Abstract: Fracture Networks in Rotliegend Gas Reservoirs of the Dutch Offshore and their Impact on Field Development Planning and Infill Drilling

B. D. M. Gauthier, R. C. M. W. Franssen

The influence of fractures upon the production behaviour of the Rotliegend (early Permian) gas fields in the Dutch offshore has been investigated. Small scale fracture networks can have a significant influence (positive or negative) on the production performance of wells or on the amount of reserves a well can drain.

Fracture data collected from core and imaged logs were corrected to account for the bias related to one dimensional sampling methods. Fracture systems have been described in terms of orientation, frequency, origin, type and in relation to larger-scale structures. In addition, integration of these data with fracture cements and diagenetic data resulted in the timing of the fracture network development.

Two fracture systems can be distinguished on basis of their regional extent: a) Fault related consist of shear fractures which occur close to and parallel with larger-scale faults. These fractures trend NE-SW and NW-SE and locally an N-S oriented set is developed. b) Regional fractures preferentially consist of tensional fractures oriented around E-W. Fault-related fractures formed during the mid/late Kimmerian rifting phase. In the Jurassic rift basins the regional fractures appear to have formed during the late Cretaceous inversion events whereas outside these basins the regional fractures probably developed during late Jurassic times.

The NE-SW and N-S fault-related shear fractures tend to compartmentalise reservoirs. The NW-SE fault-related shear fractures and the regional extensional fractures tend to enhance reservoir flow properties, especially in areas of poor reservoir quality. The results of such regional fracture studies are being incorporated in the planning of infill drilling and field development of the Rotliegend gas fields in the Dutch Offshore.

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France