Hydrochemical characteristics and genesis of Xujiahe Formation formation water in Jianyang,central Sichuan:evidence from hydrochemistry and strontium isotope
In recent years,significant achievements have been made in the exploration and development of tight gas in Xujiahe Formation,Sichuan Basin,with the Jianyang block in central Sichuan being a new focus area for increasing reserves and production.However,in the development process,a large amount of formation water was encountered during drilling,which led to a decrease in reservoir gas permeability,resulting in a gas production decrease and hindering further exploration and development.Therefore,there is an urgent need to study the source and genesis of the formation water in the study area.In this paper,formation water chemical parameters and strontium isotopes are used to systematically analyze the formation water of nine drilling wells in Xujiahe Formation of Jianyang block,Tianfu Gas Field,central Sichuan.The results show that:(1)The formation water of Xujiahe Formation in Jianyang area,central Sichuan is of type CaCl2,with an average mineralization degree of 85 969.70 mg/L,an average sodium chloride coefficient of 0.77,an average metamorphic coefficient of 7.72,a majority of 0 desulfurization coefficients,and an average cation exchange coefficient of 0.252,indicating that the formation water of Xujiahe Formation is in a closed environment.(2)The mass concentration of Sr2+,Br-,and Li+in the formation water is 146.00-1 980.00,207.00-1 510.00,2.47-22.60 mg/L respectively,which is much higher than that of seawater.It can be used as a characteristic parameter for the formation water of Xujiahe Formation.(3)The formation water has the characteristics of Ca2+enrichment and Na+and Mg2+depletion,which is related to the dissolution of calcium-containing minerals in the reservoir,the albitization of calcium feldspar,the dolomitization of calcite,and the formation of chlorite.(4)The 87Sr/86Sr value of formation water is 0.715 697-0.718 454,indicating that the Sr in formation water mainly comes from sandstone reservoirs.The distribution patterns of sodium chloride coefficient and 87Sr/86Sr in the study area are highly similar,and this parameter can provide data support for the study of formation water sources.
water chemical characteristicswater-rock interactionstrontium isotopeformation waterXujiahe Formation
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