Chemical blockage removal technologies for wellbore in production tail of low-permeability sour gas reservoirs:A case study of T2l11 gas reservoir in Moxi gasfield
The T2l11 gas reservoir in Moxi gasfield is a low-permeability carbonate gas reservoir with moderate-high sulfur content.To solve the problems of low production and shutdown of gas wells resulted from low formation pressure and severe wellbore blockage in the production tail,chemical blockage removal technologies for wellbore were studied.Based on the classification and statistics of wellbore blockage in low-pressure gas wells,the blockage mechanism was analyzed and the optimal blockage remover was selected.A typical blocked well of the T2l11 gas reservoir was chosen to conduct field test of chemical blockage removal.According to its property of low pressure,the key technological parameters were innovatively optimized,and two sets of chemical blockage removal technolo-gies,including wellhead blockage remover pumping and coiled tubing blockage remover flushing,were finally developed for gas wells with different degrees of blockage.The study results show that,(i)the wellbore blockages of T2l11 gas reservoir are mainly composed of organic matters formed by hydrocarbons and esters,as well as inorganic matters formed by FeS and Fe3O4;most of the blockages come from the corrosion products of downhole tools and pipes;only inorganic blockage removers have a dissolving and dispersing effect on blockages,among which CT4-12B has the best performance;(ii)the technology of wellhead blockage remover pumping is suitable for mildly and moderately blocked wells with certain flow channels,as well as severely blocked wells with short sections of blockage;the technology works best when the injected blockage remover is 0.5 m3 and the soak time is 24 h;and(iii)the technology of coiled tubing blockage remover flushing can effectively relieve severe wellbore blockage,however the operation difficulty increas-es below the kick-off point of wellbore;the technology works best when the injected blockage remover is 1 m3,the soak time of the vertical well section is 3 h and that of the inclined section is 24 h.The field application of the two technologies in the T2l11 gas reser-voir shows that a total of 12 wells,including 4 moderately and 8 severely blocked wells,have been unblocked,achieving good results with daily incremental gas of 24.1×104 m3,indicating that the two technologies are practicable and have certain reference significance for similar gas reservoirs.
Low permeabilitySulfur-bearingLow pressureWellbore blockageChemical blockage removalBlockage removerCoiled tubingT2l11 gas reservoir in Moxi gasfield
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