Study On The Fluvial Reservoir Architecture And Distribution Modes Of Remaining Oil In Gudao Oil Field

Targeting the fluvial reservoir characteristics of Guantao formation in Gudao oil field, and based on the research of reservoir geological model, the fluvial reservoir architecture and modes are systematically generalized by means of study on sedimentology, reservoir geology, reservoir enginerring and logging-constrained seismic conversion, numerical simulatiom, field logging and dynamic monitoring. Therefore the characteristics of fluvial reservoir are revealed and the remaining oil in the fluvial reservoir, with respect to distribution rule and controlling factors, is generalized. Accordingly, based on the work above, the approaches, taking into account of the geological characteristics of Gudao oil field, some different residual oil distribution modes, to enhance the recovery ratio, are proposed, and therefore of certain research significance and innovative suggestions as follows:1. Systematic generalization on the sedimentary characteristics, micro-facies features and over-bank deposits properties, and the discussion on hiberarchy of reservoir and correlated connectivity and permeability difference of different sandbody deposited in specific fluvial type. And, it is thought herein that the point bar in the meandering river acts as the semi-conductive medium, and the channel bar in the brained river as "pan-connective body" which is locally less permeable even connected, and blocked even connected; and the sandstone in the netted river as net-like connective body.2. The technologies, mainly post-stack wavelet separating frequency and noise elimination, and logging curve reconstruction, are adopted in the high resolution conversion of reservoir to elaborate the external shape and distribution, and the concept of single original sandstones, the accordant identification and correlation method are subsequently proposed. Moreover, the genesis of abandoned river channel and the relevant significance in the reservoir description and development are further inferred. In addition, the fluvial reservoir structure and fluid unit are further classified based on the study of uni-geneis sandstone.3. The genesis, shape, scale and occurrence of interlayer are all specific to each river types. Generally, there are 2 kinds of interlayers formed respectively by vertical aggradation and lateral deposition in meandering river and netted river, and 3 interlayers formed by falling silt in channel bar, muddy lamina in the top of channel deposition and muddy lamina in sandstone respectively. Two interlayer distribution modes, i.e. point bar interlayer and channel bar interlayer, are generalized according to the geological property and logging reponse ofinterlayers and fluvial reservoir characteristic in Gudao oil field.4. Three distribution modes, vertical facies change controlling mode, lateral facies change controlling mode and sandstone interior change controlling mode, of remaining oil in fluvial reservoir are presented. It is demonstrated by statistics that, though high in water-cut, the main production layers are still of more recoverable reserve compared that of other layers, hi one layer, the lateral facies changes account for the formation of remaining oil, therefore, the higher discrepancy of reservoir property between main stream facie and lateral facies, the more saturated of remaining oil in lateral facie, and larger in accumulation zone accordingly, hi the inner part of sand-reservoir, the distribution of remaining oil varies as a function of rhythmicity, large pore and interlayer distribution.5. Based on the distribution characteristic of interlayer in thick positive rhythm oil layers and field injection-production situation, twelve injection-production modes of three types, that is, interlayer drilled by water wells, by oil wells, and existed between water well and oil well, are suggested. The remaining oil distribution rule under different injection-production modes and the controlling effect of interlayer on the remaining oil are studied. The results show that the influence of the interlayers on the remaining oil is dependent on the thickness, spread scale and vertical position of the interlayer. When interlayer parallels sandstone layer, the remaining oil is poorest if interlayer lay between water well and oil well, and is richest only if water well drilled interlayer and the upper part on the interlayer was shot in water well. When interlayer is not parallel to sandstone layer, the distribution of remaining oil was controlled by the relationship between interlayer and injection-production well and shoot mode.6. Targeting the different mode of residual oil distribution, the corresponding methods and approaches for enhancing the recovery ratio are proposed. According to the geologic characters of the Ng53 with thick positive-thythm oil layers, and top remaining oil enrichment rule during extra-high water cut period in Zhong 1 area of Gudao, the principle of developing the potential by horizontal well is proposed. The parameters, which include the position of the horizontal well, length of horizontal section, producing pressure differential, timing of liquid lifting and so on, are optimized. Field application achieved good results in 16 horizontal wells. Under the background of composite water cut is up to 93.7% and recovery factor up to 45.3%, initial oil production rate of horizontal well is up to 18-33.5 t/d, 3-4 times more than the vertical wells around; and composite water cut is only 38.8%, 30-50% lower than the vertical wells around.