Geological Traps for Geo-resourcesLabiba Nusrat JahanLecturer,PME, SUST.

Anticlinal TrapsThis trap may exist as a simple fold or as an anticlinal dome.Two major potential advantages of the anticlinal trap reservoir are the simplicity of the geology and the potential size of the trap and therefore of the hydrocarbon accumulation. The high part of the fold is the anticline, and the low part of the fold is the syncline.The gas fields of Bangladesh are housed in folded anticlinesFig: Folded Anticline

Fault TrapsFault implies fracturing of rock and relative motion across the fracture surface.Fault traps leading to the presence of hydrocarbon reservoirs are often difficult to define because of the complexity of the geology.Fig: Fault Trap

Salt Dome TrapsMasses of salt are pushed up through rocks due to their greater buoyancy, eventually breaking through and rising towards the surface .This salt is impermeable and when it crosses a layer of permeable rock, in which hydrocarbons are migrating, it blocks the pathway in much the same manner as a fault trap.

Stratigraphic TrapsStratigraphic traps are formed as a result of lateral and vertical variations in the thickness, texture, porosity or lithology of the reservoir rock that prevent continued migration of hydrocarbons in a potential reservoir lithology.

Facies ChangeThe change in appearance that occurs when one lithologic unit ends and a new one is encountered. Consider the deposition near a shoreline of a continent, When lithification occurs, in the same sedimentary bed, as distance from the original shoreline increases, the rock grades from sandstone, through a transition zone, to shale. Later in geologic time, hydrocarbon generated in its source rock. This hydrocarbon will continue to migrate until it encounters the impermeable shale at the transition zone within the rock.

It is trapped as a result of the change of permeability within the sedimentary bed, as the transition occurs from sandstone to shale or from permeability to no permeability. This transition of properties within the rock sediment is called a facies change.

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