Primary Stratigraphic Traps in Sandstones: ABSTRACT

Abstract

Primary sandstone stratigraphic traps involve lateral termination of the reservoir as a direct or indirect result of factors related to the depositional environment; Burbank, Bell Creek, and Pembina are among the very few giant oil accumulations found in them. As these traps rarely can be detected by surface measurements, other discovery methods are essential. The understanding of depositional process and environment is a promising approach. Primary sandstone stratigraphic traps occur in many facies, including fluvial, deltaic, shallow-marine, and deeper marine. The largest sizes and greatest number occur in shallow-marine and shoreline environments. Knowledge of sandstone models of all kinds may provide valuable clues in interpreting fragmentary well data in terms of size, shape, trend, and characteristics of the reservoirs being sought. The distribution of many sandstone bodies may be End_Page 350------------------------------ controlled in part by underlying, commonly inconspicuous, erosional surfaces. Reconstruction of the paleotopography of the unconformity thus may commonly delineate prospective trends. The distribution of trap barriers may be controlled by environment. For example, discrete shoreline sandstone bodies replaced updip by lagoonal shales are better prospects than those replaced updip by sandy (leaky) deltaic deposits. Such sandstones are more likely to be related to interdeltaic rather than deltaic areas. Most progress will come from further development and refinement of depositional models. A greater understanding of shallow-marine sandstone bodies is especially needed. Moreover, as exploration emphasis shifts offshore, there will be a growing premium on one's ability to recognize depositional models in the absence of cores and outcrops. End_of_Article - Last_Page 351------------