Abstract
The combination of seismic exploration technology and drilling engineering forms the seismic measurement while drilling (SWD) technology, which can provide conventional borehole seismic measurements in real time while a well is being drilled. Just as conventional while-drilling services, it is effective and efficient in supporting drilling decisions.
With measurement device positioned near the drill bit, real-time processing of downhole seismic data can increase the safety and efficiency to the drilling work. We study the problem in a vertical layered media by using while-drilling measurements, the artificial signal emitted by the seismic source is recorded by surface / downhole sensors, then the direct arrival traveltimes could be obtained after basic data processing. Using the traveltimes as the input of a Bayesian inversion procedure for the estimation of the bit position and the velocity model, the engineers would get the estimated values and their associated uncertainty, which could be used to predict the formation geology ahead of the drill bit and to find the lithology, fracture and abnormal pressure in front of the drill bit in time.
Conventional system has been available to the petroleum industry for some time, with seismic sources located on the surface and receivers in a borehole. The downhole detection device for SWD is mainly composed of three sets of geophone arrays, which are distributed in different axial direction, as well as the corresponding control and processing circuit. We test the inversion strategy on realistic cases in the laboratory and oilfield. According to functions, the electronic circuit is divided into main control and communication unit, signal acquisition unit, storage unit, and power detection & data play back unit. By cross-correlation processing of the direct seismic wave and the reflected waves from formation boundary, the performance of the systems were well proved.
Based on theoretical analysis, system development and experimental study, this paper will highlight the technical development.