In Situ Stress Mapping: An Initiative for Exploration & Development of Deep Unconventional Gas Reservoirs in North Kuwait
Perumalla, Satya Narayana *1; Al-Fares, Abdulaziz 3; Husain, Riyasat 3; Mulyono, Rinaldi 3; Al Ammar, Nada 3; Al-Kandary, Ahmad 3; Barton, Colleen 1; Prasad, Umesh 1; Scheele, Erik 2
(1) GeoMechanics International, Baker Hughes, Dubai, United Arab Emirates. (2) Jewel Suite, Baker Hughes, Delft, Netherlands. (3) Exploration Group, Kuwait Oil Company, Ahmadi, Kuwait.
Historically, explorationists have focused primarily on structural and stratigraphic characteristics to provide play concepts for conventional reservoirs. As exploration and development activities move to more challenging domains, geomechanical studies are becoming increasingly important to address development challenges in both conventional and unconventional reservoirs. In Kuwait, most unconventional reservoirs are deep and in a highly compressive in-situ stress state as a result of Zagros tectonics - a complex interaction between the Arabian and Eurasian Plate. The overpressured, late Jurassic Gotnia Salt acts as a pressure interface between highly stressed, strong, Jurassic formations and relatively less stressed, weaker Cretaceous formations.
In this stress mapping initiative, stress maps for North Kuwait fields were generated using image log data from over 250 wells. The study reveals that the Cretaceous and Jurassic formations exhibit distinct patterns of stress orientations and magnitude. While the stress orientation in the Cretaceous formations is within a small range and consistent across major fault systems, the Jurassic formations exhibit high variability with anomalous patterns across faults as well as in the vicinity of fracture corridors. These distinctive stress orientation patterns are suggestive of different stress regimes for the Jurassic and Cretaceous reservoirs. The overall stress magnitude values are much higher in the Jurassic section compared with the Cretaceous strata. Jurassic stress orientations vary spatially too. In the West the Jurassic stress orientation is more or less consistent even across the faults, but in the East it is highly sensitive to faults and fractures with significant associated anomalies. Stress orientation anomalies near faults and fractures are possibly indicative of their critically stressed nature since they exhibit a high shear stress to normal stress ratio. An understanding of the sealing capacity of critically stressed faults is important with regards to reservoir depletion/injection. On the other hand, the critically stressed fractures can be potential conduits for gas flow with high permeability and they are important for identification of sweet spots.
Overall, this initiative has developed new insights in exploration and development of unconventional deep tight gas reservoirs in North Kuwait and helped to look for appropriate sensitive information in exploration play strategies.
AAPG Search and Discovery Article #90141©2012, GEO-2012, 10th Middle East Geosciences Conference and Exhibition, 4-7 March 2012, Manama, Bahrain