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decommissioning operations and in most situations, should be <br /> avoided. Perforating an entire well casing from bottom to top and <br /> placing grout in the casing, with or without being pressurized, is <br /> a very common procedure that is too routinely used for <br /> decommissioning wells. For most wells in sedimentary environments, <br /> this procedure should be thoroughly evaluated and probably <br /> reconsidered before being implemented. To achieve proper results <br /> for any decommissioning technique requires that permeable (as well <br /> as impermeable) zones be identified because they may hinder the <br /> sealing process. Permeable geologic materials generally accept <br /> grout and/or sealing slurries targeted for emplacement adjacent to <br /> aquitards. Some permeable geologic materials are capable of <br /> accepting so much grouting material that they will severely limit <br /> the sealing operation. <br /> Construction and design criteria are the second most important <br /> considerations for decommissioning wells. The location of filter <br /> pack materials, screen slot openings, and casing in a borehole must <br /> be determined before sealing agents are installed. Unfortunately, <br /> construction details for many wells are not available from well <br /> owners, DWR, or local governmental agencies. The absence of <br /> construction records complicates the decommissioning procedure <br /> usually requires that downhole remote sensing surveys be performed. <br /> However, even if records are available, a downhole video camera <br /> survey should always be performed to check condition of the casing; <br /> prior to performing a down-hole video survey, the casing should be <br /> vigorously brushed and left idle for at least 24 hour so that <br /> particulate material will settle. Common geophysical logging <br /> techniques that provide for establishing geologic control and well <br /> construction details include cement bond (sonic) , gamma, and casing <br /> collar locator. <br /> A simple effort exercised by many individuals to decommission wells <br /> has been to fill them with miscellaneous debris including rocks, <br /> bricks, metal, wood, and earth materials. These efforts prevent <br /> unwanted solid objects from being dropped into the well but do <br /> nothing to halt fluids from migrating into the subsurface or <br /> preventing cross contamination of ground water. The removal of <br /> fill-types of material from a well should be cautiously addressed <br /> because the most simple technique is to use a type of reverse <br /> circulation apparatus. Reverse circulation techniques will remove <br /> all water from inside the casing and if the casing is weak, it may <br /> collapse, especially below the water table. Mud rotary drilling is <br /> the best technique for removing foreign debris from wells. <br /> Wells with Extensive Filter Packs <br /> Many wells are constructed using extensive filter packs which act <br /> as conduits to vertically pass ground water and, if present, <br /> contamination. To properly decommission these types of wells <br /> without completely drilling out construction materials requires <br /> perforating the casing adjacent to aquitards, packer placement, and <br /> tremie pressure grouting sections of the well in lifts with time <br /> provided for cement curing. Special effort must be provided for <br /> 3 <br />