As waterflooding further advances

a new situation including the rise of water-bearing layer

the declining of oil production and the unbalance between injection and production has appeared in the production of the reservoirs in the Sanjianfang Formation.The oil wells located at the main river channel sandbodies are characterized not only by thick sandstone and better physical properties

but also by high initial production of single well

high recovery percentage of reserves and big decrease of reservoir pressure.The injected water flows towards the wells which have good physical properties

and the reservoir pressure decreases mainly along the extensional direction of the sandbodies.Most of the first and second order reservoirs

controlled by sedimentary cycle

developed in the middle and lower parts of reservoir group

that is to say

in the third or fourth subbeds.These subbeds have high fluid production and injectivity

which results in the water rising mostly in the single layer or direction.The variation of reservoir fluid production is closely related to water flood response

and the rise of ground water is the fundamental cause leading to the decrease of oil production in the main oil-producing areas.