Log Evaluation In The California Miocene Formations

Abstract

American Institute of Mining, Metallurgical, and Petroleum Engineers Inc. Abstract The increasing demand for oil has extended the search for new sources into formations that in the past have proven difficult to evaluate and profitably past have proven difficult to evaluate and profitably produce. The depositional facies belonging to the produce. The depositional facies belonging to the Miocene epoch in California have historically posed difficult evaluation problems with the Monterey Shale causing the most difficulties. This formation is playing an important role in the development of California Offshore reserves. It is characterized by thick siliceous and calcareous organic sediments: Vital to evaluating reservoirs located in this series is the location of fractured zones and the accurate determination of porosity. This can only be accomplished by identifying the lithologies encountered and by the proper interpretation of measurements made with available logging devices. An open hole logging suite and a computer program tailored specifically to solving problems unique to this series has been developed and successfully used. LOG EVALUATION IN THE CALIFORNIA MIOCENE FORMATIONS Introduction The Miocene formations of California have long been recognized as important sources of hydrocarbons. In the past, the geological complexities of the series made evaluation and identification of its productive intervals extremely difficult. With more readily identified reservoirs not able to supply our requirements for hydrocarbons, the search for new sources has necessitated better evaluation of this series. GENERAL GEOLOGICAL CONSIDERATIONS The Miocene has been extensively studied in the past because of its unique characteristics. It is considered to provide both source and reservoir for large quantities of hydrocarbons. Many different theories on its origin have evolved. It is not within the scope of this paper to add new light to the theories on its origin, but it is concluded that only through a basic understanding of the lithologic complexities can the evaluation by logging methods be understood and appreciated. Since the terminology of earlier workers is so entrenched in the geologic vocabulary, it will be used in this paper. The stratigraphic units as designated by R. M. Kleinpell divided the Miocene into three parts: Lower, Middle and Upper. These were then divided into six stages and twelve substages and fourteen foraminiferal zones identified.