A New Model for Calculating Deviation Factor of Natural Gas in Ultra-Deep Oil and Gas Reservoirs under High Pressure

In order to meet the drilling and production requirements of deep and ultra-deep oil and gas reservoirs under high pressure in China, PVT characteristic measurement experiments of natural gas samples with different components under high-pressure conditions were carried out by using high-temperature and high-pressure PVT characteristic measurement system. The experiments show that the deviation factor of natural gas under high pressure increases linearly with the increase in pressure and decreases with the increase in temperature, but the overall difference is small. At the same time, an experimental database of the deviation factor of natural gas in a large temperature and pressure range is established based on 1443 sets of data including Standing-Katz chart fitting data, experimental measurement data, and public experimental data. Through the numerical method of multivariate nonlinear fitting, the existing models are improved, and a new model for calculating the deviation factor of natural gas of ultra-deep oil and gas reservoirs under high pressure is established. The predicted results of the model are compared with those of HY, DPR, LXF, and other common methods. The error analysis shows that the relative error of the model is less than 2% in the high-pressure section, and its calculation accuracy is higher than that of HY, DPR, LXF, and other methods, which meets the practical needs of engineering and can provide guidance and support for safe and efficient drilling and production of ultra-deep oil and gas reservoirs under high pressure.