Oil & Gas Geology ›› 2012, Vol. 33 ›› Issue (5): 778-784.doi: 10.11743/ogg20120515

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Features of fractures in shallow- to mid-depth reservoirs with ultra-low permeability and their comparison with those in deep reservoirs in Anpeng oilfield,the Nanxiang Basin

Gong Lei1, Zeng Lianbo1,2, Li Juan1, Jiang Jianwei3, Tang Xiaomei1, Wang Zhaosheng1,4   

  1. 1. College of Geosciences, China University of Petroleum, Beijing 102249, China;
    2. Key State Laboratory of Petroleum Resource and Prospecting in China University of Petroleum, Beijing 102249, China;
    3. Research Institute of Exploration and Development, SINOPEC Henan Oilfield Company, Nanyang, Henan 473132, China;
    4. College of Mining Engineering, Hebei United University, Tangshan, Hebei 063009, China
  • Received:2012-01-10 Revised:2012-08-18 Online:2012-10-28 Published:2012-11-15

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Abstract:

Based on data of outcrops,cores,image logs and thin sections,we analyzed the features of fractures in the shallow- to mid-depth reservoirs in Anpeng oilfield of Nanxiang Basin,compared them with that of the deep reservoirs,and determined the main factors controlling the development of these fractures.The study suggests that there are two types of fractures in the shallow-to mid-depth reservoirs in the Anpeng oilfield:the tectonic fractures and the diagenetic fractures.The former of high dip-angle dominates the study area with an average linear density of 0.42/m and a height of generally less than 0.40m(averaging at 0.25m),which indicates that fractures are confined within the layers.Micro-fractures are very important channels for connecting the intergranular pores and intragranular dissolved pores,and enhance reservoir pore connectivity.Affected by horizontal tectonic compressions during the Early and Late Himalayan movements,three sets of tectonic fractures were formed in the study area,i.e.E-W,NE-SW and NW-SE striking fractures.The E-W fractures were developed better than the other two sets.The formation and distribution of these fractures in the oilfield were controlled by such factors as the tectonic stress field,lithology,porosity,permeability,layer thickness and structures.Under the same controlling factors,the fractures in the shallow- to mid-depth reservoirs of the field are thought to have the similar genetic types,occurrences and development characteristics to that of the deep reservoirs,but slightly lower degree of development than that of the deep reservoirs.

Key words: fracture, deep reservoir, shallow- to mid-depth reservoir, Anpeng oilfield, Miyang Sag, Nanxiang Basin

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