9:30 AM - 9:45 AM
[HSC07-03] Estimation of In-situ Stress Field using Deformation of Side-Wall Cores
Keywords:Side-Wall Core, Core Shape, Deformation, In-situ Stress Field, CCS
Some risks of carbon capture storage ( CCS) projects come from mechanical instability of seal layers, which directly results in leakage of injected carbon dioxide from the underground. Mechanically stable or unstable states of geological layers are controlled by rock strengths and in-situ stress field. Rock strengths can be estimated at laboratories after retrieving rock cores from the underground. However, in-situ stress field should be estimated at onsite in the underground under severe in-situ conditions. Therefore, estimations of in-situ stress field usually have large uncertainties and limit to a few sites despite proposals of several methodologies. In this paper, we present a new method for estimating in-situ stress field using deformation of side-wall cores. Geological layers are subjected to tectonic stresses. Cores retrieved from those layers expand according to reliefs of in-situ stresses. Consequently, core shapes have information about in-situ stress field. Our method estimates a full stress tensor from measured expansions and elastic properties of side-wall cores by utilizing theoretical equations defining in-situ stress field around an inclined well. Side-wall coring tools have already commercialized as one of logging tools by a few service companies and those tools have a capability to acquire dozens of cores over 20 at specified depths. If we are able to utilize those many cores, side-wall core method has a potential to reveal a tectonic stress profile along a well trajectory.
Firstly, we introduce a theoretical background of side-wall core method and summarize pros and cons of our method compared with other methods. Four side-wall cores acquired at around 1000m depths, which are typical target depths of CCS projects, are examined. Their diameters are approximately 23mm and their lengths are from 20mm to 30mm. Sinusoidal expansions of core diameters, which are expected by a theory, can be measured. The amplitudes of sinusoidal curves given by fitting measured data of diameter changes in the circumferential direction range from 0.06mm to 0.2mm. The amplitudes are expected to be caused by reliefs of in-situ stresses.
Firstly, we introduce a theoretical background of side-wall core method and summarize pros and cons of our method compared with other methods. Four side-wall cores acquired at around 1000m depths, which are typical target depths of CCS projects, are examined. Their diameters are approximately 23mm and their lengths are from 20mm to 30mm. Sinusoidal expansions of core diameters, which are expected by a theory, can be measured. The amplitudes of sinusoidal curves given by fitting measured data of diameter changes in the circumferential direction range from 0.06mm to 0.2mm. The amplitudes are expected to be caused by reliefs of in-situ stresses.