Addressing the Geological Challenges in Tight Gas Sandstones with Advanced Borehole Imaging Solutions, Sultanate of Oman
Shrivastava, Chandramani *1; Al-Mahruqy, Sultan2; Al-Mjeni, Rifaat2; Al-Busaidi, Salim3; Muslem, Khalifa3; Wang, Da Li3; Mohtadi, Ashkaan1
(1) Wireline, Schlumberger, Muscat (MCT), Oman. (2) Exploration Team, PDO, Muscat (MCT), Oman. (3) DCS, Schlumberger, Muscat (MCT), Oman.
In tight gas sandstones, detailed geological understanding of the reservoirs is imperative in preparing optimal exploration, appraisal and development plans. The distribution of sand bodies, their textures, orientation and paleocurrent directions need to be understood in the context of sedimentary depositional environments to assist in the prediction and identification of reservoir architecture, reservoir quality variability and sweet spots. The use of high salinity mud, providing a highly conductive logging environment affects the quality of borehole images. Additionally, tight formations are highly resistive, which limits traditional image interpretability for textural, structural and sedimentological analysis and petrophysical interpretation. Advances in borehole imaging in recent years have significantly helped in addressing the geological challenges in hostile borehole environments.
In the tight gas clastics of northern Oman, hyper saline mud (~300,000 ppm) and highly resistive formations (>20,000 ohm-m in some cases) have had a significant deleterious impact on the traditional imager quality. Image quality is of utmost importance in undertaking detailed sedimentological analyses and poor image quality reduces the confidence in the interpretation of reservoir architecture and textural variations. This is particularly the case in Oman’s high net to gross continental tight gas successions. The latest borehole imager with improved signal to noise ratio and tolerance to high mud salinity has been deployed to acquire good quality images that help in the interpretation of these sandstone reservoirs.
The new imager is supported by new hardware configuration and improved downhole signal processing compared to the traditional imagers. Its 16-bit data quality provides better image visualization because of improved signal to noise ratio in hostile environments. Subtle geological features which were masked with traditional imager can be studied with the improved imaging for enhanced interpretation. Three wells, logged with this new imager, have provided a good understanding of reservoir geology in the tight gas reservoirs of Northern Oman where the reservoir facies were deposited in arid fluvial sheet flood/ sand flat, sabkha and aeolian environments where sedimentary distinction between facies is subtle.
AAPG Search and Discovery Article #90141©2012, GEO-2012, 10th Middle East Geosciences Conference and Exhibition, 4-7 March 2012, Manama, Bahrain