Physical properties and main controlling factors for the low-permeability reservoirs from A oil field in the Ordos Basin

The Chang-2 reservoirs in A oil field in the Ordos Basin dominantly consist of fine-grainded feldspar sandstones which have low porosity and low-permeability,with an average porosity of 12.6% and an average permeability of 10.7×10^-3 μm²,respectively.The physical properties are mainly controlled by sedimentary microfacies,diagenesis and fissure development and scales.The braided channel bar medium-to fine-grainded sandstones have higher porosity and permeability,while the natural levee siltstones and fine-grainded sandstones have lower porosity and permeability.The mechanical compaction in the early diagenetic phase and cementation of carbonate cements serve as a main cause of the loss of the porosity in the Chang-2 reservoirs.The dissolution may improve the physical properties of the Chang-2 reservoirs.The fissures may contribute to the increase of the permeability of the sandstones.