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mecha>~I bridge plug might be set if not alre~present and if downhole conditions so <br />w•arran t <br />4) Cementine. The objective at each well w•as to first place cement through perforations to <br />seal any ex+stmg annular spaces and to then fill the remaining wellbore. The most <br />desirable result was to restore formation isolation by placing anopen-hole cement plug <br />from just above the cavity to the surface. Attainment of this goal was usually precluded <br />by the problems with cleanout and casing removal previously described. The major <br />J complication with respect to placement of cement was the presence of severe lost <br />circulation zones, which in some cases could "take as much cement as is pumped to <br />t them" (Yarosz, 1994). When attempting to cement through perforations, uncerta+nty <br />~ existed with respect to the distribution of cement through multiple sets of perforations as <br />well as the effectiveness and likelihood of actually sealing the annulus. <br />The above discussion reveals the difficulties that were frequently encountered at each step of the <br />w•ay through a relatively simple baseline procedure. Deviation from this procedure was often necessary <br />in order to achieve the best possible plug in each well without excessive efforts beyond the 32-hour time <br />j frame. As stated by Yarosz (1995), "[tJhe variety and severity of the problems with the wells prevented <br />the establishment of a comfortable routine in plugging. Completely new and different situations <br />t continued to occur. Project personnel were required to remain flexible." <br />Creative solutions to the following problems were attempted in the field, with varying degrees <br />I of success, and are briefly described in the subsequent paragraphs: <br />_1 <br />1) Shallow cleanouts, where obstructions prohibited downhole progress beyond several <br />' hundred feet above the objective depth. <br />2) Sheared wellbores, where horizontal movement displaced most of the wellbore so that it <br />could not be directly accessed from caztng above the shear zone. <br />3) Caving after casing removal, eliminating downhole progress that had been made before <br />' the casing was removed. <br />4) Lost circulation resulting in excessive quantities of lost cement. <br />5) Slanted casings in severe subsidence areas. <br />.; <br />Sholloi+~ clemiours' squeeze cemenrinQ mrd "assemb/y-line" plu¢¢ino.--On many of the oldest <br />wells, hole problems at depths of 150 to 300 feet frequently precluded cleaning out the wellbore beyond <br />these shallow depths. .4 squeeze cementing technique w•as developed which, by the project's second <br />}ear, had evolved into an "assembly-line" procedure. <br />Squeeze cementing below the cleanout depth involved two steps following the initial cleartout <br />The first step w•as setting a packer or a makeshift packer composed of a modified cement basket run or. <br />tubing. The packer and tubine would be cemented in place at or abo~•e the cleanout depth by placing. <br />erout in the annulus. After the cement was allowed to set, the second step could be the actual squeeze <br />through the tubing, at pressures under 250 p;i. Although the path a:-td destination of squeezed cemen <br />could not be determined with certainq•, man} wells plugged in this mariner took at least enough cemen <br />to fill the calculated ~cellbore volume below the cleanout depth. Questions remained, ho.+'ever, a5ou <br />whether this method resulted in a plug superior to that which would be achieved b.• mereh~ filling th. <br />wellbore with cement (Yarosz, 1994). <br />]6 <br />22 <br />