Petrophysical Rock Typing of Coquinas From the Morro Do Chaves Formation, Sergipe-Alagoas Basin (Northeast Brazil)

Abstract

ABSTRACT. This work has analyzed, considering the petrophysical point of view, samples of Coquinas obtained in the outcrop of the Morro do Chaves formation (Sergipe-Alagoas Basin). The complex sedimentological aspects for this study have been reduced by focusing on a single bed. The reservoirs found in this basin have the same age of the reservoirs of Campos, Santos and Espírito Santo Basins (Brazil) and Congo (Africa), from the end of Barremian to the beginning of Aptinian ages, which can be considered analogs of those ones. The data were collected applying routine core analysis and special core analysis techniques in five samples taken vertically, reproducing the case in a single well through a bed of coquinas, with a spacing of approximately 20 cm between each one, to replicate what might be sampled in subsurface coring operations. Measurements of porosity and effective permeability by gas expansion, Nuclear Magnetic Resonance and resistivity were conducted.The analysis of the data revealed the heterogeneity of the porous space in terms of pore sizes and correlations between permeability and electrical formation factor.Along with this detailed analysis, a petrotyping classification of the samples was done using the Global Hydraulic Elements method, to compare with a larger poro-perm data set from a lateral profile. This work shows that the heterogeneity in these few samples from a single bed along a vertical profile is representative for heterogeneity over a much larger coquina data set from the same bed away from this single profile. This work has implications for the scaling and interpretation of NMR data from plug data to log data in these sequences and the resulting prediction of permeability from the latter.Keywords: carbonate, porosity and permeability properties, NMR, electrical resistivity. RESUMO.Esse trabalho analisa, considerando o ponto de vista petrofísico, amostras de Coquinas obtidas em afloramento da Formação Morro do Chaves (Bacia de Sergipe-Alagoas). Os aspectos sedimentológicos complexos envolvidos neste estudo foram reduzidos, focando em umaúnica camada. Os reservatórios encontrados nesta bacia têm a mesma idade dos reservatórios das Bacias de Campos, Santos e Espirito Santo (Brasil) e Congo (África), final do Barremiano ao início do Aptiano, as quais podem ser consideradas análogas daquelas. Os dados foram obtidos por meio de técnicas de petrofísica básica e petrofísica especial em cinco amostras extraídas verticalmente, reproduzindo o caso de umúnico poço através de uma camada de coquinas, com um espaçamento de aproximadamente 20 cm entre cada uma, de forma a replicar o que poderia ser amostrado em uma operação de retirada de plugs em subsuperfície. Medidas de porosidade e permeabilidade efetiva por expansão de gás, Ressonância Magnética Nuclear e resistividade foram obtidas. A análise dos dados revelou a heterogeneidade do espaço poroso em termos de tamanho de poros e correlações entre permeabilidade e fator de formação elétrico. Junto a essa análise detalhada, foi realizada a classific...

Nuclear Magnetic Resonance to Characterize the Pore System of Coquinas From Morro Do Chaves Formation, Sergipe-Alagoas Basin, Brazil

“…The studied plugs (1-2A, 1-4, 1-9A, 1-14A, 1-18B, 1-19B, 1-20B, 1-28, 1-31B, and 1-34A) were sampled horizontally along one single bed named as Bed 2B (Fig. 1B and 1C), layer also studied by Estrella (2015), Corbett et al (2016), Luna et al (2016 and Hoerlle et al (2017Hoerlle et al ( , 2018.…”

“…where ρ 2 is the transverse surface relaxivity, S V is the pore surface-to-volume ratio, and F g is a geometric factor that represents planar (F g = 1), cylindrical (F g = 2) or spherical (F g = 3) pore shapes (Rios et al, 2015). In this work, pores were assumed to have a spherical shape, while ρ 2 was considered to be 35.7 µm/s, which is an average from the values calculated by Luna et al (2016), who used five samples from the same layer (Bed 2B) at Morro do Chaves Formation (Fig 1B ).…”

“…The acquired NMR data was used to quantify the total and fractional porosity and the pore size distribution. Partitioned porosity was evaluated according to the modified classification of Lønøy ( 2006) applied on the pore size distribution obtained with the average surface relaxivity calculated by Luna et al (2016). Surface relaxivity is a phenomenological parameter that relates relaxation times to pore size.…”

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.…”

“…In Brazil, the pre-salt carbonate reservoirs accounted for 50% of total national oil production in 2018 (ANP, 2018). Although the annual production from the pre-salt reservoirs is increasing constantly, there are several challenges regarding their geological and petrophysical characterization (Corbett et al, 2017;Luna et al, 2016), as well as quantifying multiphase flow in their pore systems . This because of the extremely heterogeneous nature of many carbonate rocks.…”