| It is a controversially foundational-theoretic issue about whether the large-scale feldspar dissolution pores can form in middle-deep burial clastic reservoirs.With the question whether the feldspar dissolution pores in modern sediments can be preserved to the middle-deep clastic reservoirs during the compaction process as a pointcut,based on the similarity principle of sedimentary condition and lithologic fabric,such as “climatic conditions,composition of clastic particles,size of feldspar particles,roundness,type of parent rock,and distance of sediment transportation”,the modern sediments with comparability in Qingdao area and turbidite fan in the third member of the Shahejie Formation and glutenite in the fourth member of the Shahejie Formation in Dongying Sag will be chosen as the research objects.The research methods were used in this work included core and thin section observation,X-ray diffraction composition analysis,SEM and EDX analysis,image analysis,cathodoluminescence,fluid inclusions,laser ablation inductively coupled plasma mass spectrometry analysis as well as physical simulation experiment.The purposes of this research work are to analyse the origin of feldspar dissolution pores in the closed system and establish the evolution processes of feldspar dissolution pores in the closed system.The following achievement was obtained by the research:(1)The dissolution of feldspar is well developed in the modern sediment of wind river,estuary delta,mountain river of Xiaozhushan,non-barrier coast of Green Island Bay-Phoenix Mountain as well as turbidite fan and glutenite in the third-fourth member of the Shahejie Formation in Dongying Sag.(2)The feldspar dissolution pores will not be lossed no matter though the short distance or long distance river transportation.The feldspar dissolution pores in the modern sediments will be preserved to 3000 m in the buried compaction process.It is good for the preservation of the feldspar dissolution pores in the modern sediments beacause of the stable triangular lattice formed by displacement and rearrangement of rigid quartz particles during early compaction and high content of clay and matrix.(3)There are three sources of quartz cement of the turbidite fan sandstones in the third member of the Shahejie Formation in Dongying Sag: pressure solution of quartz,feldspar dissolution and smectitie illitization.The average content of quartz cement from feldspar dissolution is 0.42%.The average content of feldspar dissolution pores calculated by the content of quartz cement from the feldspar dissolution is 0.93%.The average content of feldspar dissolution pores quantitatively delineated by drawing principles is 1.4%.The forward and inverse methods confirmed that the feldspar dissolution in closed system can not produce the scale of secondary pores.Most of feldspar dissolution pores were formed during the period of weather-sedimentation and preserved to the middle-deep depth during the burial compaction.(4)The paleoclimate of palaeogene in Dongying Sag was warm and humid,and large of feldspar dissolution pores were formed due to the strong chemical weathering.The weathering product with lots of feldspar dissolution pores deposited in the delta front during the longdistance transportation and then slipped into the deep water environment.With the increase of the burial depth,a few feldspar dissolution pores were crushed.Most of feldspar dissolution pores can be preserved into the middle-deep depth due to the high content of rigid quartz grains and clay/matric.In early diagenesis stage and middle diagenetic stage,few feldspar was dissolved by organic acid formed by thermal evolution of organic matter and accompanied by the precipitation of kaolinite and quartz in the nearby pores.The content of feldspar dissolution pores were not increased obviously.With the carbonate and silicate cementation and overpressure caused by hydrocarbon charge,lots of feldspar dissolution pores continue to be preserved into deep burial clastic reservoirs. |
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