Summary The Fuyu oil field is a typical shallow, low-temperature, low-permeability reservoir. At present, the oilfield composite water cut is 95%, artificial fractures interlace with natural fractures, and the distribution of ineffective circulation channels between wells is complex. This paper found that after reducing the permeability of the original fracture, refracturing can effectively improve the longitudinal extension range of the new fracture through numerical simulation. Therefore, a controllable permeability temporary plugging agent is studied, and controllable permeability refracture technology is proposed. The controllable permeability temporary plugging system is composed of elastic particles, quartz sand, and quick-soluble elastic enhancers, which are based on elastic particles that do not age, and long-term plugging can be achieved. Through physical experiments, 0.5–1-mm elastic particles with 70–140 mesh and 16–30 mesh quartz sand were used in different ratios (i.e., 5:5, 6:4, and 7:3). According to the closure pressure and the permeability of the fracturing layer, the ratio chart of elastic particles and quartz sand is established. The controllable permeability refracture technology can select the ratio of the quartz sand and elastic particles according to the closure pressure and the control requirements of the fracturing horizon permeability. Through field applications, we found that, compared with the conventional refracturing technology, the average daily fluid gain per well decreased from 5.0 to 3.9 tons, and the daily oil gain increased from 0.3 to 0.6 tons. The controllable permeability fracturing technology could reduce the permeability of the original fracture and improve the vertical production degree of the reservoir after refracturing. In addition, this method ensures that the original fracture has a certain conductivity and that the high-permeability layer reserves are not lost due to temporary plugging agents, thus expanding the planar sweep volume and effectively improving reservoir recovery. Nevertheless, the chart established is mainly suitable for shallow reservoirs, and the closure pressure is 3–15 MPa in this paper. Further testing and research are needed for deep reservoirs.

Based on the sedimentary character of six time cells in P1 Beierxi of Sabei developed region in Daqing oil field, this paper applies fuzzy mathematics method to divide reservoir flow unit. At present, there is no uniform division method, because flow unit is a fuzzy set with multi factor influence. There is great uncertainty among every influential factor, so does the influence extent of every factor to flow unit division. It isn’t objective to divide flow unit by one factor or simple congruence of several factors. However, the fuzzy mathematic method is fit to analyze the uncertainty relation in system or among systems. When the data of core well is in defect, applying the fuzzy clustering method to divide flow unit and combining development practice can reduce human factor greatly and make classification more objective and rational.

Combining with static information of injection wells and using effective thickness, number of layers greater than 1 meter and ratio of 3 to 4 connected thickness greater than 1 meter as evaluation index, this paper use cluster analysis method to category injection wells of west and east blocks in north first and second row of Sazhong development area in Daqing oilfield. Then, with evaluation of accumulated increased oil per unit thickness, using single dependent variable two-factor variance analysis method to optimize injection rate and injection concentration of injection well groups which have been classified into different types.

Reduction effects of grass on runoff and sediment yield and its mechanical mechanism of grass was studied under rainfall intensities of 45, 87 and 127mm/h with 20°slope gradient using simulated rainfall experiment. the results showed that average runoff rates ranged from 39.7 to 126.0 L/min for bare plots and 0.34 to 6.22 L/min for grass plots, and the runoff rates from grass plots were much less than from bare plots. Average sediment yields varied from 3636.7 to 9436.3 g/min for bare plots and from 26.7 to 581.5 g/min for grass plots. The critical flow shear stress of 2.85 N/m2 on grass slope and 0.861 N/m2 on bare slope were got under experiment condition. The sediment yield increased with the increase of flow shear stress. The experiment results are meaningful for quantifying runoff and sediment reduction and deepening soil erosion mechanical process also.

There are various shapes of capillary tubes in the rock, and the flow in triangles and rectangles capillary tubes has been studied very little. In this paper, the approximate solution of the distribution of the velocity in triangles capillary tubes has been obtained using variational method. The quantitative relation between pressure difference and flow rate in the two kinds of capillary tubes has been obtained by integrating in the entire capillary tubes, which is similar to Poiseuille's law. this study also applies the Pdetool tool in Matlab to solve the laminar flow of different sections in capillary flow numerically and compares the variational results and numerical results with the literature analytic solution, numerical solution and the experimental results. On the foundation of comparing the variational results, the numerical results and the literature analytic solution, numerical solution and the experimental results, we analyze the influence of the power-law index and cross-section shape on the comprehensive resistance coefficient and flow pressure relationship.