SCALE DEPENDENT OPTIMIZATION OF PETROPHYSICAL PROPERTIES

Abstract

Porosity plays a major role in oil and gas prospect determination. Hydrocarbons are stored in pore space so quantification of pores is of uttermost important. Water saturation and immersion techniques and other conventional methods have various limitation as all pores are not connected. Development of imaging techniques and computational capacity has taken the characterization of pores on different scales. In this work five different rocks Sandstone, Granite Gneiss , Dolomite, Limestone and Meta-Basalt are taken for detailed analysis on porosity determination and its manifestation on physical properties such as velocity. Porosity was distinctly different for different rocks. It was found that porosity measurement could be method and scale dependent within the same rock. Three measurements techniques were used for measuring porosity (i) Porosity calculation technique using a water immersion saturation technique (ii) Surface (Areal) Porosity calculation by using SEM images different resolution. (iii) Total porosity calculation from ultrasonic measurement. There is total of 5 order of magnitude difference in resolution across different techniques used for porosity measurements. The quantitative measurement of pores in reservoirs rocks like sandstone, limestone, dolomite at different scale have implication in developing exploitation strategies. As all rocks have range of porosity so, field porosity is assumed to be equal to that calculated from water immersion saturation technique. Elastic modulus of all rocks is calculated by ultrasonic method which is non-destructive method which depends on mineralogy, grain size, porosity and density. From the obtained results it was almost found same correlation between porosity and different elastic modulus in all rock types. Modulus of elasticity is decreasing with increase in porosity. The results show that scale of observation should be different for different rock types and generally can take 200μm scale of observation for porosity calculation. Dolomite showing exceptionally low porosity at scale of 1 mm and Granite showing exceptionally high porosity by ultrasonic methods (10 cm scale).