Integrating Real-Time Extra Deep Azimuthal Resistivity Inversion, Density Image, and Mud-Gas in Successful Geosteering of Near-Horizontal Wells
Authors: Wahid Ali Nurul Athirah , Viet Nguyen Hoang , Mustafa Azfar Hafizin , M Dahlan Nur Athirah , Hassan Nur Atiqah , Ariffin M Hafizi , Salleh Fairus Azwardy 
Published: October 2023

Field X is a brownfield located in offshore Malaysia with over 40 years of production. It is a highly faulted and compartmentalized field consisting of several sub-blocks with distinct fluid contacts. This paper discusses the successful geosteering of 1 infill and 1 appraisal cum development well, where both wells are near-horizontal targeting block North X by integrating real-time extra-deep azimuthal resistivity coupled with density image together with seismic interpretation, mud-gas analysis, pressure data, and fluid sampling.

Since structural dip is vital information in geosteering of these two wells along the target reservoir, a density image log was included in the real-time package to assist with dip interpretation alongside the overall reservoir structure mapped by extra-deep azimuthal resistivity (EDAR) inversion. The team’s Geologist and Geophysicist mapped the well trajectory on seismic in real-time to verify the log based structural dip interpretation. The extra-deep azimuthal resistivity inversion was also used to map the remote OWC for risk mitigation. Several pressure data and fluid samples were also acquired to confirm the fluid contacts prior to running the completions.

Both wells (Well-W and Well-P) were planned with a highly deviated pilot hole, with the option to be completed if the pilot hole is successfully placed. With the integrated information from the extra-deep azimuthal resistivity inversion, density image, seismic, mud-gas analysis, pressure data, and fluid sampling, the pilot hole of the first well that was drilled i.e. Well-W, an appraisal cum development well was successful and completed. The real-time geosteering strategies were developed primarily based on the inversion mapping of the sand geometry within 50ft TVD around the well-bore. Well-W pilot encountered approximately 2800ft MD of net sand out of which 1300ft MD of sand is completed, with an oil column thickness of 158ft TVD. The well delivered higher production rates of 1160 BOPD against the planned 1000 BOPD. The pilot hole of the second well drilled i.e. Well-P faced a substantial challenge as the well crossed a fault right before reaching the target sand. The pilot hole of Well-P was plugged after acquiring sufficient information on the fluid contacts and geological structure. The Well-P lateral was then sidetracked from the pilot hole and successfully encountered approximately 1100ft MD of net sand with 400ft MD of sand completed at an estimated rate of 400 BOPD.

All data acquisition needs to be exhaustively studied and managed as each holds an important piece of evidence on field/reservoir properties. In Field X, the integration of real-time EDAR inversion, density image, seismic, mud-gas analysis, pressure data, and fluid sampling were vital and principal drivers in making real-time geosteering decisions leading to successful well placement of two (2) near-horizontal wells.