Methods Research Of Saturation Evaluation In The Fractured Carbonate Reservoir

With the development of oil and gas exploration in carbonate reservoirs at northeastern of Sichuan, hydrocarbon evaluation of fractured carbonate reservoirs in Yuanba area has become more and more important, among them the evaluation of oil and gas saturation is the key of quantitative evaluation.This paper takes the Changxing Group on the Permian as the main object of study, the developmental fracture and dissolution pore, the strong heterogeneity, the big anisotropy, the changeable lithology and the low matrix porosity makes the characteristic of this reservoir. Because of the multiplicity of pore structure resulted by fracture, the structure of reservoir space has become complicated, thereby it forms a fracture-matrix system contained uneven reservoir space of fracture and matrix porosity. So, we have to research the structure of reservoir space before the building of rational saturation, this paper has done lithology identification and fracture identification in the objective section, which can improve the accuracy of saturation model we built.This paper has done the collection, collation and analysis of the conventional logging data, mercury data, imaging log interpretation data, core analysis data sheet, physical properties analysis data and the testing of oil and gas and other information, we start the study from conventional log interpretation aspects, and bind the characteristics of fractured carbonate reservoirs at northeastern of Sichuan, plant to establish a set of saturation interpretation model based on the conventional logging data. Based on this, we carry out the following targeted aspects:1. Based on the lithology analysis, evolution of sedimentary facies analysis, structural analysis, stress analysis, fracture analysis, holes analysis and reservoir analysis from the imaging logging interpretation data, we describe the geological characteristics and reservoir characterization accurately.2. Based on core analysis data sheet, physical properties analysis data, binding the conventional logging data we have done the description of reservoir structure and the analysis of log response characteristics. From the lithology of reservoir, analyzed the log response characteristics of dolomite and limestone reservoir; from the physical properties of reservoir, analyzed the porosity and permeability, and found the strong heterogeneity, the big anisotropy and the developmental fracture in this area; from the electricity and the gas bearing, analyzed the electrical characteristics on the basis of the gas reservoir, found the differences between the deep and shallow bilateral resistivity can reflect the gas-bearing reservoir.3. We have analyzed the spatial structure of carbonate reservoir, found that this area mainly developed pore, fracture-pore and fractured reservoirs, then we take the fracture-pore reservoirs as the main subject to study in depth. We make the capillary pressure curves based on mercury data to research the reservoir spatial structure, from the influence of the presence or absence of fracture, the difference of lithology to the form of capillary pressure curves, we have confirmed the different lithology and presence or absence of fracture can influence the evaluation of saturation through influencing the structure of reservoir.4. Logging curves can reflect the lithology, its Vertical resolution is high. Based on the lithology from the pore analysis, binding the logging response characteristics we used Fisher and analysis of mineral components to identify the lithology in well YB1, got the lithology prediction of Changxing Group, and achieved a certain effect. We can determine the amount of the mineral composition of the matrix from the analysis of mineral components, then calculate the logging response accurately, lay the foundation for the calculation of reservoir porosity.5. From the conventional logging data, research the logging response of fracture, choose the rational characteristic parameter values to identify the fracture. When the fracture exists, it will be reflected in the logging curves of lithology, electricity and physical properties, we use the intuitive judgment method to identify the fracture. At the same time, extract the sensitive information to the response of fracture and combine them to form new parameters, then use the integrated probabilistic method to add up these parameters and identify the fracture continuously.6. Based on the double porosity model calculate the matrix porosity and fractured porosity, compare its results to the core analysis data and imaging logging interpretation data, then find they can match well. Meanwhile research the cutting conditions of fracture to matrix system when the mud is invading, then use the reflection of bilateral resistivity on the water saturation to build different equations and calculate the matrix saturation and the fractured saturation, obtain the water saturation through weighted average at last. The water saturation calculated can match to the saturation of core analysis very well, it confirms that the saturation model we built can play a very good effect in this area.