DGMK/ÖGEW Frühjahrstagung 2018

Celle

18./19. April

Merz L, Manss Y, Hilgers C

Merz L

Fractured Muschelkalk carbonates are an E&P target in the Upper Rhine Graben. However, fracture spacing, age relationship and reservoir relevance are hard to establish from subsurface data. Since the Muschelkalk carbonates are well exposed on the graben shoulders, we apply our new field methods and -workflows in an open pit mine close to Karlsruhe. Our aim is to establish the history of fracture networks from vertical quarry walls and subhorizontal floors to build a discrete fracture network model to further improve exploration and production.

Our terrestrial laser scanner (Lidar) derives the fracture orientation and spacing from steep inaccessible vertical quarry walls with an in-house developed workflow. Additionally, our UAVs image the quarry floors, which enables to derive the relative age relationship and lateral continuity of fractures. Based on quarry data, we build a discrete static 3D fracture network, integrated in state of the art software tools such as FracMan, FracaFlow and Petrel.

The Knittlingen outcrop comprises of 85- 100m of Upper Muschelkalk with continuous dm-thick carbonate beds and intercalated mm-thick black shales. Rocks were affected by normal- and strike slip faults, and overprinted by thrust. Compression is indicated by gentle folds and normal kink bands both decameter in scale. Locally, gently dipping thrusts may indicate fault reactivation at a late stage of compression. They formed during inversion imposed by far field stresses induced by the Alpine orogeny, enhanced by the high mechanical anisotropy of carbonate and shale layers.

We measured open fractures across steep normal faults, but were not able to establish fault related fracture corridors as published elsewhere. These faults are sealed with carbonate veins, which we associated with the core and dm-wide damage zone.

A minimum of six fracture generations were derived from quarry wall- and floor data. Based on abutting relationships, the oldest fractures are persistent and strike N-S. They are partly carbonate cemented and may be related to rapid subsidence or early uplift. Later generations of open fractures are most likely related to regional uplift.  

Fractures will be further evaluated and implemented into a 3D dynamic fracture network model to fully constrain the role of fractures during fluid flow. The role of inversion initiating extension fracturing will be further explored using poro-elastic-thermal calculations, to further improve fracture models in subsurface reservoirs. Finally, we intend to use Structure from Motion (SfM), derived from UAV imagery to complement our results and conduct a comparison between the different methods.