Reservoir fracture characteristics and generation analysis in Anpeng oilfield, Biyang depression

The paper described the features of extra-low-permeability reservoirs in deep-buried zones of Anpeng oilfield,Biyang depression, Henan province,central China.The buried depth of reservoir is 2 800~3 100 m,The reservoirs are composed of fan-delta facies deposits.The composition and texture maturity of reservoir rocks is lower.The reservoir porosity distribution ranges 5% to 6%,the permeabilitydistribution ranges 1×10^-3 to 2×10^-3 μm².There are more natural fracture developed in Anpeng oilfield.Research on coring and FMI logging indicates that the main fracture occurrence in reservoirs is in a high degree or in vertical.The vertical fracture groups occurrence in reservoir.Adopt advanced technique-oriented coring to get the fracture azimuth.The rosette azimuth diagram shows that the open fracture azimuth range 90°to 110°.The fracture length distribution range 4 to 30 cm,the fracture apertures are smaller than 1 000 p.m, the density of fracture is 0.7 per meter,the formation fracture porosity range 0.2% to 0.3%.There are some secondary calcite fillings in the side of fractures.The space between fractures is 2 to 3 cm.It includ the extention fractures and shear fractures.The regional tensile stress is the causes of fracture.The secondary calcite stable isotope measurate of the fillings in fracture and the acoustic emission tests of the reservoir rocks indicate that there are four fracture generations.The second generation is the main fracture period.There are two main factors to affect the fracture developing:one is the structure stress field;another is the nature and the thickness of the reservoirs.Finally,the relationship between thicknes and fracture space is established.