--> An Integrated Petrophysical and Geomechanical Analysis of Deep Sedimentary Formations for Safe Carbon Storage in the Cook Inlet basin, Alaska

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An Integrated Petrophysical and Geomechanical Analysis of Deep Sedimentary Formations for Safe Carbon Storage in the Cook Inlet basin, Alaska

Abstract

This study shows the potential of safe carbon storage in the Hemlock Formation in the Cook Inlet basin of Alaska. The Cook Inlet basin is an excellent area for carbon storage and utilization for several reasons. First, the basin is located close to Anchorage, Alaska’s largest city and a major source of carbon. Second, the depleted, conventional hydrocarbon reservoirs in the basin can provide enough pore space for carbon storage and enhanced hydrocarbon recovery. Third, offshore areas in the basin can offer significant advantages compared to onshore, in terms of the reservoir extent and smaller number of stakeholders (surface and mineral owner rights, etc.), as well as reduced risks to subsurface drinking water sources. However, the basin is tectonically active, and there are large high-angle faults, which are critical in terms of fault slip related to carbon sequestration. In this study, two 3D seismic surveys, several well-logs (~200 wells), and core data (~37 wells) were integrated to analyze petrophysical and geomechanical properties and understand reservoir heterogeneities. Several reservoir and geomechanical tests were performed on the overburden (Tyonek shale), reservoir (Hemlock sandstone), and underburden formations (Talkeetna volcanics and Mesozoic igneous intrusive complex- quartz diorite) at the subsurface conditions. The fault slip potential (FSP) simulations were performed for the faults interacting with the Hemlock Formation and underlying formations, including the basement, over a 30-year injection period (2020-2050) in the Nicolai Creek and Granite Point fields using geomechanical, hydrologic, stress, and fluid injection data. Results show that the Hemlock Formation is vertically and laterally heterogeneous. The Hemlock Formation has an estimated CO2 storage capacity of ~0.91-16.61 Gigatonne (Gt), with a P50 value of ~4.33 Gt in the whole Cook Inlet basin. Although the present-day maximum horizontal stress (SHmax) is along NW-SE, which is in line with active subduction, the stress state changes locally. The FSP results show that faults can slip, depending on several factors, including the local stress state, pore pressure, distance of the wells from the faults, and CO2 injection rate. However, the numbers vary significantly across the oil fields. A sensitivity analysis shows that the azimuth of SHmax, fault orientation and pore pressure gradient are the most critical factors for fault stability.