Intelligent Tracers for Fluid Invasion Tracking During Coring Operations

Abstract

Core analysis, if conducted successfully, can provide accurate assessment of the original reservoir fluid properties, however, it is challenging to retrieve an uncontaminated core, due to mud components contaminating the fluids originally present in the reservoir. Due to invasion, the liquid extracted from the cores, does not necessarily represent the native liquid, but rather a mixture of drilling and reservoir fluid, thus affecting the results, conclusions and decisions that were based on the analysis. Therefore, deploying advanced water-based mud (WBM) tracers, during coring operations, can mitigate this issue and lead to a significant cost-reduction in field development. Tracer technology is an efficient monitoring and surveillance tool, that was proven to help in tracking and understanding the injection flow paths, and estimating the remaining oil saturation (Sor) in the reservoir, through inter-well and single-well tracer tests. Utilizing water-based tracers in the drilling mud, during coring operation, can help in quantifying the degree of invasion in the retrieved cores, therefore proper correction and more accurate assessment of the reservoir rock and fluid properties, can be made. The accuracy of the data plays a pivotal role in guiding the way forward and the future development of oilfield projects. A WBM tracer was utilized in the drilling mud, during the sidetracking of an observation well at the first and largest CO2-Project in the middle east. The objective of sidetracking the well was to obtain sponge core samples to assess the residual oil saturation (ROS) and evaluate the sweep efficiency of the CO2-flood. This report provides an overview of tracer technologies and the lessons learnt from deploying advanced water-based mud (WBM) tracers during the coring operation of a CO2 observation well, including theoretical and experimental considerations, engineering design and field test issues. The objective of this tracer survey was to estimate the invasion of the drilling mud-filtrate and correct water saturations. It will be useful to use this deployment in some of the relatively mature fields, however, it may have some limitations and challenges that need to be addressed first.