Study on geostress model of coalbed methane wells in north edge of Qinshui Basin

In order to accurately obtain a geostress model of the fractured seam with non acoustic logging, based on the coalbed methane wells in the north edge of Qinshui Basin as the study object, great indoor mechanics tests were applied to measure the mechanics parameters of coal and rock. In combination with the relationship between sonic time difference logging data and data from the deep lateral resistivity logging, natural gamma-ray logging and density logging, the data fitting was applied to establish a sonic time difference model. The pressure breakdown G Function curve after the pressurization, time square root curve and Double Logarithm Function curve were applied to predict the closure pressure of the seam fractured cracks. Based on test results, sonic time difference model, predicted closure pressure, fractured crack pressure and horizontal geostress model, a comprehensive inversion was conducted to have the geostress model of the seam in north edge of Qinshui Basin. A prediction was conducted on the geostress in the target well block. The results showed that the errors of the maximum and the minimum horizontal geostress predicted were only 0.5 MPa and 0.6 MPa respectively. The method could realize the calculation of the geostress model for the fractured seam under the condition of the non sonic time difference logging.