The Distribution Of Shale In Sandstones And Its Effect Upon Porosity

A shale volume parameter derived from the response of the gamma ray log in shaly sands is often used to correct the responses of other logs for the effects of the shale. The correlation of a gamma ray parameter to shale volume is usually presented as one direct relationship. However, because the shale can be distributed through the sand in different ways, such as laminated, dispersed, structural, or any combination of these, one may expect varying gamma ray responses dependent upon geometry. We show that each of these configurations can involve a different response from the gamma ray and this variable response can be used to determine the shale configuration. A gamma ray parameter vs. porosity crossplot can then be used to determine shale configuration, sand fraction and sand porosity; the derived equations can be used for implicit solution when processing digital log data. These configurational data can be combined with electric log parameters to determine the oil saturation of the net sand. These log derived parameters are herein verified by direct comparison to rubber sleeve core data.