The underground thermal fluid is one of the significant factors controlling the formation and quality of reservoirs.The Huangliu Formation(N_(1)h)in YF1 area of the central depression belt in the Yinggehai Basin,South...The underground thermal fluid is one of the significant factors controlling the formation and quality of reservoirs.The Huangliu Formation(N_(1)h)in YF1 area of the central depression belt in the Yinggehai Basin,South China Sea,is characterized by intense thermal fluid activities related to mud diapir and large-scale shallow-water gravity flow deposits.The multi-episodic invasion of high-temperature and CO_(2)-rich thermal fluid into the formation induces complex water-rock reaction during diagenetic pro-cess,providing a preferable investigation opportunity for revealing how thermal fluid affects reservoir quality.This study characterizes the reservoirs in the formation through core and thin section analyses as well as physical property test.The reservoirs are dominated by fine-grained sandstone characterized by medium porosity(15.2-21.3%)and lower permeability(0.56-15.75mD).Based on an analysis of casting thin section,cathode luminescence(CL),scanning electron microscope(SEM),carbon and oxygen isotope,inclusion test,and electron-probe microanalysis(EPMA),we systematically investigate the diagenetic patterns and pore evolution process for the reservoirs in the formation.The episodic invasion of thermal fluid occurred approximately 0.4 Ma ago plays an important role in controlling reservoir development:The CO_(2)-rich formation water induces massive late-stage dissolution,resulting in a higher proportion of dissolved pores(38.7-46.4%),which improves the porosity of reservoirs at a depth of 2600-3100 m.Nevertheless,the late dissolution together with carbonate cementation occurred in closed diagenetic system blocks most seepage channels.Furthermore,the relatively high level clay mineral transformation in the YF1 area leads to a higher content of authigenic illite(44-62%)in the formation.Massive authigenic illite severely blocks the pore throats in fine sandstone,reducing permeability.This study offers an insight to the understanding of mud diapir-derived thermal fluid affecting and controlling the quality of reservoirs in some areas of the Yinggehai Basin.展开更多
Although commercial gas flow was produced in several wells with recent years'exploration of Longfengshan area in Changling fault sag,the formation mechanism and controlling factors for high-quality reservoirs stil...Although commercial gas flow was produced in several wells with recent years'exploration of Longfengshan area in Changling fault sag,the formation mechanism and controlling factors for high-quality reservoirs still remained undefined.Here,the Yingcheng tight gas reservoirs of Longfengshan area are used as an example to characterize high-quality reservoir formation mechanism and distribution rules.Based on the thin section,SEM,X-ray diffraction,computed tomography(CT)scanning,burial history,constant-rate mercury penetration and physical properties testing,formation mechanism and controlling factors for high-quality reservoirs were analyzed.Results show the following characteristics.First,the reservoir is dominated by chlorite and laumontite cements,and compaction is the most important factor to control reservoir physical properties.According to this,the reservoir can be divided into compacted tight sandstones,chlorite-cemented sandstones and laumontite-cemented sandstones.Second,the high-quality reservoirs are formed due to early extensive laumontite precipitation and the later dissolution of laumontite by organic acid.Meanwhile,it is found that the distribution of cementation and dissolution exhibits some regulations in sedimentary facies,and the distribution is mainly effected and controlled by the lake water and charging of fresh water.Besides,the distribution model of various types of sandstones was established.Studies over diagenesis and sedimentary facies reveal that the high-quality laumontite-cemented sandstones exist in the outside subaqueous fan-delta of the deep sag in Longfengshan area.These findings have been validated by recent exploration wells which obtained high industrial gas flow.展开更多
文摘The underground thermal fluid is one of the significant factors controlling the formation and quality of reservoirs.The Huangliu Formation(N_(1)h)in YF1 area of the central depression belt in the Yinggehai Basin,South China Sea,is characterized by intense thermal fluid activities related to mud diapir and large-scale shallow-water gravity flow deposits.The multi-episodic invasion of high-temperature and CO_(2)-rich thermal fluid into the formation induces complex water-rock reaction during diagenetic pro-cess,providing a preferable investigation opportunity for revealing how thermal fluid affects reservoir quality.This study characterizes the reservoirs in the formation through core and thin section analyses as well as physical property test.The reservoirs are dominated by fine-grained sandstone characterized by medium porosity(15.2-21.3%)and lower permeability(0.56-15.75mD).Based on an analysis of casting thin section,cathode luminescence(CL),scanning electron microscope(SEM),carbon and oxygen isotope,inclusion test,and electron-probe microanalysis(EPMA),we systematically investigate the diagenetic patterns and pore evolution process for the reservoirs in the formation.The episodic invasion of thermal fluid occurred approximately 0.4 Ma ago plays an important role in controlling reservoir development:The CO_(2)-rich formation water induces massive late-stage dissolution,resulting in a higher proportion of dissolved pores(38.7-46.4%),which improves the porosity of reservoirs at a depth of 2600-3100 m.Nevertheless,the late dissolution together with carbonate cementation occurred in closed diagenetic system blocks most seepage channels.Furthermore,the relatively high level clay mineral transformation in the YF1 area leads to a higher content of authigenic illite(44-62%)in the formation.Massive authigenic illite severely blocks the pore throats in fine sandstone,reducing permeability.This study offers an insight to the understanding of mud diapir-derived thermal fluid affecting and controlling the quality of reservoirs in some areas of the Yinggehai Basin.
基金the financial support of the National Nature and Science Fund project(41302115)Post-doctoral Science Fund(2012M511941).
文摘Although commercial gas flow was produced in several wells with recent years'exploration of Longfengshan area in Changling fault sag,the formation mechanism and controlling factors for high-quality reservoirs still remained undefined.Here,the Yingcheng tight gas reservoirs of Longfengshan area are used as an example to characterize high-quality reservoir formation mechanism and distribution rules.Based on the thin section,SEM,X-ray diffraction,computed tomography(CT)scanning,burial history,constant-rate mercury penetration and physical properties testing,formation mechanism and controlling factors for high-quality reservoirs were analyzed.Results show the following characteristics.First,the reservoir is dominated by chlorite and laumontite cements,and compaction is the most important factor to control reservoir physical properties.According to this,the reservoir can be divided into compacted tight sandstones,chlorite-cemented sandstones and laumontite-cemented sandstones.Second,the high-quality reservoirs are formed due to early extensive laumontite precipitation and the later dissolution of laumontite by organic acid.Meanwhile,it is found that the distribution of cementation and dissolution exhibits some regulations in sedimentary facies,and the distribution is mainly effected and controlled by the lake water and charging of fresh water.Besides,the distribution model of various types of sandstones was established.Studies over diagenesis and sedimentary facies reveal that the high-quality laumontite-cemented sandstones exist in the outside subaqueous fan-delta of the deep sag in Longfengshan area.These findings have been validated by recent exploration wells which obtained high industrial gas flow.
