Bitumen impregnations is common in cores of the Lower Ordovician Penglaiba Formation of Well Lunshen-2 in Lungu area

the Tarim Basin.Through detailed observation of two cored intervals in the Formation

it is inferred that there exist six types of bitumen impregnation patterns

i.e.lamination impregnation

fissure and lamination composite impregnation

fracture impregnation

vug impregnation

irregular stylolite impregnation

and pullapart space impregnation.Different types of bitumen impregnations have different origins and hydrocarbon accumulation significances.It is indicated that the Penglaiba Formation experienced hydrocarbon charging and the different types of bitumen impregnation were caused by the differences of space types for hydrocarbon enrichment.The recognition of bitumen impregnation patterns and analysis of their relationship with reservoir genesis provide a geological basis for fine characterization of the dolomite reservoirs in the study area.Study shows that the silicate in the Penglaiba Formation is the main factor leading to the increase of drilling time and the previously predicted “catenular” dolomites are not favorable reservoirs.