Santos Limited successfully drilled three dual-lateral wells using PeriScope Edge™ multilayer mapping-while-drilling service, holding both laterals within very narrow target seams for extended-reach wells between about 2,200-m and 3,200-m MD. Seismic data was virtually nonexistent because the reservoir was under a national park with restricted access, and the formation structure was complex with several faults.

Drill dual long-lateral wells in faulted formation without prior seismic data

The Santos Brisbane coal-seam-gas project in Southwest Queensland, Australia, edges against an escarpment that belongs to a protected area, resulting in a large uncertainty because there is no available seismic data.

Targeting the coal-seam-gas reserve requires Santos to perform extended-reach drilling (ERD) on horizontal wells. Coal seams are very thin, with varying thickness from 2 m to 5 m. The objective was to drill dual-lateral wells at least 1,000 m within the seam boundaries, where they may encounter faults with unknown throws.

Use ultrahigh-definition inversion, multilayer mapping while drilling

Based on experience with drilling ERD wells greater than 2,000 m in exquisitely thin coal seam boundaries, SLB recommended using PeriScope Edge multilayer mapping-while- drilling service. It provides larger depth of detection with the newly introduced deep resistivity and anisotropy measurements, and higher resolution attributed to the innovative high-definition inversion process.

PeriScope Edge service has axial, tilted, and transverse antennas integrated in one tool, measuring resistivity and anisotropy deep into the surrounding formations. This provides high-resolution measurements on the R_h and R_v of each formation layer, enabling a cloud-based inversion to work out the accurate multilayer mapping around the wellbore while drilling.

Drilled two record-setting dual-ERD wells while expanding data on area

Santos successfully drilled its first dual-lateral well in this campaign. PeriScope Edge service enabled holding both laterals within the seams and achieved the required meterage in seam. Several faults were encountered, but Santos was able to quickly navigate the well path back to the coal seams by using the PeriScope Edge service.

Satisfied with results on the first dual-lateral well, Santos pushed the limit on the second well by targeting more meterage in seam, extending TD by 1,000 m for each lateral (from 2,200-m MD to 3,200-m MD). The shallow lateral and deep lateral achieved 1,706 m and 1,645 m in seam, achieving several records:

• highest ERD ratio for Santos onshore
• longest lateral in Bowen Basin
• longest lateral length from heel to toe in Santos onshore.

Additionally, Santos extended the well to gather information farther out than originally planned, which reveals more data on an area otherwise impossible to explore.