Seismic While Drilling (SWD)

[1] Introduction:

Even though the seismic while drilling (SWD) tool is coupled to the Bottom Hole Assembly like a standard tool, its operation and set-up is far from standard. It requires proper planning ahead of the acquisition and a proper understanding of full potential of data to make this service a powerful drilling decision tool.

SWD Tool:

The tool contains 4 geophones, 8 accelerometers of which 4 are external and 4 internal and 4 hydrophones that can be configured and mounted for operation in any of the three principal axes. 12 of the sensors are exposed to the borehole annulus. The sensors are mounted such that they are passively coupled to the surfaces and structures of interest in the well, and they are robust enough to withstand the vibration, temperature and pressure conditions that the tool will experience while drilling. The sensors are designed to withstand temperatures up to 165 degree C and pressure of 25000 psi on all three axes. Down-hole data processing is performed by a high performance floating point digital signal processor DSP (Digital Sensor Processor) on the full waveform. The tool employs a quartz crystal oscillator to provide timing within 1 millisecond variation in 200 hours operation. The system is synchronized via a GPS clock.

Objectives:

1. Good quality data set in memory
2. Proof of concept
3. Data evaluation for future planning
4. Velocity data
5. Waveform data for subsurface evaluation
6. Minimal use of rig time

Design considerations:

1. Geological structure and stratigraphy
2. Characteristic surface seismic waveforms
3. The local P- and S- velocity fields, including well VSP data and seismic processing and migration velocity cubes
4. Local and area well information, including multi-pole sonic and density logs

[2] Coiled tubing Seismic while Drilling:

Conventional wireline VSP’s can provide valuable assistance but such operations require either the drill string to be removed from the hole or the pumping of the geophone tool through the drill string. This method adds time to well construction. In long sections of open-hole wireline operations may present risks, in the form of sticking and potential fishing operations, which prevent VSP surveys being acquired. Ongoing development for cost effective exploration of mature and pressure-depleted reservoirs have led to wider applications for coiled tubing drilling. The combination of a seismic tool with the coiled tubing drill string therefore provides ideal configuration to reduce drilling costs and optimize well placement.

References:

[1]  SPE-109893-MS

[2] SPE-67753-MS