Unlocking the Potentials by Optimizing the Landing of Horizontal Wells in Shale Oil Reservoirs –Case Studies in Jiyang Sag
Authors: Xu Wei , Yu DaiGuo , Yang DongGen , Zhao DaoHan , Liu XiFeng , Zhao JianYe , Gu Xiao , Zhao XianRan , Wu JinLong , Li ShenZhuan , Lu QingZhi , Liu XunQi 
Published: May 2024

Lacustrine shale oil has been a major exploration target in basins in China in recent years. Horizontal well drilling is becoming the key to realize the productivity of a shale oil reservoir in the exploration phase. Different operators have made significant progress in many basins, such as the Qingshankou formation in the Songliao basin, the Lucaogou formation in the Junggar basin, the Shahejie formation in the Jiyang sag, etc. In the shale oil reservoir in the Jiyang sag, the understanding and characterization of "sweet spots" is not always clear in the pilot wells due to the high vertical heterogeneity. This makes selecting the horizontal well landing window in the pilot well challenging. This study aims to characterize and unlock the shale oil reservoir's potential by optimizing the horizontal wells' landing sections to maximize productivity.

In this work, an integrated workflow was developed for the characterization of shale oil reservoirs and optimizing the landing windows of horizontal wells in the Jiyang sag. The workflow integrates gamma-ray spectroscopy, 2D nuclear magnetic resonance (NMR), and borehole image logging measurements. The heterogeneity characterization includes the mineralogy, lithology, total organic carbon (TOC), rock texture, pore structures, porosity, bound oil, and movable oil, etc. Gamma-ray spectroscopy measurements were used to characterize the complex mineral types, mineral compositions, and TOC quantitatively through a customized mineralogical model. 2D NMR measurements enabled the separation and quantification of different fluids in the pores by the 2D data analytics technique on the T1-T2 map besides the pore structure and porosity. Previous studies have shown that the lamination degree has a significant relationship with the reservoir quality in a lacustrine shale oil reservoir. With high-resolution borehole image logs, the detailed rock texture characterization for the lamination degree was automatically defined by an innovative image processing method in addition to the identification of the fractures, structures, and other features. By integrating the mineral compositions, TOC, porosity, fluid compositions, and rock textures, the vertical heterogeneous reservoir quality was characterized, and the horizontal well landing window was optimized in the pilot well. The potential of the shale oil reservoir was confirmed by the productivity of the horizontal wells.

The promising production in the horizontal well confirmed the understanding and characterization of the sweet spots in this shale oil reservoir that resulted from integrated studies. The integration of the advanced logging measurements to characterize the vertical heterogeneity and optimize the horizontal well landing window can help the operators get a deeper understanding of the reservoir characteristics and drill the horizontal wells in the right places. It also can help operators accelerate the exploration progress and save costs. The integrated workflow as verified in case studies can be applied and extended to other shale oil reservoirs in China.