A new calculation method for geological reserves of sour gas reservoirs: The GOCAD software used in the Changxing Formation Qilibei gas reservoir of the Sichuan Basin

The Qilibei Gas Field is one of the most important gas fields in the cooperative project of sour gases in the northeastern Sichuan Basin, and the exploitation of the Changxing Formation gas reservoir will help extend the period of this field's stable production and enhance the economic benefit of this project. Therefore, the static model construction and reserve evaluation for the Changxing Formation gas reservoirs become one of the most important tasks in the development of the gas field. In view of this, based on the related geological data in this field, a geological model and an attribute model are both built for the Changxing Formation gas reservoir with the aid of the GOCAD tool. On the basis of this, the attribute model is first used to carry out an uncertainty analysis on such geological parameters that influence the probable geological reserves; then, the OGIP equation is replaced by a proxy pattern to obtain the probable geological gas reserves. The calculated probable geological reserves of the Changxing reservoir are compared with those calculated previously by the PetroChina and the reasons why the probable reserves are less than the geological reserves are also given herein. The method for the calculation of geological reserves of sour gas reservoirs can be introduced to other similar gas fields.