Challenges and Way Forward in Exploration of Unconventional Najmah Reservoir in Kuwait

Khan, Badruzzaman ¹; Singh, Sunil K.¹; Arasu, Raju T.¹; Al-Adwani, Talal F.¹; Abu-Taleb, Reyad I.¹; Bader, Sara ¹
(1)Exploration Group, Kuwait Oil Company, Ahmadi, Kuwait.

Najmah Formation of Kimmeridgian stage is an unconventional hydrocarbon bearing source-cum-reservoir play in Kuwait. It is comprised of mudstone to wackestone facies with high TOC content. Matrix porosity ranges between 3-5 pu and matrix permeability is between 0.01-1.5 md. Sustained economic production from this reservoir depends entirely on connectivity of the open fracture network. The fractures vary in scale from isolated micro-fractures to km wide interconnected “fracture corridors” which are key to commercial productivity from the reservoir.

The reservoir poses multi-faceted challenges at different stages of exploration, starting from identification of drillable locations to tackling problems encountered during drilling, testing and post-drill evaluation. Fracture Cluster Mapping in seismic interpretation is critical in identifying appropriate drilling locations. Due to thick overburden of complex lithology, conventional seismic is severely affected by signal attenuation in the target interval, making prediction of fracture locale difficult. High barite content in oil base mud causes irreversible formation damage. Petrophysical evaluation is constrained by the presence of organic carbon, which cannot be accurately estimated due to high uncertainty over its standard log responses. This brings ambiguity in estimation of porosity and water saturation. High quality borehole images cannot be acquired in OBM environment, which adversely affects fracture characterization. In most cases effective acid stimulation is not achieved as is indicated by PLT results.

An integrated workflow to mitigate these challenges has been developed. Fracture cluster mapping can be improved by enhanced subsurface sampling and target oriented seismic data acquisition and processing. Building a robust DFN model by integrating seismic, well logs, geomechanics and core data has helped in predicting open fracture corridors. Solid free formate mud should be used as the drilling fluid and balanced drilling technique should be adopted to minimize formation damage. Conventional coring and advanced laboratory analyses must be performed to determine the total adsorbed gas content and gas storage capacity of the formation. A complete suite of logs are vital for more reliable formation evaluation. Open hole completions are good option to enhance production. Horizontal drilling is being actively considered for better exploration success and productivity.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.