Sedimentary Structure in the oil and gas industry

Sedimentary Structure in the oil and gas industry
Sedimentary Structure in the oil and gas industry

1. Interpreting depositional environments from sedimentary structures is a key aspect of sedimentology and stratigraphy. Here's how we can use sedimentary structures to infer the depositional environment: Bedding and Lamination: Thick, massive beds suggest a high-energy environment, such as a fluvial channel or deep-marine turbidite . Thin, parallel laminations indicate a low-energy, stable environment, like a tidal flat or a quiet lake. Cross-bedding and cross-lamination indicate the presence of unidirectional or oscillatory currents, as seen in fluvial, eolian , or shallow marine environments. Grain Size and Sorting: Well-sorted, fine-grained sediments suggest a low-energy environment, like a deep-water marine setting or an aeolian dune. Poorly sorted, coarse-grained sediments indicate a high-energy environment, such as a high-energy fluvial system or a glacial outwash plain. Sedimentary Structures: Ripple marks and current ripples indicate the presence of unidirectional or oscillatory currents, as found in fluvial, tidal, or shallow marine environments. Mud cracks and desiccation features suggest a subaerial, arid or semi-arid environment, like a playa or a tidal flat. Flaser , wavy, and lenticular bedding are indicative of tidal environments, where the alternation of current and slack water conditions is recorded .

2. Fossil Content: The presence and types of fossils can provide valuable clues about the depositional environment. For example, the presence of marine fossils suggests a marine environment, while terrestrial fossils indicate a continental setting. The diversity and abundance of fossils can also indicate the energy level and overall environmental conditions. Trace Fossils: The type, size, and orientation of trace fossils ( ichnofossils ) can reveal information about the substrate conditions, water depth, and energy levels of the depositional environment. Vertical burrowing structures suggest a low-energy, stable environment, while horizontal trace fossils indicate higher-energy conditions. By integrating the information from these various sedimentary structures and features, geologists can develop a comprehensive understanding of the depositional environment, including factors such as water depth, current energy, salinity, and oxygen levels, among others. This knowledge is crucial for reconstructing the geological history and understanding the processes that shaped the Earth's surface.

3. : Diagnetic features formed in association with the growth of minerals or cement, part 1.  A ) Cross-section through a concretion.  Although this example has a striking radial fabric, you can still see faint concentric layering ( Mark Buchanan  via  Wikimedia Commons ;  CC BY-SA 3.0 ). B ) Vertical rhizoconcretions  developed around roots ( Jfoote  via  Wikimedia Commons ;  CC BY-SA 3.0 ). C ) Internally massive nodule developed around a coiled cephalopod ( Hannes Grobe /AWI  via  Wikimedia Commons ;  CC BY-SA 4.0 ). D ) Dense accumulation of modern caliche nodules in Texas ( David R. Tribble  via  Wikimedia Commons ;  CC BY-SA 3.0 ). E) Nodules in a sample of bauxite ( USGS  via  Wikimedia Commons ;  public domain ). F ) Septarian nodule with distinctive cracked texture ( Neptunerover  via  Wikimedia Commons ;  public domain ). Replacement features Dolomitization  – calcite/aragonite is replaced by dolomite. Dolomite shows up as rhombohedral crystals in thin section. Replaced fossils  (or other material) - forms when silica, pyrite, or some other mineral replacement occurs.  Carbonate skeletons are prone to replacement.  Chickenwire structures  – distinctive nodular zones in evaporates, commonly formed in response to the transition from gypsum to anhydrite and the incorporation of clastic sediment.  

4. : Diagnetic features formed in association with the growth of minerals or cement, part 1.  A ) Cross-section through a concretion.  Although this example has a striking radial fabric, you can still see faint concentric layering ( Mark Buchanan  via  Wikimedia Commons ;  CC BY-SA 3.0 ). B ) Vertical rhizoconcretions  developed around roots ( Jfoote  via  Wikimedia Commons ;  CC BY-SA 3.0 ). C ) Internally massive nodule developed around a coiled cephalopod ( Hannes Grobe /AWI  via  Wikimedia Commons ;  CC BY-SA 4.0 ). D ) Dense accumulation of modern caliche nodules in Texas ( David R. Tribble  via  Wikimedia Commons ;  CC BY-SA 3.0 ). E) Nodules in a sample of bauxite ( USGS  via  Wikimedia Commons ;  public domain ). F ) Septarian nodule with distinctive cracked texture ( Neptunerover  via  Wikimedia Commons ;  public domain ).

5. Diagnetic features formed in association with the growth of minerals or cement, part 2. C) Manganese dendrite in finely crystalline volcanic rock. Unknown unit and age. D) Green mottles (reduction halos) developed around organic material in a sandstone from the Mississippian Mabou Group, Nova Scotia. All images from Michael C. Rygel via Wikimedia Commons; CC BY-SA 4.0. A & B) Liesegang rings in sandstone. B shows a detail of the right center of the boulder in A.