| Currently, the fractured low permeability reservoirs have a low degree of producing and the effect of low permeability oil field developing is not good, both of which are associated with the distribution of fracture in reservoir. Therefore, development countermeasure research of fractured low permeability reservoirs has important theoretical and practical significance for expanding its reserves, improving the development effect、recovery efficiency and the level of overall development of low permeability oil field. In particular, as the high permeability layers mainly in old oilfields in eastern China are gradually entering medium-high water containing stage, developing such oilfields reasonably with high efficiency undoubtedly has a long-term strategic significance to the sustained stable development of China’s petroleum industry.Ansai Oilfield is an ultra-low permeability oilfield, with poor reservoir properties, and micro-fracture development lead to a strong reservoir heterogeneity. The existence of the cracks plays a dual role for the development of low permeable oil fields.On one hand, cracks improve the permeability of the reservoir and increase the absorbent capacity of the reservoir, which make up for the lack of penetration, thus greatly improved the seepage flow and the production capacity of the wells.On the other hand, the crack system exacerbated the heterogeneity of low permeable oil fields, which lead to the injected water’s one-way onrush, oil well water’s quickly rises and soon flooding, while the injection effect of cracks lateral wells is in vain. Inhomogeneity of the injected water promote to the lower degree of reservoir using, which lead to a large amount of oil remaining in the formations.Data for oil and gas reservoir description generally come from comprehensive methods of geology, logging, core analysis, fluid physical analysis and well testing. The mutual complementation of those methods keeps them in constant adjustment in contradiction demonstration, finally discard the gross and retain the essential. Among these methods, well testing is the only way that can achieve the description of reservoir performance and monitoring of flow parameters. It is significant for the rational use of finding formation parameters and the accurate explanation of well testing data.At home and abroad, well test interpretation models of fractured reservoirs are mainly the crack models, including dual-medium model (matrix and cracks), triple-medium model (matrix, cracks and caves) and vertical crack model. The research of percolation characteristics of these kinds of oil and gas reservoir, well test curve characteristics and well test interpretation method are more mature. But for complex sandstone fractured reservoir (reservoir with irregular high-angle fractures in tight sandstone), the current well test data processing and interpretation software can’t accurately evaluate the well test data of irregular fractured reservoir.In recent years, much more attention has been paid to well testing in Ansai oil field exploitation. The well testing data are abundant, which provide essential original materials for the oil and gas reservoir recognition and reservoir evaluation. However, due to the complexity of oil and gas reservoirs, there are still some difficulties in the interpretation of well testing data. To meet the needs of further exploration, researches on a proper set of interpreting methods that fit the corresponding reservoir and the effect of cracks on waterflooding should be carried out, which is significant for either exploitation service or economic benefits.This study bases on a large number of literature research and summing up the results of previous studies, studing on Ordos Wangyao area, focusing on Wangyao crack distribution characteristics, establishing the corresponding geological model and interpretation method;on the basis of the previous research,analysising the exiting data of Wangyao area, the interpretation of results combining other production materials establish crack grading standards of Wangyao area. Recognizing the different levels of fractures on waterflooding effect can help improve oil recovery and ensure stable production of WY area,we get the following major findings:1、A comprehensive analysis of the reservoir geological characteristics of the study area has been done, including sedimentary features, characteristics of the sand body distribution and the reservoir characteristics.2、A lot of statistical work for distribution characteristics of natural fractures of Wangyao area has been done, such as stratigraphic section, the core cast thin that can observe the pound sign and its plane distribution of fractured wells. Application of paleomagnetic methods and imaging logging the methods have also been used for a clear understanding of the spread of crack orientation.3、A lot of statistical work for distribution characteristics of artificial fractures of Wangyao area has been done. First, the data of18wells which are monitored real-time by the micro-seismic and the district of fracture orientation, height and occurrence statistical are analyzed;tracers monitoring data of18injection wells of Wangyao area have been analyzed;64oil wells which the hydrous reached100%have been done a statistical;analysis aquifer rising velocity and pressure variation characteristics of the cracks in the main and lateral direction wells.4、The curve of Wangyao area can be divided into the following four categories through analysis and summary:homogeneous, compound, overlap and fracture type curve. The static pressure, permeability and the plane distribution characteristics and variation characteristics of well test model have been studied based on the summaring253wells testing data interpretation.5、Depending on the type of water breakthrough fracture in Wangyao area,combined with the crack length which dynamically determined and other factors, the72macro cracks of current distribution were defined as Ⅰ,Ⅱ,Ⅲ cracks; according to the relationship between fracture half-length and permeability of oil and water wells, the artificial cracks are defined as large, medium and small crack; discrimination method and evaluation method of crack formation were established.6、Four crack lines in the east of Wangyao area and six well groups of the midwest, a total of18wells and production performance of92Wells were analyzed; combined with water driving front and well test data, the impact of fractures on waterflooding development effect has been studied.7、Evaluation of improving the cracks seepage measures such as well spacing encryption, strengthened water injection along fractures and injection wells deep profile control measures have been made, and reasonable method to improve the development effect and water flooding adjustment measures have been put forward. |
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