Bioturbation: Reworking Sediments for Better or Worse

Oilfield Review Winter 2014/2015: 26, no. 4. Copyright © 2015 Schlumberger. FMI is a mark of Schlumberger. Sediments undergo several modifications to become the source rocks, reservoirs and seals that generate and contain petroleum reserves. The changes that occur between deposition and lithification, collectively known as diagenesis, include the processes of compaction, cementation, dissolution and recrystallization. But before any of these occur, another process can considerably affect rock properties. As soon as they are deposited, sediments can be altered by bioturbation: the disruption of sediment and soil by living things. Bioturbation is typically a small-scale but potentially significant geologic process that may occur wherever plants or animals live. It can take several forms, including displacement of soil by plant roots, tunnels created by burrowing animals and footprints left by dinosaurs (next page). Of most interest to the oil and gas industry are the changes brought about by organisms that are active near the water/sediment interface in marine settings. Such activities are typically limited to a meter or so in depth but may cover an area of tens to hundreds of square kilo1. Ali SA, Clark WJ, Moore WR and Dribus JR: “Diagenesis and Reservoir Quality,” Oilfield Review 22, no. 2 (Summer 2010): 14–27. 2. Al-Hajeri MM, Al Saeed M, Derks J, Fuchs T, Hantschel T, Kauerauf A, Neumaier M, Schenk O, Swientek O, Tessen N, Welte D, Wygrala B, Kornpihl D and Peters K: “Basin and Petroleum System Modeling,” Oilfield Review 21, no. 2 (Summer 2009): 14–29.