ABSTRACT

Lower Hackberry (mid-Frio) reservoirs are highly unpredictable in the subsurface due primarily to variations in sand thickness and sand distribution. Most exploration for Lower Hackberry reservoirs has been limited to turbidite sand-filled channels cut between seafloor paleotopographic highs, and to Lower Hackberry sands on the northern flanks of salt domes, where excellent stratigraphic traps are created that exhibit north dip--sometimes with significant closure. Two other types of reservoirs exist that have received little attention, both in the literature and in exploration. The suprafan lobe in the mid-fan position lying at the base of the slope is a prime exploration target, where massive Lower Hackberry sands should be found. Several wells in northwestern Cameron Parish have penetrated thick Lower Hackberry sands in a downdip position from the channel plays, suggesting that a mechanism for large-scale downslope movement was present during Hackberry time.

Another potential reservoir that deserves more exploration is that of interdomal sediment "ponding" of Lower Hackberry sands into topographic lows created by the scouring of the pre-Lower Hackberry surface and the withdrawal of salt due to subsidence. These sands tend to be concentrated in the center of the pond and generally may not be present in traditional updip anticlinal positions. These ponds occur independent of ideal structural location--typically in synclinal positions and oftentimes with a pinchout of the sands serving as the trap. Ideal prospect locations are where the pre-Lower Hackberry unconformity and top of the Lower Hackberry marker diverge, indicating the presence of a sand-filled scour feature. Southwestern Calcasieu Parish provides excellent examples of this ponding feature in the subsurface. Successful exploration efforts will depend upon careful attention to paleontological information, which is critical in establishing the identification and placement of the pre-Lower Hackberry unconformity that records erosion of the early Frio surface.