Abstract

The Estancia Basin of central New Mexico is an asymmetric, north-south trending structural depression that originated during the Pennsylvanian. The present-day basin covers 1,500 mi². It is bounded on the east by the late Paleozoic Pedernal uplift, on the west by the Tertiary-age Los Pinos, Manzano, and Sandia Mountains, on the north by the Española Basin, and on the south by Chupadera Mesa. Depth to Precambrian basement ranges from 8,700 ft in a narrow graben (the Perro sub-basin) in the eastern part of the basin to less than 1,000 ft on a shelf to the west. Basin fill consists primarily of Pennsylvanian and Wolfcampian shales and sandstones in the graben and shales, sandstones, and marine limestones on the shelf.

Total organic carbon (TOC) exceeds 0.5% in many Pennsylvanian shales and micritic carbonates, an amount sufficient for hydrocarbon generation. The Permian section contains insufficient TOC for hydrocarbon generation. Mature to marginally mature dark-gray Pennsylvanian shales are probable source rocks. Thermal Alteration Index (TAI) ranges from 2.0 to 3.2. Shales become thermally mature with depth in the Perro sub-basin. On the western shelf, thermal maturity of Pennsylvanian strata increases to the west; this westward increase in maturation appears to be a result of a heating event associated with formation of the Rio Grande rift during the Tertiary. In Pennsylvanian shales of the Perro sub-basin, kerogens are dominantly a woody gas-prone facies (kerogen type III). In Pennsylvanian limestones and shales on the western shelf, kerogens are an oil-prone facies consisting mostly of algal, amorphous, and herbaceous types (kerogen types I and II).