Glacial Sedimentological Interpretation from Microresistivity Images, Al Khlata Formation, Oman
Wang, Da Li 1; Helmy, Mohammed 2; Rawnsley,
Keith 2
(1)Schlumberger, Al-Khobar, Saudi Arabia. (2) Petroleum
Development Oman, Muscat, Oman.
High-resolution borehole
microresistivity image data for 14
vertical wells was used for glacial sedimentological interpretation in a field
in Oman. The sedimentological interpretation was based mainly on the
identification on
borehole
images of the characteristics of glacial
depositional environments. The characteristics involve sedimentary lithotypes
and deformation sedimentary structures, such as diamictites, cross-bedded
pebbly sandstones, sandstone breccias, dm-scale faults, sandstone steep
beddings, and slump structures. Diamictite deposition is associated with the
glaciolacustrine depositional environment, and cross-bedded pebbly sandstones
correspond to glaciofluvial depositional processes. The breccias, faults, steep
beddings, and slump structures indicate ice-contact glacial depositional
processes, which were caused by collapse of supporting ice when buried ice
melts away. These glacial-specific characteristics are easily recognized on the
borehole
microresistivity images that provide continuous records of sedimentary
features along well trajectories. However, it is difficult to recognize these
glacial specific characteristics on the conventional openhole logs and in
poor-resolution seismic.
The 14 wells cover an area of about 400 km², and the minimum
extent of space between two of the 14 wells is about 2.4 km. The main challenge
to the sedimentological interpretation in this field was that the glacial
deposition caused extremely rapid vertical and lateral variability of
lithofacies and completely unpredictable geology, particularly owing to the
poor seismic resolution of the field and limited available core data. There was
only an 18-m-thick core acquired in this field. Hence, one had to concentrate
mostly on the 14-well borehole
microresistivity image data for the
sedimentological interpretation.
The paper highlights the glacial sedimentological interpretation
of the 14 wells and demonstrates how to set up a conceptual sedimentological
model for further developing a 3D facies model. The case study in this paper
improved our understanding of the glacial sedimentological properties and
reservoir characteristics of the field, and it also provided a new approach to
maximize the usage of borehole
image data to perform sedimentological
interpretation in glacial depositional formations.
AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.