Three Dimensional Permeability Associated with Diplocraterion Burrows

Leaman, Mary; McIlroy, Duncan

Three dimensional mini-permeametry of a Diplocraterion ichnofabric will increase our understanding of the relationships between ichnofossils and reservoir quality in conventional siliciclastic petroleum reservoir facies. Diplocraterion isp. is an easily recognizable trace fossil owing to the U-shaped burrow with spreite between the tubes. This work includes three dimensional modeling of the morphological features of Diplocraterion to gain a better understanding of the effect burrowing behavior has on permeability. This is the first documented attempt at combining serial grinding and mini-permeametry techniques which will lead to an integrated understanding of both morphology and associated reservoir quality of a trace fossil in three dimensions.

Samples from the Scarborough Formation (Middle Jurassic), Cloughton Wyke (North Yorkshire), England were cast in plaster and clamped into a milling machine programmed to precisely remove increments of 0.5mm on the Z-axis. After each 0.5mm increment was removed, a photo was taken of the rock face and subsequently reground. Permeability measurements were collected at 1cm intervals, using a Temco mini-permeameter machine that analyses 1cm3 volume of rock. This process of serial grinding and permeametry at 1cm intervals was repeated through 15cm of sample until the whole rock was quantified. Photos were stacked into Adobe Photoshop where the Diplocraterion burrows were selected and stored as separate files. The selected burrow images were reconstructed into a three dimensional morphological model using VG StudioMax. From the 3-D model a variety of morphological features are observed, that have not previously been described. The features reveal new insights into the behavior of Diplocraterion, including a means to explain some of the high permeability values surrounding the burrows.

Higher than expected permeability values (<150mD) were observed in and around the sandy core shafts of Diplocraterion relative to the surrounding burrow-mottled matrix. The areas of enhanced permeability are associated with the large ‘dumbbell' morphology of Diplocraterion, and are likely a result of the trace maker using bioirrigation and various selective feeding and cleaning strategies to optimize nutrient selection. These behaviors have enhanced reservoir potential by creating vertical fluid flow conduits in an otherwise low permeable reservoir.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013