Joint interpretation of magnetotelluric, seismic, and well-log data in Hontomín (Spain)

Abstract

Abstract. Hontomín (N of Spain) hosts the first Spanish CO 2 storage pilot plant. The subsurface characterization of the site included the acquisition of a 3-D seismic reflection and a circumscribed 3-D magnetotelluric (MT) survey. This paper addresses the combination of the seismic and MT results, together with the available well-log data, in order to achieve a better characterization of the Hontomín subsurface. We compare the structural model obtained from the interpretation of the seismic data with the geoelectrical model resulting from the MT data. The models correlate well in the surroundings of the CO 2 injection area with the major structural differences observed related to the presence of faults. The combination of the two methods allowed a more detailed characterization of the faults, defining their geometry, and fluid flow characteristics, which are key for the risk assessment of the storage site. Moreover, we use the well-log data of the existing wells to derive resistivity-velocity relationships for the subsurface and compute a 3-D velocity model of the site using the 3-D resistivity model as a reference. The derived velocity model is compared to both the predicted and logged velocity in the injection and monitoring wells, for an overall assessment of the computed resistivityvelocity relationships. The major differences observed are explained by the different resolution of the compared geophysical methods. Finally, the derived velocity model for the near surface is compared with the velocity model used for the static corrections in the seismic data. The results allowed extracting information about the characteristics of the shallow unconsolidated sediments, suggesting possible clay and water content variations. The good correlation of the velocity models derived from the resistivity-velocity relationships and the well-log data demonstrate the potential of the combination of the two methods for characterizing the subsurface, in terms of its physical properties (velocity, resistivity) and structural/reservoir characteristics. This work explores the compatibility of the seismic and magnetotelluric methods across scales highlighting the importance of joint interpretation in near surface and reservoir characterization.

Determination of the electrical resistivity of rocks by scanning method while searching and exploring hydrocarbon deposits

“…Последняя, как известно, представляет собой сложную энергетически открытую гетерогенную и полифазную систему, находящуюся в локально неустойчивом состоянии. Неклассическая геоэлектрика открывает новые перспективы к более тонкому изучению строения геоэлектрической среды и происходящих в ней геодинамических и иных процессов [3][4][5][6].…”

“…Реальная кривая МТЗ считается искаженной, если она не совпадает с кривой для горизонтальнослоистого вертикального разреза в интервале, где получена эта кривая. Но в природе в подавляющем большинстве случаев реален трехмерный горизонтально-неоднородный геоэлектрический разрез, и поэтому кривую над таким разрезом в строгом понимании нельзя назвать искаженной -именно она и [3,4,8,9].…”

3-D seismic travel-time tomography validation of a detailed subsurface model: a case study of the Záncara river basin (Cuenca, Spain)

“…The travel times to all receiver or source positions are computed from the resulting time field and ray tracing is performed backwards, perpendicular to the isochrons (Vidale, 1988;Hole, 1992). The inversion is performed with the conjugate gradient solver LSQR (Paige and Saunders, 1982). One of the main requirements for a successful inversion is the selection of an appropriate initial model (Kissling, 1988;Kissling et al, 1994).…”

Using downhole resistivity to better understand magnetotelluric inversion

“…Yan et al, 2017) or during the interpretation process (e.g. Ogaya et al, 2016). Down hole resistivity log data have also been used either as a constraint during inversion (e.g.…”