Post-depositional controls on siliciclastic tight reservoirs

Implications from the Oligocene Nyalau Formation (Cycle 1), onshore Central Sarawak, Borneo

Ekundayo Joseph Adepehin, Che Aziz Ali, Abdullah Adli Zakaria, Zainey Konjing

Research output: Contribution to journalArticle

Abstract

Subsurface tight reservoir sandstones of the Oligocene Nyalau Formation (Cycle I), NW Borneo were studied to understand the variability of its reservoir quality with depth, determine major controls responsible for porosity loss, identify reservoir facies and reconstruct paragenetic sequence. Core samples representing an estimated 125 Feet (38.1 m) interval from an onshore well in Central Sarawak were subjected to thin section, Helium porosimetry, inductively coupled plasma mass spectrometry, x-ray powder diffractometry, scanning electron microscopy and energy diffractive x-ray spectroscopy. The sandstones are fine-to-medium grained and comprise of sublithearenite and subarkose primarily sourced from recycled orogenic sources. Four lithofacies base on textural composition and diagenetic events were identified: (A) matrix dominated sandstone, (B) matrix-free sandstone, (C) quartz-cemented sandstone and (D) clay-coated sandstone. Obtained helium porosity, 0.90–11.52% (Average 4.27%) and Klinkenberg permeability, <0.001 to 0.071mD (Average of 0.041mD) support their categorisation as tight sandstone. Correlation of poro-perm values with depth and elemental datasets divided the sandstones into four and five distinctive zones respectively. Calcium generally displayed an inverse vertical relationship with porosity. Evidences of early mesodiageneis in the sandstones include compaction, precipitation of pore-filling quartz crystals, pyrite and calcite cement. Approximately 21.4% of the samples experienced porosity loss due to cementation, while 78.6% are due to mechanical compaction. Although mechanical compaction is the predominant mechanism of porosity reduction, the degree of porosity loss by cementation (40–58%), exceeds the degree of porosity loss by compaction (22–53%). Morphologically, kaolinite occurs as pore-filling clay. Illite and smectite are dominantly pore bridging, while chlorite generally coats grains. This study shows that tight reservoir sandstones exists in onshore Central Sarawak, at a relatively shallower depth, and thus constitute a major exploration risk in the area.

Original languageEnglish
Pages (from-to)786-806
Number of pages21
JournalMarine and Petroleum Geology
Volume111
DOIs
Publication statusPublished - 1 Jan 2020

Fingerprint

sandstones
Oligocene
sandstone
porosity
cycles
compaction
cementation
helium
clays
quartz
clay
illite
matrix
kaolinite
inductively coupled plasma mass spectrometry
pyrites
montmorillonite
cements
matrices
calcite

Keywords

  • Cementation
  • Mechanical compaction
  • NW Borneo
  • Recycled orogenic sediment
  • Reservoir quality
  • Tight reservoir

ASJC Scopus subject areas

  • Oceanography
  • Geophysics
  • Geology
  • Economic Geology
  • Stratigraphy

Cite this

Post-depositional controls on siliciclastic tight reservoirs : Implications from the Oligocene Nyalau Formation (Cycle 1), onshore Central Sarawak, Borneo. / Adepehin, Ekundayo Joseph; Ali, Che Aziz; Zakaria, Abdullah Adli; Konjing, Zainey.

In: Marine and Petroleum Geology, Vol. 111, 01.01.2020, p. 786-806.

Research output: Contribution to journalArticle

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abstract = "Subsurface tight reservoir sandstones of the Oligocene Nyalau Formation (Cycle I), NW Borneo were studied to understand the variability of its reservoir quality with depth, determine major controls responsible for porosity loss, identify reservoir facies and reconstruct paragenetic sequence. Core samples representing an estimated 125 Feet (38.1 m) interval from an onshore well in Central Sarawak were subjected to thin section, Helium porosimetry, inductively coupled plasma mass spectrometry, x-ray powder diffractometry, scanning electron microscopy and energy diffractive x-ray spectroscopy. The sandstones are fine-to-medium grained and comprise of sublithearenite and subarkose primarily sourced from recycled orogenic sources. Four lithofacies base on textural composition and diagenetic events were identified: (A) matrix dominated sandstone, (B) matrix-free sandstone, (C) quartz-cemented sandstone and (D) clay-coated sandstone. Obtained helium porosity, 0.90–11.52{\%} (Average 4.27{\%}) and Klinkenberg permeability, <0.001 to 0.071mD (Average of 0.041mD) support their categorisation as tight sandstone. Correlation of poro-perm values with depth and elemental datasets divided the sandstones into four and five distinctive zones respectively. Calcium generally displayed an inverse vertical relationship with porosity. Evidences of early mesodiageneis in the sandstones include compaction, precipitation of pore-filling quartz crystals, pyrite and calcite cement. Approximately 21.4{\%} of the samples experienced porosity loss due to cementation, while 78.6{\%} are due to mechanical compaction. Although mechanical compaction is the predominant mechanism of porosity reduction, the degree of porosity loss by cementation (40–58{\%}), exceeds the degree of porosity loss by compaction (22–53{\%}). Morphologically, kaolinite occurs as pore-filling clay. Illite and smectite are dominantly pore bridging, while chlorite generally coats grains. This study shows that tight reservoir sandstones exists in onshore Central Sarawak, at a relatively shallower depth, and thus constitute a major exploration risk in the area.",
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