Evaluation Method of Shale Oil Reservoirs Fracability—A Case from Seventh Member of Triassic Yanchang Formation in Ordos Basin 2018 IFEDC

Abstract

Fracability is the capability of the shale that can be fractured effectively during hydraulic fracturing. Now, the fracability evaluation mainly focuses on shale gas reservoirs, and there are few researches on shale oil reservoirs. Taking the seventh member of Triassic Yanchang formation shale oil reservoirs in the Ordos basin as an example, the geological sweet point of shale oil reservoirs is given in the quantitative evaluation of physical property and geological characteristics of shale oil reservoirs. An evaluation method of shale oil reservoirs fracability is developed combining with the fracture index and fracture toughness based on petrophysical experiments and existing well logging data. The evaluation method is applied to more than 10 wells of Chang 7 reservoirs in which fracability profile is established. The results show that the shale oil reservoirs fracability can be accurately evaluated by the developed model which can be used to screen the fracturing engineering sweet spot. The fracture distribution and fracturing effect of each well were evaluated by combining with the fractured profiles and anisotropic production diagrams of pre-frac and post-frac, and the results were compared with the actual fracturing effect of each well. Compared with the adjacent sandstone section, the Chang 7 shale oil reservoir has a lower level of natural fracture development, higher crustal stress and lower brittleness. The study provides a more accurate and effective method for shale oil reservoirs fracability evaluation and engineering sweet spot screening, which will contribute to increase the success rate of fracturing treatments and reduce the blindness of pre-fracture wells selection.