Novel Alternative Solution for Deviated or Horizontal Geo-Steering in High and Ultra-High Temperature Reservoir, A Case from Australia

Operator is developing an unconventional gas reservoir, drilling horizontal 6 1/8" production wells in an Ultra High Temperature (UHT) basin with Bottom Hole Temperature (BHT) of up to 200°C. Rotary Steerable Systems (RSS) are not commonly available with temperature rating to 200°C. Standard rated RSS (150°C) are used instead. The first well (offset well H-5) was drilled using this methodology and achieved a 1000m lateral section, however the tools were exposed to operating temperatures of 172°C. The operating temperature exceeded tool specification and resulted in significant Damaged Beyond Repair. The operator sought an alternative solution, using robust fit for purpose steerability that would survive the high temperature environment while achieving the Minimum Acceptable Outcome (MAO) of 900m of horizontal reservoir exposure. The contractor offered a novel solution combining technologies to drill the second (subject well) of this paper, H-4. An Adjustable Gauge Stabilizer (AGS) rated to 200°C was incorporated into a Bottom-Hole Assembly (BHA) with a UHT rated Logging While Drilling (LWD) tool rated to 200°C. This tool incorporated directional survey, gamma ray (GR), pressure-while drilling (PWD) and downhole vibration sensors. The AGS could be set to Full-Gauge (FG) or Under-Gauge (UG) diameter and the BHA was designed to drop or build inclination (respectively) depending on the setting. This provided a simple 2-D steerable assembly. UHT-rated directional, GR and PWD sensors provided directional surveys, formation correlation and downhole annulus and internal pipe pressure data. Downhole vibration sensors provided drilling efficiency data and facilitated mitigation of downhole vibration extending tool reliability.