Variation characteristic and mechanism of carbon isotope composition of coalbed methane under different conditions and its tracing significance

•The research has the most types of gas samples and the most comprehensive basic data at present.•The composition, variation trend and mechanism of CBG δ13C1 were revealed.•The tracer significance and application scope of CBG δ13C1 under different conditions are put forward.•It is of great significance to enrich the theory of CBG isotope geochemistry.