Abnormal Pressures and Conductivity Anomaly Northern Green River Basin, Wyoming

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. This paper was prepared for the 43rd Annual Fall Meeting of the Society of Petroleum Engineers of AIME, to be held in Houston, Tex., Sept. 29-Oct. 2, 1968. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made. provided agreement to give proper credit is made. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines. Abnormally high formation pressures are present in the northern Green River basin, Wyoming. Minimum pressure data can be obtained from scout tickets and from reported well kicks against drilling mud of known weight. Highest pressures are found in the lower Tertiary-Upper Cretaceous interval in a belt along the front of the Wind River Mountains. Mud weights in this area commonly exceed 12 pounds per gallon. Somewhat lower pounds per gallon. Somewhat lower pressures are encountered on the west pressures are encountered on the west side of the basin, near the Wyoming overthrust belt, in the Cretaceous Hilliard-Frontier-Dakota interval. Here mud weights tend to be greater than 11 pounds per gallon. In the central part pounds per gallon. In the central part of the basin pressures are near normal, at least to depths of 10,000 feet, with mud weights ranging from 10 to 11 pounds per gallon. per gallon. A reversal of the slope of the conductivity plot is associated with the abnormally high pressures. Mapping of the top of the conductivity slope reversal on a regional scale defines large areas which are suspected to be underlain by over-pressured shale sections. The distribution of these areas with respect to major tectonic elements, notably the Wind River uplift and the Wyoming overthrust belt, suggests that tectonism is the cause of the abnormal pressures. Introduction The Green River basin, one of the major Tertiary features developed during the building of the Rocky Mountains, occupies 12,500 square miles in southwestern Wyoming. The basin is topographic as well as structural, being drained southward by the Green River. Basin boundaries are the Uinta Mountains on the south., the Rock Springs uplift on the east, the Wind River Mountains on the northeast, the Gros Ventre Mountains on the north, and the Wyoming overthrust belt on the west (Fig. 1). Surface elevations range from 6000 to 9000 feet. The sedimentary section ranges in thickness from 15,000 to 30,000 feet.