. Bulletin. ngis quite possible where the wells have been drilled with the hole fullof water and mud, as this may preclude any showing on the a new field the operators are usually looking for the big producingsand. Oil may show in the ditch or on the fluid from the bailer afterit has been run to bottom, but if the well does not flow the sand maybe passed by without testing. The proper test is to bail the well down and liring the oil into thehole. Swabbing and shooting may accomplish the same result. Thedriller will readily understand whj the oil does not come into thehole when it is e
. Bulletin. ngis quite possible where the wells have been drilled with the hole fullof water and mud, as this may preclude any showing on the a new field the operators are usually looking for the big producingsand. Oil may show in the ditch or on the fluid from the bailer afterit has been run to bottom, but if the well does not flow the sand maybe passed by without testing. The proper test is to bail the well down and liring the oil into thehole. Swabbing and shooting may accomplish the same result. Thedriller will readily understand whj the oil does not come into thehole when it is explained to him that in a hole filled with 2,000 feetof water the outward pressure at the bottom is at least 868 pounds 170 UNDERGROUND CONDITIONS IN OIL FIELDS. per square inch, and if the fluid carries mud, the pressure is greaterin proportion to its specific gravity. Obviously the oil or gas cannot enter the hole if the pressure of the fluid is greater than the rock Fresh wafer send ~-Z-Z-----Z- r Casings. Figure 36.—Generalized sketch .showing unsystematic casing of wells. Gas pressuregreater than water pressure. After Bull. 134, Bureau of Mines, p. 38. pressure. The rock pressure of a district is usually less than thehydrostatic head, and is always less after the first wells have depletedthe pressure. OIL AND GAS SANDS LOCATION, THICKNESS. AND QU:\LITY. 171 Stky BlGy. Bl. Shell Hd Shows oil Soft() Very Sdy|0 and G.) In parts of the Mid-Continent, Lima-Indiana, and other fields, awell will not show any appreciable production until after it has beenshot. In such districts the upper possible producing zones shouldbe shot and tested, unless this has already been done. This may re-sult in wells capable of producin: 50 barrels of oil a day. Possibly all the wells ona projierty have cased offa good oil sand. Its dis-covery would increase thevalue of the property bymany thousands of a uniform shut-offon all wells and no infor-mation
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