Abstract The Conroe oil field, located in Montgomery County, Texas, was discovered in 1931. It is a broad ovate structure crossed by several normal faults which form a central graben area. The maximum vertical displacements of these faults range from 130 to 165 feet. Production is obtained at an average depth of 5,050 feet from the Cockfield formation of Upper Claiborne (Eocene) age, which has been uplifted more than 800 feet above its normal position. The average thickness of the Conroe producing sand throughout the field is 60 feet. The recoverable reserves have been estimated to be about 600 million barrels. Currently the field is producing daily 47,700 barrels of oil from 829 wells, of which 53 wells are producing salt water in varying amounts. There is free communication and equalization of fluid across the fault planes so that there exists a unit reservoir wherein the fluids segregate themselves at uniform levels throughout the field. The interval within which sand may contain oil is 130 feet, or between the —4,860-foot and —4,990-foot datum planes. A large gas cap overlies the oil and occupies an interval of 170 feet, or between the datum planes of —4,690 and —4,860 feet. Conroe has a proved area of 17,200 acres and has produced a little more than 40 million barrels of oil up to January 1, 1935. Reservoir pressures became stabilized after the field has produced about 29 million barrels of oil and the pressure decline since then has been less than one pound per million barrels of oil produced.

Abstract Discovery of the Conroe oil field in 1932 has brought into prominence the Cockfield as an oil-producing horizon in the Gulf Coast area. The various oil-producing horizons of the Gulf Coast are reviewed and discussed. Typical sections of several of the Gulf Coast oil fields are shown to indicate the position of the oil-producing sands. The possibility of production from deeper horizons in the Cook Mountain and Mount Selman formations is pointed out.

Abstract The first U.S. oil discovery using any geophysical method came in 1924 at Nash Dome, Texas, as a result of a survey with the Eötvös torsion balance. This gravity-measuring device was invented in 1888, and first was used for hydrocarbon exploration in Czechoslovakia in 1915 16. It was very slow to operate and was sensitive to near-surface irregularities, and these problems provided the impetus for developing a sensitive pendulum apparatus. Wyckoff and Eckhardt tested a practical pendulum instrument in Kansas and Oklahoma in 1925 26. After joining Gulf in 1928, they refined and developed the tool and it was field-tested in Michigan in April 1930. Gulf and other companies tried other pendulum methods, but by July 1932 the Gulf (Wyckoff) pendulum was in regular operation. Cleveland Oil Field (Texas) was found by Gulf with this pendulum; Conroe Dome, which was invisible in torsion-balance data, also was defined. The pendulum was a great improvement, but still did not have the sensitivity and speed of operation required for efficient exploration. At their peak, pendulum crews could observe a maximum of about 250 stations per month. The next step was the gravimeter. Apparently, Humble Oil tested the first gravity meter in the United States, in 1930, but never placed it in regular use. Gulf developed a gravimeter in 1932 35 which began routine operation in May 1935. This instrument was the first practical field gravimeter, with an accuracy of better than 0.1 milligal, and it was very fast to operate. The Gulf (Hoyt) gravimeter received general