PREDICTION OF PETROPHYSICAL PARAMETERS BASED ON DIGITAL VIDEO CORE IMAGES

Core-slab photography is a common way to document geological informati on from cores. Past practice has been to photograph core slabs with or dinary cameras that produce paper photographs. The presented method re trieves petrophysical properties from high-resolution digital video co re images. The procedures described in this work are based on video im ages (standard RIO/B camera) of cores taken with a digital recording s ystem. The system is able to record in both visible and UV light at di fferent illumination angles, store images, compress/decompress images, and display one or several images as a continuous long core. The seam less core image is marked with depth Scale and can be scrolled, scaled , and zoomed. Facilities for correlation with other related data, such as wireline logs, discrete core data, and microscopy images, are also included in the system. We used homogenous dry core plugs from three North Sea oil fields in this work. We recorded images of plug surface, together with conventional core-analysis data (i.e., porosity, gas pe rmeability, average grain size, and mineralogy). The new method is bas ed on processed digital images:light/shadow patterns are obtained by u se of asymmetric, low-angle illumination in the green channel. Texture spectra of the rock material are obtained by dedicated image-analytic al processing of these gray-scale images and by detecting textural fea tures by use of a unique set of specially designed texture filters. We then calibrate these spectra with respect to measured petrophysical p arameters by use of multivariate calibration [partial least squares (P LS)-regression]. Multivariate calibration is based on a set of represe ntative training images, selected to span representative ranges of the intensive petrophysical parameters being modeled. On the basis of thi s calibration model, similar gray-level video images from new, unknown core sections (with geologically similar facies) are used to estimate properties of the core material by PLS-prediction. In this study it h as been possible to model porosity, gas permeability, and average grai n size (ORZ) of different formations with a relatively high accuracy a nd precision. PLS-modeling/-prediction is a strict empirical calibrati on procedure. The present method is critically dependent upon a thorou gh, geologically well-documented training data set. Results show that the method is capable of predicting a continuous log of these three pe trophysical parameters based on core images calibrated against a set o f routine laboratory core-analysis data taken at discrete intervals fo r a particular formation. The advantages of the new method are rapid a nd cost-efficient methods for prediction of petrophysical parameters, particularly from slim cores, and improved integration of geological r ecords with wireline data. The method is proposed to be included in fu ture routine laboratory core analysis studies because of its low cost and ability to predict values continuously along the core.