Through the analysis of casting thin sections, 3D geological modeling, special logging series and micro seismic monitoring, reservoir stress characteristics of Jing’an area were studied. The results show that: 1) the distribution of the direction of micro pore and throat would cause the stress anisotropy; 2) differences in each layer of Chang 4+5₂ sandstone are big, the lateral superposition characteristics of multi-periods channels have the major influence on stress distribution; 3) the stress difference in the study area is generally not large with the value of 3?6 MPa, with the development of water flooding development, the variation of the two main stress varies in the reservoir, resulting in the multi-directional development of fractures in the process of repeated fracturing. The results can provide a scientific basis for improving oil recovery in the middle and late development of low permeability reservoirs.

Through the core observation, inter-well tracer test and water flooding front test, the fracture development characteristics of Chang-7 tight sandstone reservoir in Xin’anbian area of Ordos Basin are studied. The results show that maximum horizontal principal stress direction of Chang-7 tight sandstone oil reservoir in Xin’anbian area is NE60°?80°. The fracture type is mainly high angle fractures or vertical fracture, and fracture direction is NE75°?85°, the dip angle is 70°?85°. Dynamic monitoring data analysis shows that the micro fracture research area of tight sandstone oil reservoir developed widely and plays an important role in increasing the seepage channel and improving the permeability of matrix, water channeling easily along the fracture formation, resulting in the production of well water is fast. 3D geological modeling results show a high degree between oil saturation of tight sandstone oil reservoir in the study area and the degree of fracture development, which can effectively support the fracture of oil and gas reservoir and accumulation.

As to Chang 4+5 formation of special low-permeability Baiyushan reservoir in Ordos Basin reservoir, the hydraulic fracture distribution is not regular and difficult to predict. The method of traditional engineering geology and special logging, conventional well logging, micro facies research were combined. Through the stablishment of three-dimensional rock mass mechanics model of reservoir, the full length fracturing numerical simulation was carried out with the change of stress field. More accurate geometry parameters of fractures were got, stress interlayer insulation could be regarded as a kind of new development of geological property which would play an important role in fracture extension, then the development adjustment measures are put forward. The conclusion would provide an important scientific basis on decision-making efficiency in low permeability reservoir development and improve the residual oil recovery degree.

In order to study the effect of confining press and pore press on permeability, the new method of evaluation on stress sensibility is proposed. Three pieces of low permeable reservoir rock samples in Songliao Basin are selected. A servo-controlled triaxial rock mechanics test system is employed to investigate the permeability of sandstone samples under conventional conditions and in situ conditions. The results show that: 1) The permeability of three pieces of samples reduce with confining press increasing and pore press reducing. 2) The denser the rock is, the stronger stress sensitivity is, in situ conditions, which explains the mechanism of low permeability reservoir sensitivity differences by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), constant speed mercury injection experiment. What’s more, throat size and shape, plastic mineral content and type contribute to the differences of permeability sensitivity. 3) Mineral content and type of plastic are the major factor of the sensitivity of permeability differences. The stress sensitivity of tight reservoir permeability rock becomes strong with the increasement of mica, clay and other plastic mineral content. In the practical work, evaluation on stress sensitivity of permeability, the effect of confining pressure single factor is mostly considered, butthe effect pore presss would be ignored, which is bound to bring larger human error. So evaluation on stress sensibility in situ conditions is essential, which is significant for further understanding of stress sensitivity of low permeability reservoir characteristics and development.

After two infilling adjustment and repeated fracturing on the third type of Chaoyanggou oil field, effective drive systems are still unable to be established in part of the reservoirs, and the measure effect and oil recovery degree is poor. Considering the insufficient understanding on fracture extending and fracturing stimulation scale of heterogeneous reservoir, 3D modeling on reservoir are performed by combining logging and seismic data and the asymmetric cracks are predicted based on elastic theory. Concepts named “relative stress” and “stimulation ratio” are raised, and the nonlinear relation between these two parameters is given. The scale of “relative stress” which could produce the supporting fracture is confirmed, and the fracturing stimulation scale could be judged. It would play important role on the layers selecting during the late development of oilfield and eventually to improve oilfield recovery degree.

For the sake of solving the problem in Daqing Fuyang low permeability reservoirs which is scattered distribution, and changes so rapidly in the mechanical properties of rock that restricts the reservoir reconstruction, a new method was presented in this paper. On the basis of lots of rock mass mechanics model of in situ experiments, the relationship between P-wave and S-wave velocities was studied, and P-wave and S-wave velocity bodies from pre-stack elastic parameter inversion were obtained. Besides, the rock mass mechanics parameters according to rock physics equation were gotten and the multiple regression analysis method was used to get well point elastic parameter values. The well points and cross-hole elastic parameter values were combined, and geostatistics method was utilized to establish the heterogeneity of rock mass mechanics field. The geological basis was provided to optimize hydraulic fracturing parameter design to increase production.