Gradients of Vitrinite Reflectance and Present Temperature in the Los Angeles and Ventura Basins, California

Abstract

Measurements of the optical reflectance of vitrinite are used frequently to indicate the maturation of organic matter and generation of petroleum in potential source rocks. Particularly in offshore drilling the accurate and early determination of the organic maturation, or especially the prediction of maturation level before drilling, would be very valuable. To help accomplish this we report the results of coordinated research on vitrinite reflectance, rock temperature, and burial history. Data were collected from 110 samples of conventional core from 17 boreholes, some as deep as 5800 meters, from five sites in the Los Angeles basin and one site in the Ventura basin. The rocks are upper Miocene and younger, and we believe that the present temperatures are maximal in their history. The determined gradients are 24° to 35° C per km and 0.033 to 0.090 % vitrinite reflectance per km. The methods of determining vitrinite reflectance, rock temperature, and burial history are described, and the figures and tables of data are annotated to give others information needed to evaluate the accuracy and significance of our data.