Horizontal well drilling is becoming the key to realizing the productivity of shale oil reservoirs in the exploration phase. Significant progress has been made in many basins for different operators, such as Qingshankou formation in Songliao basin, Lucaogou formation in Junggar basin, Shahejie formation in Jiyang depression, etc. However, in Jiyang depression, the understanding and characterization of sweet spots has some disagreement with the pilot wells due to the high vertical heterogeneity along the shale oil reservoir. This creates great challenges in the selection of the horizontal well landing window in the pilot well. The objective of this study is to characterize the vertical heterogeneity of the shale oil reservoir and optimize the landing window to maximize productivity.
This paper proposed an integrated workflow by combining gamma-ray spectroscopy, 2D nuclear magnetic resonance (NMR), and borehole image logging measurements. The heterogeneity characterization includes the mineralogy, rock textures, pore structures, and movable oil. Gamma-ray spectroscopy was used to characterize the mineral compositions and total organic carbon (TOC) quantitatively through a customized mineral model. 2D NMR measurements enabled the separation and quantification of different fluids with the high-resolution borehole image logs, and the detailed rock texture characterization for the development degree of lamina was automatically defined by an innovative image processing method. By integrating those measurements, the vertical heterogeneities and horizontal well landing window were optimized in the pilot well.
Case studies are presented in the Shahejie formation for shale oil reservoirs in Jiyang depression. The vertical heterogeneity variation inside the formation was well defined in terms of mineralogy, lithology, TOC, rock texture, pore structures, porosity, bound oil, movable oil, etc. by the integrated analysis. The horizontal well landing window was also optimized with respect to the sweet spots of the reservoir. The promising production in the horizontal well confirmed the understanding and characterization of the sweet spots in this shale oil reservoir with the integrated studies.
In this study, the integration of advanced logging measurements enabled characterizing the vertical heterogeneity and optimizing the horizontal well landing window. This can help the operators to get a deeper understanding of the reservoir characteristics and drill the horizontal wells in the right places. It also can help operators speed up the exploration progress and save costs. The integrated workflow illustrated in our case studies can be applied and extended to other shale oil reservoirs in China.