The pore-throat heterogeneity of dolomite reservoirs is mainly reflected by their complex structure and distribution that are difficult to sufficiently and quantitatively analyze with conventional reservoir characterization methods.In this study

nine samples from dolomite reservoirs in the 3rd member of the Ordovician Yingshan Formation (Ying 3 member)

Gucheng area

eastern Tarim Basin

were CT scanned to establish a 3D network model for the pore-throats.Such reservoir parameters as pore-throat radius

pore and throat numbers

total porosity

spatial connectivity

and etc.

were calculated based on the model.The results show obvious differences among the pore-throat radius distribution curves for the samples.These curves can then be grouped into three categories in terms of shape features

that is

Type Ⅰ

the normal unimodal curve; Type Ⅱ

the unimodal curve for pores and multi-modal curve for throats; and Type Ⅲ

the multi-modal curve for both pores and throats.The genesis of the curves was analyzed and pore-throat radius distribution patterns were set up based on core observation and casting thin section identification of the samples.In conclusion

the pore-throat radius distribution curves for dolomite reservoirs dominated by intra-crystalline pores are generally evenly skewed unimodal distribution

except for some tinny peaks beside the main summits caused by the development of local micro-fractures.The curves may show obvious multiple summits with pores converging along some residual sedimentary structures such as bedding surfaces.All the curves may show the multi-modal distribution with increasing numbers of inter-crystalline dissolved pores under stronger dissolution that indicates high heterogeneity of reservoirs.