Abstract
We present systematic investigations on the physics, detection performance and inversion of logging-while-drilling extra-deep azimuthal resistivity measurements (EDARM). First, the definitions of EDRAM measurements are discussed, followed by the derivation of the attenuation and phase-shift geometrical factors to illustrate the relative contributions of formation units to the observed signals. Then, a new definition of detection depth, which considers the uncertainty of inversion results caused by the data noise, is proposed to quantify the detection capability of EDARM. Finally, the Bayesian theory associated with Markov chain Monte Carlo sampling is introduced for fast processing of EDARM data. Numerical results show that EDARM is capable of detecting the azimuth and distance of remote bed boundaries, and the detection capability increases with increasing spacing and resistivity contrast. The EDARM tool can accommodate a large range of formation resistivity and is able to provide the resistivity anisotropy at arbitrary relative dipping angles. In addition, multiple bed boundaries and reservoir images near the borehole are readily obtained by using the Bayesian inversion.
Highlights
Geosteering is one of the key techniques for the exploration and development of complex oil/gas reservoirs (Li et al 2005; Wei et al 2010; Bittar and Aki 2015)
We extend the geometrical factor (GF) theory to extradeep azimuthal resistivity measurements (EDARM) and the detailed derivation is given in “Appendix.” Assuming the transmitter and receiver lie in
The reliable inverted distance to boundary reduces to 17 m when the tool lies in a conductive formation. This is because the EDARM responses are very sensitive to the nearby conductive surrounding bed and the tool has better detection capability in a resistive bed
Summary
Geosteering is one of the key techniques for the exploration and development of complex oil/gas reservoirs (Li et al 2005; Wei et al 2010; Bittar and Aki 2015). CNPC Key Laboratory for Well Logging, China University of Petroleum, Qingdao 266580, Shandong, China azimuthal resistivity measurement (ARM), have been specially designed for this purpose. The former, equipped with a coaxial transmitter and coaxial receiver, is capable of providing accurate formation resistivity (Hagiwara 1996). ARM incorporating a transverse or tilted antenna has eliminated the boundary azimuth uncertainty and enables the detection of a bed boundary up to 5 m away (Li and Wang 2016; Bittar et al 2009; Wang et al 2018b) Despite these advantages, the depth of detection (DoD) of current EM tools is still relatively shallow. The difference between the two modes is that the former uses a symmetric configuration to maximize the sensitivity to bed boundaries
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