Study on the extension limit model of a horizontal well with supercritical carbon dioxide drilling

Rational prediction of the extension limit of a horizontal well under the condition of supercritical carbon dioxide drilling can ensure drilling security for developing unconventional oil and gas resources. Based on the physical property of supercritical carbon dioxide and the mechanics theory on the rock surrounding the wellbore, the extension limit model of a horizontal well under the condition of supercritical carbon dioxide drilling has been established, which can analyze the flow distribution in the horizontal well and the influence of the azimuth angle, the bedding dip angle, drilling parameters, and so on. The result shows that when the supercritical carbon dioxide is flowing in the borehole, the pressure at the horizontal section at 3320 m is 2.21 MPa lower than the pore pressure, which is in the safe pressure range of underbalanced drilling (similar to 0-3 MPa), and the wellbore is stable. The extension limit changes periodically as the azimuth angle increases. Under actual working conditions, reducing the inlet mass flow rate or wellhead back pressure within a safe range helps to increase the extension limit. The maximum extension limit of a horizontal well with supercritical carbon dioxide drilling is 8081 m in the paper, which is longer than that of clear water drilling under the same condition due to low pressure loss. (c) 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.