Recalculation and understanding of middle and low rank coalbed methane reserves: a case study of Baode Coalbed Methane Field on the eastern edge of Ordos Basin

The Baode Coalbed Methane Field is located in the northern section of Jinxi Flex Belt on the eastern edge of Ordos Basin. It is a typical coal seam gas field of middle and low ranks. In 2011, the gas field proved 18.363×10⁹ m³ of proven geological reserves and 9.182×10⁹ m³ of technically recoverable reserves. The reserve area has been developed on a large scale for 6 years. The reserve calculation parameters have changed significantly, so it is necessary to reassess the utilization and availability of reserves. In September 2018, we recalculated geological reserves using the volume method and dynamic information by combining reserve specification with the output mechanism and development characteristics of coalbed methane. The production decline method and analogy method were used to recalibrate the recovery rate. Then, the proved reserves submitted in 2011 were recalculated. The proved reserves of coalbed methane increased by 2.986×10⁹ m³ after compounding. The recovery calibration result is 52%, up 2% from 2011. The recoverable reserves of calibration technology were 11.094×10⁹ m³, with an increase of 1.912×10⁹ m³ over 2011. Reserve recalculation focuses on the changes in calculation parameters. In the calculation of technical recoverable reserves and the determination of recovery rate, it is necessary to carry out classification and calculation according to geological conditions in the developed area.