Styles of Burial Diagenetic Porosity Modification on the Arabian Plate

Hollis, Cathy; Al Hajri, Aisha

Albian to Turonian carbonate sediments on the Arabian Plate are characterised by high pore volumes and an associated permeability range of several orders of magnitude. Detailed core characterisation reveals complex pore networks, dominated by high volumes of microporosity. Petrographical data provide good evidence for porosity enhancement during burial in the form of 1) porous halos along and adjacent to stylolites and fractures 2)corrosion of (ferroan) carbonate cements 3) uncompacted, highly porous (leached) peloids surrounded by grain rimming and pore-filling cements 4) open networks of delicate and complex pores that have not undergone pore collapse, as might be be expected if dissolution had taken place at shallow depths

Given the potential for this porosity to contribute to in-place volumes and recovery efficiency, it is critical that its genesis is constrained.

This presentation will describe the character of secondary porosity from a range of datasets across the Arabian Plate, including quantitative multi-scale data describing pore shape, size and volume. This data, along with geochemical analyses of precursor, often corroded, carbonate cements will be used to further assess the evidence for porosity creation in the burial realm. On a field scale, ‘passive', laterally extensive porosity enhancement is common, in the form of solution-enhanced inter- and intraparticle microporosity (<30microns). Where biomoulds are abundant, they are commonly solution enhanced. This creates a strong contrast in pore size, with mm-scale vugs embedded within a microporous matrix. Typically, there is little evidence of large-scale solution collapse and there is only localised evidence for mineralisation by ‘exotic', non-carbonate minerals.

Pore shapes and sizes usually vary between facies associations, emphasising the importance of precursor permeability and sediment composition on the style of porosity modification. The relationship between the kinematic evolution of the Arabian Plate and the distribution of burial porosity is less well constrained. Regional and local basin modelling relates hydrocarbon charge to reactivation of deep-seated lineaments during basin inversion, and potentially a supply of reactive fluids to reservoirs occurred at this time. Ongoing and future work will focus upon constraining the source, composition and migration pathways of fluids, and the process by which they could generate significant pore volumes during burial.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013