Evaluation On Gypsum Mudstone Caprock Of Eogene System In Kelasu Structural Belt Of Tarim Basin

In order to evaluate seal gas effectiveness of Lower Tertiary cap rock in Kelasu structural belt of Tarim basin, the development characteristics of cap rock were studied firstly by use of the existing drilling and seismic data, and it was concluded that the main cap rock was gypsum mudstone, upper part of Kumugliemuian, Lower Tertiary. This kind of mudstone was distributed in Kelasu structural belt, whose maximum total thickness could be up to more than 700m; The damage degree of cap rock by fault was studied by use of the relative size between fault throw and cap rock thickness, and it was concluded that the damage degree of Lower Tertiary mudstone cap rock in Kelasu structural belt by fault was relatively greater; Faults whose damage degrees are medium and small are only distributed in the north and southwest of Kela 3 well, and in the southwest of Kela 203 well. Secondly by use of interval travel time data, and by calculating the difference between measured displacement pressure and interval transit time, it was concluded that the displacement pressure of Lower Tertiary mudstone was about 2MPa-17MPa. The area of high value is distributed near Kela 3 well, where the displacement pressure is 10-17MPa and the seal ability of overpressure is relatively strong. Thirdly the seal ability was comprehensively evaluated by use of the development features and micro-sealing capacity of cap rock. It was considered that the cap rocks with good sealing capacity were distributed in the north of Kela 3 well and the area between Kela 4 well and Kela 1 well. Finally, the seal efficiency was studied according to the matching relation between the formation period of Lower Tertiary mudstone cap rock in Kelasu structural belt and the main hydrocarbon generation period of Triassic-Jurassic source rock. It was considered that the formation period of sealing capacity of cap rock in Kelasu structural belt was the sedimentary period of Kangcun formation; the main gas expulsion period of Triassic and Jurassic source rock was Neogene. The former is earlier than the latter. It is effective to seal the gas generated by Triassic and Jurassic source rock and favorable for the large-scale accumulation of gas.