Seismic While Drilling is Emerging as a Practical Tool to Reduce Drilling Cost

 

 

The concept of seismic while drilling was introduced many years back. It uses the “noise” of the drill bit as a seismic source and measures the signals from the phones laid out along the ground, near by wells or seabed. The drill bit “noise” are created by the teeth of a rotary-cone drill bit as a well is being drilled to reach a geologic target. Seismic while-drilling can yield immediate time-depth information and, less frequently, reflection information. This information can be used to improve time-depth conversions while drilling, decide where to set casing a well, evaluate drilling hazards, such as overpressure zones, or guide the drill bit to better track more productive zones of the reservoir.

 

Seismic While Drilling (SWD) specifically encompasses the seismic techniques operated while the drillstring is lowered in the borehole, during effective drilling, during maneuvers or while connecting drill pipes. A related concept introduced by Schlumberger is Vertical Seismic Profile While Drilling. VSP-WD is  recording the seismic signal generated by a surface seismic source on seismic sensors integrated inside the downhole Borehole Assembly (BHA).  

 

Although benefits of SWD have been demonstrated by several field tests. Its full potential is yet to be realized.  It will probably take some time before SWD becomes a house hold name as is the case for logging while drilling (LWD). Eni is one of the leading companies who have developed techniques in this area and had many experiments, showing how the data can be used to reduce drilling costs, predict drilling hazards and improve efficiency of drilling operations on a real time basis.  

 

Real-time monitoring of a target production zone was the subject of another development many years ago (United States Patent 5,242,025, the author of this analysis as a co-inventor). Such monitoring is followed by an oscillatory drilling path to create a borehole having improved zone drainage capability. Real-time monitoring uses geophones placed in adjacent wells or the well being drilled. The drilling process itself generates the seismic signals. When the geophones are located in the well being drilled, the seismic signals are transmitted from downhole to surface through intermittent pressurization of drilling mud. Once drilling penetrates the zone, the oscillatory path is followed by fracturing to improve fluid drainage paths and minimize additional drilling.

 

The recent DOE announcement on the successful testing of the SeismicPulser is certainly a welcome news for the possibility of a more wide spread use of SWD. It appears that this system is the only one that has the potential to meet the requirements different operating companies planning to drill withstand high-pressure, high-temperature deep wells It is believed that SeismicPulser provides accurate drillbit location relative to predrilling reservoir models in a cost effective manner. It should give the operator real-time images roughly 1,000 ft ahead of the drillbit, all without interfering with normal drilling operations.  Drillbit SWD technology uses a downhole acoustic source and receivers at the surface to create real-time images that allow operators to “see” ahead of the drillbit. 

 

As a Chevron engineer said, right now it is like we are drilling with the headlights turned off at night. The only thing we can do is stop the car after we have hit something. With seismic-while-drilling, we’ll be able to look ahead and drill safely. The answer is yes, it will be used, in critical wells where abnormal pressures exist and where the seismic data is vital to the geologist, geophysicists and engineers. It appears that now, we no longer have to drive in the dark as we are pushing through the subsurface strata in search of the black gold.