The authors focus on the ultra-low permeability reservoirs of Chang 4+5 reservoir period of Yanchang Group, Jing’an oil field, Ordos Basin. Cores, thin sections, wireline logs, and imaging logs were used to understand depositional systems, reservoirs and to furtherly characterize vertical and horizontal distribution patterns of sandstones. The results show that main reservoirs of Chang 4+5 of Yanchang Group are composed of medium-tofine grained arkose. Parallel beddings and cross beddings are common. Interpartical pores and a few fractures are main reservoir spaces and reservoir quality is poor. Sand bodies are uniformly distributed in the horizontal direction with brand shape and thickness between 2 to 5 meters. Front delta is the main sedimentary subfacies. Distributary main channel, distributary shallow channel, distributary shoal, and inner distributary bay are four main sedimentary microfacies. In the vertical direction, distributary main channels and distributary shallow channels are distributed reciprocally related to the variation of hydrodynamic power. The research result is a guidance on the hydrocarbon exploration in this region.

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.

Based on the current situation of stress direction change and its mechanism insufficiently understanding during oilfield development, anisotropic drilling from four cores in Chang-6 oil layer group of a block of Ansai oilfield in Ordos basin, stress direction relative change is measured respectively in dry sample and stratigraphic condition and analyzing the machanisms of effects. Results indicate that there is an obvious difference under the dry sample and stratigraphic condition, which suggests that it has an important meaning to test stress under in-situ condition. Maximum horizontal principal stress direction changes from 4.65° to 8.73° during oilfield development, the average is 7°, and analysis of characteristics of reservoir physical property and mechanism of rock fracture suggests that “natural channel” has an important control function to in-situ stress direction change. Combined with the initial in-situ stress direction, current stress direction of the study area is regarded as about NE58°. The conclusion does make crucial sense to oilfield reconstructive measure such as well network adjustment and artificial fracturing.

In the middle and late stage of oilfield exploitation of multi-period superimposed channel tight sandstone oil reservoir in Ansai oilfield, water content of the well is increasing and the effective production of the reservoir is uneven. The breakthrough and water-flooding occur easily during the integral fracturing, which can’t be adapted to the oilfield production situation today. In order to solve this problem, rock mechanics model and triaxial stress field distribution model are built by subdivision and correlation of single sand body between oil and water wells, full-length fracturing numerical simulation are carried out by combining with fracturing parameters design, stress intercalations were formed, which could constrain the distribution of fracturing fracture. Although fractures in the intercalations are formed during fracture operation, gaping fissures are closed with the decrease of pump pressure so that propping agents can’t enter into the intercalations to cause effective fractures, effective production of single sand body in the reservoirs is uneven, and effective producing degree of 60% of layers is relatively low. Thus for the 11 wells which have a low producing degree in the small layer, measures of additional perforation, multiple fracturing, shutting off water and exploitation when separated with other pay zone are proposed, which have an apparent stimulation effect after site implementation. Average daily increase of production is more than 1.2 t. In summary, the technique approach system of subdivision and fracturing treatment of multi-period superimposed channel tight single sand body is formed, which could guide the future development of the similar reservoirs.

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.