Abstract

The Lankahuasa Field is located on the continental shelf, offshore Veracruz. It consists of a series of dry gas accumulations in multiple upper Miocene and lower Pliocene sandstones. The integration of 3-D seismic data, well logs, cores and biostratigraphic data has led to an understanding of the origin, geometry and internal architecture of the sand bodies as well as been critical for planning the exploitation of these reservoirs.

Six main depositional sequences can be recognized in the upper Miocene and lower Pliocene section of the Lankahuasa area. The sequence containing the upper Miocene reservoirs can be subdivided into three dominantly progradational parasequence sets, with the best reservoirs located at the tops of these packages. High resolution seismic data reveal small-scale (20-40 m thick) clinoforms prograding eastwards over the shelf within some of the parasequences. These clinoforms correspond to sedimentary bodies elongated in a NNW-SSE direction, parallel to the contemporaneous shoreline, as revealed by seismic attribute maps. Well log and core characteristics indicate that the best sands were eroded from the upper parts of the parasequences and redeposited during high-frequency transgressions.

Deposition of these sands is inferred to have taken place in two stages: 1) as shoreline-parallel bars in wave-dominated deltas and prograding coastal systems during sea level highstands, and 2) as lag sheets in inner and middle shelf during transgressions. The main sedimentary bodies have a NNW-SSE orientation, and preferential drainage is expected in this direction. Erosion and redeposition of the sands during transgressions interconnected these bodies and conferred a good lateral continuity to the reservoirs.