ABSTRACT:

As a hot spot for oil and gas exploration and development, shale oil reservoirs are widely distributed in the domestic Changqing Oilfield, Xinjiang Oilfield and Daqing Oilfield. Shale oil reservoir rocks mainly include shale, mudstone and sandstone. This article carried out creep experiments on Chang-7 reservoir shale in Changqing Oilfield and Changning shale in Southwest Oilfield. In this study, shale specimens were studied through triaxial experiments and a power-law creep constitutive model was established. In the experiment, room temperature and indoor humidity were applied. The three loading stages include axial pressure and confining pressure acting on the specimen at the same time, and the deviator stresses are 10, 15 and 20 MPa, respectively. Each loading lasts for 8 hours, and one entire experiment lasts for 1 day overall. The experimental temperature is 110°C. Through the relationship between creep strain and time in the experiment, the creep law of shale rock can be obtained. The strain rate is mainly affected by differential stress and temperature. It can be seen from the results that at 110 °C, the shale creep of Chang-7 reservoir exhibits steady-state creep behavior within the experimental time range, and the creep rate increases with the differential stress. Under the condition of 20MPa, the creep rate is about 1.00×10−8s−1. Under the condition of 15MPa, the creep rate is about 5.28×10−9s−1. Under the condition of 10MPa, the creep rate is about 2.73×10−9s−1. For Changning shale rock, under the condition of 20MPa, the creep rate is about 1.9×10−9s−1. Under the condition of 15MPa, the creep rate is about 1.32×10−9s−1. Under the condition of 10MPa, the creep rate is about 9.08×10−10s−1. The main purpose of studying the long-term creep mechanical behavior of shale is to develop the change of fracture width after long-term production and its influence on the conductivity. Quantitative simulation research can be performed. The purpose of this study can make a prediction and assessment of the decline in production capacity.

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