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Applied Subsurface Geological Mapping by Daniel J.Tearpock, Richard E. Bischke

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Chapter 14. Isochore and Isopach Maps

Introduction

Two key terms, isochore and isopach, are often used synonymously in the petroleum industry as measures of thickness, but they are different. An isochore map (Fig. 14-1a) delineates the true vertical thickness of a stratigraphic interval, whereas an isopach map (Fig. 14-1b) illustrates the true stratigraphic thickness of a stratigraphic interval. These two terms are often confused with respect to their geologic meaning. It is vital for both exploration and development work that the correct meaning and, more importantly, the correct application of these two thicknesses be understood.

(a) An isochore map delineates the true vertical thickness of a stratigraphic interval, such as a rock unit containing a reservoir. (b) An isopach map delineates the true stratigraphic thickness of a stratigraphic interval. The same dipping stratigraphic unit is used in both (a) and (b), with the same edge-of-map boundaries. Note different thickness values assigned to the isochore map versus the isopach map of the same unit.

Figure 14-1. (a) ...

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