The Otis Gas and Oil Pool, Rush and Barton Counties, Kansas

Abstract

The Otis gas and oil pool is located in central Kansas, in Rush and Barton counties, and embraces about twenty-three square miles. Production is obtained from the Lamotte sandstone of Late Cambrian age. The reservoir is estimated to have contained originally 207,900 million cubic feet of gas and 5,913,400 barrels of oil, both quantities expressed at standard surface conditions. As of May 1, 1941, a total of 93,100 million cubic feet of gas had been produced, of which 31,900 million cubic feet had been vented to the air in the production of oil, and the testing and blowing of wells; 1,411,386 barrels of oil had been marketed as of the same date.

Two elements of waste exist in the pool: (1) oil production with excessively high gas-oil ratios, and (2) premature decline in the reservoir pressures. Unless the oil is produced prior to the time when the static reservoir pressure becomes so low that operating pressure gradients sufficient to move the oil to the wells efficiently cannot be established, a large part of the otherwise recoverable oil will be left in the reservoir as underground waste.

In order to prevent such waste it is suggested (1) that the oil wells be allowed to produce at a rate sufficient to deplete the reservoir of its recoverable oil content before the withdrawal of too much gas for pipe-line sales, and (2) that the production of gas with the oil be prohibited unless such gas be recompressed and returned to the reservoir. The most feasible plan for such action lies in the unitization either of the entire pool or at least of that portion containing oil.

A tabulated summary of information pertaining to the Otis pool follows:

1. Area of the Otis pool; gas (includes oil), 14,780 acres; oil, 455 acres; total 14,780 acres.
2. Percent of area in Otis pool capable of producing gas, 100 per cent; capable of producing oil, 3.09 per cent.
3. Original gas content of the Otis reservoir, estimated in cubic feet at 60° F. and 16.4 p.s.i. (pounds per square inch), 207,900 million cubic feet.
4. Gas in reservoir on May 1, 1941, estimated under same conditions as in no. 3, 114,800 million cubic feet.
5. Total pipe-line sales, as of May 1, 1941, corrected for deviation from ideal gas laws, and computed under same conditions as in no. 3, 61,196 million cubic feet.
6. Original reservoir pressure at 109° F., 1,178 p.s.i.
7. Volume of gas (measured at same conditions as in no. 3) required to form one cubic foot of gas at initial reservoir conditions in the Otis pool, 78.07 cubic feet.
8. Original quantity of oil, estimated under reservoir conditions, 6,045,205 barrels.
9. Original quantity of oil, estimated as stock tank oil, 5,913,419 barrels.
10. Total oil produced from the Otis pool, prior to May 1, 1941, 1,411,386 barrels.
11. Per cent of original quantity of oil in reservoir estimated to be commercially recoverable, 50 per cent.
12. Amount of future recoverable oil, as of May 1, 1941 (estimated), 1,545,323 barrels.
13. Reservoir pressure (equals average bottom-hole pressure), as of May 1, 1941, 702 p.s.i.
14. Thickness of gas pay (estimated average), 30 feet.
15. Thickness of oil pay (estimated average), 13.7 feet.
16. Porosity of pay sand (estimated average), 12.5 per cent.
17. Volume of gas vented with oil production, September 1, 1936, to May 1, 1941 (estimated), 26,100 million cubic feet.
18. Reservoir volume of gas vented with oil, for same period, expressed as barrels, 59.5 million barrels.
19. Volume of gas used in operating gas wells, and vented prior to oil production, cumulative to May 1, 1941 (estimated), 5,800 million cubic feet.
20. Ratio of gas vented to oil recovered during the period of September 1, 1936, to May 1,1941, expressed at standard surface conditions (estimated), 18,750 cubic feet per barrel.