Seamless in seam – new geosteering technology delivered challenging coal seam gas project with success

Abstract

A recent coal seam gas (CSG) appraisal project posed several challenges. The target reserve area had limited seismic data available and yet had complex structure with several faults of variable orientations and throws between 2 and 25 m. Dual-lateral extended-reach drilling (ERD) wells needed to be drilled in order to access this reserve, with a 1000 m in-seam section for each lateral planned to maximise production. Conventional technologies for CSG projects included motor bottom hole assembly with a boundary mapping tool for geosteering in the coal seams. However, for drilling ERD wells in this unknown area, these methods were insufficient to deliver success, due to the limited mapping capabilities and drilling efficiencies. Recently there has been significant development on the directional resistivity-based mapping tool, on both the measurements and processing. The operator adopted a new mapping-while-drilling technology which has the first-in-industry tool with axial, tilted and transverse antennas integrated in one module. This new technology can provide high-resolution multilayer mapping with doubled depth of investigation, even when drilling out of the coal seam. The results from utilising this new tool, together with a rotary steerable system for directional control, were very encouraging. The new multilayer mapping-while-drilling tool mapped both the top and base of the coal seam throughout horizontal sections in-seam. In addition, it detected the coal seams during landing and after fault-crossing from up to 4 m true vertical depth away, enabling the team to navigate through complex fault zones confidently, and to deliver the project with success.