Hydro-Fracturing For Low Yield Wells Water Well DrillingPumps - Service & Installation
The Hydrofracturing Process
The procedure involves the installation of an inflatable or mechanical packer which is placed in the well bore at least 20 feet below the casing and drive shoe seal and at least 60 feet below the 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) and in some cases 3000 psi pressure may be needed in tight rock formations. Examples 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 75 gallons per minute (gpm) have proven successful. Generally, 1500 to 2000 gallons of water are pumped into the bedrock formation. Continued... It is extremely important that only clean, disinfected water is used for injection water because of the extreme pressure involved and the potential for forcing contaminants deep into the bedrock aquifer. One or two packers may be used for hydro-fracturing. 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 frac sequence, the packer is deflated or unlocked and lowered further into the hole and the process is repeated as many times as necessary. Commonly two sequences are performed. Zone fracturing utilizes a two packer system where the packers in series and water is pumped into the zone between the packers. This system can be more effective because it concentrates pressures within a small area, typically 30 to 60 foot intervals, and individual fractures can be isolated and hydraulically fractured. With this method, the procedure starts within a specified section of the well targeted by the water well contractor. Each successive 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 being hydro-fracked. 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 but still may produce adequate results for private wells serving individual households. Zone fracturing is more expensive and time consuming procedure and is generally used only on difficult wells or public supply wells or if a larger flow of water is desired.