An investigation of porosity–velocity relationships in faulted carbonates using outcrop analogues

Abstract

Porosity and permeability are notoriously difficult to predict in carbonates, especially prior to drilling when there is a lack of direct petrophysical data. The aim of this paper is to document the initial results of an integrated outcrop and laboratory study designed to investigate the relationships between pore systems and acoustic velocities in faulted Oligo-Miocene carbonates on the Mediterranean islands of Malta and Gozo. Depositional facies is shown to have a significant effect, with velocities in grain-dominated carbonates up to 1000 m s−1 higher than those in micrite-dominated carbonates. Based on outcrop structural data, the fault zones can be separated into three architectural components: a fault core; an intensely damaged zone; and a weakly damaged zone, with the last passing into undamaged protolith. Our data suggest that only the fault core component can be identified using porosity–velocity data, with P-wave velocity (Vp) values of 5000–6500 m s−1 at helium porosities of less than 5%. Our study is novel in that the prediction of elastic properties and acoustic velocities across fault zones is anticipated by linking laboratory-scale measurements with seismic-scale predictions through quantitative rock physics modelling.

Fault zone fluid pathways in the carbonate Irecê basin, NE Brazil

“…Fluid pathways in carbonate rocks are strongly dependent on depositional petrofabrics and their tectonic and diagenetic history (Agar & Geiger, 2014;Pili et al, 2002). Current approaches to better understand fluid flow in carbonate rocks and associated structures from large to small scale include seismic-scale data (Masaferro et al, 2004;Melville et al, 2004), field observations (Agosta et al, 2010;Del Sole et al, 2020;Ferrill et al, 2011Ferrill et al, , 2017Ferrill & Morris, 2008;Michie et al, 2014;Peacock, 2002;Peacock et al, 2016Peacock et al, , 2017Peacock & Sanderson, 2018;Petracchini et al, 2012), petrophysical and micro-CT data (Beaudoin et al, 2018;Healy et al, 2014;Lézin et al, 2009), isotope geochemistry (Agosta et al, 2008;Bertotti et al, 2017;Gomez-Rivas et al, 2014;Zaarur et al, 2013), physical modelling (Cilona et al, 2012;Spratt et al, 2004) and numerical modelling including fluid flow and reactive transport (Antonellini et al, 2014;Bisdom et al, 2017;Corbella et al, 2014;Fitz-Dias et al, 2011).…”

Fracture patterns and petrophysical properties of carbonates undergoing regional folding: A case study from Kurdistan, N Iraq

“…Outcrop analogue studies can improve understanding of some aspects of fracture distributions and their influence on fluid flow in fractured reservoirs (e.g. Antonellini and Mollema, 2000;Aydin, 2000;Nelson, 2001;Stephenson et al, 2007;Lacombe et al, 2011) and their influence on petrophysical properties such as porosity and velocity (Nemati and Pezeshk, 2005;Healy et al, 2015). However, the scaled outcrop data should be used with care in order to improve M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT 5 orogenic belt in Kurdistan can be divided into five distinct structural zones, that from the NE hinterland to the SW foreland, and are named the: Zagros Suture, Imbricated Zone, Highly Folded Zone, Foothill Zone and Mesopotamian Foreland Basin (Jassim and Goff, 2006) (Fig.…”