(1) Formation characteristics

The Dujiatai oil layer in the Du 66 block is located in the front of a large fan-delta developed under the condition of slow water inflow. The sand bodies in the upper strata are very well developed. The average thickness of the Du II-1 sandstone is 12.5 m, and that of the Du I-2 sandstone is 6.5 m. The interlayers are relatively well developed with a maximum thickness of 44 m, generally 0.6–20 m. However, the development of different oil layers is different, and the distribution characteristics are also quite different. The maximum thickness of the interlayers from the upper layer to the Du 0 layer is 21.7 m, generally 10 m to 20 m. And the average thickness is 16.3 m. The lithology is brown–gray mudstone and the undeveloped areas of sandstone are often interbedded with oil shale, dolomitic limestone, and brown–grey mudstone. The porosity of the upper layer is generally 15% to 25%, with an average of 20.7%. The permeability is generally 200 to 1200 mD, with an average of 920.6 mD, which is a typical medium–high porosity and medium–high permeability reservoir. The oil layer group division and oil layer thickness statistics of the Du 66 block have been listed in Table 1.


**Table 1.** Oil layer group division and oil layer thickness statistics of the Du 66 block.
