Abstract

We document a technology for environmental corrections during logging while drilling (LWD in wash down mode) operations in closed hole circulation drilling (CHCD). The technology documents a new way to estimate hole size (caliper) and other environmental corrections through implementation of a neural net model to identify zones of varying bore hole fluids followed by new algorithms to create final products. Results with new drill wells spurred a re-evaluation of historical wells ending in a new porosity estimation methodology.

Initial quality checks of Neutron-Density cross-plot data for new wells drilled in CHCD mode indicated that applied environmental correction resulted in potential errors in porosity estimations. Investigation of static and dynamic annular pressure data suggested that mixed density annular fluids, drilling mud and sacrificial fluid, created varying logging conditions. A neural net model was developed to account for these conditions. From this analysis a set of lab test were completed and new algorithms were applied to develop a synthetic caliper.

The results of this work provided internally consistent porosity estimation methodology in zones of wells that are typically difficult to evaluate due to complex drilling conditions. The products provide a more thorough understanding of the distribution of porosity in formation and understanding of potential non-matrix features (fractures/karst). The methodology allowed for re-examination of historical wells that were deemed unusable and unsuitable for porosity estimation. Both of these insights are being considered in the history match and prediction of the reservoir model. The integrated approach of the team demonstrates the value of the technical approach by the contractor and operator to deliver results for the project.

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