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.