Log Evaluation Of Tight And Low Resistivity Reservoirs In Suotu Oilfield

In recent years with the oil price going up, the field of oil exploration has been extended and prolonged. With the oil exploration and development, the roles of advanced technology in the progressively development of tight (low-permeability) and low resistivity reservoirs has become more and more important.The low-permeability always results in low-resistivity reservoir. The identification of the low-permeability and low-resistivity reservoir has been one of the urgent problems in the oil field. If we want to find out the oil and gas reservoirs, the well logging skill is the crucial performance in varies of key technologies. It is very necessary to study the identification of the low-resistivity oil/gas formation for low-permeability block. In this paper, through exploring the method of well logging, identification of the low-permeability and low-resistivity reservoir with the Suotu oilfield as an objective area. There has formed a system of well logging identification which fits the reservoir in this block. Suotu oilfield is located in Qian'an County, Jilin province, near the Daqingai field. The exploring formation is the Gaotaizi oil reservoir in the second and third section of Qingshankou group. The structure is located in the centre-south of Changling concave in the centre concave of Songliao basin. Although the field has a small scope, it is a very complicated basin. The decrease of resistivity of oil reservoirs resulted from the small construction rate, fine grain, small pore and throat and the high shale content, has made the identification of reservoir fluid to become hard.This paper studied the cause of formation mechanism for Suotu low-resistivity reservoir through the study of reservoir geology and petrophysical experiments. On this basis, establishing the well logging interpretation model, studying the effective and practical new projects aimed at the low-resistivity reservoir identification and evaluation of needs, which form a integrated identification technology system for Suotu low-resistivity and low-permeability.On the basis of the deep study of reservoir structure, deposition and lithology, physical properties, fluid characteristics, the low-resistivity factors of Suotu reservoir were divided in this paper into two types: internal and external. The internal factors include:1. Small pore and small throat which result in the high content of irreducible water;2. The low structure amplitude and wide oil-water transition zone which result in low oil saturation and high free water saturation;3. High formation water salinity;4. High clay mineral content; The external factors include:1. Freshwater mud invasion;2. The high resistivity of part calcareous rock which resulted in a relatively low-resisitivity reservoir.Combination of the oil reservoir characteristics of Suotu, developed the study of rock conductivity experiments, it can result that the formation factor and porosity, increase index of resisitivity and water saturation of Suotu oilfield showed a good linear relationship in the two-coordinate system and coincided with Archie formula. And study the effective of formation water salinity and shale content of reservoir to rock conductivity parameters, study the well logging interpretation models of low-resistivity reservoir, and established a logging interpretation which fits low-resistivity reservoir of this field. Established the quantitative formula of porosity, permeability and saturation by application of the core analysis information and well log, and formed a resisitivity ratio method, low-resisitivity ring identification method such oil and water layers recognization methods. The application of NMR interpretation method and the fluid identification in the low-resisitivity in the low-resisitivity reservoir were also discussed.Through the application of the results in Suotu oilfield, the accuracy of the secondary processing and interpretation of the old well has been greatly improved, well processing and interpretation of the new well rate of 15%, hit testing rate reached more than 90% .Through an increased measurement of high frequency induction logging and the use of low-resistivity ring interpretation method find the new oil-resistivity reservoir and increased the productivity. A combination of conventional and new technology, the mutual certification of qualitative and quantitative of the integrated identification technology has formed for low-resistivity reservoir of Suotu.