This study was performed to evaluate pore systems of reservoir lithofacies within the De- vonian Three Forks Formation in the Williston Basin through micro-scale pore characterization. These lithofacies are from the Upper Three Forks section, which is a prominent drilling target within the Bakken- Three Forks Petroleum System. Samples from the Formation were examined by (1) physical core de- scription, (2) petrographic thin section microscopy, (3) x-ray diffractometry (XRD) minerals analysis, (4) scanning electron microscopy (SEM), and (5) porosity measurements from helium porosimetry, nu- clear magnetic resonance (NMR), gas adsorption and mercury intrusion porosimetry (MIP). These were done to provide better understanding of the local variations in pore structures and how such structures impact reservoir quality within the Three Forks Formation. Seven reservoir lithofacies were identified and described, including laminated lithofacies, massive dolostone, mottled dolostone, massive mudstone, mottled mudstone, mudstone conglomerates, and brecciated mudstone. Samples show a di- verse variation in mineralogical composition, pore types, porosity, and pore-size distribution. Six types of pores were identified: interparticle, intercrystalline, intracrystalline, vuggy, microfractures, and mudstone microporosity. Dolostone-rich lithofacies have abundant dolomite and less siliciclastic miner- als such as quartz, feldspar, and clays. They also have relatively low porosity and generally larger pore size. A general positive trend exists between porosity with clay minerals and feldspar, in contrast to a negative trend with dolomite, and no clear relationship with quartz content. Results from the gas ad- sorption analysis, NMR and MIP pore-size distribution confirm an abundance of macropores (>50 nm in diameters) in dolostone dominated lithofacies while other lithofacies generally have abundant meso- pores (2–50 nm).

Adedoyin Adeyilola;Stephan Nordeng;Qinhong Hu

Department of Earth and Atmospheric Science,Central Michigan University,Mount Pleasant,MI 48859,USA;Harold Hamm School of Geology and Geological Engineering,University of North Dakota,Grand Forks,ND 58202,USA;Department of Earth and Environmental Sciences,The University of Texas at Arlington,500 Yates Street,Arlington,TX 76019,USA

地球科学学刊（英文版）

[1]Adedoyin Adeyilola;Stephan Nordeng;Qinhong Hu-.Porosity and Pore Networks in Tight Dolostone––Mudstone Reservoirs:Insights from the Devonian Three Forks Formation, Williston Basin, USA)[J].地球科学学刊（英文版）,2022(02):462-481

Dolostone,Mudstone,Forks,Williston,vonian,mottled,conglomerates,brecciated,intracrystalline,vuggy

Porosity,Pore,Networks,Tight,Reservoirs,Insights,from,Devonian,Three,Formation,Basin,USA,This,study,was,performed,evaluate,systems,reservoir,lithofacies,within,through,scale,characterization,These,are,Upper,section,which,prominent,drilling,target,Bakken,Petroleum,System,Samples,were,examined,by,physical,core,scription,petrographic,microscopy,ray,diffractometry,minerals,analysis,scanning,electron,measurements,helium,porosimetry,nu,clear,magnetic,resonance,NMR,gas,adsorption,mercury,intrusion,MIP,done,provide,better,understanding,local,variations,structures,such,impact,quality,Seven,identified,described,including,laminated,massive,dolostone,mudstone,show,verse,mineralogical,composition,types,size,distribution,Six,interparticle,intercrystalline,microfractures,microporosity,rich,have,abundant,dolomite,less,siliciclastic,quartz,feldspar,clays,They,also,relatively,low,generally,larger,positive,trend,exists,between,contrast,negative,no,relationship,content,Results,confirm,abundance,macropores,diameters,dominated,while,other,meso

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