| Yuanba gas field is an acid large-scale marine gas field with deep burial,high development risk and high construction difficulty.The buried depth of the gas reservoir is 6500-7100m,the gas reservoir pressure reached 66-72MPa,and the gas reservoir temperature reached 145-160℃.The average content of H2S and CO2 in natural gas is 5.53%and 9.31%respectively.With the continuous development of high-sulfur gas reservoirs in China,the development of the Yuanba gas field in the Sichuan Basin has received much attention.In recent years,some gas wells have experienced different degrees of wellbore blockage in the process of production,which resulted in the decrease of the single well production and the increase of the cost of unblocking operations.Therefore,it is very necessary to study the plugging mechanism and unblocking measures of the wellbore.This paper analyzes the physical properties of plugged materials and basic components by chemical analysis methods,analyzed its main components and sources.According to the components contained in it,in order to achieve high-efficiency unblocking of the wellbore,the molecular structure of the plug removal agent was designed,and a new plug removal agent was developed.In order to enhance the general utility of pipe-freeing agents,the compound plug removal agent formulation was developed.Finally,evaluated it compatibility of the stratum,static corrosion,temperature resistance and blockage removal performance.This paper mainly studies from the following aspects:(1)Macroscopic photography and particle size analysis of plugs by stereo microscope and digital camera;thermogravimetric analysis showed that the weight loss rate of plugs was 53.64%between 230～510℃,Therefore,the mass of organic components in the plug was 53.64%;SEM analysis of the plug showed that the edge and surface of the debris were enriched with organic compounds.The main elements of EDS analysis were confirmed by XRD analysis.The inorganic components were mainly FeS2 and BaSO4.the relative percentages are 86.53%and 13.47%,respectively;the FT-IR analysis of organic components shows that the stretching vibration of CH3 and CH2 occurs in the II and III regions,indicating that the plug contains alkanes organic compounds.It can be concluded that the asphaltene mixed hydrocarbon substance.(2)From the source and cause analysis of natural gas in the Yuanba area,the superheated chemical sulfate reduction occurred in the Yuanba gas field in the early stage,causing four factors in the wellbore blockage of the Yuanba gas well,firstly the sulfur deposition factor;followed by the dispersion migration of the asphaltene impurity molecules;further due to the formation of well hydrate in the shallow well section of the gas well;finally,due to the incompatibility of the well fluid with the formation water or the lack of temperature resistance,mixing with the inorganic matter to form insoluble residue deposits caused the wellbore blockage.(3)From the perspective of the effective dissociation,dissolution and dispersion of the organic components in the role of cementation and coagulation,the development of plug removal agent(D-XL)is carried out,and then compound plug removal agent is developed on this basis.The compound plugging agent is:20%D-XL+25%inorganic acid+8%chelating agent+20%sulfur solvating agent+15%ethanol.Compatibility experiment of compound plug removal agent with formation water was studied.When the formation water salinity is less than 170000 mg/L,the compatibility was good.The corrosion rate of P110 coupon is 0.3517 mm/a in the mixed medium of de-plugging agent and formation water(1:1).Due to the inorganic acid component in the compound plug removal agent,the corrosion rate is slightly higher than that of the formation water with a chlorine ion content of 24.26g/L;at the temperature of 20～120℃,the dissolution efficiency of the plug is gradually increased.When the temperature was 120℃,the ability of the solution to dissolve the plug was 41.2%. |
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