Characteristics of Gas Reservoirs with High Content of H2S in the Northeastern Sichuan Basin and the Consumption of Hydrocarbons〖KG*2〗due to TSR

Key words: 
• hydrogen sulphide(H2S)

Abstract: During the recent years, several medium and largescale gas fields, such as the Luojiazhai, Dukouhe, Tianshanpo and Puguang, etc, whose most remarkable features being the higher H2S contents, have been discovered in the northeastern Sichuan basin. Their H2S contents among the gas compositions account for 10 to 17 percent while the average being 14 percent. Based on the thorough study, it can be found that although these largescale oolitic shoal gas reservoirs usually have rich reserves along with high individualwell producing rate, their coefficients of fullness, which ranging from 25 to 91 percent, are generally rather low, also, their pressure coefficients are not high and mostly less than 1.2. According to their reservoir forming conditions, i.e., the abundant oolitic dissolution pores, the efficient reservoirs with huge thickness, the robust gas source, the welldeveloped transport systems, together with the excellent seal ability of the caprocks constituted by shale and gypsolyte, their lower coefficients of fullness were possibly due to a large quantity of hydrocarbons had been consumed or depleted within the traps. In the northeastern Sichuan basin, due to the H2S contained within the Feixianguan formation was generated from the TSR reactions, which occurred within reservoirs, between hydrocarbons and sulfate, there exist negative correlations between the H2S contents and the pressure coefficients, the reservoir water salinity together with the hydrocarbons contents, etc. Therefore, as far as the gas reservoirs with high H2S contents of the Feixianguan formation was concerned, their lower pressure coefficients and coefficients of fullness are likely caused by both the hydrocarbons had been consumed greatly due to TSR and the volume of reservoirs had been expanded.