skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Dolomite diagenesis and porosity preservation in lithic reservoirs: Carmopolis member, Sergipe-Alagoas Basin, northeastern Brazil

Abstract

The lithic sandstones and conglomerates of the Carmopolis Member of the Muribeca Formation (Aptian) were deposited by fan deltas, alluvial fans, and braid deltas that prograded from low-grade metamorphic terrains into the Sergipe-Alagoas rift basin during the opening of the South Atlantic. Initial carbonates in the Carmopolis reservoirs (presently at depths of 180-2200 m) were marine (high-Mg calcite/aragonite) grain rims, allochems, stromatolitic laminites, and meteoric calcite. These carbonates were subsequently replaced by dolomite/ankerite ({delta}18O{sub PDB} = -7.3 to -4.1{per_thousand}; {delta}{sup 13}C{sub PDB} = -15 to +16.2{delta}) derived from ascending thermobaric fluids prior to oil emplacement. These fluids also caused the direct precipitation of dolomite/ankerite cements and the replacement of dolomite/ankerite cements and the replacement of nonferroan dolomite by ferroan dolomite/ankerite. Rocks lacking early cements were strongly compacted, losing their primary intergranular porosity and permeability, whereas massively cemented rocks show only minor compaction and further diagenetic modifications. Partial cementation has greatly limited the compaction and preserved intergranular porosity, allowing the partial dissolution of carbonates and framework grains and the precipitation of replacive ferroan dolomite/ankerite and pyrite. Offshore reservoirs show late porosity reduction by the precipitation of quartz, kaolinite/dickite, saddle dolomite, and ferroan calcite. Experimental analyses of porosity and permeability reduction undermore » pressure confirmed the importance of early cementation in the preservation of porosity in lithic rocks with ductile framework.« less

Authors:
 [1]; ;  [2]
  1. Cidade Universitaria, Rio de Janeiro (Brazil)
  2. Uppsala Univ. (Sweden)
Publication Date:
OSTI Identifier:
68380
Resource Type:
Journal Article
Journal Name:
AAPG Bulletin
Additional Journal Information:
Journal Volume: 79; Journal Issue: 5; Other Information: PBD: May 1995
Country of Publication:
United States
Language:
English
Subject:
02 PETROLEUM; BRAZIL; OIL FIELDS; PETROLEUM DEPOSITS; ALLUVIAL DEPOSITS; STRATIGRAPHY; RESERVOIR ROCK; POROSITY; PERMEABILITY; ORIGIN; CARBONATE ROCKS; SCANNING ELECTRON MICROSCOPY; CEMENTING; MINERALOGY; X-RAY DIFFRACTION; DOLOMITE; SANDSTONES

Citation Formats

Souza, R.S. de, De Ros, L F, and Morad, S. Dolomite diagenesis and porosity preservation in lithic reservoirs: Carmopolis member, Sergipe-Alagoas Basin, northeastern Brazil. United States: N. p., 1995. Web.
Souza, R.S. de, De Ros, L F, & Morad, S. Dolomite diagenesis and porosity preservation in lithic reservoirs: Carmopolis member, Sergipe-Alagoas Basin, northeastern Brazil. United States.
Souza, R.S. de, De Ros, L F, and Morad, S. 1995. "Dolomite diagenesis and porosity preservation in lithic reservoirs: Carmopolis member, Sergipe-Alagoas Basin, northeastern Brazil". United States.
@article{osti_68380,
title = {Dolomite diagenesis and porosity preservation in lithic reservoirs: Carmopolis member, Sergipe-Alagoas Basin, northeastern Brazil},
author = {Souza, R.S. de and De Ros, L F and Morad, S},
abstractNote = {The lithic sandstones and conglomerates of the Carmopolis Member of the Muribeca Formation (Aptian) were deposited by fan deltas, alluvial fans, and braid deltas that prograded from low-grade metamorphic terrains into the Sergipe-Alagoas rift basin during the opening of the South Atlantic. Initial carbonates in the Carmopolis reservoirs (presently at depths of 180-2200 m) were marine (high-Mg calcite/aragonite) grain rims, allochems, stromatolitic laminites, and meteoric calcite. These carbonates were subsequently replaced by dolomite/ankerite ({delta}18O{sub PDB} = -7.3 to -4.1{per_thousand}; {delta}{sup 13}C{sub PDB} = -15 to +16.2{delta}) derived from ascending thermobaric fluids prior to oil emplacement. These fluids also caused the direct precipitation of dolomite/ankerite cements and the replacement of dolomite/ankerite cements and the replacement of nonferroan dolomite by ferroan dolomite/ankerite. Rocks lacking early cements were strongly compacted, losing their primary intergranular porosity and permeability, whereas massively cemented rocks show only minor compaction and further diagenetic modifications. Partial cementation has greatly limited the compaction and preserved intergranular porosity, allowing the partial dissolution of carbonates and framework grains and the precipitation of replacive ferroan dolomite/ankerite and pyrite. Offshore reservoirs show late porosity reduction by the precipitation of quartz, kaolinite/dickite, saddle dolomite, and ferroan calcite. Experimental analyses of porosity and permeability reduction under pressure confirmed the importance of early cementation in the preservation of porosity in lithic rocks with ductile framework.},
doi = {},
url = {https://www.osti.gov/biblio/68380}, journal = {AAPG Bulletin},
number = 5,
volume = 79,
place = {United States},
year = {Mon May 01 00:00:00 EDT 1995},
month = {Mon May 01 00:00:00 EDT 1995}
}