INVESTIGATIONS INTO BURIAL HISTORY AND PETROLEUM SYSTEM DEVELOPMENT IN THE SALINAS BASIN, CALIFORNIA THROUGH 1-D MODELING

The Salinas basin is a Cenozoic strike-slip basin in western central California, bounded to the east by the San Andreas Fault. A one-dimensional (1-D) burial history model was created in the Hames Valley syncline, the thickest depocenter of the basin, located 9 km southwest of the San Ardo oil field. The half-billion barrel San Ardo oil field is anomalously large in contrast to the six other oil fields in the Salinas basin, which collectively amount to 2% the size of San Ardo. The Salinas basin is no longer at maximum burial depth: the shallowest thermally mature (0.6% Ro) source rock, which occurs within the Hames Member of the Miocene Monterey Formation, is currently at a burial depth of 2400 m (8000 ft); however, the present-day threshold for thermal maturation of the Monterey Formation in the neighboring San Joaquin basin occurs at 4000 m (13,000 ft) burial depth. Thermal maturity data from pyrolysis analysis serves as calibration for a 1-D model to determine the time and depth of hydrocarbon generation. A pseudo-well for the model was created between two 3,000+ m (10,000+ ft) wells, Texaco Shell NCT-1 1 and Shell Labarere 27X-21, located on opposite flanks of the Hames Valley syncline, and controlled by reflection seismic data. The pseudo-well penetrates the Hames and Sandholdt members of the Monterey Formation, and penetrates basement at 4,000 m (13,000 ft). Based on previously collected geochemical data, the 1-D model incorporates source rock properties of a type II kerogen with 3 wt% TOC and 700 mgHC/gTOC hydrogen index. Multiple models were developed to identify the burial history scenario required to produce the thermal maturation signature in the source rock. However, these early models reveal unexpectedly high thermal maturity values. Uncertainties in heat flow and overburden thickness are being explored to explain and resolve this inconsistency.