Hartzog Draw field is a stratigraphically controlled oil reservoir which produces from the Upper Cretaceous Shannon Sandstone at depths from 9000 to 9600 feet. The producing interval consists of a large mid-shelf sand-ridge (bar) complex deposited below effective normal wave base more than 100 miles from shore. The productive (net pay) interval in the bar complex has a maximum thickness of 60 feet, is 22 miles long, and is one to four miles wide. The field was discovered in 1975 and 177 producing wells were completed on 160 acre spacing during the primary production phase of development. Initial oil in place was calculated to be 350,000,000 barrels.
The shelf sand-ridge complex is competely enveloped in shale, has a solution gas drive, no water table and no produced formation water. Net pay is primarily a product of porosity, permeability and thickness of the sandstone, and is related primarily to sedimentary facies and the degree of diagenesis.
Of the six to eight facies observed in cores, only one, the Central Ridge Facies, a high-angle trough cross-bedded glauconitic quartz sandstone, is consistently high-quality reservoir. Two others, High-Energy Ridge-Margin Facies, a predominantly trough cross-bedded highly glauconitic sandstone with abundant shale and siderite clasts, and Low-Energy Ridge-Margin Facies, inter-bedded trough and rippled sandstone, also may be good quality reservoirs. Inter-Ridge Facies which consist of rippled interbedded sandstone and shale, generally are poor quality to non-reservoirs.
Values from the Central Ridge Facies from three of the cores taken early in the development of the northern part
Figures & Tables
Shelf Sands and Sandstone Reservoirs
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.