Systematic analyses of the formation water and natural gas geochemistry in the Central Uplift of the Tarim Basin （CUTB） show that gas invasion at the late stage is accompanied by an increase of the contents of HeS a...Systematic analyses of the formation water and natural gas geochemistry in the Central Uplift of the Tarim Basin （CUTB） show that gas invasion at the late stage is accompanied by an increase of the contents of HeS and CO2 in natural gas, by the forming of the high total dissolved solids formation water, by an increase of the content of HCO3^-, relative to Cl^-, by an increase of the 2nd family ions （Ca^2＋, Mg^2＋, Sr^2＋ and Ba^2＋） and by a decrease of the content of SO4^2-, relative to Cl^-. The above phenomena can be explained only by way of thermochemicai sulfate reduction （TSR）. TSR often occurs in the transition zone of oil and water and is often described in the following reaction formula： ∑CH＋CaSO4＋H-2O→H2S＋CO2＋CaCO3. （1） Dissolved SO4^2- in the formation water is consumed in the above reaction, when HeS and CO2 are generated, resulting in a decrease of SO4^2- in the formation water and an increase of both HeS and CO2 in the natural gas. If formation water exists, the generated CO2 will go on reacting with the carbonate to form bicarbonate, which can be dissolved in the formation water, thus resulting in the enrichment of Ca^2＋ and HCO3^-. The above reaction can be described by the following equation： CO2＋HeO＋CaCO3→Ca^2＋＋2HCO3^-. The stratigraphic temperatures of the Cambrian and lower Ordovician in CUTB exceeded 120℃, which is the minimum for TSR to occur. At the same time, dolomitization, which might be a direct result of TSR, has been found in both the Cambrian and the lower Ordovician. The above evidence indicates that TSR is in an active reaction, providing a novel way to reevaluate the exploration potentials of natural gas in this district.展开更多
Longmen Mountain located at the boundary between the Sichuan Basin and Tibetan Plateau,representing the steepest gradient of any edges of the plateau.Three endmember models of uplift process and mechanism have been pr...Longmen Mountain located at the boundary between the Sichuan Basin and Tibetan Plateau,representing the steepest gradient of any edges of the plateau.Three endmember models of uplift process and mechanism have been proposed,including crustal thickening,crustal flow,and crustal isostatic rebound.Here we use coeval sedimentary sequences in the foreland basin to restraint uplift process and mechanism in the Longmen Mountain.The more than 10,000 m thick Late TriassicQuaternary strata filled in this foreland basin and can be divided into six megasequences that are distinguished as two distinct types.The first type is the wedge-shaped megasequences which are sedimentary response of strong active thrust loading events,characterized by a high rate of subsidence and sediment accumulation,coarsening-upward succession and a dual-sourced sediment supply.This type includes Late Triassic,Late Jurassic to Early Cretaceous and Late Cretaceous to Paleogene megasequences.The second type is the tabular megasequences,characterized by the low rate of subsidence and sediment accumulation,finingupward succession,and a single-sourced sediment supply,which is sedimentary response of isostatic rebound and erosion unloading.This type includes the Early to Middle Jurassic,Middle Cretaceous and Neogene to Quaternary megasequences.Basing on sedimentary,active tectonic,geomorphic evidence,we infer that the direction has been reversed from SSWdirected sinistral strike-slip to NNE-directed dextral strike-slip during 40-3.6 Ma,and since 3.6 Ma,the Longmen Mountain thrust belt belong to times of isostatic rebound and erosional unloading with NNEdirected dextral strike-slip.This suggests that crustal isostatic rebound is a primary driver for uplift and topography of the present Longmen Mountain.The Wenchuan(Ms8.0) earthquake,which ruptured a large thrust fault with NNE-directed dextral strikeslip along the range front,is an active manifestation of this crustal isostatic rebound process with dextral strike-slipping and shortening.This process may be the cause for the Wenchuan Earthquake and the apparent paradox of high relief,little shortening,the relative dearth of historical seismicity in the region.展开更多
A comprehensive sedimentary and reservoir analysis was conducted based on seismic,well logging,core and relative test data,taking Members 1 and 2 of Shahejie Formation of the early Oligocene in the steep slope belt,ea...A comprehensive sedimentary and reservoir analysis was conducted based on seismic,well logging,core and relative test data,taking Members 1 and 2 of Shahejie Formation of the early Oligocene in the steep slope belt,eastern Shijiutuo Uplift(STU),Bohai Bay Basin(BBB)as a case.The study indicates that a near-shore mixed fan deposit formed in the study area and developed characteristics and pattern of a high-quality reservoir.The mixed clastic-carbonate rocks constitute Members 1 and 2 of Shahejie Formation which developed along the steep slope belt and is named as a near-shore mixed fan.The mixed fan of the study area is mainly composed of microfacies of proximal channel,mixed deposited channel,mixed clastic beach,mixed bioclastic(grain)beach,with vertical multi-stage superimposition feature,and basically a similar shape as modern near-shore fans.It constitutes a new depositional type developing in the steep slope belt of a characteristic and complex lacustrine rift basin in the study area.This mixed fan in the steep slope of eastern STU is controlled by comprehensive factors including tectonics,clastic material supply,climate,palaeogeomorphology and hydrodynamic conditions.The reservoir quality of Members 1 and 2 of Shahejie Formation of eastern STU is,however,actually controlled by the sedimentary environment and diagenesis processes.Coarse-grained mixed rocks of near-shore fans,rich in bioclastics,can form excellent reservoirs,characterized by resistance to compaction,easy to dissolution,little influenced by burial depth and high production of oil and gas,which enable them become key exploration targets of medium-deep strata of BBB.Analyses of high-quality reservoir,its controlling factors and the oil and gas exploration implications of the near-shore mixed fan developing in the study area give a deeper insight into discussions of the same type of mixed rocks of other lacustrine rift basins worldwide.展开更多
基金supported by the State 973 Project(Grant No.2006CB202308)the National Natural Science Foundation of China(Grant No.40872097)
文摘Systematic analyses of the formation water and natural gas geochemistry in the Central Uplift of the Tarim Basin （CUTB） show that gas invasion at the late stage is accompanied by an increase of the contents of HeS and CO2 in natural gas, by the forming of the high total dissolved solids formation water, by an increase of the content of HCO3^-, relative to Cl^-, by an increase of the 2nd family ions （Ca^2＋, Mg^2＋, Sr^2＋ and Ba^2＋） and by a decrease of the content of SO4^2-, relative to Cl^-. The above phenomena can be explained only by way of thermochemicai sulfate reduction （TSR）. TSR often occurs in the transition zone of oil and water and is often described in the following reaction formula： ∑CH＋CaSO4＋H-2O→H2S＋CO2＋CaCO3. （1） Dissolved SO4^2- in the formation water is consumed in the above reaction, when HeS and CO2 are generated, resulting in a decrease of SO4^2- in the formation water and an increase of both HeS and CO2 in the natural gas. If formation water exists, the generated CO2 will go on reacting with the carbonate to form bicarbonate, which can be dissolved in the formation water, thus resulting in the enrichment of Ca^2＋ and HCO3^-. The above reaction can be described by the following equation： CO2＋HeO＋CaCO3→Ca^2＋＋2HCO3^-. The stratigraphic temperatures of the Cambrian and lower Ordovician in CUTB exceeded 120℃, which is the minimum for TSR to occur. At the same time, dolomitization, which might be a direct result of TSR, has been found in both the Cambrian and the lower Ordovician. The above evidence indicates that TSR is in an active reaction, providing a novel way to reevaluate the exploration potentials of natural gas in this district.
基金supported by the China National Natural Science Foundation (Grant No. 40841010,40972083,41172162)CGS Foundation (Grant No.1212011121268)Foundation from State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation (Grant No. SK-0801)
文摘Longmen Mountain located at the boundary between the Sichuan Basin and Tibetan Plateau,representing the steepest gradient of any edges of the plateau.Three endmember models of uplift process and mechanism have been proposed,including crustal thickening,crustal flow,and crustal isostatic rebound.Here we use coeval sedimentary sequences in the foreland basin to restraint uplift process and mechanism in the Longmen Mountain.The more than 10,000 m thick Late TriassicQuaternary strata filled in this foreland basin and can be divided into six megasequences that are distinguished as two distinct types.The first type is the wedge-shaped megasequences which are sedimentary response of strong active thrust loading events,characterized by a high rate of subsidence and sediment accumulation,coarsening-upward succession and a dual-sourced sediment supply.This type includes Late Triassic,Late Jurassic to Early Cretaceous and Late Cretaceous to Paleogene megasequences.The second type is the tabular megasequences,characterized by the low rate of subsidence and sediment accumulation,finingupward succession,and a single-sourced sediment supply,which is sedimentary response of isostatic rebound and erosion unloading.This type includes the Early to Middle Jurassic,Middle Cretaceous and Neogene to Quaternary megasequences.Basing on sedimentary,active tectonic,geomorphic evidence,we infer that the direction has been reversed from SSWdirected sinistral strike-slip to NNE-directed dextral strike-slip during 40-3.6 Ma,and since 3.6 Ma,the Longmen Mountain thrust belt belong to times of isostatic rebound and erosional unloading with NNEdirected dextral strike-slip.This suggests that crustal isostatic rebound is a primary driver for uplift and topography of the present Longmen Mountain.The Wenchuan(Ms8.0) earthquake,which ruptured a large thrust fault with NNE-directed dextral strikeslip along the range front,is an active manifestation of this crustal isostatic rebound process with dextral strike-slipping and shortening.This process may be the cause for the Wenchuan Earthquake and the apparent paradox of high relief,little shortening,the relative dearth of historical seismicity in the region.
基金This study is supported by National Science and Technology Major Project(2016ZX05024003).
文摘A comprehensive sedimentary and reservoir analysis was conducted based on seismic,well logging,core and relative test data,taking Members 1 and 2 of Shahejie Formation of the early Oligocene in the steep slope belt,eastern Shijiutuo Uplift(STU),Bohai Bay Basin(BBB)as a case.The study indicates that a near-shore mixed fan deposit formed in the study area and developed characteristics and pattern of a high-quality reservoir.The mixed clastic-carbonate rocks constitute Members 1 and 2 of Shahejie Formation which developed along the steep slope belt and is named as a near-shore mixed fan.The mixed fan of the study area is mainly composed of microfacies of proximal channel,mixed deposited channel,mixed clastic beach,mixed bioclastic(grain)beach,with vertical multi-stage superimposition feature,and basically a similar shape as modern near-shore fans.It constitutes a new depositional type developing in the steep slope belt of a characteristic and complex lacustrine rift basin in the study area.This mixed fan in the steep slope of eastern STU is controlled by comprehensive factors including tectonics,clastic material supply,climate,palaeogeomorphology and hydrodynamic conditions.The reservoir quality of Members 1 and 2 of Shahejie Formation of eastern STU is,however,actually controlled by the sedimentary environment and diagenesis processes.Coarse-grained mixed rocks of near-shore fans,rich in bioclastics,can form excellent reservoirs,characterized by resistance to compaction,easy to dissolution,little influenced by burial depth and high production of oil and gas,which enable them become key exploration targets of medium-deep strata of BBB.Analyses of high-quality reservoir,its controlling factors and the oil and gas exploration implications of the near-shore mixed fan developing in the study area give a deeper insight into discussions of the same type of mixed rocks of other lacustrine rift basins worldwide.
