Fracture Evaluation Of Shale-oil Reserviors

The accuracy of fracturing evaluation is the key to the effective development of shale oil.Therefore,taking the Chang 7 shale oil reservoir in Ordos Basin as the research object,clarfying the geological characteristics,brittle mineral content characteristics and fracture toughness characteristics of the study area through laboratory experiments and empirical formula calculations.Combing with brittleness and fracture toughness to establish a fracturing evaluation model that is suitable for the study area,and apply it to 5 wells in the study area.The results show that:(1)The mineral components of Chang 7 shale oil reservior include quartz,feldspar,carbonate,pyrite and clay minerals.The average quartz content is 28.99%,the average feldspar content is 14.8%,the average carbonate content is 20.9%,the average pyrite content is 5.04%,and the average clay mineral content is 30.27%.While the average quartz content in the Chang 7 tight sandstone reservoir is 41.8%,the average feldspar content is 23.5%,and the average clay mineral content is 17.4%,the brittle mineral content of shale oil reservior is lower than it in sandstone reservior;(2)The average geostress of 5 wells shale oil reservoirs is between 23.81 and 37.21 MPa,which is generally higher than that of adjacent sandstone reservoirs and with a marginal range between 1.82% and 10.82%;(3)The average brittleness index of the shale reservior is between 0.296 and 0.400,which is lower than that of the adjacent sandstone section and the low amplitude is between 6.22% and 38.46%,the average fracturing index is between 0.341 and 0.404,which is lower than that of the sandstone section and the low amplitude is between 9.89% and 23.89%;(4)The model was applied to 5 wells in the study area and the evaluation results are in good agreement with the actual fracturing results,fully embodying the the accuracy and applicability of the model in this paper.It is suggested that the engineering dessert should be selected in shale oil reservoir segments with low ground stress,high brittleness,low fracture toughness,and high fracture index.