A Perspective On Subsurface Fluvial Strata Correlation Methods

Subsurface fluvial strata correlation has been a long-standing problem, and three basic methods are reviewed in this article. Base level correlation relies on logging facies analysis in great detail, and as a conceptual surface, base level change can be interpreted differently by various people. The subjective nature will increase the risk of diachronous correlation in the absence of other supportive evidence. In spite of this, high resolution analysis has superior advantages that other methods cannot match. A flooding surface is an isochronous physical interface, and all the sedimentary bodies on either side are regarded as isochronous strata. However, how to distinguish a flooding or transgressive mudstone from normal mudstone just by log signals is difficult. Where isolated sand bodies are surrounded by mudstone, or where braided fluvial strata incise into each other it is very challenging to correlate timeline surfaces with any confidence. Although lateral continuity of paleosols is often not as extensive as a flooding surface, some contrasts of low density and high neutron value can be distinguished and thus have correlation value similar to a flooding surface. Thus, individual correlation methods have drawbacks, but paleosol correlation is more promising in subsurface fluvial strata correlations and can corroborate other methods that are collectively necessary for high resolution correlation in reservoir exploration.