AAPG Bulletin, V. 84,
No. 7 (July 2000), P. 1015-1040.
Diagenesis and Reservoir-Quality
Evolution of Fluvial Sandstones During Progressive Burial and Uplift: Evidence
from the Upper Jurassic Boipeba Member, Reconcavo Basin, Northeastern Brazil1
Alaa M. Salem,2
S. Morad,3 Luiz F. Mato,4 and I. S. Al-Aasm5
©Copyright 2000. The American
Association of Petroleum Geologists. All rights reserved.
1Manuscript received October 8, 1998;
revised manuscript received October 6, 1999; final acceptance November
28, 1999.
2Institute of Earth Sciences, Uppsala
University, Villavägen 16, SE-752 36, Uppsala, Sweden. Present address:
Faculty of Education at Kafr El-Sheikh, Tanta University, Kafr El-Sheikh,
Egypt.
3Institute of Earth Sciences, Uppsala
University, Villavägen 16, SE-752 36, Uppsala, Sweden; e-mail: [email protected]
4Petrobras E&P-BA, Av. ACM 1113,
CEP 41856-900, Salvador, Bahia, Brazil.
5Department of Earth Sciences, University
of Windsor, Windsor, Ontario N9B 3P4, Canada.
We are grateful to Petrobras for access
to samples and data, and for permission to publish this work. A. M. Salem
is grateful to the Swedish Institute in Stockholm for providing him a postdoctoral
grant. The research was supported by funds from the Swedish Natural Science
Research Council (NFR, to S. Morad) and the Canadian Natural Sciences and
Engineering Research Council (NSERC, to I. S. Al-Aasm). We are grateful
to Luiz C. Coutinho for discussions about the burial-thermal history parameters
and to L. F. De Ros and AAPG referees David Houseknecht, Jorg Schulz-Rojahn,
and Rogerio Souza for the constructive review of the manuscript.
ABSTRACT
The reservoir quality of fluvial
sandstones of the Upper Jurassic Boipeba Member, Reconcavo basin, northeastern
Brazil, is highly heterogeneous and controlled by eodiagenesis under semiarid
climate, mesodiagenesis during burial to a depth of 3500 m, and telodiagenesis
due to local uplift. Eodiagenesis resulted in mechanical compaction, calcite
cementation, clay infiltration, and limited grain dissolution, whereas
mesodiagenesis resulted in the precipitation of calcite cement and quartz
over growths, intergranular quartz-grain dissolution, chloritization and
illitization of smectite, and albitization of feldspars. Sandstones continuously
buried at maximum burial depths of about 1600 m (T = 65°C) since
125 Ma display a relatively greater degree of mesogenetic modifications
and, on average, poorer reservoir quality than sandstones that were buried
deeper (2100 m, T = 75°C) prior to uplift, but only since 13
Ma. Uplift, which affected the sequence along the western border of the
basin, has resulted in telogenetic dissolution of framework silicates and
formation of kaolinite. Relatively good reservoir quality in the deeply
buried sandstones occurs when (1) the grains are coated with a thin layer
of chloritized infiltrated smectite, (2) there is little or no pseudomatrix,
and (3) there are widely scattered patches of eogenetic calcite cement
that supported the framework of sandstones against compaction.
