Quantitative evaluation model of shale oil adsorption:A case study of the first member of Cretaceous Qingshankou Formation in northern Songliao Basin,NE China

A quantitative evaluation model that integrates kerogen adsorption and clay pore adsorption of shale oil was proposed,and the evaluation charts of adsorption-swelling capacity of kerogen(Mk)and adsorbed oil capacity of clay minerals(Mc)were established,taking the 1st member of Cretaceous Qingshankou Formation in the northern Songliao Basin as an example.The model and charts were derived from swelling oil experiments performed on naturally evolved kerogens and adsorbed oil experiments on clays(separated from shale core samples).They were constructed on the basis of clarifying the control law of kerogen maturity evolution on its adsorption-swelling capacity,and considering the effect of both the clay pore surface area that occupied by adsorbed oil and formation temperature.The results are obtained in four aspects:(1)For the Qing 1 Member shale,with the increase of maturity,Mk decreases.Given Ro of 0.83%–1.65%,Mk is about 50–250 mg/g.(2)The clay in shale adsorbs asphaltene.Mc is 0.63 mg/m^(2),and about 15%of the clay pore surface is occupied by adsorbed oil.(3)In the low to medium maturity stages,the shale oil adsorption is controlled by organic matter.When Ro>1.3%,the shale oil adsorption capacity is contributed by clay pores.(4)The oil adsorption capacity evaluated on the surface at room temperature is 8%–22%(avg.15%)higher than that is held in the formations.The proposed evaluation model reveals the occurrence mechanisms of shale oils with different maturities,and provides a new insight for estimating the reserves of shale oil under formation temperature conditions.

A new method for evaluating the oil mobility based on the relationship between pore structure and state of oil

An accurate evaluation of the shale oil mobility is crucial to its cost-effective exploitation.This study presents a method to assess shale oil mobility by integrating the pore structure and oil states distributions.First,a set of three discrete organic extracts(EOM-A,B and C)were obtained by sequential extraction.The relationships among the EOMs and the oil states were inferred from the group compositions and fluorescence properties of the produced shale oil(free state).The results showed that EOMs A and B represent free oil in the open and closed pores,respectively,while the EOM-C represents adsorbed oil.Then,NMR T_(1)-T_(2)map is used to determine the T_(2-cutoff)values that indicate the pore size ranges of different oil states.Free oil resides mainly in larger pore space(T_(2)>0.5 ms),while the adsorbed oil in smaller pore space(0.2 ms<T_(2)<0.5 ms).Finally,the ratio of free to adsorbed oil(F/A)>0.5 and T_(2-cutoff)>1.0 ms suggest that the free oil in connected pores has the highest mobility.This work can provide a reference for evaluating the shale oil potential and prospectivity in other regions.