Shallow Aquifer Sampling for Carbon Capture and Storage – Development of a Low Toxicity Tracer to Enable Low Contamination Water Sampling in a Water-Based Mud System

Aquifer water samples are a key component of carbon capture and storage (CCS) site characterization and are needed to satisfy data requirements in many jurisdictions (The EU, 2009). Often, these aquifers must be drilled with a water-based mud (WBM) system due to the potential for interaction with potable water or the marine environment. As part of the Northern Endurance Partnership (NEP) CCS project, high-quality aquifer samples were required from the Bunter Sandstone Formation to assess the far-field water chemistry. Sampling formation water in a WBM system is often difficult as the fluids are miscible, and determining contamination can be challenging. To assist with this, an environmentally acceptable WBM system was developed with a tracer chemical to monitor the sample pumpout. This system was successfully deployed in a shallow aquifer sampling job using a wireline formation tester, resulting in fluid samples with < 3% contamination. Results from the water sampling were then validated using data acquired from other sources (core plugs from whole core, wireline logs, and formation pressures).