Control of micro-wettability of pore-throat on shale oil occurrence:A case study of laminated shale of Permian Lucaogou Formation in Jimusar Sag,Junggar Basin,NW China

The control of micro-wettability of pore-throat on shale oil occurrence in different types of reservoir spaces remains unclear.Take the shale oil reservoir of the Permian Lucaogou Formation in the Jimusar Sag,Junggar Basin as an example,the reservoir space in laminated shale and the control of micro-wettability of pore-throat on shale oil occurrence were studied by using scanning electron microscope(SEM),multi-stage pyrolysis,quantitative fluorescence,nuclear magnetic resonance(NMR)and other techniques.The results show that there are mainly two types of laminated shale in the Lucaogou Formation,namely laminated shale rich in volcanic materials+terrigenous felsic,and laminated shale rich in volcanic materials+carbonate.The former type contains feldspar dissolution pores and intergranular pores,mainly with felsic mineral components around the pore-throats,which are water-wet and control the free shale oil.The latter type contains carbonate intercrystalline pores and organic pores,mainly with oil-wet mineral components around the pore-throats,which control the adsorbed shale oil.The oil-wet mineral components around the pore-throats are conducive to oil accumulation,but reduce the proportion of free oil.In the Lucaogou Formation,free oil,with high maturity and light quality,mainly occurs in the laminated shale rich in volcanic materials+terrigenous felsic.

Experimental study on the oil production characteristics during the waterflooding of different types of reservoirs in Ordos Basin, NW China

Waterflooding experiments were conducted in micro-models(microscopic scale)and on plunger cores from low permeability,extra-low permeability and ultra-low permeability reservoirs in the Ordos Basin under different displacement pressures using the NMR techniques to find out pore-scale oil occurrence state,oil production characteristics and residual oil distribution during the process of waterflooding and analyze the effect of pore structure and displacement pressure on waterflooding efficiency.Under bound water condition,crude oil mainly occurs in medium and large pores in the low-permeability sample,while small pores and medium pores are the main distribution space of crude oil in extra-low permeability and ultra-low permeability samples.During the waterflooding,crude oil in the medium and large pores of the three types of samples are preferentially produced.With the decrease of permeability of the samples,the waterflooding front sequentially shows uniform displacement,network displacement and finger displacement,and correspondingly the oil recovery factors decrease successively.After waterflooding,the residual oil in low-permeability samples is mainly distributed in medium pores,and appears in membranous and angular dispersed phase;but that in the extra-low and ultra-low permeability samples is mainly distributed in small pores,and appears in continuous phase formed by a bypass flow and dispersed phase.The low-permeability samples have higher and stable oil displacement efficiency,while the oil displacement efficiency of the extra-low permeability and ultra-low permeability samples is lower,but increases to a certain extent with the increase of displacement pressure.