doveton0 - CONTENTS Resistivity logging Induction Laterolog...

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CONTENTS Resistivity logging Induction Laterolog Vertical resolution and radius of investigation Porosity logging Density log Neutron log Neutron - density log combination Primary and secondary porosity The Archie Equation Formation factor - porosity relationships for sandstones Formation factor - porosity relationships for carbonates Resistivity index - saturation relationships Temperature and water resistivity Estimation of formation temperature Temperature correction of water resistivity Example Example of S W computation: Mississippian carbonate Digital log data Example of S W computation: Ordovician sandstone References 1 1 2 2 8 8 8 8 9 11 13 15 20 21 22 24 24 25 32
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RESISTIVITY LOGGING In most runs of a resistivity tool, the major purpose is to obtain measurements of Rt, the true resistivity of the formation. However, there are a variety of complicating factors involved which may require corrections to be made to the recorded values in order to obtain good estimates of the true resistivities. All resistivity tools are to some extent “averaging” devices that record resistivities of zones rather than resistivities of discrete points. So, for example, the resistivity of a thin resistive horizon will generally be underestimated by most tools since its reading will be partly reduced by contributions of more conductive adjacent beds. The process of drilling actually modifies the resistivities of formations in the vicinity of the borehole through the process of “invasion”. In addition to its other functions, the drilling mud forms a mudcake seal on the borehole wall of permeable formations. In doing this, mud filtrate penetrates the formation, displacing formation water and oil or gas. In a zone immediately adjacent to the borehole the mud filtrate displaces all the formation water and any “moveable oil saturation” (the “flushed zone”). Beyond this, the mud filtrate displaces part of the formation water in a “transition zone” which ultimately peters out at a contact edge with the undisturbed formation. The relative depth of invasion is broadly a function of formation porosity/permeability properties, so that less porous formations (typical carbonates) are more highly invaded than moderately porous units (typical sandstones). Pore volume appears to be a major control on invasion depth, because this dictates the volume available to accomodate invading mud filtrate. Once the permeability of a formation exceeds a critical lower value (perhaps about 0.1 md), the formation will be invaded, but invasion depths appear to be insensitive to variations in permeability at higher values (Jorden and Campbell, 1984). The replacement of formation water by mud filtrate involves a change of pore
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This note was uploaded on 10/30/2011 for the course PETROLEUM Short cour taught by Professor Dr.paulglover during the Spring '11 term at University of Aberdeen.

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doveton0 - CONTENTS Resistivity logging Induction Laterolog...

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