Research and Application of Sweet Spot Evaluation Technology for Shale Oil Reservoir Engineering in Qaidam Basin

Shale oil was first identified in the upper member of Paleogene Lower Ganchaigou Formation of Yingxiongling area, Qaidam Basin in 2021. It is a low porosity and ultra-low permeability reservoir, which needs to take fracturing stimulation measures to obtain industrial oil flow and development value. It is an effective way to develop shale oil in this area to “break reservoir” and improve reservoir seepage capacity through horizontal well volume fracturing technology. In the process of horizontal well volume fracturing, it is difficult to evaluate the engineering sweet spot accurately. This greatly affects the effect of fracturing. The techniques of mineral composition analysis, rock mechanics experiment and fracability evaluation of reservoir are studied and applied. Based on micro-hyperspectral test and micro-nano indentation test, the mineral element composition, content and rock mechanics parameters are obtained by scanning, testing and analysis of rock cuttings. Combined with the characteristics of Yingxiongling shale oil reservoir and previous fracturing experience, based on logging interpretation and rock cuttings gene scanning test results, The brittleness index, horizontal stress difference coefficient and micro-fracture density were taken as the evaluation indexes of fracturing performance, and the weights of the parameters was determined by the analytic hierarchy process (AHP). A fracability evaluation model suitable for Yingxiongling shale oil was established, and the evaluation technology of engineering sweet spot with “cuttings mineral analysis technology and fracturing analysis technology” as the core of Yingxiongling shale oil in Qaidam was formed. After the application of the engineering sweet spot evaluation technology, the average daily oil production of vertical Wells reached 14.7 tons and that of horizontal Wells reached 55.23 tons. It helped make new breakthroughs in shale oil exploration and development.