Optimization of Complex Channel Sand Development Using Ultrahigh-Definition Multilayer Mapping-While-Drilling Technology in Offshore China
Authors: Guo Xijia , Yang Liuhe , Li Chao , Wang Chao , Wu Kai , Li Shuzhong , Fu Zairong , Zhang Lili , Xu Tianyun , Hu Zhong , Wang Fei , Wang Haifeng 
Published: March 2024

After around 3 years of exploration and evaluation, K Oilfield, the largest newly discovered oilfield in Bohai Bay in recent years, has entered the development stage since 2022. In the braided river delta and fluvial deposition environment, the characteristics of thin sand channels, leading to severe lateral change, unstable structure, low sand connectivity and anisotropic formation, made it difficult to place the wellbore within the complex reservoir. Consequently, the low recovery rate caused by the low reservoir encountered rate would be inevitable.

The ultrahigh-definition multilayer mapping-while-drilling (MLM) service based on underlying propagation azimuthal electromagnetic measurements was deployed as the fit-for-purpose geosteering solution to address the above challenges. Compared with the existing distance-to-boundary services, the new one offers the industry's first combination of axial, tilted and transverse antennas to produce a completed measurement set and an enhanced inversion algorism. It could provide a larger depth of detection (DOD) and higher sensitivity under anisotropy and local sedimentary variety, particularly in the complex channel sand, facilitating an earlier proactive strategy for the wellbore position optimization and a better understanding of the whole sand channel distribution.

From 2022 to 2023, 48 horizontal wells in Block-A of K Oilfield have been steered using the ultrahigh-definition multilayer mapping-while-drilling service during landing and the lateral section. Leveraging the upgraded capabilities, the key outstanding achievements we observed during the implementation: Significant improvement in DOD, facilitating both landing and lateral geosteering operations. Both the roof and floor of the target sand channel (&lt;8m thick) could be delineated during the lateral, enabling a desired wellbore position. Besides, it's also feasible to identify the target roof during landing due to the larger DOD.Multi-layer reservoir mapping. As both the target boundary and the interbeds could be depicted and distinguished, the reservoir property beyond the interbed could be evaluated, within which the well path could be placed if it's doable.Depiction of the discontinuous sand-bodies geometry. The geometry of the isolated or overlaid sand bodies could be depicted, enabling an optimized trajectory to connect them.

Thanks to the advantages of the ultrahigh-definition multilayer mapping-while-drilling service, not only did the average net-to-gross (NTG) ratio reach 95%, much higher than the original estimate, but it also helped improve drilling efficiency, reduce costs, and mitigate drilling risks. In addition, new technology could help delineate the reservoir profile with more accurate models and achieve an in-depth understanding of the complex channel sand reservoir.

The authors believe that the fit-for-purpose geosteering solutions could be expanded to other similar projects by showcasing the distinctive case studies in this paper.