Perm Journal of Petroleum and Mining Engineering (Sep 2019)
Analysis of the fractal structure and stochastic distribution of pores in oil and gas reservoirs
Abstract
It is known that the natural potential of terrigenous reservoirs’ capacity significantly depends on interparticle porosity and particle packing type. Other significant factors that impact reservoir porosity are the shape of particles and the proportion of content and distribution of particles of various sizes in the rock. The attempts to simulate a net effect of factors influencing the multimodal distribution of interparticle porosity are well known; some of them are discussed in this work. The simulated data will be compared with actual measured data, obtained from particle size distribution analysis of core samples from a well-known and long operated oil and gas field in Azerbaijan. For the purpose of the survey, these measured data were generalised and analysed in detail. The research covers the most typical for the region particle size fractions: pelite, silt, fine-grained sand, and medium-grained sand. Pie charts of the particle size distribution analysis results indicate that in the first group of rocks (argillaceous silt sand) the largest portion is represented by 0.175 mm particle size fraction. Two other particle size fractions of 0.055 and 0.01 mm constitute approximately the same potions, and, finally, the coarse-grained fraction (0.25 mm) represents an insignificant part of the total rock volume and may be neglected. Though the apparent correlation between porosity quality and such factors as particle size distribution and mechanical densification of sediments were identified, still the calculated paired correlation coefficient between particle size fractions and parameters, used to average particle size distribution and sort rocks by their type have shown that these are two independent and unrelated functional dependencies. At the same time, the influence of particular fractions and, which is more important, the influence of their proportions on the interparticle porosity is not the same. A more detailed simulation of multimodal distribution has shown that in this case, the use of fractal concepts proved to be more efficient. As an alternative, we have analysed a method for the evaluation of rock oil-bearing properties based on calculated dependence between the fractality index and oil saturation.
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