矿井水深部存储温度响应特征及优势渗流层段定量识别

[Background] Storage in deep strata represents an effective approach to treating high-salinity mine water in mining areas of western China. For this technology, the use of directional wells can significantly enhance water injection efficiency, while selecting primary permeable intervals with high injectivity as drilling targets is key to its successful implementation. However, the accurate identification of these intervals in deep strata remains challenging. [Methods] By analyzing the wellbore temperature variations in the injection well during water injection, a qualitative model was developed to evaluate primary permeable intervals based on wellbore temperature curves. Following the principles of momentum and energy conservation, a forward model accounting for multiple thermal effects was established to predict the wellbore temperature of the injection well. Based on measured distributed temperature sensing (DTS) data, an inversion model was developed for temperature interpretation. Using temperature errors as the evaluation metrics, a method for the quantitative identification of primary permeable intervals was established through iteration and fitting. A deep-well water injection test was then conducted in a selected test well within a representative mining area. During the test, distributed optical fiber was used to monitor the temperatures across different well depths in three stages: initial well shut-in, water injection, and post-shut-in thermal recovery. The temperature curves of the injection well were predicted using the forward and inversion models, and the injection rates at various intervals were calculated. [Results and Conclusions] The bottomhole temperature of the injection well remained at approximately 71.8 ℃ throughout the entire test. During the initial well shut-in stage, the wellbore temperature of the injection well varied linearly with depth, closely matching the local geothermal gradient. In the water injection stage, the wellbore temperatures at injection intervals gradually decreased under the influence of low-temperature injected water, stabilizing at 23.5 ℃‒31.8 ℃ as water injection ended. During this stage, the low temperatures extended to a depth of 1 970 m in the injection well, with a boundary of significant temperature contrast forming at the well bottom. The wellbore temperature curve model reveals that this depth corresponds to the lower boundary of the primary permeable interval. In the post-shut-in thermal recovery stage, the wellbore temperature of the injection well was slightly lower than that in the initial well shut-in stage. Furthermore, slow thermal recovery was observed at depths between 1850 m and 1 950 m. This interval was preliminarily identified as the primary permeable interval based on the wellbore temperature curve model. The predicted temperature of the injection well showed strong agreement with the measured DTS data, with fitting errors of less than 0.05. Calculations reveal that the injected volumes at depths of 1 850−1 950 m and from 1 505−1 850 m accounted for 69% and 31% of the total injected volume, respectively. These results indicate that the middle-to-lower section of the Triassic Liujiagou Formation serves as the primary permeable interval. In contrast, the Heshanggou Formation and the upper part of the Liujiagou Formation act as secondary permeable intervals, while the remaining strata are non-permeable. These findings are relatively consistent with comprehensive discrimination results based on lithology, volumes of drilling fluids lost, and fracture development in cores, verifying the reliability of the DTS-based interpretation method. Overall, the results of this study provide a valuable reference for optimizing well configuration and selecting the optimal target intervals for mine water storage in deep strata.