A Comparative Study of Preparation Methods, Weighting Agents, and Temperature on Quality of E-M Compatible Borehole Imaging Fluid

Imaging fluids plays a crucial role in mitigating the impact of borehole groundwater on borehole E-M imaging results. Such fluid must possess specific characteristics such as low conductivity to minimize electromagnetic wave attenuation, appropriate dielectric permittivity to prevent signal ringing at the fluid-wellbore boundary, higher density than water for settlement at the bottom hole, and long-term stability throughout the imaging process. This study meticulously examines the influence of agitation and temperature on the quality of oil-based imaging fluids, comparing two major preparation methods with distinct grain sizes of the weighting agent. One is the conventional method involving a critical heating step of the emulsifier in 20% of the imaging fluid liquid base, while the second involves dissolving the emulsifier in the liquid base by agitation. Evaluation of the produced fluids encompasses considerations of their stability over time, settlement in various water temperatures, and rheological properties. The results of these experiments reveal the pros and cons of the agitation process compared to the conventional method, weighting agent grain size, and temperature on the overall quality of the produced imaging fluid. 1. INTRODUCTION High frequency electromagnetic waves are used as the source of Ground Penetrating Radar (GPR) to image and map subsurface geological formations and structures (Jol, 2008). Borehole GPR utilizes high frequency electromagnetic waves for mapping out the downhole subsurface geology. This GPR data quality can be influenced by the presence of borehole water or the media between the antenna and the wellbore Li (2023). Hence, the selection of a proper borehole fluid will help overcome the impact of ground water on imaging data quality. Borehole water should be replaced by an imaging fluid at the bottom hole and cover the E-M antennas while imaging. The ideal borehole fluid (imaging fluid) should have specific properties such as low conductivity (low EM wave attenuation), appropriate dielectric permittivity close to that of the host rock to avoid signal ringing between the fluid-wellbore boundary, higher density than water to enable it settle at the bottom hole, and stability such that it does not discompose while imaging. Following the above characteristics, the imaging fluid is made up of a liquid base with low dielectric permittivity and conductivity, a weighting agent to increase its density than water to about Specific Gravity (SG) of 1.2 and an emulsifier to ensure its stability by preventing the separation and settlement of suspended solids.