Investigation of anisotropy in nonsaturated and heterogeneous carbonate series using crosshole acoustic techniques

Dawin Baden (1) , Pierre Henry (1) , Ginette Saracco (1) , Lionel Marié (2) , Yves Guglielmi (1)

1 CEREGE - Centre européen de recherche et d'enseignement des géosciences de l'environnement
2 EA 4234 - Géologie des systèmes carbonatés

Physical properties of carbonate rocks cannot be fully captured from laboratory-sized samples. Indeed, heterogeneous facies distribution and/or diagenetic alterations may lead to significant variations in petrophysical properties within few meters. In carbonates, diagenetic transformations are tightly related to nature of fluids flowing through the formations, e.g. via fractures network. Consequently, reservoir properties may have patchy distribution, and may not be correlatable (e.g. using facies distribution or wells-logs correlations) within few meters. Our works aim at characterizing carbonates anisotropy at different scales, and are subject of two presentations at SEG's 87th Annual Meeting. This abstract deals with the first part of our approach, that's to say characterizing impact of diagenetic alteration on reservoir properties and seismic anisotropy, from meter to multi-meter scale. Crosshole acoustic-survey has been carried out using ultrasonic frequencies (50kHz), and vertical-resolution of 10cm. The main conclusions are: (1) multi-meter crosshole surveys, enable measuring elastic properties of both matrix, and fractured-matrix. Wave velocities measured at multi-meter scale are comparable to that from laboratory measurements, and this analogy is attributed to poor likelihood of finding dense fractures-sets –which would drastically change elastic moduli– at reduced scale. (2) Weak anisotropy is detected, varying between +10% (slow axis perpendicular to strata) and –2% (slow axis parallel to strata), and likely results from combination of matrix anisotropy (mineral orientation and pore geometry) and fractures effects. (3) In heterogeneous layered formations, variation of mean velocity with source and receivers locations significantly impact anisotropy parameters estimated by curve fitting. One should be aware of this potential bias, while interpreting crosshole surveys with sparse data, especially in carbonate formations. This paper has been withdrawn from the Technical Program and will not be presented at the 87th SEG Annual Meeting.

Mots clés: carbonate; crosswell; ultrasonic; VTI; anisotropy

Domaines: Planète et Univers [physics]; Pétrographie; Géophysique [physics.geo-ph]; Sciences de l'ingénieur [physics]; Acoustique [physics.class-ph]; Mécanique des solides [physics.class-ph]

Dawin Baden, Pierre Henry, Ginette Saracco, Lionel Marié, Yves Guglielmi. Investigation of anisotropy in nonsaturated and heterogeneous carbonate series using crosshole acoustic techniques. SEG Technical Program Expanded Abstracts 2017, Sep 2017, Houston, United States. pp.310-315, ⟨10.1190/segam2017-17587284.1⟩. ⟨hal-01914557⟩