In the Rocky Mountains from western Canada to Mexico, Cretaceous rocks are major sources and reservoirs for oil and natural gas, accounting for about 40% of the cumulative production to date. Some of the largest hydrocarbon accumulations discovered are Hartzog Draw, Hilight, and Salt Creek oil fields of Wyoming, Bell Creek oil field of Montana, and Blanco gas field of New Mexico and Colorado. Resource estimates indicate that large amounts of hydrocarbons remain to be discovered in these rocks. The purpose of this volume is to examine the relationship of reservoir quality, resource evaluation, and exploration strategy to depositional environment, thermal maturity, and diagenetic history of Cretaceous rocks in the Rocky Mountain area.
Chapter 2 deals with the general characteristics of the Cretaceous Western Interior Basin and seaway. The application of organic geochemistry to hydrocarbon occurrence and exploration is the subject of Chapter 3. In Chapter 4, three principal aspects of diagenesis that affect reservoir quality and source-rock potential are discussed: (1) early diagenesis, (2) burial diagenesis of shales, and (3) sandstone diagenesis.
In general, five main depositional facies can be recognized from west to east across the basin and they are described in Chapters 5 through 9. Fach facies is characterized by distinct reservoir properties controlled by depositional environment and by diagenesis.
Nonmarine rocks (Chapter 5)--Nonmarine rocks are restricted to the western part of the seaway adjacent to major orogenic source areas. Fluvial channel sandstones are the main reservoirs; coal and carbonaceous mudstones are abundant and provide the source