Research on the effect of heterogeneity of the thick delta reservoir to early polymer flooding: A case study of Lower Dongying Formation, palaeogene, in Suizhong 36-1 Oilfield, Northern Bohai Bay Basin, North China

For thick delta oil reservoir, early polymer flooding production method is put forward to shorten production time. Strong heterogeneity of the delta thick reservoir has an important influence on early polymer flooding, but... [ view full abstract ]

For thick delta oil reservoir, early polymer flooding production method is put forward to shorten production time. Strong heterogeneity of the delta thick reservoir has an important influence on early polymer flooding, but understandings of it are not deep enough. Taking the delta reservoir of Lower Dongying Formation, palaeogene, in Suizhong 36-1 Oilfield, Northern Bohai Bay Basin, North China as an example, basing on cores, well logging, and dynamic data, by geological analysis and numerical modeling, this paper studies the quantitative effect of the heterogeneity to early polymer flooding. Followings are the main results and conclusions.(1) Vertical sealing of in-layer interlayer is good for polymer flooding and oil recovery could be increased about 20%. And the better the Continuity of vertical sealing is, the higher the recovery effect of the polymer flooding is. But the different interlayer spacing could have opposite effect to early polymer flooding. When underwater distributary channel is relatively stable, arched pattern interlayer is frequently formed in mouth bar. And this kind of interlayer is mainly vertical sealing to oil flow. (2) Lateral sealing of the in-layer interlayer could make reservoir enrich remaining oil to early polymer flooding and decrease the oil recovery by 3%. But to water flooding, oil recovery could be decreased about 18%. Therefore, early polymer flooding has already depressed influence of lateral sealing. When the underwater distributary channel migrates frequently, lateral superposed interlayer is widely formed in mouth bar. And this kind of interlayer is mainly lateral sealing to oil flow. (3) While permeability heterogeneity, rhythm and the change of planar sand body property are stronger vertically, the recovery effect of the polymer flooding gets lower. Variable coefficient of permeability heterogeneity has linear relation with oil recovery and sweep efficiency. And to weak heterogeneity reservoir (Vk<0.3), it could eliminate the effect of rhythm to early polymer flooding. But to strong heterogeneity reservoir (Vk>0.3), compound rhythm reservoir could reduce oil recovery. (4) In the plane, early polymer flooding could prevent the formation of breakthrough flow channel. And the distribution of the remaining oil is relative scattered. Therefore, early polymer flooding could increase oil recovery to a great extent.