Characterisation of carbonate reservoir heterogeneity using borehole image logs

[...]... resolution of openhole logs Carbonate heterolithic classification/2 Image log facies analysis – reef facies Resistivity Image Acoustic Image Reef core Resistivity Image Acoustic Image Back-reef lagoon Carbonate heterolithic classification/2 Facies stacking patterns and dip analysis Oil based mud Carbonate heterolithic classification/2 Image facies prediction in uncored wells Interpretation Image facies... thickness (ft) 8 4 2 0 60 50 40 30 20 10 0 Image facies Well 3 % B-Zone 6 Image facies 4 2 0 60 50 40 30 20 10 0 Image facies Well 2 % B-Zone 6 Image facies 4 2 0 Image facies 8 60 50 40 30 20 10 0 Image facies 60 50 40 30 20 10 0 Well 1 6 % B-Zone Average thickness (ft) Image facies statistics 8 4 2 0 Image facies IF1 IF2 IF3 IF4 Image facies IF5 IF6 IF7 IF8 IF9 IF10 IF11 Carbonate heterolithic classification/1... Carbonate heterolithic classification/3 Reservoir rock typing A RRT has a unique reservoir quality but not necessarily lithofacies • Typically established in cored wells on basis of thin section and SCAL data • Extrapolation into uncored wells using openhole logs and used to predict permeability – fine scale permeability heterogeneity below resolution of standard openhole logs – subtle changes in pore system... several orders of magnitude • High resolution image logs used for Image Rock Type (IRT) identification and permeability prediction Carbonate heterolithic classification/3 Image facies Stacked smallscale finingupward units, with high K grainstones at base grading up into low K wackestones Conductive, high K vuggy skeletal grainstones at base of units Resistive, low K wackestones at top of units Carbonate. .. interpretation of image logs Carbonate heterolithic classification/1 Stylolites and dissolution seams Conductive, tension gashes Stylolitic seams Resistive cemented limestone Dissolution seam Carbonate heterolithic classification/1 Cross-bedding Carbonate heterolithic classification/1 Nodular limestone image facies STATIC DYNAMC STATIC DYNAMC STATIC DYNAMC STATIC DYNAMC STATIC DYNAMC STATIC DYNAMC Carbonate. .. stacking pattern in upper part of reservoir Coarse, vuggy rudist float to rudstones Stacked fining-upward grain/pack/ wackestone units Mostly trendless succession of mudstone/ wackestones Carbonate heterolithic classification/2 Reservoir architecture Carbonate heterolithic classification/2 Lateral facies variations in horizontal wells Unit A Breccia Unit B Image facies Carbonate heterolithic classification/2... enhancement Completion strategy Selection of perforation intervals GO Carbonate heterolithic classification/1 Image facies • Image facies assigned on basis of image character, open hole log response • Image response is related to electrical or acoustic properties, responds to rock texture, fluid saturation and mineralogy • Not possible to distinguish all core lithofacies • Calibration with core allows... orientation and analysis of primary stratification surfaces/heterogeneities •Identification of key stratal surfaces Borehole image facies analysis •Depositional modelling •Sequential analysis •Pore fabric analysis •porosity and permeability distribution •Palaeotransport /reservoir geometry analysis Carbonate heterolithic classification/2 High resolution image log response STAT DYN MINIPERM PROFILE Thin bed identification... workflow Organise core poro-perm data by image facies (cross-plots) Calculate K statistics and define K rank Group image facies into K classes: image rock types” Assign image image rock types using porosity from openhole log data as guide to ‘background’ rock type Assign K rank and value alongside image rock types interpretation QC predicted K against measured core K Carbonate heterolithic classification/3... threshold the image and determine the % vuggy macroporosity and degree of interconnectivity Carbonate heterolithic classification/3 Microporous nodular limestones Thin section Core Permeability map Log K _ 3.41 _ 2.81 _ 2.35 _ 1.81 _ 1.64 _ 0.75 _ 0.21 Carbonate heterolithic classification/3 Porosity distribution from images STATIC Cemented tight limestone Microporous high permeability limestone Carbonate . image logs Carbonate heterolithic classification/ 2 1 km 100 m 200 microns Scales of carbonate reservoir heterogeneity Scales of carbonate reservoir heterogeneity Carbonate heterolithic classification/ 3 • Borehole. heterogeneities Carbonate heterolithic classification/ 6 Micro-resistivity Acoustic Fracture Bedding Feature classification and characterisation Feature classification and characterisation Carbonate heterolithic. dissolution seams Stylolites and dissolution seams Carbonate heterolithic classification/ 17 Cross-bedding Cross-bedding Carbonate heterolithic classification/ 18 STATIC DYNAMC STATIC DYNAMCSTATIC