WORK PLANS - Laserfiche WebLink

Home Browse Search

CA ARNG Field Quality Assurance Project Plan 8.4.9 For a 600 -foot well, the pressure of a grout column (assuming an average grout weight of 13 pounds per gallon fibs/gal]) is calculated as follows: 600 ft x 13 lbs x 0.0322* = 250 psi (Equation 15) gal *Conversion factor. Source: Woodward, 1996. 8.4.10 If a 600 -foot column of grout exerts 250 psi of pressure, the pump pressure should be approximately 350 psi to reach the maximum 600 psi pressure. 8.4.11 Grout placement by applying external pressure in excess of hydrostatic pressure is known as squeeze grouting. Pressure is maintained by sealing of the casing while pumping fluid into the casing with a positive displacement pump and monitoring pressures at the surface with a gauge. When the seal is placed at the surface, the technique is referred to as a Bradenhead squeeze. This technique would be less effective in wells with perforations above the interval being sealed. Pressures may also be maintained downhole through the use of drillable grout plugs, or retrievable balloon packers, retrievable tension -set packers (set by applying a tension on the packer with the pipe attached to the packer), or retrievable cup - packers (set by the fluid pressure below the packer, which creates a seal by forcing the cup against the well casing). Grout is squeezed through the perforations and into the gravel pack by the high forces developed through the hydraulic effect of transmitting pressure through a small -diameter pipe and into the large -diameter casing. 8.4.12 Potential problems may result when grouting next to very permeable formations. Inability to maintain pressure at the wellhead may be encountered by any or a combination of several techniques (Halliburton Services, 1985): • Decreasing the injection pressure; • Blocking circulation loss with flaky, fibrous, granular, or jelling additives; • Plugging with quick -setting cements; and • Periodically pumping and waiting during grout injection. 8.5 Perforation of the Casing 8.5.1 In order to minimize the possibility of vertical fluid migration and annular channeling between aquifers after abandonment, the casing may be perforated as specified below and pressure sealed. A mill knife or hydraulic device will be lowered into the hole to perforate (rip) the steel casing at selected intervals. Sections of the casing to be perforated will be based on existing well information and the results of the video and geophysical logging. Casing sections selected for perforation will include: • Unperforated casing sections where void space exists between the casing and the formation, as inferred from the sonic log; and field QAPP.DOC 8-4 May 2000