Effect of Sulfur Deposition on Rock Permeability in Sour Gas Reservoir

Abstract Reduction in pressure and temperature generally reduces the solubility of sulfur in sour gas reservoir. Once the reservoir fluid has reached a sulfur-saturated state, further reduction in pressure and temperature will cause sulfur to deposit. Sulfur deposition in the formation, induced by a reduction in the solubility of the sulfur in the gas phase, may significantly reduce the inflow performance of sour gas wells and even wells have become completely plugged with sulfur in sour gas reservoir within several months. In this paper, effect of sulfur deposition on reservoir permeability in sour gas reservoir was investigated from a laboratory perspective. A series of displacement experiments were conducted using gas sample with H2S mole concentration of 14.99% and 24.69%, rock sample of permeability of 1.37, 3.6 and 46.5 millidarcy, different flow rates of 3.25 and 12.5cc/min, and average pore throat size in the range of 0.1 to 1.0 um. Experimental results indicated that the higher of hydrogen sulfide concentration have a severe effect on sulfur deposition and subsequently the rock permeability decreased rapidly. When element sulfur grain size is more than average pore throat size, rock permeability changed strongly. Through a regression analysis, variation of rock permeability (K vs. P) was linear relation under high pressure, while approximate exponential function under low pressure. This work will help engineers evaluate accurately well deliverability in sour gas reservoir.