CO2 Injectivity Test Proves the Concept of CCUS Field Development

Abstract The paper presents a unique case study on injectivity tests done in the Kingdom of Saudi Arabia to prove the concept of Carbon Capture, Utilization, and Sequestration (CCUS) capability. It describes the design of surface and downhole testing systems, lessons learned, and recommendations. The energy company drilled appraisal wells to evaluate the multi-zone reservoirs with saline aquifers. The objectives of the injectivity test were to confirm the seal integrity (initial wells), reservoir injectivity, and surface injection pressure. The injectivity tests included the injection of water, N2, and CO2 at different regimes followed by fall-off after each phase. The Surface Testing System was used to pump and control the flow and measure the injection pressure and temperature. The Downhole Testing System is represented either by Monobore completion or DST where the downhole pressure and temperature measurements with wireless real-time telemetry are done at different depths. The injectivity test brought great value in identifying and confirming the best reservoir for CO2 injection and defining the best completion strategy. Creating the injection conditions close to CCUS is vital, especially in heterogeneous carbonate reservoirs where the petrophysical correlations for the reservoir model require calibration with dynamic data. The initial campaign consists of injecting the water up to frac pressure to confirm the seal integrity. Then, the water and N2 injection tests were done to determine the reservoir injectivity with different phases. These tests included injectivity profiling to evaluate the vertical heterogeneity. After an initial assessment of reservoir injectivity and selecting the reservoir for CCUS CO2 injection tests were conducted. The CO2 injectivity test was challenged by the limited volume of CO2 tanks, its corrosive nature, and very low temperature. The surface and downhole system had to withstand these conditions and also the test duration should be optimized to get the representative pressure transient response for the available volume of CO2. The downhole gauges provided the data for pressure transient interpretation during injection and fall-off periods. The real-time monitoring allowed us to interpret in real-time and optimize the test duration. The combining of multiple gauges at different depths allowed us to evaluate the friction losses in completion during high-rate injection and CO2 phase changes during the fall-off due heating effect. The CO2 injection creates an extreme cooling inside the well and this affected the downhole gauge behavior at certain conditions. For the first time, the injectivity test with CO2 was completed at the appraisal well. Authors will provide the unique workflow, lessons learned and recommendations to the industry based on more than 10 wells with 4-6 individual injectivity tests.