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From Monterey to Mowry, With Many Stops in Between


Geochemistry has long been a critical aspect of defining conventional oil and gas exploration. In the development of unconventional oil resource plays utilizing geochemical properties, both organic and inorganic, enable an understanding of rock properties to be able to define the best places to expect commercial production from low permeability source rock. Presented here is a brief history of the co-authors use of geochemistry as another tool for developing an exploration program specifically targeting these oil-prone, low permeability reservoirs. The Monterey Shale has long been known as a fractured “shale” reservoir and productive primarily in coastal California. Using geochemisty, a diagenetic and thermal maturity controlled stratigraphic trap was defined and resulted in two discoveries, the North Shafter and Rose Fields in Kern County, California. Other oil prone shales exhibit both similar and different characteristics. A sequential exploration program that started in the Monterey in the mid-1990's led to studying the similarities and differences of a variety of oil resource plays in the Rocky Mountain region, including the Niobrara, Mowry, Bakken, Heath, Chuar, Green River and several others. Some of these plays have been commercial success stories, some have failed, and others are still in the process of being evaluated by industry. While specific attributes of geochemistry vary from play to play, the initial analysis of total organic content and thermal maturity remain critical to gain clear understanding of the resource. Also, the use of simple geochemical techniques in addition to standard pyrolysis has been shown to be critical in defining critical items such as parent source, reservoir compartmentalization, timing and filling histories.