Lab No 14

Isopach and Isochore Maps

University of SulaimaniSchool of Science

Department of Geology

Practical Structural Geology

Instructor: Halko M. Mahmoud

2014-2015

Why does thickness change?

Sedimentary beds may show lateral changes in thickness, either in connection with an erosional episode that created an unconformity or due to lateral facies changes.

It is very crucial for the hydrocarbon industries to document the lateral changes in the layer thickness.

Thickness Maps

Thickness maps are fundamental tools in structural geology. They represent thickness variations and thickness trends of a given unit.

There are two different types of thickness map which are Isochore and isopach maps.

An isochore is a line that connects points of equal vertical thickness.  An isopach is a line that connects points of equal true thickness (i.e.

measured perpendicular to bedding)

Thickness Maps

Thickness of subsurface unit can be obtained from seismic section and drilled wells.

Vertical thickness increased with increasing dip angle and when dip angle is zero the true thickness and vertical thickness are equal.

Cos Ɵ= true thickness/ apparent thickness

The thickness map of any unit can be obtained from the structure contour for the top and bottom of the unit.

How to construct isopach lines

Construction of isopachs from strucutre contour maps. a) structure contour of top (solid lines) and bottom (dashed lines) of a limestone bed. b) Isopach map. c) sections across the limestone.

Isopach Maps

Along with the porosity and water saturation data, isopach map is used to estimate the volume of hydrocarbon in a reservoir.

Exercise

There is a sandstone bed in this map south of A-B line. The solid lines represent the structure contours of the upper surface of the sandstone and the dash lines represent its lower surface.