Hydrocarbon Inclusion Characteristics in the Cambrian-Ordovician Carbonates of the TS2 Well:Implication for Deep Hydrocarbon Exploration in the Tahe Oilfield,Tarim Basin,Northwest China

Going deep has been the strategy for the sustainable development of the Tahe Oilfield.Following the TS1 well in block 1,which revealed excellent combinations of hydrocarbon generation,migration and accumulation in the deeper parts of the Tarim Basin,the TS2 well was drilled to learn more about the prospectivity in the deeper parts of the main blocks of the Tahe Oilfield.Seventeen core samples were collected to perform fluid inclusion studies,including petrography,fluorescence microspectrometry,and microthermometry.The results show that the deeper parts of the Tahe Oilfield have a good hydrocarbon potential.The Cambrian source rocks can supply sufficient oil for not only the Cambrian reservoirs,but also for the Lower Ordovician reservoirs.The CambrianOrdovician carbonates reservoirs experienced at least three oil charging events and one late gas charging event.Oil accumulations formed in the early stage of basin evolution were likely destroyed in the late stage with deep burial,tectonic movements,or invasion of hydrothermal fluids.Therefore,the deep hydrocarbon exploration of the Tahe Oilfield,even the whole Tarim Basin,should focus on gas accumulations,although oil accumulations,especially in Cambrian reservoirs,cannot be neglected.

Characteristics of Hydrocarbon Fluid Inclusions and Their Significance for Evolution of Petroleum Systems in the Dabashan Foreland,Central China

Field investigation combined with detailed petrographic observation indicate that abundant oil,gas,and solid bitumen inclusions were entrapped in veins and cements of sedimentary rocks in the Dabashan foreland,which were used to reconstruct the oil and gas migration history in the context of tectonic evolution.Three stages of veins were recognized and related to the collision between the North China block and the Yangtze block during the Indosinian orogeny from Late Triassic to Early Jurassic（Dl）,the southwest thrusting of the Qinling orogenic belt towards the Sichuan basin during the Yanshanian orogeny from Late Jurassic to Early Cretaceous（D2）,and extensional tectonics during Late Cretaceous to Paleogene（D3）,respectively.The occurrences of hydrocarbon inclusions in these veins and their homogenization temperatures suggest that oil was generated in the early stage of tectonic evolution,and gas was generated later,whereas solid bitumen was the result of pyrolysis of previously accumulated hydrocarbons.Three stages of hydrocarbon fluid inclusions were also identified in cements of carbonates and sandstones of gas beds in the Dabashan foreland belt and the Dabashan foreland depression（northeastern Sichuan basin）,which recorded oil/gas formation,migration,accumulation and destruction of paleo-reservoirs during the D2.Isotopic analysis of hydrocarbon fluid inclusions contained in vein minerals shows that δ^（13）C_1 of gas in fluid inclusions ranges from-17.0‰ to-30.4‰（PDB） and δD from-107.7‰ to-156.7‰（SMOW）,which indicates that the gas captured in the veins was migrated natural gas which may be correlated with gas from the gas-fields in northern Sichuan basin.Organic geochemical comparison between bitumen and potential source rocks indicates that the Lower Cambrian black shale and the Lower Permian black limestone were the most possible source rocks of the bitumen.Combined with tectonic evolution history of the Dabashan foreland,the results of this study suggest that oil was generated from the Paleozoic source rocks in the Dabashan area under normal burial thermal conditions before Indosinian tectonics and accumulated to form paleo-reservoirs during Indosinian collision between the North China block and the Yangtz block.The paleo-reservoirs were destroyed during the Yanshanian tectonic movement when the Dabashan foreland was formed.At the same time,oil in the paleo-reservoirs in the Dabashan foreland depression was pyrolyzed to transform to dry gas and the residues became solid bitumen.

The dating and temperature measurement technologies for carbonate minerals and their application in hydrocarbon accumulation research in the paleouplift in central Sichuan Basin, SW China

A new method for reconstructing the geological history of hydrocarbon accumulation is developed, which are constrained by U-Pb isotope age and clumped isotope((35)47) temperature of host minerals of hydrocarbon-bearing inclusions. For constraining the time and depth of hydrocarbon accumulation by the laser in-situ U-Pb isotope age and clumped isotope temperature, there are two key steps:(1) Investigating feature, abundance and distribution patterns of liquid and gaseous hydrocarbon inclusions with optical microscopes.(2) Dating laser in-situ U-Pb isotope age and measuring clumped isotope temperature of the host minerals of hydrocarbon inclusions. These technologies have been applied for studying the stages of hydrocarbon accumulation in the Sinian Dengying gas reservoir in the paleo-uplift of the central Sichuan Basin. By dating the U-Pb isotope age and measuring the temperature of clumped isotope((35)47) of the host minerals of hydrocarbon inclusions in dolomite, three stages of hydrocarbon accumulation were identified:(1) Late Silurian: the first stage of oil accumulation at(416±23) Ma.(2) Late Permian to Early Triassic: the second stage of oil accumulation between(248±27) Ma and(246.3±1.5) Ma.(3) Yanshan to Himalayan period: gas accumulation between(115±69) Ma and(41±10) Ma. The reconstructed hydrocarbon accumulation history of the Dengying gas reservoir in the paleo-uplift of the central Sichuan Basin is highly consistent with the tectonic-burial history, basin thermal history and hydrocarbon generation history, indicating that the new method is a reliable way for reconstructing the hydrocarbon accumulation history.

Hydrocarbon fluid inclusions and source rock parameters:A comparison from two dry wells in the western offshore,India

Fluid inclusions represent the direct evidence of paleofluids and can provide valuable information on the evolution of sedimentary basins and oil-bearing strata.Hydrocarbon fluid inclusion(s)(HCFIs)are the vestiges of oil from the geological formations.The paper delineates the paleotemperature(T_(h))/oil window,the oil quality of HCFIs and Raman peaks corresponding to hydrocarbon species of HCFIs using fluid inclusion techniques,and source rock potential of hydrocarbon generation,thermal maturity,the quantity of organic matter,and the kerogen types obtained through Rock-Eval pyrolysis data from two dry wells RV-1 well of Mumbai offshore and KKD-1A well of Kerala-Konkan Basin.The present study compares the fluid inclusion parameters as well as the source rock geochemical characteristics of these two dry wells to address the scientific problem of the wells going dry.Further,evaluated whether the results agree with an earlier finding from a case study of two wells named KK4C-Al(Kerala-Konkan basin)and RV-1 well where only a few parameters such as temperature of homogenization(T_(h))&API gravity were utilised,and the chances of getting oil in the nearby areas of these two wells were reported.In the present study,the fluid inclusion parameters such as the palaeotemperature(T_(h)),API Gravity and Raman spectra were obtained from micron sized fluid inclusions at different depths for a quick assessment of nature of oil inclusions within the two dry wells.Along with fluid inclusion parameters,different source rock parameters obtained from Rock-Eval Pyrolysis analysis(secondary data)such as S1,S2,S3,(T_(max)),Hydrogen Index(HI),Oxygen Index(OI),Potential Yield(PY),Production Index(PI)and Total Organic Carbon Content(TOC)were also considered for a detailed source-rock evaluation of two wells(RV-1 and KKD-1A)and the results act as the supporting evidence to address the reason for the wells gone dry.Temperature of homogenisation(T_(h))of hydrocarbon Fluid Inclusion Assemblages(FIAs)from both the wells fall in the oil window(60-150℃)range indicating that there was a conducive thermal condition favourable for oil generation in these two basins.API gravity of oils in RV-1 well of Mumbai offshore(48-53)was lighter when compared to those in KKD-1A(18-22)of Kerala-Konkan basin.Raman spectra of HCFI samples could decipher important hydrocarbon species from RV-1 well samples.Raman spectra of KKD-1A well show less prominent peaks(broad)only.Pyrolysis data shows that Paleocene-Early Eocene source rocks of Panna formation of RV1 well are mature enough to generate hydrocarbons.On the other hand,Paleocene aged source rocks of Kasargod formation of KKD-1A well are immature.Source rock maturity therefore could be considered as crucial in hydrocarbon generation in these two wells even if oil-window was achieved.This study reports that,in RV-1 well,even though it is a dry well in a proven basin,the oil window,API gravity of oils and constituents from HCFIs of RV-1 well and the source-rock maturity opens up a demand for detailed exploration in nearby areas of RV-1 in the Mumbai offshore basin hopeful of finding a high-value prospect for oil,whereas the fluid inclusion studies in the HCFIs of KKD-1A well of Kerala-Konkan basin is showing only a minimal chance of oil generation that too of a heavy nature and the source rock immature characteristics suggesting only minimal generation of hydrocarbons.Due to the heaviness of the available oil in the KKD-1A well impedes migration.Our study suggests that there is no potential for finding oil in the nearby areas of KKD-1A well of Kerala-Konkan basin.