ABSTRACT

Southwest Lake Arthur Field is a classic example of one of the rare, non-salt associated stratigraphic traps found in Southwest Louisiana by geological-geophysical exploration techniques. The stratigraphic traps is constituted by an east-west trending sand barrier bar and a tabular shaped marine sand that shales out to the north, west and south. The sand deposits are superimposed on a present day southeast dipping homocline.

Integration and review of the geology and geophysics of this documented stratigraphic trap was undertaken in order to determine whether the Planulina #2 Sand pinchout could be visually observed on the available conventional split-spread reflection seismic record section and if essential criteria could be developed to locate similar fields.

The procedure employed was: 1) A thorough geological study was made from logs, cores and production data of numerous wells in and around the field from which structure and isopachous maps were made of the reservoirs constituting the stratigraphic trap; 2) The original field records were transcribed onto magnetic tape and then to a processed seismic record section; 3) A synthetic seismogram was constructed from a Sonic log of a well near the seismic line along with the Spontaneous Potential and Resistivity curves of the same well plus another well along the section; 4) The digitized Spontaneous Potential and Resistivity curves for these wells were converted to a time scale using the values of time depth derived from the integrated Sonic log; 5) The synthetic seismogram and digitized logs were superimposed and compared to the record section. A change of character was observed which showed thickening of the section approximately equal to the developed sand. Since conventional seismic recordings in the area are generally plagued with various noise problems, this change of character may be coincidental. Additional work is needed to confirm such a liberal interpretation.

Production is from the Planulina #2 Sands which occur in the Earth member of the Anahuac Formation (Goheen, 1959). This member coincides with the Planulina palmerae biostratigraphic zone which is Lower Miocene.

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