Borehole Image Log Analysis for Sedimentary Environment and Fractures Identification in Jake East Field

Abstract

The borehole imaging technology has great advantages to provide more information for subsurface formations for exploration wells in Sudan. The electrical image log tool Stimu Taneous Resistivity Imager (STAR) used in this case study for an exploration well in Jake East oil field. The electrical image log tool (STAR) includes 144 electrodes which measure the formation microresistivity and the log is displayed as an image of the borehole. Necessary preparations including log data processing and corrections on the (STAR) log Checked the data quality of log record before image log before started the data processing and interpretation. All corrections are used to enhance the log quality, locate the image data in the correct depth position and match the image log with the conventional logs. According to image log result well section has been divided into four different sections in Abu Gabra formation, for the interpretation used special petrohysical software (Cif Log Geomatrix) .Image log interpretation is carried out in the information about different types of fractures developed. In this study the electrical image logs and conventional logs together with mud logging datawere studied. The purpose of this work is to interpreted the reservoir sedimentary environment .lithofacies and fractures analysis. In addition a quantitative analysis of sedimentary features like bedding, faults and fracture dip angle and azimuths were studied. This is an integrated study combined independent Image Log interpretation data for single well with others logs to accurate analysis for the reservoir in Abu Gabra Formation. The result is used for identification of the sedimentary bedding features, depositional settings andstructural elements in the image log. Plenty of geologic features detected 753 Cross beddings, 241 Bed boundaries, 541 Laminasand few Erosional layers. The statistics of sedimentary geological features in the STAR showed very rich laminas and cross beddings developed in the logged interval, which indicate the sedimentary facies of the logged interval.The dip magnitudes and dip azimuths reflect the structure features or sedimentary environment. Lithofacies and possible depositional environment have been interpreted first based on the mud logging samples description from master logs combined with conventiallogs. The depositional environments, from Abu Gabra 3, Abu Gabra 2e, Abu Gabra 2d to Abu Gabra1 group, indicated by lithofacies, sedimentary structure and bedding on the GR curveand the image, were probably shallow lacustrine to delta facies. Finally different types of natural fractures were detected in case study well in Jake East area around 3 conductive fractures and 35 discontinuous conductive fractures interpreted with highdip angle in Abu Gabra Formation.