The complex case of Macaronichnus trace fossil affecting rock porosity

Abstract

Bioturbation is an important factor for reservoir quality due to the modification of host rock petrophysical properties (i.e., porosity, permeability, and connectivity). However, there is no predictable relationship between bioturbation and its effect on rock properties, due to the variability of the involved ichnological features. A detailed ichnological analysis is necessary to determine how bioturbation affects petrophysical properties in a bioturbated reservoir. Traditionally, ichnological features such as density, tiering, size, orientation, architecture, and fill, have been considered. However, other properties have been undervalued as is the case of lining. Here, we present a detailed study on the effects of Macaronichnus burrows, an ichnotaxon usually related to hydrocarbon exploration due to its high concentration in rock notably affecting petrophysical properties. Macaronichnus, a subhorizontal cylindrical burrow, is characterized by a well-defined and developed outer rim surrounding the tube core. Our data indicates a clear zonation in porosity according to burrow structure, with the lowest porosity in the tube core and higher values associated with the surrounded rim. This duality is determined by the tracemaker grain selective feeding activity and the consequent concentrated cementation. The organism concentrates the lighter minerals in the tube core fill during feeding, favoring post-depositional cementation during diagenesis and this results in lower porosity than the host rock. However, heavy minerals, mainly glauconite, are located in the rim, showing higher porosity. Our results support the view that ichnological analyses are essential to determine reservoir quality in bioturbated reservoirs, evidencing that other ichnological properties in addition to those traditionally considered must be evaluated.

Trace Fossils Of The Selorejo Formation, Rembang Zone, North East Java Basin, Indonesia

“…Macaronichnus is usually identified as an unbranched, cylindrical, sub-horizontal burrow from a few millimeters to 15 mm in diameter. Macaronichnus is primarily found in shallow coastal and shallow subtidal deposits but also occurs in deep-sea sediments (Dorador et al, 2021) 7. Bergaueria is a trace fossil that is short in size, round in shape, and protruding to the surface like a burrow.…”

Eocene to middle Miocene contourite deposits in Cyprus: A record of Indian Gateway evolution

“…Reworked turbidites containing more homogenous sands could give higher porosity than classical turbidites, owing to the redistribution of finer particles as a result of bottom current action. Moreover, in the studied sections, applications of techniques such as X-ray micro-computed tomography (Micro-CT), mercury intrusion porosimetry, and analysis of impregnated thin sections have served to reveal the impact of ichnological feaures on rock properties (e.g., porosity and permeability), particularly in contourites (Dorador et al, 2021;Miguez-Salas et al, 2021Rodríguez-Tovar et al, 2021).…”

Evaluating cementation factor for bioturbated sandstones, Bhuj Formation, Kachchh Basin, India: a novel approach using triple-porosity model

“…Bioturbation in clastic reservoirs is one of the least analyzed phenomena resulting in heterogeneity, which is primarily the sediment reworking or modification in the textural and fabric attributes of sediments (Dorador et al 2021;Gingras et al 1999Gingras et al , 2002Gingras et al , 2012Meadows and Tait 1989;Pemberton and Gingras 2005;Perret et al 1999;Pierret et al 2002).…”

“…Various researchers have postulated the effect of bioturbation on the reservoir quality and heterogeneity, resulting in either enhancing or diminishing the petrophysical properties (Pemberton and Gingras 2005;Dorador et al 2021).The bioturbation results in a generation of complex network of burrows filled with contrasting sediments than the surrounding matrix. These burrows fill introduces anisotropy in porosity and permeability (Fig.…”