Clastic rock gas reservoir abnormal low pressure cause quantitative calculation method

The invention provides a clastic rock gas reservoir abnormal low pressure cause quantitative calculation method, which comprises the following steps of: calculating an abnormal low pressure cause based on time t in a stratum lifting process and a stratum compaction coefficient, an overlying stratum pressure, a stratum pressure, a temperature and a natural gas compression factor when t is 0; the formation temperature before formation uplift, the overlying rock pressure, the formation pressure, the water saturation, the natural gas compression factor, the formation water thermal expansion coefficient, the formation water compression coefficient, the earth surface pressure, the earth surface temperature, the density of the natural gas under the standard condition, the density of the formation water, the solubility of the natural gas in water and the residual coefficient of the natural gas after loss are calculated; a formula coefficient is calculated for a natural gas compression factor, a calculation formula of