Enhancing Reservoir Contact in Clinoform Structure: A Geosteering Approach

Abstract

Addressing challenges in well planning and execution within the Northern part of Reservoir A involves complexities arising from Clinoform structures with variable bed thickness, porosity differences, and notable permeability contrasts. This has led to the subdivision of Zone N into two distinct subzones: N (upper, with moderate to high permeability) and No (lower, exhibiting poor rock quality). Efficiently developing reserves in No requires overcoming connectivity issues and low permeability. The development strategy involves drilling horizontal wells with dual string completion in Zone N, particularly open hole barefoot in the tighter unit No. However, existing wells face challenges in proper horizontal section placement due to variable lithostratigraphy, thin reservoir thickness, and high bed dips, resulting in significant loss of reservoir footage. To counter unplanned exits from the reservoir due to complex geology, an extra deep resistivity tool with high depth detection capabilities was employed. This tool aimed to identify boundaries and enable proactive adjustments to well trajectory for optimal reservoir exposure, mitigating challenges posed by the intricate geological conditions. A systematic review of seismic, chronostratigraphic, and lithostratigraphic data, combined with comprehensive reservoir surveillance analysis, was conducted to assess the continuity of all sub-zones within Zone N. This exercise pinpointed the optimal litho-unit to target for prospective wells. This identification streamlined pre-well modeling, aiding in the selection of suitable Geosteering tools for precise well placement. Utilizing a deep resistivity tool, both forward and inversion pre-well models were constructed in collaboration with a service company, enabling boundary detection. Insights from previous operations, notably challenges in accurate horizontal section drilling due to improper landing angles and non-porous bodies, informed the refinement of this workflow. Consequently, a list of well candidates was generated. This paper highlights the successful deployment of proactive Geosteering technology alongside thorough reservoir geology and surveillance analysis, resulting in notable improvements in drilling efficiency and precise well placement within Zone N. Monitoring six wells closely and employing a boundary tool proactively ensured the prevention of unplanned reservoir exits. Post-well assessments emphasized the necessity of maintaining bit inclination above 88 degrees unless certain of porous body penetration during landing. Noteworthy is the achievement of complete reservoir exposure across the horizontal section, promising higher production potential compared to existing analog wells. This collective approach not only mitigated risks associated with unplanned exits but also anticipates a substantial increase in production from these wells. The integration of proactive Geosteering techniques, rigorous reservoir analysis, and comprehensive evaluations sets a promising stage for maximizing Zone N's productivity, indicating a positive trajectory for future drilling initiatives.