The Application of Horizontal Wells in Effectively Developing Thinly Bedded Carbonate Reservoirs of Block 5, Oman

Located between the Eastern Platform and Bab Basin, Oman, Block 5 includes the DL, MZ, BSH and SD fields. Reservoirs are dominated by Cretaceous thinly-bedded bioclastic packstones and wackstones, which are buried at depths of 1,500 to 1,700 m. As of end-2010, 195 horizontal wells containing 273 laterals with an average horizontal section of 1,000 m had been drilled in Block 5, which has significantly improved field development and production.

From 2002 to end-2004, based on reservoir characterization, horizontal wells were used to find and develop new oil bearing blocks and zones, which tripled production rate from 4,500 to 15,000 bo/d in three years.

Thinner reservoirs with net pays of 3-5 m have been effectively developed using geological steering technology. Four geological steering scenarios of horizontal wells have been summarized based on practical drilling experiences. In practice, a total of 1,500 Mbbl oil has been recovered by 8 horizontal wells from the MZ field, which was considered sub-commercial before.

Water flooding has been implemented based on an alternating pattern of horizontal water injectors and oil producers, with approximately 1 km horizontal section, spaced 100 m apart. For Fault Block B of the DL field, the production has rapidly increased from 1,500 to 9,000 bo/d after water flooding in horizontal wells.

In response to thinly-bedded carbonate reservoirs with higher porosity and lower permeability of the DL field and rapid water cut rise during water flooding in horizontal wells, horizontal well correlation under depositional model, small fault interpretation, refined geo-modeling have been thoroughly studied. In the framework of depositional model, data from horizontal wells has been fully used and pseudo-wells have been designed to build refined geo-models, which have accurately delineated small fault, inter-well subtle structure and reservoir pinch-out. The results provided a reliable geological base for water flooding adjustment in horizontal wells.

In summary, horizontal wells with long horizontal section are helpful to discover new hydrocarbon-bearing potentials and to effectively develop thin and low permeability reservoirs. Water flooding in horizontal wells can markedly increase recovery factor of high porosity and low permeability reservoirs.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California