Shots, wellbore

Walk (of hole) The tendency of a wellbore to deviate in the horizontal plane. Wellbore survey calculation methods Refers to the mathematical methods and assumptions used in reconstructing the path of the wellbore and in generating the space curve path of the wellbore from inclination and direction angle measurements taken along the wellbore. These measurements are obtained from gyroscopic or magnetic instruments of either the single-shot or multishot type. 

Nature exploratory well Deviated depth, mid-perforations 13130 feet (4002 m) Completion cased hole, perforation density 1 shot/foot Wellbore radius 3 inches (0.0762 m) Formation height 561 feet (171 m)... 

Theoretically, to fragment the block of oil shale by detonating wellbore charges of pelletized TNT, the area around center well 5 should be enlarged or sprung. This would be accomplished by repeated wellbore shots from bottom to top of the test zone. The broken and enlarged area surrounding the wellbore would serve as a free face to enhance effects from later simultaneous wellbore shots across the pattern. 

Figure 5. Position of explosive charge in sequence of wellbore shots in five-spot pattern, Rock Springs site 5...

Six shots (C, D, G, H, I, K) using approximately 1000 lb of TNT, were detonated in well 5 at depths ranging from 67 to 88 ft. The first three shots were not stemmed consequently, water and debris were blown to the atmosphere. The last three shots were sand tamped to the surface to fragment the maximum amount of oil shale around the wellbore and to permit the contained explosive gases to extend the induced fractures. 

Two shots (E-E, F-F) using a total of 536 lbs of TNT were detonated in wells 3 and 4 between depths of 71 and 87 ft. After cleanout in wells 1 and 2, 150-lb charges of TNT were placed in each hole to depths of 85 and 83 ft, respectively, and detonated (shot J-J). Wells 2 and 4 were cleaned out, and a total of 250 lb of TNT filled the holes to depths of 76 and 77 ft, respectively, and were detonated (shot L-L). Wells 1 and 3 were prepared for reshooting by charging 150 lb of TNT in each wellbore at depths of 77 and 74 ft, respectively, and were detonated (shot M-M). This explosive fracturing series was concluded by loading... 

Purpose. This fracturing program was intended to devise an effective method to fracture the formation with wellbore shots. More specifically, Green River site 1 was developed to test chemical explosive fracturing procedures for establishing communication between wells at greater depths and well spacings than had been previously attempted in oil shale. 

The final explosive-fracturing test performed on this site was a simultaneous shot detonated in the wells of the five-spot pattern. Wire-line measurements were obtained to determine total depth, and caliper logs were run to determine wellbore enlargement from which to calculate the amount of TNT to fill each well. Water was swabbed and bailed... 

A combination of displacing NG1 into a natural fracture system and using pelletized TNT in wellbore shots fragmented oil shale between wells at relatively shallow depths ranging from 60 to 100 ft. Extensive fragmentation extending to a radius of approximately 48 ft and extensive fractures to a radius of 90 ft were disclosed by various evaluation methods. 

Further, pelletized TNT performed satisfactorily in wellbore shots in wells 150-385 ft deep. Fractures were created between wells as indicated by airflow tests, but numerous other evaluation techniques did not indicate the extent of rock fragmentation. 

As discussed by Maerker, shear degradation is a function of perforation density in the wellbore, water salinity, and sand-face permeability. To study the effect of degradation on oil recovery, one case was run assuming no degradation, a second case assumed a perforation density of 20 shots/ft, and a third case assumed 10 shots/ft. Apparent viscosities for these three cases are shown in Table 6. Perforations were assumed to be 0.5 in. in diameter 10 in. long. 

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