Quantitative Description Of Reservoir Fracture In The Second Member Of Funing Formation Of Tian 33 Fault Block In Tongcheng Fault Zone

Tian 33 fault block is located in the eastern flank of Tongcheng fault zone of Jinhu sag,Subei basin;Tongcheng fault was a zone-scale transfer fault in the late of Funing period,and then became a right-lateral strike-slip fault in the late of Sanduo period.The second member of the Funing formation of Paleogene is the target layer,which has a poor reservoir property,the lithology of which is composed of siltstone with of low permeability,and fractures play a vital role in oil and gas flow in this layer.This paper is based on the effective demand of exploration and development of oil field,and has carried out the related work in terms of the core fracture orientation in deviated borehole,the characterization of fracture kinematics,the quantitative prediction of fracture permeability tensor,the fracture development model,and the reservoir development suggestions.In order to accurately achieve core fracture orientation of the deviated borehole,based on the bed attitude method and the dip logging method,the ideas and the corresponding algorithm of core fracture orientation of deviated borehole is proposed,and it is applied to the core fractures observation data in Tian 33 fault block.In the process of the core fracture orientation of deviated borehole,the true attitude of fractures can be obtained only after correcting for deviation.Before the deviation correction,the strike of core fractures advantage direction is N-S direction,and after the deviation correction,it is nearly E-W direction,which is in step with the late oilfield dynamic data analysis and regional tectonic stress field.By the data analyzing,it is found that whether borehole deviation's correction is needed can not be simply based on the relative size of inclination,because the formation angle and fracture angle also affect the inclination of fractures.The correction algorithm is also applicable to other linear and planar geological body observed in the cores.According to the fact that tectonic fracture attitude evolution is difficult to accurately quantitative prediction,by determining the mechanical properties of fractures and the mechanic parameters of rocks,based on the restoration of the ancient tectonic morphology,the optimal failure criterion has been selected after making numerical simulation of ancient stress field in the fracture period and get fracture occurrence distribution.Put forward to new idea to predict ancient fracture occurrence by fracture stress field and reconstruct fracture occurrence by the late tectonic activity.That is,through the three-dimensional spatial variation rule of rock strata of early and late,established the fracture space corresponding to different tectonic active period of the transfer theory,utilizing the mathematical derivation of the algorithm,the quantitative analysis of evolution of fracture,and then to improve the prediction accuracy of the fracture occurrence.Combined with the tectonic evolution,the tectonic fracture evolution can be divided into three stages:the formation of fracture in late of Funing movement,the development of fracture in the Dainan movement,and the separation of fracture in the Sanduo movement.Aiming at difficulties to quantitatively predict fracture permeability tensor,present liner density of fracture was predicted based on the facture surface energy theory and the rock strain energy theory of fracture mechanics.According to the results of present stress field numerical simulation,fracture opening was calculated in three direction extrusion stress state and then present facture parallel permeability was determined.By using present fracture attitudes,static and dynamic coordinate systems were unified into geodetic coordinate system,a quantitative prediction model of multi-group fracture permeability tensors was constructed,formula for calculating the principal value of permeability and main value direction were given,and permeability at different directions in unit body was predicted by adjusting the dynamic coordinate system rotation angle.Three parameters,the ratio of the maximum and minimum value of the permeability,heterogeneity coefficient of permeability and variation coefficient of permeability,were defined to quantitatively evaluate fracture permeability heterogeneity.Present in-situ stress state for wells is determined using the core velocity experiment and micro seismic monitoring technology;the magnitude of present in-situ stress for wells is determined by the combination of the fracturing data;numerical simulation of present stress field is carried out by ascertaining the rock mechanical parameters and establishing the finite element model;reservoir natural fracture open pressure and open sequence are predicted on the basis of fracture occurrence and present stress field simulation state.The results are shown as follows:the orientation of the present maximum principal horizontal stress is N-E-E direction;fractures of N-E-E direction open first and fractures of S-E-E direction open afterwards in the process of waterflooding;fracture open pressure increases when the angle between fracture direction and maximum horizontal stress direction increases;fracture depth and open pressure also have positive correlation,fracture open pressure is between 25MPa?45MPa at high location of structure(1850m?2350m)and 45MPa?75MPa at lower location of structure(3300m?4000m);it is proposed that different blocks use different injection pressure so as to ensure high and stable production of oil and gas wells by calculating actual reservoir breakdown pressure.