Jaguar-1 HPHT Well, Geological Operations Lessons Learned
Geological Operations Manager, Repsol Latin America Exploration
Drilling in a HPHT environment is a challenge for well control operations. In the case of Jaguar-1, a wildcat HPHT well drilled in a remote area (Guyana), the geological information acquired while drilling was crucial for both Exploration and Drilling Teams. In Jaguar-1, the unexpected pore pressure ramp was observed while drilling (high gas peaks) where the indirect methods didn't show any hazard. The integration of data (mud log and electrical logs data) helped to understand the well observations and define the lookahead options for the well, determining the underbalance drilling conditions in the lower sections and decisions taken to insure safety.
The narrow drilling operating window and the limited operating range of down-hole tools make mandatory the use of surface technology (EKD, Prevue) for drilling in safety conditions. The Pore Pressure electrical logging tool (MDT) was crucial to verify the origin of the gas shows in low permeability sands. The methodology for the acquisition of pressure and hydrocarbon samples helped us to understand the thin low permeability sands and the gas shows observed during the drilling operations.
All of these techniques helped to identify the drilling hazards in Jaguar-1, to take the decision of well abandonment, to capture the lessons learned for future exploration activities and safe drilling operations.
Pore Pressure Data Acquisition–Jaguar-1 is a wildcat well in HPHT environment where the use of the LWD is limited by the tools temperature range. This limitation in the LWD downhole technology over the 300 F operating range requires the use of advance surface technology (EKD, Flair) and services (Prevue) for pore pressure studies and well control operations. However, the chemical compaction in formations with temperatures over 340 F, makes that the indirect methods (resistivity, sonic, VSP) unable to show any evident of this high pore pressure regime.
A full set of electrical logs was run to identify the gas influx zones, however the petrophysical evaluation did not show any potential hazard due to the thickness and low permeability of the sands. Only the integration of mud logs, well observations and image logs, gave all the information to obtain the pore pressure data and samples.The low permeability in the sands was also a challenge for the MDT operation but the high pore pressure values helped to get some pressure and samples points under underbalance conditions which gave the information needed to Drilling to abandon the well in a safety way.
Conclusions–Even if the primary exploration objective was not reached, the data acquired in the lower sections identified the drilling hazard and its behavior, helping Drilling to react in a safety way. The success of the MDT operation determined the success of the well as an indication of the real pore pressure value, permeabilities and the acquisition in the drilling of the first MDT oil sample in the basin.
AAPG Search and Discovery Article #90203 © AAPG Geoscience Technology Workshop, Trinidad and Tobago Deep Horizon and Deep Water Frontier Exploration in Latin America and the Caribbean, March 9-11, 2014, Port of Spain, Trinidad