Abstract: Tight sandstone reservoir in Wuqi Oilfield is disadvantaged by poor physical properties, complex pore structure, serious heterogeneity, and poor water injection effect. In response to these shortcomings, the pore structure characteristics and clay mineral composition of Chang₆ Oil-bearing Formation in Wuqi oilfield were analyzed with high-pressure mercury porosimetry, scanning electron microscope and X-ray diffraction and other tests. Nine pore structure parameters were selected as characteristic parameters, and a comprehensive evaluation standard based on reservoir pore structure was established. The reservoirs were divided into three categories: Type I (excellent), Type II (moderate) and Type III (poor). The rock samples of each type of reservoir were evaluated for sensitivity and analyzed for influencing factor. The results of the study show that the sensitivity of the three types of reservoirs was significantly different. Specifically, Type I presented low velocity sensitivity, low water sensitivity, moderately low salt sensitivity, moderately high acid sensitivity, and moderately low alkali sensitivity. Type II presented moderately low to low velocity sensitivity and water sensitivity, moderate to low salt sensitivity, low acid sensitivity, and moderate to low alkali sensitivity. Type III presented moderate to low velocity sensitivity, low water sensitivity, low salt sensitivity, moderately low to low acid sensitivity and low alkali sensitivity. The pore structure and clay mineral composition were the main reasons for the difference in reservoir sensitivity. The study results can provide a reference for optimizing water injection and reservoir stimulation for similar tight oil reservoirs.

Key words: tight oil reservoir, sensitivity, pore structure, clay minerals, key trolling factors, Wuqi Oilfield