I.Introduction Fracturing technology is extremely crucial in oil and gas field development. The characteristics of post - fracturing pressure decay and the acquisition of instantaneous shut - in pressure are of great significance for evaluating the fracturing effect and optimizing production strategies. However, the fracturing process is complex and uncertain, so it is quite difficult to accurately analyze post - fracturing pressure decay and obtain the instantaneous shut - in pressure. Therefore, this study is committed to proposing a feasible analysis method to meet the actual production needs.
II. Analysis of Fracturing Process and Pressure Changes Brief Introduction of Fracturing Process Fracturing is a process in which high - pressure fluid is injected into the formation to cause fractures in the formation. During fracturing, the formation pressure rises suddenly and gradually decays with the injection of fracturing fluid and the expansion of fractures. Characteristics of Pressure Changes Post - fracturing pressure decay often exhibits exponential decay or double - exponential decay characteristics. The instantaneous shut - in pressure is a process in which the formation pressure rises rapidly to a peak value and then gradually decreases after the fracturing fluid injection stops.
III. Theoretical Basis of the Analysis Method Seepage Mechanics Theory Build a mathematical model of formation pressure decay based on seepage mechanics theory. This model covers the influence of factors such as formation permeability, porosity, and fluid viscosity on pressure decay. Fluid Mechanics Theory Use fluid mechanics theory to analyze the flow of fracturing fluid in fractures, and solve the fluid mechanics equations to obtain the flow velocity distribution and pressure distribution of fracturing fluid in fractures. Thermodynamic Theory Combine with thermodynamic theory and consider the heat transfer effect during the fracturing process. Heat transfer will affect the viscosity of fracturing fluid and formation permeability, and thus affect pressure decay.
IV. Specific Steps of the Analysis Method Data Collection Collect data on the change of post - fracturing pressure with time at the fracturing site, including pressure data before shut - in and pressure decay data after shut - in. Data Pre - processing Pre - process the collected data, such as removing noise and data smoothing operations, to improve data quality and reliability. Model Parameter Estimation Build a mathematical model of formation pressure decay based on seepage mechanics, fluid mechanics, and thermodynamic theories, and use the collected data to estimate model parameters. Optimization algorithms such as the least - squares method and genetic algorithm can be used. Instantaneous Shut - in Pressure Calculation After obtaining the model parameters, calculate the instantaneous shut - in pressure using the mathematical model. It can be calculated through numerical simulation or analytical formulas. Result Analysis and Verification Analyze and verify the calculated instantaneous shut - in pressure, compare it with the actual measured value, and evaluate the accuracy and reliability of the analysis method.
V. Case Analysis Taking a fracturing project in an oil and gas field as an example, apply the above - mentioned analysis method to analyze and calculate post - fracturing pressure decay. After data processing and model parameter estimation, the instantaneous shut - in pressure is successfully obtained and compared with the actual measured value. The results show that the analysis method can accurately reflect the characteristics of post - fracturing pressure decay, and the obtained instantaneous shut - in pressure has a good agreement with the actual measured value.
VI. Conclusion This paper proposes a method for analyzing post - fracturing pressure decay and obtaining instantaneous shut - in pressure. This method is based on seepage mechanics, fluid mechanics, and thermodynamic theories. Through steps such as data collection, pre - processing, model parameter estimation, instantaneous shut - in pressure calculation, and result analysis, the instantaneous shut - in pressure can be accurately obtained. Case analysis shows that this method has high accuracy and reliability and provides an important basis for evaluating the fracturing effect and subsequent production decisions. However, this study has limitations, such as model simplification assumptions and parameter estimation uncertainties. Future research can further improve the analysis method, consider more influencing factors, and improve the accuracy and reliability of the analysis results.