Next Level of Complex Reservoir Geosteering: The New Generation of Ultra-High-Definition Directional Resistivity Propagation Method
Authors: Zhao Guoquan , Jin Baoqiang , Yang Liuhe , Li Wei , Zhou Junliang , Zhang Lili , Wang Fei , Wang Haifeng , Li Shuzhong , Hu Zhong , Xu Tianyun , Dolan James 
Published: February 2022

Abstract
For most offshore and tidal zolone oil development in North China, one of the major challenges of the industry is high drilling uncertainty and low reservoir encountered rate at the braided river delta and fluvial deposition environment with the common characters of thin sand channels, severe lateral change, unstable sand structure and low sand connectivity. Optimizing the wellbore placement inside the complex reservoir and depicting the sand with detailed information are gradually being critical to real time geosteering in these areas.
Over the last decades, the continuous improvement of distance-to-boundary logging while drilling workflows has dramatically enhance the drilling efficiency of horizontal well. However, relatively short depth of detection (DOD) and low sensitivity to multi-layer environment still cannot meet the requirement of drilling under these complicated geologies.
To reduce the geosteering uncertainty and enhance formation evaluation in complex environment, a new advancement in mapping-while-drilling electromagnetic propagation resistivity method, with the industry's first combination of axial, tilted and transverse antennas and significant software enhancements, made a momentous progress for complex reservoir geosteering and characterization.
Compared to the previous generation, this service could provide:
Larger depth of detection which doubled the previous generation. For one hand, larger DOD means earlier proactive strategy for the well position optimization; For the other one, enlarged vision also helps achieve whole delineation of the target sand channel and thus much better geological understanding for the reservoir. More sensitivity for anisotropy and local sedimentary character. Improved measurements set and enhanced software algorithm can visualize the detailed characteristics inside the sand channel. With its up-to-eight-layer resistivity reconstruction, the refined inversion exceeds the existing propagation resistivity answer product.
Outstanding performance was observed during the implementation. The target sand channel of 6-7m thickness could be delineated clearly by the refined inversion. It not only depicted the whole picture the sand body, but also provided an earlier sign of structural fluctuation, which ensured the success and high oil recovery rate of the horizontal section.
For the well with higher anisotropy or more local sedimentary features, comparing to the blur reflection of the previous method, this ultra-high-definition technology could provide a sophisticated vision of the shape, thickness, direction and resistivity property of the local thin layers and shaly block. Reliable evidence of both outline and inside characteristics of the sand channels improved the further well path design and geological understanding.
The ultra-high-definition mapping-while-drilling technology opened the market of complex deposition environment drilling. It remarkably increased the reservoir encountered rate and predictability of the environment, helping to reduce the budget and enhance drilling efficiency. The ultra-high-definition directional resistivity propagation method will surely lead the industry to the next level of the complex reservoir development.