Many stratigraphie traps are related directly to their respective environments of deposition. An understanding of the depositional environment is essential to successful prospecting for oil or gas in this type of reservoir. Isopach studies of shale sequences directly above, or both above and below, a lenticular reservoir sandstone, are of considerable value in reconstructing depositional environments. Variations in thickness of such shale intervals, either directly above a reservoir sandstone, or embracing it, are completely independent of present-day structural configuration. Isopach maps of such genetic sequences serve as realistic indicators for locating certain lenticular sands. Depositional trends of beach sands, strike-valley sands, and offshore bars are determined readily from such studies. Structure maps, constructed on a reliable time marker within the arbitrarily selected genetic interval, serve as a means of locating oil or gas accumulation within any of these reservoir types. In all such studies electric-log data are essential because such genetic sequences rarely are named formational units. The thinner the genetic sequence, the greater the necessity for accurate selection of correlation points on electric logs.
Deltaic reservoirs are poorly understood and only rarely recognized by the geologist. This type of reservoir is, nevertheless, abundantly preserved in the sedimentary section. Regional isopach studies of depositional environment are a prerequisite for the construction of meaningful exploration maps of this type of reservoir. An understanding of the trends of distributary fingers and of the influence of differential compaction in producing drape structures, likewise, is essential.
Figures & Tables
Geometry of Sandstone Bodies
This volume contains the eight papers presented as a symposium of the Research Committee of The American Association of Petroleum Geologists at the 1960 annual meeting in Atlantic City, New Jersey. One paper presented in the General Session at that meeting, one reprinted paper, and three other solicited papers are also included.
The choice of “Geometry of Sandstone Bodies” as a timely and pertinent subject lor the 1960 symposium was made after an extensive canvass of Research Committee members and about fifty other geologists vitally interested in research in petroleum geology. From a group of about 15 proposed subjects, this one was selected as first choice by almost all those canvassed. Partly because of this high level of interest, the decision was made to attempt publication of the symposium as a special volume of The American Association of Petroleum Geologists. The word geometry in the title probably had several different meanings among the selectors, and for this reason an attempt was made to define the term adequately in order to establish uniformity of communication among symposium participants.
The dictionary definition of the word “geometry” is the science of magnitudes in space. In applying the term to the symposium theme, some modification and interpretation of its formal meaning were needed, and the following definition was therefore proposed for use in this volume—
Geometry of Sandstone Bodies—Spatial relationships of sandstone deposits within the sedimentary framework.
As used in this book, the subject is more than just a three-dimensional study in which thickness is added to areal distribution.