In recent years, a series of advances have been achieved in the exploration of shale gas in the Ordovician Ulalike Formation, middle section of the Western Ordos Basin. In order to comprehensively evaluate shale reservoirs, a logging evaluation method for the brittleness index is developed in this paper. This study consists of the following three steps: 1. Through the quantitative analysis technique of X-ray diffraction, the brittleness index was calculated based on the mineral composition of the test sample; 2. Using array acoustic logging data, the brittleness index was calculated based on acoustic properties; 3. A quantitative expression for the correlation between the conventional logging data and the brittleness index was established mathematically. Four main understandings and conclusions are summarised in this study. 1. In the study area, more than half of the shale samples of the Ulalike Formation have a brittleness index greater than 60%. 2. The distribution trend of the brittleness index calculated from the array acoustic logging data is consistent with the test results, indicating that the calculation results based on acoustic properties are accurate and reliable. 3. There is a clear correlation between the newly constructed lithology coefficient and the brittleness index, with a correlation coefficient of up to 0.8899. 4. Applying the developed mathematical expression between the lithology coefficient and the brittleness index, the brittleness index gradually increases from west to east in the study area. The methodology involved in this study enables quantitative evaluation of brittleness without the need for test samples or array acoustic logging data, which can help reduce the cost of shale gas resource exploration in the study area.