The Low Permeability Of A Fine Description Of The Reservoir And The Remaining Oil Distribution

Based on the study of fluvial sandstone reservoir in Chang 1 group in Youfngzhuang oilfields, this paper first introduces A.D.Miall's(1996a) architectural-element analysis method that was summarized form ground outcrop scale into the reservoir formation research of the study area, more subtly divides sedimentary microfacies and establishes sedimentary model of research area. on this paper summarizes the laws of residual oil distribution of fluvial formation and the control effect of sedimentary microfacies to residual oil distribution, and reveals residual oil formation mechanism. These results have been applied to residual oil production, and the economic effect is good. This paper will be useful for residual oil research and production and enhancement of oil recovery in similar resevoir.The major conclusions of this paper are as follows.1,Seven architectural-elements are divided in Chang 1 group of study area. The Chang 1 sandstone group belongs to high sinuous fine grain meandering river.2,Inter layer, the residual oil saturation of"non-main layer"is higher than"main layer", but the residual recoverable of former is larger. Therefore, "main Iayer"is the main body of residual oil distribution. The upper and middle part of inner layer has lower permeability and strong seeping resistance. Addition to gravity effect in process of driving, its driving efficienvy is low, resiJual oil saturation is high. Because of controlling of inside non-permeable interlayer or sedimentary construction, the residual oil saturation of non-driving or lower driving efficiency position also is high. On plane, the position of high residual oil saturation mostly is at element LV, CS, CH(FF), FF etc, Which has lower porosity and permeability, as well as lens sand-body and sand-body edge that is not controlled by well-net, non-perfect area of injection and production, lower press difference resort area of inter-well diffluent-line and shelter from fault, local high position of small structure.3,Microscopic residual oil mainly includes the non-moved oil in the structure of fine pore network, oil in fine pore and path, oil segment in pore and path and path vertical to flow direction, oil spot or oil film in big pore, residual oil in non-connective pore.4,The most essential and internal controlling factor of fluvial formation residual oil distribution is sedimentary microfacies. Status of injection and production is the exteriorcontrolling factor of residual oil distribution. The controlling effect of formation sedimentary microfacies to residual oil distribution indicates inter-layer vertical sedimentary facies change in scale of injection and production layer-series, planar sedimentary face change and inner-layer vertical sedimentary rhythm and interbed in single layer to residual oil distribution.5, It is difficult to clear up the inter-layer difference in scale of injection and production layer-series. The using status of minor layer is not good and its residual oil saturation is high relatively. It is obvious that inter-layer vertical sedimentary facies changes control inter-layer residual oil distribution at the same or similar conditions of injection and production. For fluvial formation, this vertical sedimentary facies change mainly is positive gyration. Namely, form down to top, channel sediment(element CHL,LA)changes into over-bank sediment(element LV, CR, CS).6, In water-injection developing process of transverse connecting fluvial sandstone oil formation, injection water always comes into channel nearby, and breaks through along channel and orientation of high pressure gradient, does not expand into side of channel until pressure gradient of channel orientation changes into low. It brings about that water-driving status of over-bank sedimentary element formation(LV, CR, CS) is not good, residual oil saturation is high. In non-connective abandoned channel element(CH>FF>) formation with channel, because this reverse is difficult to control by injection and production well-series, its using status is not good, even terribly not good, residual oil is enrichment.1 ■> The rhythm and sedimentary structure, sedimentary facies change in single sand body brings about vertical changes of formation character, growth character of inner layer interbed. These are important factor of controlling and affecting vertical water spread volume and inner layer residual oil forming and distribution in single sand body. Positive rhythm is the principal part of fluvial sandstone inner layer sedimentary rhythm. Namely, form down to upside, rock grain granularity changes from coarse to fine, seeping ability changes from strong to feebleness. It brings about that water-driving status of inner layer upside is not good, residual oil saturation is high. Inner layer interbed has different degree affecting and controlling effect to seeping of oil and water. Its affecting degree lies on interbed thickness, extending scale, position, and jeted segment of production or injection well. The effect of interbed at upside of oil formation to oil and water seeping is less, the effect of interbed at middle of oil formation to oil and waterseeping is more.8,The residual oil forming mechanism: the over-bank sedimentary element and upper part of a positive rhythm sandstone have fine pore and throat network, permeability is low, displacement pressure of pore and throat is high. The water-driving power usually falls short of displacement pressure that brings about injection water does not spread into these pore and throat network, thereby immovable oil area, namely residual oil, is formed. At underside of channel sedimentary element and positive rhythm sandstone, porosity and permeability is relatively high, connecting degree of pore and throat is high, displacement pressure of pore and throat is low. Thereby injection water is easy to enter into pore and throat, driving oil in them. Because the pore space is irregular, the surface of pore wall is coarse and non-flat. That the oil locate on concave hole of pore wall and the dead angle of pore, and the oil attaches on surface of pore wall by surface tension, are difficult to be peeled off, becoming water-driving residual oil(remaining oil). On the other hand, Because flowing section lessens, flowing resistance increase, action of capillary fore, or seeping speed decreases at process of transfer at pass narrow throat path in the course carried by driving water. The "oil drop", "oil bead", or"oil segmenf'peeled off by driving water is difficult to carry and to drive out by water at less pressure difference. Thereby they are enclosed in pore to form discontinuous residual oil.9, This results described above have been applied in develop blocks of D31 well group. Its applying effect is marked through loacal injection production adjustment,deploying replacement well,repair hole, replacement envelop,block off water and profile control etc. Relative method and technology can be applied to other oil production area of ChangQing oilfield, and obtain better economic and societal effect.