"Following is a table giving the amount of blasting gelatin held by various sized torpedoes per foot. The diameter of the torpedo is regu lated so as to carry the desired amount of explosive per foot. The larg est diameter of a torpedo used is usually about one inch less than the diameter of the smallest casing through which it has to pass.
"The amount of explosive used should be regulated by the physical condition of the well between the shooting depth and height of the fluid above the shooting point, and the results desired." Use of Mud Fluid in Abandonment.—Mention has been made of the scarcity of positive proof of the effectiveness of the use of mud-fluid in sealing formations. An instance of actual demon stration at Coalinga, California, under the supervision of R. D. Bush, may therefore be worthy of complete description. The location of the well is shown by the map (Fig. 29).
The accompanying graphic log (Fig. 30) shows the condition of the lower portion of the well just previous to the last redrilling and abandonment work, the latter having been decided upon after mechanical troubles made it doubtful whether the in. casing could be successfully recemented so as to exclude top water. The 10 in. casing was originally the water string, and the well produced oil for several years from the sands below it. Later, edge water appeared in the upper sands and was shut off with the 8% in. casing at a depth of 1885 ft.
In preparation for the mudding and abandonment, 1864 ft. of 65g in. and 1826 ft. of 8N in. casings were pulled out, and another string of 8% in. casing was carried to 1980 ft. and the well cleaned out to 2004 ft. Mud fluid was obtained by mixing the surface formation, which was fairly good clay containing a small amount of fine grained sand, with water. A 40-horsepower boiler and Gumbo Blister pump were set some 900 ft. from the well, where the mud was mixed by circulating the fluid through the pump and discharging it through a hose into a shallow reservoir made by plowing the ground and banking up the sides. The sand settled to a great extent before the fluid reached the suction box at the pump. The pump discharged directly into the top of the 8j in. casing at the well through a 2 in. pipe line.
The work at this plant was attended to by one man, with occasion ally an extra helper, and the work at the well by two drilling crews of two men each.
No figures are available as to the amount of material pumped into the well, but some idea may be gained by a statement of the approximate time during which mud was being introduced into the well. The total time consumed in mudding, moving casing, plugging and cleaning out, was 46 days of 24 hours each, and on every day except six mud was pumped into the well a portion of the time, occasionally with the 2 in. valve wide open, but generally only barely open, allowing just enough fluid to run in to keep the hole full (but not' running over between the 8% and 10 in. casings). By conducting the work in that manner the oil sands took all the mud put in, the quantity gradually decreasing until the hole stood full under the hydrostatic pressure only. A casing-head was then put on, with packing clamps between the 8% and 10 in. casings, and more mud pumped in until the pressure was raised to 200 lb. per square inch. At the end of the operations the pump pressure fell only 20 lb. in one hour while standing.
During the first sixteen days the 8i4 in. casing was held at 1927 ft., and the sand at that point mudded until it required pump pressure to force more mud into the well. The casing was then lowered to 1976 ft. and the sands below 1990 ft. mudded in the same manner. Plugs composed of brick and rope were then put in from 2004 ft. up to 1949 ft. The casing was then pulled up to 1784 ft. and the upper sands mudded under pressure.
During the first portion of the work the mud fluid was mixed rather thin so that it would be carried a considerable distance from the well and be deposited in the sand voids, thus building up an artifical and impervious body of clay around the well. As the sands became clogged with mud, the mud-fluid was thickened so that the final colum of fluid standing in the well up to the surface was of maximum density, and its hydrostatic pressure greater than that of the water in any stratum of sand. It was thus aimed to confine all water to the sands in which it occurred.