| The hydrocarbon accumulation condition of carbonate reservoir in Tarim Basin is superior, but the reservoirs are deeply buried, varying in types, complex in distribution, strong in diagenesis, result in diverse types of oil and gas reservoirs which bring many difficult problems in the oil and gas exploration and development. This article bases on the characters of carbonate reservoirs of the Tarim basin district, by combining theory with practice, a relatively perfect and practical fractured reservoir parameters calculation is established.It is difficult to divided the reservoirs and to calculate its parameters with the complex pore space and non-homogeneous of the reservoirs, through a large number of core observations, thin section analysis, physical analysis and the capillary pressure analysis, the rock characteristics and reservoir characteristics of Tarim carbonate reservoir are systematically recognized. Synthesize the results of mud logging, well logging and core observation and analysis, the reservoir is divided into the type of hole, fracture-vug, fracture and cave, the log response characteristics of the different types of reservoirs is analyzed as well. Before calculating the reservoir parameters, the logging curves are standardized to exclude the influence of non-geological factors and human factors as far as possible to ensure that the logging data can reflect the real situation of the formation and to improve the accuracy of the reservoir parameter calculation. On the basis of the analysis of the work area logging data, geological logging, core data, experimental laboratory analysis and oil test data, this article focus on the study of the following log parameter quantitative evaluation of various types of reservoirs, with emphasis on the analysis of the advantages and disadvantages of the methods which are practically used in the work area:(1)Core scale based on core analysis data to calculate the total porosity of the reservoir method; the evaluation method of calculating reservoir total porosity based on the volume model of carbonate reservoir double pores system characteristics; the evaluation method of calculating reservoir total porosity which utilize the stratigraphic component analysis model that apply the optimization principle to logging curves to reduce the formation heterogeneity, anisotropy and to correct the frame affect. Because of carbonates reservoirs bedrock’s low-porosity, strong heterogeneity, bad relativity between laboratorial core porosity and log calculated porosity, the calculation of reservoirs total porosity based on core scale method is not applicable to such reservoirs; volume model method is able to take full advantage of logging information, but cannot use the constraints, possibly causing the obtained solution meaningless; stratigraphic component analysis model to calculate reservoir porosity is a complex of multidimensional information which based on the geophysical inversion theory, and use the nonlinear weighted least squares principle to synthesize the logging curve, the theoretical logging response, the error and the region geological experience, and the optimization of mathematical principle is used to obtain the total porosity of the reservoir, making the calculated results more reliable.(2)Conductive path of crack formation can be divided into the cracks and block, the dual porosity model method of building relationship between block porosity,total porosity and crack porosity and calculating crack porosity by different conductive characteristics; world widely used method of crack porosity calculation which based on the reservoir fluid properties uses bilateral conductivity to calculate crack porosity; method applys simplified inversion to crack’s dual lateral logging and formation parameters to calculate the crack porosity.; method of calculating the crack’s joint opening according to its occurrence before calculating its porosity; single deep investigation resistivity can be used to calculate crack porosity when the data is incomplete; with the electrical imaging logging data, the ratio of crack opening area in the statistical window and the FMI image area ratio is the electrical imaging fracture porosity. Dual porosity model can obtained fracture porosity with conventional logging data, but m value may be inaccurate and make the fracture porosity range exceed the meaningful interval; the method of applying dual laterolog conductivity to calculate the fracture porosity assumes that the mud conductivity is the same with the formation water, but applies only to net fracture porosity calculation; the method of dual laterolog resistivity for crack porosity calculation is convenient, reliable in practical application, it also can provide continuous porosity curves, but will be affected by factors of mud, mud invasion and fluid properties; calculation of fracture porosity based on openness of fracture is influenced by the occurrence and the combination of characteristics of the fracture, and is only suitable for the single group of the fracture to calculate its porosity, when it comes to the net fracture, only qualitative discrimination can be done; the way of single deep laterolog resistivity calculation for fracture porosity solves the fracture porosity calculation problem of the lack of dual lateral logging data or shallow lateral is bad, but the scope of application is narrow FMI fracture porosity processing computing can obtain continuous fracture porosity, but deeply affected by the borehole conditions and mud, the porosity curve obtained through hand-pick fracture is not continuous, it can only reflect the macro-fracture but the micro-fracture.(3)Depending on the crack occurrence, there is a different relationship between laterolog conductivity with block conductivity and mud filtrate conductivity with openness of fracture, by the approximate expression to obtain the openness of different crack occurrence; Schlumberger uses the finite element method to calculate the difference response of laterolog of the crack occurrence, and proposed that use the differences of laterolog to estimate the fracture porosity, it could get the openness of network fracture from the high and low angle fracture. Use the laterolog logging data to calculate the fracture openness is an approximate method and the results subject to the restrictions of the crack occurrence and the judging of assemblage characteristics.(4)For these dual media reservoirs in carbonate rocks, fracture permeability is much larger than the block permeability, so the fracture makes a big affect of the reservoir permeability calculation; so it is necessary to discuss and divided the reservoir to different types. The permeability formula of the hole type reservoir is familiar with the general porosity reservoir; according to the experiment shows:fracture width and fracture permeability was a positive correlation; while the fracture-vug reservoir permeability include both the block permeability and fracture permeability.(5)Through the study of the core mercury injection data, there exists relatively highly correlation between unsaturation mercury saturation and porosity, average pore throat radius the relative sorting coefficient, it could establish the irreducible water saturation computational model of the hole type reservoir in this work area; according to the experiments of the French National Institute of Petroleum, as the fracture width decreases, the irreducible water saturation was significantly higher, on the basis of comprehensive analysis of mercury injection data and logging data, from the data study and known that:the irreducible water saturation of fracture type reservoir in this work area is high to83.81%,which basically reflect the bound water content of the matrix porosity in the fracture type reservoir; fracture-vug type reservoir belong to the dual media porosity reservoirs is the similar with fracture reservoir, the factor of the irreducible water could both consider the factors of two types reservoirs which is fracture reservoir and hole reservoir. (6)The hole type reservoir of carbonate accord with the pore conductive mechanism and it could be use the Archie’s equation to calculate the water saturation of the reservoir, but must be select rocks with a certain porosity and no micro-fracture strictly to do rock electricity experiments, meanwhile, the carbonate rocks belonging to the dual-pore structure reservoir, so the different reservoir space for holes and fractures in the two different electrical properties to establish the logging response equation of the dual hole structure to calculate the water saturation of the reservoir, further, the carbonate rocks contribute of the conductive subdivide into four parts:little pore throat of matrix porosity, connected matrix porosity, porosity of the fracture and shale, not only consider that the total conductivity of rock is the result of their multiple, but also establish the water interpretation model of multiple-pore structure reservoir on carbonate. Calculation results through this work area show that:the result calculated by Archie equation is often lower than the true value and the water saturation model of multiple-pore structure gives absolutely consideration effect of different type of pore, and the result is more correspond with well production test.The parameter evaluation method of carbonate above-mentioned through comparison repeatedly validated and optimized the parameter evaluation methods which are appropriate for this work area, the application effect is obvious. |
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