Ultrasonic and low field magnetic resonance study of lower Monterey formation - San Joaquin basin

The Monterey formation has a wide variety of lithologies (diatomites and diagenetically derived cherts, porcelanite, organic-rich mudstones, phosphatic, and carbonate rocks) representing the effect of tectonic, oceanographic, and climatic events. Although the Monterey formation has been studied extensively, the lithology has not been correlated with saturation and pore size distributions. Despite recent reports of vast amount of recoverable oil (15.42 billion barrels of technically recoverable oil); no significant hydrocarbon discovery had been made to date in the lower section of Monterey Formation. Current exploration practice of the lower Monterey formation sections use models and techniques from conventional siliciclastic reservoirs. In this thesis, I have investigated the difference between biogenic and detrital silica as well as effects of additional influx of clay and carbonate material in the biogenic lithology.;My work involved a combination of laboratory and well log analysis. The laboratory measurements of seismic velocities and NMR show the effects of mineralogy on ultrasonic velocities and pore size distributions. For example, rocks with considerable amount of carbonate content have higher compressional wave velocity than the silicate rocks. NMR pore size distributions show that small pore sizes in the biogenic quartz phase rocks make up a considerable amount of the porosity. These differences also correlate well with higher (above 0.35) oil/water ratios. Well log analysis reveal that detrital clay content can be identified by high Thorium content from spectral gamma ray log. This increase in clay content can mask reservoir response since it leads to an increase in neutron porosity (NPHI) and lower resistivity values in well logs.