Method of distinguishing types of geologic sedmentation

Abstract

A method for interpolating the environment and geological age at all levels in a borehole from information provided by a limited number of depths and the use of a synthetic stratigraphic cross-section for the interval between these depths. In hydrocarbon exploration, a borehole provides a suite of logs, plus estimates of geologic age at a number of spaced markers. This method uses a sea-level cycle chart, a calculation of subsidence from the thickness of the interval, and postulated values for several variables. If it is known that the supply of sediment always exceeded the available accommodation during deposition, the corresponding synthetic cross-section may then be optimized for geological plausibility (as gauged by visual observation or quantitative criteria) by perturbing the postulated variables and iterating the calculations. Otherwise, the additional step of determining where in the interval the accommodation exceeded the sediment is performed by comparing the signs of the slopes of an observed log estimating sediment grain size and a calculated log estimating layer thickness.

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