Quantitative characterization of pore structure based on PCAS:A case study on Qianfoya sandstone in Guangyuan,Sichuan,China
In this study,we analyze thin slices of images of sandstone in the Qianfoya Formation in the Guangyuan area to quantitatively characterize its pore structure by using pores/particles and cracks analysis system(PCAS),and discuss measures to improve the accuracy of porosity identification by using this software.The results showed that the pores identified by the default single-threshold method of segmentation of PCAS were inconsistent with manually identified pores.The porosity of the sandstone calculated by PCAS was also too high,at 31.21％.To improve the identification of pores by the software,we preliminarily optimized the images in Adobe Photoshop,and then used a multi-threshold method of segmentation to set the tolerance of each threshold according to the difference in color between pores in the image slices.The resulting calculated porosity of sandstone was 14.18％,the pores were correctly identified,and the software was able to accurately represent the internal structure of sandstone.A comparison was made between the porosity after optimization,the porosity identified by the default single-threshold method of segmentation,and the face ratio estimated using the thin slices of images,revealed that the optimized porosity was close to that estimated by using the thin image slices,with a difference of only 1％～2％.And refer to the porosity which was obtained from previous tests on the physical properties of reservoirs in adjacent areas,it can be confirmed that the result has a certain accuracy.Moreover,PCAS was able to quickly and accurately extract various characteristic parameters of the pores.This is important for the study of pore genesis,pore evaluation,pore characteristics,gas injection mechanism and seepage network.These results confirm the potential of using PCAS for the quantitative characterization of pores.
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