Abstract:

Guang’an gas field, a gas field in the central Sichuan basin, has a very considerable geological reserve of natural gas from the Xujiahe Formation coal measures which is not very perfect. In order to give the reason, the generation characteristics of natural gas from the Xujiahe Formation coal measures in the Guang’an area was studied by means of the MSSV pyrolysis experiment and chemical kinetic method. The result indicates that natural gas was mainly generated during the MiddleLate Jurassic (156.6-140 Ma), a relative short period. The total amount of gas generation is 0.89×10¹²-1.86×10¹² m³ and more than 7.26% gas was accumulated. The gas generation intensity is 3.35×10⁸-11.83×10⁸ m³/km² which is lower than the usual value (>20×10⁸ m³/km²) for a great gas field. It is the efficient accumulation of natural gas that results in the formation of a great gas field with a relative low gas generation intensity in Guang’an area. Besides the presummarized factors, the generation of amount gas in a short period is an important reason resulting in the efficient accumulation of natural gas in Guang’an area. With a superior accumulation condition, the threshold of source rock for forming a great gas field can be lowered properly.

Key words: central Sichuan basin, Guang’an gas field, Xujiahe Formation, coal measures, gas generation characteristics, petroleum geology