Hartzog Draw Field, located in the Powder River Basin, Wyoming, was discovered in August, 1975. It is one of the largest oil fields discovered in the Rocky Mountain province in recent years, with initial estimates of ultimate recovery exceeding 100,000,000 barrels of oil. Field development through the fall of 1977 extended more than 20 miles lengthwise in a northwest-southeast direction and up to three miles in width, encompassing in excess of 22,000 productive areas. Development drilling on 160 acre spacing has had a better than 95% success ratio and initial production rates commonly exceed 1,000 barrels of oil per day, with several wells having potentialed in excess of 3,000 barrels per day.
Production at Hartzog Draw is from the Upper Cretaceous Shannon Sandstone Member of the Cody Shale, at a depth of 9,000 to 9,600 feet. Oil accumulation is stratigraphically controlled, structure having almost no influence on entrapment. The reservoir sandstones (mostly MARINE CENTRAL BAR and BAR MARGIN FACIES) are quartzose and glauconitic, fine to medium grained, moderately well sorted, highly trough cross-bedded, and occur in stacked sequences up to 60 feet in thickness. Sideritic clasts and shale rip-up clasts occur locally in the high angle trough cross-bedded units.
In the reservoir facies, effective porosities average around 13% and permeabilities 12 md. There is no apparent water table, and net pay thickness closely parallels net sand thickness. The reservoir sandstones are associated with a 30 to 80 foot thick package of rippled interbedded very fine-grained sandstone and shale (INTERBAR and
Figures & Tables
Shelf sandstone reservoirs are becoming a more and more common exploration target. What they are, how they may be characterized, and how they differ from shoreline and deep-water deposits in the subject of this publication. Shelf sands and sandstone reservoirs are among the more poorly understood types of sandstones. Continental, shoreline and deep water sandstones have all been studied in much more depth than have shelf sands and sandstones. However, during the last fifteen years significant progress has been made in understanding shelf sands and sandstones. Studies of modern sediments have allowed us to understand many of the depositional processes active on the shelf. This book is intended to be an up-to-date summary of shelf processes and products. The papers are intended for those new to shelf sands and sandstones as well as the shelf specialist.