Study On Geochemical Characteristics And Origin Of Formation Waters Of The Xujiahe Gas Reservoirs In Xinchang Field

As the displacing force and carrier,the groundwater play an important role all the way for producing,migration,accumlation and dissipation of petroleum in the pool-forming.The hydrochemistry and hydrodynamics is one of the factors for the chemical and physical change of petroleum. Mass and energy exchanges were found between groundwater and surrounding media (including surrounding rock and oil and gas),and entailment a lot of Information which related to the formation and preservation of oil and gas, so geologists through the analysis on geochemistry of palaeohydrology for a long time,we can know the origin of the oilfield water and then conclude the geofactor and the geochemical factor of the formation water .Through the study and the comeback of the palaeohydrodynamic field ,we can judge the migration direction of the petroleum , the separate between gas and water , and the relation between the petroleum and the pool and preservation condition of oil and gas, and so on.The origin of the groundwater of oil and gas field is a comparatively complicated important problem.Before 1965, based on the water chemical constituents, most oilfield water of marine sedimentary environment is considered as seawater in sedimentary trap. However, After introducing hydrogen and oxygen isotopes,it is considered as mainly related with meteoric water influx and displacement primary water. Thereafter, many scholars based on hydrochemistry and isotope to comprehensive research, puts forward some ideas ,such as evaporation of seawater and concentrated, mixed with freshwater, completely exposure of evaporative seawater,and recognition of petrogenic and reformed syngenetic waterThe Xujiahe gas reservoirs in Xinchang Gas Field are of such characters as tight reservoir , gas-bearing universality, good sealing , ideal matching of source-reservoir-cap , encirclements were full-fledged and large deposit.The groundwater of Xinchang field Xujiahe formation type mainly is CaCl2 which Stack of seal—closed and buried sedimentary water of marine origin and meteoric water.Through the level and section form characteristic analysis of gas-water distribution of Segment Xu4 and Segment Xu2 gas reservoirs in Xinchang Gas Field, It is suggested that the upper sub-member of the sand body in T₃x₄ reservoir was water-bearing universality, the under sub-member of The sand body in T₃x₄ reservoir was water-bearing locality. the sand body in T₃x₄ reservoir was gas-bearing universality without unified gas-water interface; There are multiple factors for the distribution characteristics of the groundwater of The Xujiahe gas reservoirs in Xinchang Gas Field; By comprehensive analysis, the control actions of old and present structure, reservoir ' s heterogeneity and gas-water replacement incomplete of low permeability reservoir were the main cause of gas-water distribution of Segment Xu4 and Segment Xu2 gas reservoirs in Xinchang Gas Field ,and so on.