Integration of Cretaceous Morro do Chaves rock properties (NE Brazil) with the Holocene Hamelin Coquina architecture (Shark Bay, Western Australia) to model effective permeability

Abstract

Coquinas are significant producing facies in the pre-salt reservoirs of Brazil and Angola. This paper describes an analogue model study to help understand the reservoir characterization of coquina reservoirs. Porosity and permeability measured in 39 core plugs from a single coquina bed in a Lower Cretaceous outcrop in NE Brazil have been combined in a three-dimensional geological model for use in reservoir simulation. A training image derived from the geometry of a Holocene coquina analogue in Western Australia controlled the distribution of the bed-scale petrophysical properties from the outcrop. A synthetic well test showed that the effective permeability of the system lies between the geometrical and harmonic averages of the plug data in the layer. There is also moderate flow anisotropy, with preferential fluid flow aligned along the beach ridges. This paper demonstrates how the combination of outcrop data and an appropriate modern environment might be used to improve our understanding of the behaviour of coquina reservoirs and to guide future reservoir studies.

Petrophysical Correlations for the Permeability of Coquinas (Carbonate Rocks)

“…The plot shows data from all samples according to their petrophysical properties, highlighted by two groups: one with a relatively low permeability and the other with a high permeability. Two low-permeability samples had relatively low porosities, and two high-permeability samples had higher porosities, as expected and discussed by Corbett et al (2016) who noted substantial changes in permeability with only slight changes in the porosity. However, two samples (122.45 and 187.95) had nearly the same porosity but showed a large difference in their permeability (to be discussed later).…”

“…These processes impacted directly the pore systems of the rocks, leading to the preservation of primary porosity, the creation of secondary porosity, and pore obliteration. As a consequence, a very heterogeneous porous framework was generated, reflected especially in their permeability (Corbett et al 2016).…”

Computational and experimental pore-scale studies of a carbonate rock sample

“…A well-studied layer (Corbett et al, 2016;Luna et al, 2016) in the Morro do Chaves Formation ( Fig. 2a), called Bed 2B (Fig.…”

“…2b) was selected. Corbett et al (2016) pointed out that it is possible to use cross-stratification as evidence that the coquinas in this layer were deposited lakewards or lagoonwards as accreting bioclastic bars. A plug from that layer (Fig.…”

“…One challenge of the pre-salt reservoirs is the difficulty to obtain samples for purposes of geological, sedimentological and petrophysical characterization. An alternative is to use analogue samples that are geologically similar to the pre-salt reservoir rocks (Corbett et al, 2016). For this many have used carbonate rocks samples from an outcrop in the northeast region of Brazil (Azambuja Filho et al, 1998), mostly to study their porosity and permeability properties.…”