--> A New Parallel Fold Construction Method From Borehole Dip for Structural Delineation

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A New Parallel Fold Construction Method From Borehole Dip for Structural Delineation

Abstract

Dips derived from borehole images are used to create high quality structural models in the vicinity of boreholes using an existing workflow based on conventional geological concepts. Such local models significantly improve the estimation of the oil in place and help determine the most effective way to produce it. Another workflow applies the same concepts to dip data from multiple wells in combination with surface seismic data. The main concept of both workflows is the similarity of the layers during deformation. Although this is robust whatever the deformation type (e.g. fold, drag, rollover), it is not very accurate for folds, yet most oil reservoirs are in the parallel fold domain. Methods for parallel layers construction are much more challenging than the similarity approach. The existing parallel method being not sufficiently stable, we propose a totally new approach. Our method starts by delineating structures along the well using a new automatic stereonet analysis applied to dips selected by an interpreter. This technique helps the interpreter identify the structure type (i.e. zones with same structural axis) at different scales. Based on this delineation, the interpreter selects for each structure a type from monocline, drag folds (normal/reverse), rollover, and similar/parallel fold. The corresponding cross section is automatically displayed. A major improvement to previous approaches has been made in the parallel fold model. The new method is not only very accurate but also very robust. Results are no longer disturbed by erratic dips. The computed geological layers are first displayed on a cross section perpendicular to the structural axis. Once validated by the interpreter they can be displayed on a curtain section or as three-dimensional surfaces. Case studies demonstrate that the new technique to reconstruct parallel folds greatly improves the accuracy of the reservoir geometry. The workflow enables interpreters to run different scenarios when several structural types are considered. Local structural information such as surfaces and the structural axis can be further used to constrain three-dimensional reservoir models built from multiple wells and seismic, facilitating well placement decisions and reserve evaluation.