Analysis of characteristics of low-permeable reservoir with micro-fracture and their origins of the Neogene Youshashan Formation in Nanyishan Oilfield，Qaidam Basin
Zang Shibin, Cui Jun, Zheng Yongxian, Xu Wenmei, Wei Jinxing
Research Institute of Exploration and Development，Qinghai Oilfield Company，PertoChina，Dunhuang 736202，Gansu
Abstract：The reservoir characteristics of the Youshashan Formation of the Neogene in Nanyishan Oilfield were analyzed according to core observation，thin section identification and X-ray diffraction.The lithology of the reservoir can be classified as mudstone，carbonate rocks，sandstone and hunji rock.The clay content of the rock is high and the reservoir properties are complex.Intergranular pores，dissolution pores，micro-pores and micro-fractures are developed，so the reservoir has the characteristics of dual porous media.In general，the physical properties of the Nanyishan reservoir are poor.It is pointed out that the micro-fractures play an important role in the flowing of formation fluids，but micro-pores contribute little to the flowing.The micro-fractures in the reservoir include tectonic micro-fracture，dissolution micro-fracture，and diagenetic micro-fracture.Sandy lamination and argillic or marlaceous lamination are developed alternately in the rock.The unbalanced force，dissolution and shrinkage of reservoir rock during sedimentation and diagenesis resulted in the formation of micro-fractures which improve physical properties of the reservoir.However，compaction and cementation happened simultaneously，which destruct the reservoir properties.The mercury injection curves of the reservoir are composed of two parts: Inclined upward curve and approximately horizontal curve.The tilted curve represents the micro-fracture，and nearly horizontal curve represents micro-pores.Parameters such as threshold pressure and mean pore radius cannot be used to evaluate the reservoir correctly.So，a parameter of effective pore radius is put forward in this paper and can be applied to evaluate the reservoir properly.
. Analysis of characteristics of low-permeable reservoir with micro-fracture and their origins of the Neogene Youshashan Formation in Nanyishan Oilfield，Qaidam Basin[J]. JOPC, 2012, 14(1): 133-141.
