Characteristics,genesis,and petroleum geological implications of solid bitumen in Cambrian-Ordovician carbonate reservoirs in the Ordos Basin
The Cambrian-Ordovician ancient carbonate reservoir is an important replacement area for natural gas exploration in the Ordos Basin.Recently,solid bitumen is discovered in the Cambrian-Ordovician carbonate reservoir in the Ordos Basin.The study on the characteristics and genesis of solid bitumen is conducive to understanding the process of hydrocarbon accumulation more accurately.Therefore,by means of core,microscopic,and scanning electron microscope observation,combined with laser Raman,X-ray energy spectrum,and saturated hydrocarbon chromatogram-mass spectra analysis and test,the paper analyzes the morphology,elemental composition,maturity,and biomarker compounds of solid bitumen,investigates the genesis types and evolution processes of solid bitumen,and discusses the distribution and petroleum geological implications of solid bitumen of different genesis.The following results are obtained.First,solid bitumen of the Cambrian-Ordovician carbonate reservoirs in the Ordos Basin exhibits a high degree of thermal evolution,and it fills fractures,sutures and intergranular pores,while bitumen inclusions are developed on calcite veins.Second,thermal chemical alteration(TCA)is the dominant genesis type of bitumen,and thermochemical sulfate reduction(TSR)and gas deasphalting also contribute to its formation.The bitumen formed by TSR and TCA has a high reflectance and a high degree of thermal evolution.The TSR genetic bitumen has a higher S/C ratio,while the bitumen formed by gas invasion deasphalting has a lower reflectance,with gas holes visible locally.Third,the TCA genetic bitumen is distributed through the Cambrian-Ordovician in the study area,while the bitumen of TSR and gas invasion deasphalting origins are mainly distributed in the Majiagou Formation in the central basin.Forth,compared with TCA genetic bitumen,TSR genetic bitumen is earlier in formation time,and forms in the regions with oil charging and sufficient water-soluble sulfate.As the formation temperature rises gradually,oil cracking occurs,resulting in the formation of TCA genetic bitumen.Gas invasion deasphalting is formed by the deasphalting process of residual oil caused by the invasion of natural gas during the late uplift process.In conclusion,the differences in the formation mechanisms of the three different types of solid bitumen indicate that the study area has experienced the hydrocarbon accumulation evolution process such as oil charging,oil cracking into oil type gas,and alteration and transformation.The research results are of great scientific significance and application value for analyzing the formation,evolution and accumulation potential of deep and ultradeep oil and gas.
万方数据
