Flow patterns of the Jurassic tight reservoirs,central Sichuan Basin
Exploited by their own natural energy,the Jurassic tight oil reservoirs,central Sichuan Basin,feature a high solution gas-oil ratio,better gas drive,large flow resistance greatly induced from throat and microfracture,small output and low primary recovery.It is essential to probe into flow mechanisms during the drive for these ultra-low permeability reservoirs in order to intensively draw on their reserves.Thus,matrix cores and artificially fractured cores were used for discussion on permeability,relative permeability and saturation.In addition,some flow resistance experiments and relative-permeability tests were performed under the same irreducible water conditions.Results show that(ⅰ)for both matrix and fractured cores,the saturation in dual-phase flow zones increases and the residual-oil saturation decreases with the increase of permeability;(ⅱ)the lower the permeability is,the earlier the resistance arises,and the earlier the gas bubble originates from degassing affects on permeability;(ⅲ)when the bottomhole flowing pressure is larger than the backpressure at the resistance's knee point,there is a favorable pressure zone for solution-gas drive,and the degassing has a slight impact on oil flow,allowing for energy utilization of drive with effect;and(ⅳ)according to the trial simulation on the drive model,oil wells with solution-gas drive may exhibit small drainage radius,faster pressure drop near the wellbore,and nonlinear pres-sure distribution.All results provide certain reference for optimizing development modes together with maintaining and improving productivity in the tight oil reservoirs.
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