Oil-Impregnated Lacustrine and Fluvial Sandstone in Green River Formation (Eocene), Southeastern Uinta Basin, Utah: ABSTRACT

Oil-impregnated sandstone, in units up to 75 ft thick, are present in the lower Green River Formation in the P.R. Spring area, southeastern Uinta basin. Reserve estimates indicate that there may be about 3.7 billion bbl in place. A total of 308 paleocurrent measurements were made at 13 localities in the upper Wasatch Formation (Paleocene-Eocene) and the lower Green River Formation. Of these measurements, 123 were from fluvial sandstone and 185 were from lacustrine sandstone. Streams flowed northward into Lake Uinta in the P.R. Spring area. The considerable scatter in the fluvial paleocurrents suggests that the streams had low gradients and were meandering. Many of the fluvial sandstone bodies are oriented approximately north-south. Lacustrine paleocurrents are generally southeasterly, representing dominantly onshore lake currents. Thus, the shorelines trended northeast through much of the area, although in local embayments shorelines were oriented northwest. The paleocurrent patterns of fluvial and lacustrine sandstone are both unimodal with equal distribution of directions. The 2 environments can be differentiated, however, on the basis of paleocurrent orientations. Fluvial currents flowed northward; lacustrine currents were southerly. Both fluvial and lacustrine sandstones are mostly arkose. Potassium feldspar is more abundant than plagioclase. Quartz-feldspar ratios are greater for lacustrine sandstone than for fluvial sandstone. Lacustrine sandstone contains more quartz and authigenic carbonate and less feldspar, coarse mica, and matrix than fluvial sandstone. Some lacustrine sandstone is also characterized by intraclasts, oolite, fossil fragments, and analcime in contrast to fluvial sandstone. Most of the oil-impregnation is in lacustrine sandstone. Detailed sedimentological study has led to the discovery of new intervals. Such studies will also be useful when these and similar reservoirs are developed. End_of_Article - Last_Page 357------------