PRESSURE DISTRIBUTION AND GENESIS OF FLUID IN THE UPPER PALEOZOIC OF THE ORDOS BASIN

The fluid pressure in the Upper Paleozoic of the Ordos Basin reflects the type of gas reservoir from one aspect. The deep gas reservoir has the negative abnormal pressure, and with rises of the buried depth and R_o value of coal layer, the negative abnormal pressure would rise correspondingly. The gas reservoir in connection with the structure shows hydrostatic pressure or positive abnormal high pressure. The negative abnormal pressure is related to the regional structure uplift denudation and the pressure is controlled by evolution degree of maturation. The high gas generation of the coal layer and high vaporization in high evolution zone caused the low nature gas moisture, low gravity and low pressure coefficient in the center of the basin. With the lower thermal evolution at the basin magin, the nature gas moisture, gravity and pressure coefficient will be higher. The regular variation of pressure coefficient in the deep gas accumulation reflects the short distance gas migration and in-situ gas reservoir formation.