CHARACTERIZATION OF MICRO-PORES IN ORGANICRICH UNCONVENTIONAL RESERVOIR ROCKS

摘要

Physical measurements of pore-size distributions in many unconventional reservoir rocks are hampered by a combination of very small features that push the limits of many measurement techniques and the challenges associated with removing residual liquids from the pores. Organic-rich reservoir rocks that act both as source and producer are especially difficult to analyze because of the residual liquids,hydrocarbons and formation water that are trapped in the smallest pores. A combination of low-pressure gas adsorption and differential thermal analysis measurements are used to quantify the proportion and distribution of pores in the micro-scale(less than 5 nm). Pore-size estimation with conventional low-pressure gas adsorption using N2 has a lower limit of several nanometers,but is severely affected by the presence of organic carbon. The use of CO2 as the absorbent gas improves the size range down to 0.5 nm. Solvent extraction on small chips of sample was successful in removing small amounts of residual water and hydrocarbon that increased the total pore volume by approximately 10-20% compared to as-received samples. That volume increase was dominated by the very smallest pores,less than 5 nm,as measured with CO2 adsorption. Thermal analysis measurements verified the loss of water and light hydrocarbons from the extracted samples,while the more complex kerogen that decomposed at higher temperatures was less affected by the extraction. The solvent extraction step removed oil from the solid organic matter and opened very small pores in the sample. The combination of results indicated that a majority of pores in these organicrich samples fell in the 100-500 nm range and that only a small proportion were true micropores. While extraction of residual hydrocarbons opened up a number of very small pores,their contribution to the overall pore volume was small.