Characterization of Pore Structure inCarbonate Rocks of Luojiazhai Gas Field and Study onSulfur Deposition Damage under Water Conditions

Abstract High-H 2 S gas accumulations in the Sichuan Basin commonly produce water during the production process and sulfur deposition phenomenon occurs, resulting in lower permeability of the reservoir, which greatly restricts the efficient development of gas reservoirs; however, there has been no systematic study of the harm of sulfur deposition under the presence of water so far. To this end, this paper takes the carbonate rocks of Luo Jiazhai gas field in Sichuan Basin as the research object, and carries out cast thin section and X diffraction experiments to quantitatively analyze the rock and mineral characteristics of the research block, and combines scanning electron microscopy, nuclear magnetic resonance and CT scanning to quantitatively characterize the pore-throat parameters and morphology of the reservoir rock samples; on the basis of which, seven core samples with superior petrophysical properties were sampled., and sulphur deposition experiments are carried out with different water saturations and different experimental differential pressures to analyze the characteristics of sulphur deposition injury. On this basis, seven rock samples with good physical properties were selected to carry out sulfur deposition experiments under different water saturations and different experimental pressure differences, to analyze the damage characteristics of sulfur deposition, and to obtain the location of sulfur deposition by combining with NMR and CT scanning. The results show that the reservoir rock types in this area are dominated by calcite and dolomite, the reservoir space types are mainly dominated by intergranular pores, intragranular solvation pores and microfractures, the reservoir rock samples throat are dominated by punctate throat and lamellar throat, and the average value of pore radius is 47.53 μm, and the average value of throat radius is 21.72 μm; the porosity, permeability and pore-throat structure of the samples have not been changed after nitrogen contrast experiments, and the sulfur deposition injury After the experiment, based on the NMR T 2 spectral curve shifted downward to the left and the increase in dry weight of the rock samples indicated that there were sulfur deposition products generated, which was verified by the energy spectral analysis; through the joint characterization of the sulfur deposition location by scanning electron microscopy, CT scanning and NMR. Analysis shows that the sulfur deposition of the class Ⅰ samples was concentrated in the range of 0.01-60μm, and that the class Ⅱ samples were concentrated in the range of 1-30μm, and the interconnected pore structure in rock samples became worse and the porosity and permeability decreased after the sulfur deposition. After sulfur deposition, the pore connectivity of the rock samples deteriorated, the porosity and permeability decreased, and the larger the experimental pressure difference, the larger the degree of sulfur precipitation impairment, the higher the water saturation of the rock samples the smaller the degree of sulfur precipitation impairment, but the degree of sulfur deposition damage basically does not decrease when the water content reaches about 36%.