Laserfiche WebLink
L:. µ <br /> IJI6L-UM� rlay 114 0 11 •u I V� <br /> well or borehole is drilled using casing advance, the drive casing <br /> is withdrawn back to the surface by hydraulic Jacking (pulling) as <br /> the well is constructed. Sometimes during withdrawal., the casing <br /> may break leaving the lower end in the open borehole. <br /> common practice to decommission blanK well caziing (cable tool <br /> drilled wells or lost drive casing) is to simply place grout in the <br /> open holm to near-surface and cover with fill. In many instances, <br /> pea-gravel or earth collected on-site have been used to Fill t2ze <br /> open void for which the consequences can be tragic. Conversely, as <br /> with all wells, the removal of fill-types of material (i.e. rocks, <br /> brick, metal, wood, etc.) Pram a cable tool well is particularly <br /> critical and should be approached with caution because eablu tool <br /> wells have no cement annulus for support; in addition, they are <br /> generally old and probably have weaken casing because of age and <br /> corrosion. The use of reverse circulation techniques will remove <br /> all water from inside the casing and may cause casing collapse. <br /> This situation is even mare critical below the water table where <br /> hydrostatic forces are -generated. Mud rotary drilling is the <br /> simplest and probably best technique for removing foreign debris <br /> from a cable tool well. <br /> if a "perforate and grout technique" is employed to decommission <br /> cable tool wells or lost drive casing in the environmental field, <br /> it usually involves perforating the entire length of casing and <br /> pressure grouting in-place. Lost drive casing completely within a <br /> erm� =able geologic unit can generally be grouted in-place to <br /> achieve an adequate seal. However, if lost casing interconnects <br /> one or mole aquitards, a more complex decommissiOring may be <br /> involved. <br /> To adequately decommission lost drive casing requires an in-depth <br /> interpretation of its borehole position respective to geologic <br /> units (permeable and impermeable) and knowledge of the location of <br /> the water table or water-bearing zonas_ The significance of each <br /> aquitard that is interconnected needs to be evaluated. All <br /> aquitards that do not appear to be sticky clay should probably be <br /> sealed by perforating the drive casing at these intervals and <br /> grouting using a packer at moderate to low pressures. if several <br /> significant aquitards are interconnected by a lost casing, <br /> perforating and grouting activities may need to be completed _i <br /> s es for each significant aquitard. <br /> It is noted, decommissioning techniques directed toward sealing <br /> aquitards, as described for wells with extensive falter wells, <br /> sbe the brhe focus of effort. As with filter P <br /> perforating cable tool wells or lost drive casing adjacent to a <br /> Bale zone may severely limit efforts to achieve an adequate <br /> seal adjac�'t to aquitards because permeable geologic materials <br /> will more readily accept grout during the sealing operation, <br /> If lost drive casing £s perforated adjacent to a pe.—meable zone <br /> bailbvr tlae wmtet table and water has been evacuated from inside the <br /> casing, formation mat4gri IN will floss t21 ough the perforations into <br /> the casing. The situation thus created will be nearly i.mpossibla. <br /> 5 <br />