Abstract

Paleoenvironmental reconstruction analysis characterizes the Atoka sands of the N. Vacuum Field, Lea County, New Mexico, as being deposited in a braided fluvial system. The channels trend from the northwest to the southeast. In the past the only sure way of identifying the depositional environment of a sand was by cutting a whole core. With the addition of Formation MicroScanner images (FMS), one can now better interpret the depositional environment with a greater confidence without the cost of a whole core. The environment of deposition was determined for Atoka age sands by using the FMS. The FMS was run in two wells and the results verified by whole core and FMS in one well.

The FMS data interpreted on Schlumgerger’s Sun workstation indicated that the sand was deposited in a braided channel system. The following sequence was observed: 1) erosion of the underlying shale first occurred, 2)a then coarse-grained sands were deposited in a downflow direction until the eroded channel was filled, 3) then the sands were laterally accreted perpendicular to flow direction, this process producing the thickest sand bodies, and 4) the final stage occurred during sea-level transgression when fine-grained sand and shale lenses capped the massive sands with depositional current bedding in a landward direction indicating fluvial-marine influences.

The conclusions based on the FMS images were supported by a whole core interpretation of a complete sand sequence in one well. Several additional locations have been chosen in the channel trend based on this model.