WORK PLANS - Laserfiche WebLink

Home Browse Search

CA ARNG Field Oualitv Assurance PrniPrt Pian the minimum amount of potable water that will permit handling should be added to the grout in order to minimize circulation of water between formations. 8.4.3 The volume of plugging material required for each well will be calculated after first taking into consideration applicable loss of material to the formation, voids intersecting the borehole, changes in borehole diameter, and washout zones. Loss of plugging material into the formation may occur rapidly (within minutes) or after several hours or days. The volume of plugging materials required to be on site should be one borehole volume at a minimum. However, it is advisable to have available a minimum of 25% to 50% in excess of the calculated borehole volume. Additional plugging material should be readily available to site personnel under short notice. 8.4.4 The estimated well volume will be calculated using an approximate casing diameter from the available well construction specifications and the following equation: where: V = nr2L (Equation 14) v = volume L = length of borehole or well to be plugged, and r = radius of hole 8.4.5 Manuals listing the volume of a hole per linear foot are also available. It will be assumed in the calculations or table used that the derived volume is the minimum required for actual conditions due to possible loss of plugging material into the formation. For all wells, the volume of material emplaced will be measured and appearance of the material at the top of the casing will be checked when possible. 8.4.6 Location of the grout at depth can be difficult because the top of the grout may not be distinguishable from water or other fluids in the borehole. One field procedure that has been applied to measure the level of the grout is to use a wooden sounding block with a weight attached to the block. The weight should be slightly denser than the grout (ASTM, 1993). 8.4.7 During grout placement, injection pressures needed to achieve effective seals will be calculated using specific gravity of the sealant and hydrostatic head of the grout column above the packed off zone. The pressure causes grout to flow through breaches in the casing and invade and seal off aquitards. The amount of pressure applied depends on the characteristics of the cement slurry, size of the perforations, characteristics of the filter pack and formation, temperature, and depth of the interval being sealed. Injection pressure should usually be as low as possible to prevent hydrofracturing that would complicate the decommissioning activity and cause excessive grout loss into the formation. The duration of that injection pressures are maintained and any other conditions that arise during the process will be rigorously monitored (McJunkin, 1993). 8.4.8 An acceptable practice in water well abandonment is to seal the well by injecting pressurized grout into the well from the ground surface. Typically, the pressure applied to the grout should be sufficient to penetrate the geologic materials surrounding the screened interval. The maximum pressure for grout placement is approximately 1 pounds psi per foot below grade to the bottom of the well. This pressure corresponds to the combined pressure of the column of grout injected into the well plus the pressure induced by the pump. field QAPP.DOC 8-3 May 2000