Regional mapping and maturity modeling for the northern deep water Gulf of Mexico

Colling, E. L., R. J. Alexander, and R. L. Phair, Texaco, Inc., Bellaire, TX

Abstract

Regional mapping and maturity modeling show distinct patterns that are characteristic of the complex petroleum system in the north central deep water Gulf of Mexico. Maturity for source rocks within the Cretaceous and Jurassic sections tends to increase from the abyssal plain to the Sigsbee Escarpment to the slope. One striking feature is the Cuba fracture zone that extends from South Pass to the southern Gulf of Mexico. Observed as a strong magnetic anomaly in basement maps, the Cuba fracture zone shows other impressive anomalies. Heat flows tend to increase approximately 25% relative to calibration points on either side of the Cuba fracture zone, which suggests that it is an important crustal feature. Empirically, the Cuba fracture zone appears to be a major dividing point in the north central Gulf of Mexico, where on its northeast side gas appears to be much more prominent than on the southwest side.

Mapping the Gulf of Mexico on a regional scale required the integration of 2D and 3D seismic data; gravity and magnetic data sets; and large-scale velocity models that include complex salt picks. Basement maps were generated from the integration of gravity and magnetic data with relatively accurate acoustic basement assessments from the abyssal plain. Salt was picked and a regional velocity model applied to multiple horizons. Probably the most difficult mapping task was making ties between areas with enormous amounts of data and those with a paucity of data. The paucity of data applies just as well to poor seismic sub-salt imaging. Developing maturity models required a reasonably accurate set of stratigraphic depth maps; calibration and mapping of heat flow on a large scale; and the appropriate choice of source rock horizons.

Results from this regional evaluation indicate that there is a definite relationship between source rock maturity and major oil and gas discoveries. The timing of hydrocarbon generation and migration relative to the timing of structuring is critical to each successful discovery. This can be evaluated on a regional scale when maturity results are placed in context with general structural trends.