Petrophisical Evaluationonthe Microfracture-typed Complex Carboniferous Carbonate Reservoirs In The Eastern Margin Of The Caspian Sea Basin

The microfracture-typed complex Carboniferous carbonate reservoirs in the eastern margin of the Caspian Sea basin have the characteristics of complex sedimentary setting, frequently changing in lithofacies, complicated diagenesis process, rich in diagenetic fissures and strong heterogeneity, etc. In this article, guided by the theories of carbonate sedimentology, reservoir geology and well logging geology, etc., with the combination of core analysis, well logging and field production data, by the aid of mathematical statistics, the techniques of cross plot and the re-construction of well log curves, an in depth study of carbonate reservoirs has been carried out in such aspects as rock types, sedimentary settings and features, types of storage spaces, characteristics of pore structures, and the fracture scale and characteristics, etc., and a multi-dimensional multi-parameter characterized all in one well logging appraising technology is built up, and a set of fissure-typed complex carbonate reservoir oriented well logging appraising method is developed.Researches in storage spaces of complex carbonate reservoirs show that different types of pores vary in microscopic pore structure. From the views of the scale and genesis of fractures, the development features of fractures in the area has been analyzed, and based on the combination patterns of storage spaces of reservoirs, reservoirs are divided into five types which are composite type of pores, fractures and vugs, fracture-pore type, pore type, fracture type and scattered-pore type. Different types of reservoirs vary in physical features, and the composite typed and the fracture-pore typed reservoirs which constitute the principal reservoirs in the area have the best physical property, and the next is pore typed. The physical property of the fracture typed reservoirs is determined by the scale and permeability of the fractures, and where fractures develop well may develop this type of reservoir. The scattered-pore typed reservoirs are characteristic of low permeability and high porosity, and generally are not producible.The well logging responses characteristics of reservoirs of different lithology, pore type, reservoir type and bearing different fluid have been summarized, and a database of typical well logging response characteristics is built to identify reservoir type quickly in various circumstances.On the base of core analysis and petrophysics, a rational well logging model for lithophacies interpretaion is established, with which, the percentage of principal minerals of the carbonate formation can be calculated, and with the help of geological data, core data and well logging response characteristics, the sedimentary facies and micro-facies can be identified, and the facies distribution features can be described.By the aid of core sections, mercury injection data and well logging data, fractures genesis and scale in the area is studied, and fracture identification is realized by the means of conventional well logging data and imaging well logging data, etc. Based on core calibrated well logging data, fracture porosity can be calculated from the logarithm of the difference between the deep and shallow lateral resistivity curves, further, according to its relationship to the permeability increment factor, the total permeability of reservoirs can be calculated and which is one of the innovative points in this research work.Based on core data and storage space classification, a theoretical tri-pore volumetric model is built, and on the basis that the acoustic transmit velocity is a function of pore type, a way to calculate the scattered porosity is worked out, which makes it a reality to calculate the porosity of connective, scattered pores and fractures of complex carbonate reservoirs, and which is the second innovative point in this research work.Following the mechanism of electricity conductivity of different porosity models, a research is performed in variance in the porosity index m and the saturation index n of different reservoir types. It shows that the occurrence of fractures in porous carbonate reservoirs may cause a decrease in m, and an increase with the occurrence of vugs, and microfractures have little influence to m value, and that saturation index n has no obvious relation to reservoir types which is subject to complex influence factors.Based on core data, core sections and well logging data, the cutoff values for different reservoir types are determined by the aid of multi-parameter cross plot technique, furthermore, it comes true that pore types of complex carbonate reservoirs are quantitatively appraised, and reservoir types successively identified by well logging data, which is the third innovation point in this research work.To calculate intensity of produced liquid by layer by the aid of production profile testing data, furthermore, with the combination of well logging interpretation result, the productive capability of each pay layer is appraised, and from good to poor, by the rank of reservoir quality, the well logging interpretation criteria of seven types of reservoirs is established.In this article, aiming at the correct identification of reservoir type, the quantitative appraise of different typed pores and microfractures, by the utilization of such key techniques as the fracture characteristics analysis, diagenesis model analysis, reservoir type classification, identification and quantitative appraise of microfractures and quantitative appraise of pore types, with the combination of theoretical research in the aspect of petrophysics, a set of innovative well logging appraisement approaches and technologies for microfracture typed complex carbonate reservoirs are developed, which increase the accuracy and reliability of well logging appraisement of complex carbonate reservoirs, and provides important basis for reserves appraising and field development programming of such type of reservoir.