A New Borehole Resistivity Imager for Non-Conductive Mud System: Field Case for Unconventional Reservoir Characterization in Saudi Arabia

Abstract

The non-conductive mud systems including oil-base mud (OBM) are commonly used in clay rich formations for inhibiting clay swelling and ensuring better borehole stability. These drilling fluids determine the type of logging tools and can affect the formation evaluation process. The resistivity imaging tool is one of such tools where fluid conductivity determines the tool type. For the legacy borehole resistivity imaging tools, the use of OBM system acquires low resolution images. Interpreting the sedimentological and structural features using the legacy tool has been a challenge process. In addition, the tool has limitations on borehole coverage, vertical resolution and inability to extract reliable textural analysis from the data. A new imaging tool for OBM system has been tested in the field for the first time in the Middle East in clay rich sands and organic rich formations. In order to evaluate the reliability of the new tool's results, it was combined in a single string with the legacy resistivity and the acoustic imaging tools. The new resistivity imaging tool provided higher vertical resolution and near full bore coverage in 8-inches hole. Results showed improved reliability in data acquisition in high and low resistivity formations. From a sedimentological view point, features such as cross bedding, thin laminations as well as soft sediment deformation features were identified, thus improving the interpretation of the depositional environment. In addition, the structural features like micro faulting were picked along with high angle fractures which were not possible using the legacy resistivity imaging tools.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015