Mechanism Of Remaining Oil In North-Two-West Area,Daqing Oil Field

With the oil field coming into high water cut stage, the distribution of water and oil becomes very complicated, remaining oil exists with sporadic state. The distribution features and types of remaining oil are varied, while they are integrally gathering at parts of area. Heterogeneity of reservoir causes remaining oil. Therefore, in order to enhance the oil recovery, we should anatomize internal structure of the reservoir and depicts the typical structure style leads to the remaining oil, which will guide the application in other areas.The target district is located in Southwest of Saertu oil field,which is delta plain and delta front system, in which exists Saertu and Putaohua oil layer, and both of them are clastic reservoirs. The district has 6 sets of well patterns with about 100 meters high density at present, which has experienced 3 times large scale adjustment since the major reservoirs put into exploitation in 1964.With the incessant exploitation, we have faced these problems in Saertu oil field as follows:high integrative water cut, high oil exploitation speed rate, high degree of oil production, a low recovery and low reserve-production ratio, which lead to large scale flooding area and complicated oil-water distribution. Besides,the development contradiction of target oil layers has turned from early interlayers to in-layers. The situation of high exploitation and low oil recovery ratio puts forward higher requirement on the study of remaining oil.The reservoir is the key factor to control the remaining oil, especially the large scale and contiguous distribution sandstone with high heterogeneity and complex internal structure. First of all, from the point of reservoir, describing the internal structure of reservoir to study the remaining oil between wells. Secondly, analyzing the plane distribution of remaining oil through the injection production relationship. Finally, a comprehensive analysis of the reservoir internal structure and the plane distribution of remaining oilto study the mechanism of remaining oil. This article we use the following method to do the research:using the basic geological data and well logging data to divide the sedimentary microfacies, which can be the foundation for the later study on the mechanism of inspection wells and remaining oil formation; and then, makes statistics about different flooding characteristic of different sandbody types, and makes clear potential sand types full of remaining oil. Finally, according to the relationship between injection production effect characterizations of injected water movement trends revealing the scale flooding relation. And, adopting geological analysis thought, analyze the mechanism of remaining oil and make a summary about architecture structure leading oil to be masked off by using the methods of anatomy of the internal structure of the reservoir. Some works have been done as follows:1. Based on interlayer contradiction geological and well log data, combining with depositional environment and achievements of formers, these sedimentary microfacies of Saertu and Putaohua oil layers have been maken clear. The 7 main types of sedimentary facies are identified:distributary channel microfacies, main thin sand microfacies, non-main thin sand microfacies, inter-distributary microfacies, subaqueous distributary channel microfacies, the main sheet sand microfacies, non-main sheet sand microfacies.Beside the horizontal distribution of sandbodies and differences of reservoir architecture have been acquainted. All the study provide the foundation for analysis of distribution and formation of remaining oil.2. In study area, the statistical analysis of four adjacent inspection wells are conducted. Firstly, according to the statistic results of four inspection wells, the sandbody type is divided into 10 types which are the bottom of channel sand, the middle of channel sand, the top of channel sand, the thin-layer tabulated reservoir, the bottom of tabulated reservoir, the middle of tabulated reservoir, the top of tabulated reservoir, the isolate untabulated reservoir, the bottom of untabulated reservoir and the top of untabulated reservoir. Then,on the basis of the accurate water-washed results of the inspection wells, the water-washed characteristic of all the sandbody types are analyzed intensively by which the analysis of the different water-washed characteristic in different sandbody types and the same water-washed characteristic in different sandbody types. And the potential of residual oil is investigated, including the sandbody types and where the remaining oil exists.3.Considering relative position between producing well and injecting well and perforation position in section, distribution plot of planar flooding are drawn through the detailed flooding data and history of well pattern. Then adopting the thought of "low level older wells and high level new wells", the flow trends of injecting water are finally depicted, which interpret the low level flooding area and potential position.4.Dissecting the sandbodies internal framework of this area in each layer at the foundation of above works, this article analyzes the mechanism from geology insight and makes a summary of 6 kinds of typical sandbodies internal framework types as follows,1 super sandbodies terminal screening;2 ectopic sandbodies screening;3 channel sandbodies cutting screening;4 interlayer screening in point bar of meandering river;5 sandbodies transitional zone screening;6 super channel leading screening, which make oil screened easily. At last,4 kinds of remaining oil distribution types are generated:1 sandbodies structure screening producing remaining oil;2 mud-veins controlling oil;3 deficient well patterns producing remaining oil;4 remaining oil in non-major thin sandbodies.Comprehensive, this paper has a new understanding of the geological characteristics about Saertu oil field in North-Two-West area through the field data and a lot of basic geological work. We can pinpoint the types of sandbody and distribution characteristics of the remaining oil in this area by the satistics of sandbody types and water-washed characteristic of the inspection wells. And then, dissect the internal architecture of sandbody in the low degree of water flooding parts according to the interpretation results of inspection wells. So we can summarize the structure style of the remaining oil produced and discuss the oil controlling mode, which provides a reference for the next stage of oil field production and adjustment.