Prediction Method and Application of Pore Pressure in Fine-Grained Mixed Sedimentary Rock Reservoirs in the Lucaogou Formation, Jimusar Sag

Overpressure often occurs in fine-grained mixed sedimentary rock reservoirs. If the overpressure cannot be accurately predicted, drilling accidents may occur, and even geological disasters may be triggered. Therefore, the accurate prediction of formation pore pressure is related to various fields of oil and gas exploration and development. However, the existing methods are mainly derived from the research on shale. The lithology of fine-grained mixed sedimentary rocks is complex, and the causes of overpressure are diverse. It is difficult to accurately predict the overpressure in fine-grained mixed sedimentary rock reservoirs by applying the existing methods. Through the core experiments of fine-grained mixed sedimentary rocks and relevant testing and analysis, the relationships between the effective stress and the acoustic velocity corresponding to sand-sized particles and mud-sized particles were summarized, and it was determined that the acoustic velocity decreases with the increase in the contents of quartz, feldspar and organic matter, and increases with the increase in the contents of dolomite and clay minerals. Based on fully considering the influences of minerals, lithology, grain size, porosity, organic matter and effective stress on the acoustic velocity, a new method for predicting the pore pressure of fine-grained mixed sedimentary rock reservoirs based on the acoustic velocity model was established. This method can predict the abnormal pore pressure of fine-grained mixed sedimentary rocks caused by various mechanisms such as unbalanced compaction and hydrocarbon generation. Taking the fine-grained mixed sedimentary rock reservoir of the Lucaogou Formation in the Jimusar Sag as an example for reservoir pore pressure prediction, it was found that the prediction results have high accuracy, which can provide technical support for the exploration and development of fine-grained mixed sedimentary rock reservoirs.