Abstract: Sediment changes may include the water consumption of mineral alteration, the compaction drainage action and the dehydration from clay minerals transformation, etc. during the burial diagenesis and compaction. This paper calculates the water drainage from deep strata compaction and the dehydration from clay minerals transformation in Dongying sag, compares the total water growth rate and the total water consumption at the same depth intervals, and indicates that the balanced depth between them is about 2 500 m, above which the strata are dominated by water increase, below which by water consumption. The water consumption intervals in the deep strata of Dongying sag range from 2 500 m to 3 500 m. Within the effective intervals the reservoir quality can be improved, including enlarging oil?gas storage space, reducing closed fluid pressure, enhancing oil?gas accumulation power, etc. These are all favorable for oil?gas accumulation in this area