Lateral distribution of the upper Amundsen shale in potential CO2 storage site Aurora, northern North Sea

Abstract

Fluid-injection induced reservoir pressure increase, influenced by lateral and vertical connectivity of the reservoir rocks. Along with the potential fault and fracture barriers, fine-grained layers within the reservoir interval might influence the total capacity and optimum injectivity. Therefore, it is critical to characterize the shaly unit within the reservoir intervals. This study evaluated the upper Amundsen (Burton) shale, which resides within the Cook and Johansen reservoir sandstones in the Aurora CO2 injection site from the Horda Platform, northern North Sea. Wireline logs and 3D inverted seismic properties have been considered to evaluate the elastic properties and lateral and vertical distribution of that shaly unit. Considering gamma ray log as proxy for shaliness, upper Amundsen shale is observed in the Tusse-Svatalv fault block, while a blocky sandstone with no shale is found in the Vette-Tusse fault block. A separation of elastic properties between the Amundsen and Johansen formations has also been observed. According to the seismic inverted properties, upper Amundsen shale is not laterally continuous within the injected fault block, which indicated direct communication between the upper Cook and lower Johansen reservoir sandstones. This is also specified there might be less influence of the fine-grained shale layer on capacity and injectivity in the Aurora injection site.

Keywords: The Longship; Aurora; upper Amundsen shale; Burton Shale; Seismic inverted properties