The new JM project is a tight oil drilling campaign started in 2016, aiming at the development of LCG formation, a typically tight reservoir featuring low porosity and extremely low permeability. This paper mainly describes how the distinct geosteering solutions have been applied to solve the different geosteering challenges respectively, help improve the net-to-gross ratio by placing the trajectory in the desired place and increase the ultimate recovery rate.
LCG target is divided into the up-sweet-spots and the low-sweet-spots vertically. The lithology of the up-sweet-spots is mainly siltstone and fine sandstone, characterized by low or medium resistivity and high gamma on the logging curve. The cap and base rock are dolomite with high resistivity. The target layer is 3-5m thick with high structure uncertainty. However, different from the up-sweet-spots, the low-sweet-spots is dolomitic siltstone with high heterogeneity. And within the range of 2m thickness of the target layer, it can be subdivided into 4-5 sublayers with different logging responses, leading to the range of resistivity in the target varying from 2 to >2000 ohmm, bringing a huge challenge to the lateral geosteering.
To address the challenges mentioned above, fit-for-purpose geosteering solutions have been applied. The High-Definition multi-boundary mapping service based on electromagnetic propagation logging while drilling is deployed, given the case of the up-sweet-spots where the resistivity difference between the target and the surrounding rock is evident, and the target layer is homogeneous internally. This solution can depict the reservoir boundary clearly within 3-5m TVD, and it enables adjusting the trajectory accordingly in advance, consequently avoiding drilling out of target effectively.
At the same time, aiming at identifying and tracing the multiple sublayers within the low-sweet-spots, the Ultra- High-Resolution Image LWD technology is applied. In the case of low-sweet-spots, it can not only help adjust the trajectory to match with the structure change relying on the formation dip derived from the resistivity image, but also it can measure the formation resistivity more accurately compared to propagation tools.
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.