Experimental investigations about the effect of pressure on gas generation from coal

Closed-system pyrolysis experiments were conducted on a coal sample with a maturity of 0.57 %Ro using gold tubes pressured to 10 MPa, 25 MPa, 50 MPa, 75 MPa and 100 MPa to investigate the influence of increasing pressure on gas generation. The variation of gaseous components generated by coal, the H/C atomic ratio and the vitrinite reflectance of pyrolysis residues with pressure and temperature indicate that pressure does not linearly impact gas generation from coal. Pressure has no effect on primary gas generation, but it does affect secondary gas generation. Retardation of secondary generation is highest at 50 MPa. Our investigations reveal that previously published and partly opposing results about the effect of pressure on hydrocarbon generation can be mainly explained by the difference in the pressure range under which those experiments were conducted. Our experimental results demonstrate that hydrocarbon generation is generally least retarded at pressures exceeding 75 MPa. Nevertheless, hydrocarbon generation in natural systems usually occurs at pressures of 10–60 MPa (1–6 km burial depth) and might therefore be secondarily controlled by pressure retardation effects.