The Research and Application on Microscopic Pore Structure in XingNan Development Area
|School||Ocean University of China|
|Keywords||pore structure microcosmic remaining oil deposition diagenesis oildisplacement efficiency|
In high water cut period of old field, tapping the potential of remaining oil becomes more and more difficult, therefore, the reservoir research is developing toward the fine and quantitative direction, from the reservoir microscopic features, making clear fluid percolation mechanism in reservoir is effective way to enhance the accuracy of prediction of remaining oil distribution, but the gap between the macro and micro characteristics in reservoir is great, how to establish the link between the two, to integrate macro and micro research findings, and to predict the distribution of residual oil is still in the trying and development stage. In this paper, in the theory of sedimentary petrology, reservoir physics and reservoir engineering, in Xingnan oilfield, the Portuguese formation as an example, the reservoir sandbody types, pore structure, percolation characteristics and mode of occurrence of microscopic remaining oil are studied respectively. The sand body types are as the research object, pore structure types are as unit division, the remaining oil distribution law and potential tapping measures in different reservoir are put forward.In the paper, microscopic and flow characteristics of different reservoirs are studied in detail first with the data of integrated core, mirror, porosity and permeability analysis, mercury, displacement experiment and numerical simulation methods. The pore structure of the reservoir is divided into five categories, from one class to five class of the pore structure of the reservoir, particle size becomes finer, pore structure variation. The geological effect on the pore structure is Analysised. The sand body size is more coarse under the conditions of strong hydrodynamic, and average pore throat radius is more greater, the ratio of big pore throat that contribute to permeability is greater. Various reservoirs are modified in different degrees by Diagenesis. The lower the permeability of the reservoir is, the higher the reduction of porosity is by the compaction and cementation. The rate of enhanced hole of reservoir is higher by the dissolution. Since the pore structure characteristics are different, its flow characteristics are varying. From the first class the fifth class, the irreducible water saturation increases, the oil phase permeability changes faster, oil-water coexistence zone is reduced, water permeability decreased, and moisture content increases quickly. It’s showed that the reservoirs with better pore structure are more evenly.With core displacement experiment, micro percolation simulation and remaining oil study of visible fluorescence, remaining oil distribution in reservoirs with different pore structure is different:residual oil in the reservoir with the first and the second class of pore structure includes:pore throat remaining oil vertical to water flow, corner, adsorption of remaining oil caused by the heterogeneity and partial oil on hole wall. The pore throat radius of the other three kinds of pore structure are smaller than the previous two types of pore structure, intergranular residual oil is increases. In addition, the pore throat ratio increases and the wettability of partial hydrophilic, block, Jia Min effect increases, so that the cluster remaining oil increases.There are different combinations of pore structure in different sand body. The distributary channel sand body have the first, the second and the third class of pore structures, the properties at the lower part is better than the upper reservoir, the type of residual oil include the pore throat shape, corner shape, adsorption and membrane shape in lower part of reservoir. Changing the direction of injection, injection of polymer method can be used to enhance water oil displacement efficiency. There is more residual oil in the upper reservoir; it should be output by separate mining or drilling of horizontal wells. The pore structure type of sheet sand reservoir includes third, fouth and fifth type. In this kind of reservoirs, the pore throat radius decreases and small pore throat increases, but99%permeability contribution is provided by50-70%big pore throat, small throat oil unused, so intergranular residual oil is more. The remaining oil in the pore throat includes the corner shape, clusters form. This kind of reservoir should consider the use of fracturing method to improve the producing degree, increase oil recovery with polymer flooding.Research in this paper has guide significance on fine determine remaining oil distribution, designing enhanced oil recovery scheme and tapping the potential of residual oil.