FALSE CAP ROCK OVER THE OIL AND CAS ACCUMULATION OF THE CARBONIFEROUS DONGHE SANDSTONE IN THE UPWELLINC AREAS OF THE MID-TARIM BASIN

The oil and gas accumulation of the Carboniferous Donghe sandstone in the upwelling areas of the Mid-Tarim Basin is a structural trap accompanying with stratigraphic control factors.The analysis on well and test data appears that petroleum in the accumulation of Donghe sandstone seemingly has not filled to structural spillpoint in wells 10,16 and 20 in field of the Mid-Tarim Basin.The sedimentary factes in gravel-bearing sandstone member over Donghe sandstone vary dramatically and their porosity changes between good and bad.Mercury-injection data show that in the porosity-worsening areas of the member,oil and gas accumulation plays an insulating membrane-typed plugging part to Donghe sandstone,belongs to transitional bed betweeen mudstone member(cap rock)and sandstone member(reservoir)and is called "false cap rock".