A Novel Casing Antenna System for Crosswell Electromagnetic Telemetry in Pad Drilling

Abstract

Pad drilling is the widely implemented practice of drilling multiple wells from a single surface location during exploration of unconventional resources, such as shale gas and shale oil. The percentage of multi-well pads in the nine unconventional US plays (Bakken, Barnett, Eagle Ford, Fayetteville, Haynesville, Marcellus, Niobrara, Permian, and Woodford) has increased from 5% in 2006 to 58% in 2013 (Thuot, 2014). Telemetry is an essential component of measurement-while-drilling (MWD) and logging-while-drilling (LWD), and it can be conducted in a more economical way in pad drilling if electromagnetic methods are employed. The compact spacing between wells allow propagation of electromagnetic waves between adjacent wells, i.e. crosswell wireless communication, which can lead to a substantial saving of operational time and cost.

An innovative casing antenna system has been developed and applied to crosswell electromagnetic telemetry. A downhole source, such as a voltage gap placed near the drilling bit, sends out real-time measurements via low frequency electromagnetic waves, and an adjacent existing well with the casing antenna system is used to pick up the measurement data. Two cables are connected to the two terminals of the receiving device: one cable is attached to (but electrically insulated from) the outside of the casing string and connected to the casing shoe; the other cable is connected to the wellhead or to a metal stake driven into the ground some distance away from the rig. Telemetry signals propagate between the drilling well and the receiving well through the underground formation.

The new telemetry system essentially measures the potential differences between the casing shoe of the receiving well and a point near the surface, instead of measuring potential differences between two locations on the surface as with conventional electromagnetic telemetry settings. Theoretical and numerical analysis suggest that this new telemetry technology may have a much lower signal attenuation compared with conventional telemetry under certain circumstances. Field demonstrations are also described in this paper.

This novel electromagnetic telemetry system with casing antenna is promising for crosswell communication in pad drilling, which becomes increasingly important for drilling and exploration of unconventional resources such as shale gas and shale oil.