PETROPHYSICAL STUDIES

Sand injectites form important components within subsurface plays and reservoirs in many petroleum provinces. Characterising sedimentological and petrophysical heterogeneities within such systems helps to develop a better understanding of hydrocarbon fluid flow and thus maximise economic potential.

Mesoscale (millimetres to metrescale) structures are found within sand injectites at many outcrop localities. These include banding (Fig 1), breccias (Fig 2), laminations (e.g. convolute, wavy, parallel, inclined and horizontal), pipes and clay seams, to name but just a few.

      Fig 1. Horizontal banding found within an injectite Complex (California).

 Fig 2. Brecciated host rock within
       an intrusion (California)  

 

Importantly such structures characterise facies that be found distinct associations according to the type of architectural element (e.g. parent bed, dyke, sill and extrusion). These facies and facies associations help differentiate different architectural elements in analogous subsurface reservoirs.

Petrophysical properties of sand injectites have been shown to vary according to the injection style, host rock type and its geological setting.  

| Click on the images to see a high resolution version |

Fig 3. Loosely packed matrix with high porosity and permeability

Fig 4. Tightly packed matrix with low porosity and permeability


In many localities porosities > 30% and permeabilities > 2500 mD have been found consistently across sand injectite complexes (Fig 3). Contrastingly, other complexes have low porosities <3% and permeabilities < 10 mD (Fig 4).  This clearly has implications for the prediction of hydrocarbon storage capacity and fluid flow properties within injectite reservoirs. 

 

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