| The reservoir of Yanchang group in Ordos Basin Zhenjing exploration area is oflow porosity and low permeability or even ultra-low permeability, poor reservoirproperties and strong heterogeneity. The existence of fracture increase the percolationcapacity of the reservoir to some extent, and provide to the oil and gas resvoir spaceand migration pathways. In2009, The Honghe42well, a exploratory well in thesoutheast of Chuankou target area, perforated the Chang9oil layer and well tested for3.88T oil, which declared the new breakthroughs of Chang9. In2010,10exploratorywells and7appraisal wells have been deployed in Chang9reservoir, which openedthe prelude of the study of Chang9oil-producing. Drilling and geophysical resultsshow that fracture develops in this area. What’s more, porosity-permeabilityrelationship also show its dual media pore type in experimental analysis. Therefore,the role of the fault and fracture system can not be ignored in the Chang9oil layer.Discussing the study area characteristics of fracture and its distribution can providethe basis for reservoir development of Chang9in Zhenjing exploration area.On the basis of in-depth understanding and analysising the tectonic evolution ofthe Ordos Basin, the work of researching the fracture characteristics and itsdistribution is carried out. It can be seen from the tectonic evolution that Chang9hasgone three major tectonic movement, namely, Indo-China movement, Yanshanmovement and the Indosinian part of Himalayan movement. In Indo-China period, thebasin basically continued the pattern of high north side and low south side in CratonBasin. Then in Yanshan period, a counter-clockwise rotation happened to the basin,which made the ancient structual surface change from high west and low east that hasbeen in existence since Paleozoic to high east and low west. At last, in Himalayanperiod, intense rifting and stretching activities happened. By observation of fracturethrough the fracture in outcrops and core, grouping, occurrence, development density,opening width, length, effectiveness, threading layers and so on of fracture areanalyzed.According to the observed characteristics of fracture, the responsecharacteristics of the fracture in the conventional well logs is analysised, and various lithology fracture comprehensive identification standard that base on conventionallogging are established. Fracture comprehensive identification of73exploratory wellsin study area has been done by application of this standard. Then imaging loggingfracture identification is carried out, and the tectonic fracture and high resistancefilling fracture are identified, and occurrence and trends of fracture are extracted. It isconcluded that, lithology, thickness, faults, the regional tectonic stress and so on arealso control the development of the natrual fracture. Combined with the results ofregional tectonic evolution, isotope analysis and rock acoustic emission test, it isfound that the advantage group of the fracture NEE-near EW and conjugate groupNW and NE, is relevant to Yanshan and Himalayan movement, mainly Yanshanmovement. Using Flac3D stress simulation software, the ancient stress field of theHimalayan and Yanshan period is simulated. According to the coefficient of the rockfracture, plane is divided to fracture developed area, fracture relatively developed areaand no fracture developed area. Further more, the development index of the fracturenear the fault is predicted. Combined with this two analytical methods, planedistribution of the fracture is sumerized by superposition, which is in good agreementwith single well fracture development index that identified by logging. |
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