilize at a lower pressure. The drop in pressure indicates that the formation is accepting water and the resistance to flow is diminished. Water is pumped into the formation for 5 to 30 minutes. Injection pump delivery rates of 50 to 85 gallons per minute and generally 800 to 1200 gallons of water per zone.

One or two packers may be used for hydrofracturing. When utilizing one packer, it is set near the top of the well but at a minimum safe distance below the drive shoe. After the initial pressurization or “hydrofrac” sequence, the packer is deflated and lowered further into the hole and the process repeated. Commonly two hydrofrac sequences are perfomed.

Zone isolation hydrofracturing utilizes a two packer system where the packers are placed in series and water is pumped into the isolated zones between the packers. This system can be more effective because it concentrates pressures within a small area, typically 40 to 60 foot intervals, and individual fractures can be isolated and hydraulically fractured. With this method, approximately 8 zones are isolated within the well starting within a specified section of the well. Each successive hydrofrac sequence stresses one interval higher than the last. In this way, all potential water bearing fractures or fracture zones are worked independently within the section of the well bore being hydrofracked. This differs from, the single packer, one or two frac sequence method which probably only affects the weakest, least resistant point(s) in the well.