Fracture and Sub-Seismic Fault Characterization for Tight Carbonates in Challenging Oil-Based Mud Environment—Case Study From North Kuwait Jurassic Reservoirs

Abstract

Abstract Evaluating natural fractures in tight carbonate reservoirs during the exploration and early development stages is critical in order to reduce geological uncertainty and determine well trajectory in future horizontal drilling. Challenges are often found in both acquiring the adequate data and assessment of the fractures/sub-seismic faults in the oil based mud borehole environment. This paper summarizes part of the experience learned from the use of an optimal dataset in addition to a workflow on fracture characterization for tight deep carbonate reservoirs in Kuwait. In the process of exploration and development of these particular reservoirs, oil-based mud has been used in the drilling process due to the concerns of wellbore stability. Acoustic images and core was acquired in the early stages of the field development. After the invention of a micro-resistivity imaging tool it was used in combination with the acoustic imaging for integrated and enhanced formation evaluation, which allowed reduced coring for a cost saving. The paper explains the advantages and limitations of each image dataset and describes how the acoustic and micro-resistivity images are complementary to each other. The paper also presents how different datasets gives partial contribution to the overall geological understanding of the field. More importantly, the case study shows that the combination of both image data sets provides a much better and more complete picture of fractures in the wellbore with limited core calibration. Smaller scale faults, which are usually not detected or poorly imaged on seismic, can be interpreted on images with definition of vertical displacement through the integration of well correlation and cross sections. The output from this study provides an essential database for well completion decision, fracture reservoir modeling, infill drilling plan and future horizontal well placement.