Techbits: LWD Sonic Technology Focus of Emerging Technology Workshop
Authors: JPT staff _ 
Published: February 2015

Techbits
A technology designed to help drillers make improved real-time decisions in uncertain environments was the focus of an Emerging Technology Workshop (ETW), held 12–13 May in San Antonio, Texas. Seventy workshop participants representing drillers, petrophysicists, geophysicists, geologists, and tool/service providers discussed the current value and future potential of logging-while-drilling (LWD) sonic technologies to increase the quality and speed of downhole data measurement.
LWD sonic technologies use a wave propagator or signal source to send a sonic signal from the wellbore out into the formation, and receivers to pick up the return signals which are stored in memory. Derived formation-sonic-travel time measurements are sent through a telemetry mud pulse system to the surface in real time. LWD offers several benefits that enable nearly instantaneous data collection to improve the safety of drilling operations and create a more efficient business process by improving the speed and quality of geological interpretations and operational decisions, as Gopal Amruthapuri, Operations Geologist for Chevron and Chairperson of the ETW, explained.
"Drilling without any LWD tools on the bottomhole assembly is like walking in a dark tunnel, and as seismic resolutions are poor under salt, we need a flash light to better understand these complex structures," he said. "Drilling activities continue to move into deeper waters and high-pressure/high-temperature (HP/HT) reservoirs… there are many uncertainties that cannot be determined with predrill seismic studies.
"A LWD sonic tool enables us to drill safely and efficiently in subsalt sections," Amruthapuri continued, "and the velocity measurements let you predict bore-hole stability, understand rock mechanical properties and time-to-depth seismic correlation while drilling, measure petrophysical properties like porosity determination, and even identify cement top. This allows us to prepare for or circumvent potential problems."
Yet given this level of potential, there is still hesitation within the industry to more fully adopt the technology. A major aim of the ETW was to bring together the industry's experts to openly discuss why this hesitation persists, and to address the technology gaps that must be filled before more widespread industry acceptance is possible.

Keynote Address Frames Potential
The keynote address was delivered by Brian Hornby, Geophysical Adviser for BP. "My aim in the keynote was to focus on what LWD sonic technology could realistically deliver. In my view, new technologies normally generate a lot of enthusiasm on introduction and this can lead to failure because of unrealistic expectations that are not fulfilled. A conservative approach where one focuses on initially achieving basic, robust deliverables followed by introduction of more exotic developments is recommended."
Hornby started with the basic question of why a company would want to run LWD sonic in the first place. "The main pull for this technology is compressional-wave (P-wave) logging, so the key to introducing this technology to more of the industry is to focus on delivering a reliable P-wave logging service. On the business side, decision makers may ask if LWD sonic adds something in combination with a wireline tool, or if it can replace wireline outright.