A Petrographic Study of the Three Forks Formation (Upper Devonian), Williston Basin, North Dakota: Based on Thin Section Analysis, XRD and SEM

Table 3

Thin section petrographic summary of three dolomitic samples from Facies 1, 2, and 3 of the Three Forks Formation.

Facies ID		1	2	3
Mineralogy	Calcite, feldspar, pyrite	TR	TR	TR
	Dolomite	54	57	40
	Quartz	10	11	5
	Mica	3	2	2
	Hematite	13	10	37
	Clay + organic matter	20	20	16
Total rock volume (%)		100	100	100
Detrital grains	Quartz	10	11	5
	Feldspar	TR	TR	TR
	Mica	3	2	2
	Total	13	13	7
Matrix	Clay and organics	20	20	16
	Total	20	20	16
Pore-filling; cement	Calcite	TR	TR	TR
	3rd/euh dolomite	1	1	3
	2nd/sub dolomite	35	26	29
	1st/anh dolomite	10	13	TR
	Fe-dolomite	8	17	8
	Hematite	13	10	37
	Total	67	67	77
Replacement Pyrite		TR	TR	TR
Total rock volume (%)		100	100	100
Crystal texture (matrix)		Anh	Anh	—
Crystal texture (cement)		Anh-Euh	Anh-Euh	Anh-Euh
Original texture		Mudstone	Mudstone	Mudstone
Porosity	Intercrystalline	2	2	TR
	Microvuggy	1	—	—
	Total TS porosity (%)	3	2	TR
Reservoir Quality		P-M	P-M	P

Euh: euhedral; Sub: subhedral; Anh: anhedral; TR: trace; G: good; M: moderate; P: poor.