Fracture length of fractured well is the important factor to determine the fracturing effect. Taking the diamond shaped inverted nine spot pattern in a block of Xinjiang oilfield as an example, based on the reservoir numerical simulation software.Considering the starting pressure gradient and stress sensitivity, the cumulative degree of reserves recovery of crude oil is simulated under the conditions of different fracture length. The relationship between the reserves recovery degree of hydraulic fracture and comer well, edge well and central well is analyzed. The comparison results show that: the fracture of edge well may give rise to the invasion of injected water, corner well cannot be affected by injection well, causing the precipitous decline of production rate in corner well. For the central injection well, it is not only to reduce the fracture length in order to improve the water drive spread coefficient, but also to ensure that the length of the fracture is enough to supplementary formation energy. The best solution: the diversion capability of fracture is 20 μm2·cm,the fracture length of corner well is 100 to 120 meter, the fracture length of edge well is 50 meter, the fracture length of central well is 50 meter. This conclusion provides new recognition for the optimization of fracture parameters.

For the sake of environment protection, shallow formation waters were studied for the preparation of guar gum fracturing fluids in gas fields, west Sichuan. The fracturing fluid prepared with formation water had viscosity of 100 mPa·s after shearing 60 min(170 s-1) at 45 ℃, rate of permeability impairment of only 23.86%, surface tension of 27.82 mN/m, rate of swelling reduction of 87.5%, residue content of 518 mg/L. The formation water fracturing fluids were successfully used in SF382 and SF384, which respectively improved natural gas production of 1.14×104 m3/d and 1.68 ×104 m3/d. This technology enabled the reuse of formation sewage water in gas fields.

The MA18 block of Xinjiang oil field belongs to lowpermeability reservoir, whose pressure sensibility is medium to strong. Fracture is adopted to develop this block. The effect of fracture was simulated by diamondshaped inversed 9 point pattern using Eclipse. The threshold pressure gradient and the voltagesensitive effect were taken into consideration in this pattern. Considering the position diversity of edge well，corner well and central well in the field of seepage flow， the different length of fracture was simulated In this way, the optimum parameters of the fracture were obtained. Finally, the regression relation of the fracturing effect and the fracture parameters acquired by the simulation of FracproPT were got which could guide the construction of optimal project efficiently.

 

The high water cut oil wells were unable to product normally because of the existance of fracture and natural microfracture in the low permeability fractured reservoir. In order to avoid the injected water going across to the old seam of oil wells in the process of water flooding and enhancing the sweep efficiency and oil recovery, the superfine cement plugging technology was put forward. Based on the optimization of water cement ratio of superfine cement, the concentration of corrosion inhibitor, reducing agent and defoaming agent in the plugging system was optimized, and the mechanical deformation capacity was also evaluated. The results showed that the optimum water cement ratio of superfine cement was 0.7 and the optimum cement slurry was the mixture of 800 head superfine cement, 0.4% corrosion inhibitor, 0.5% reducing agent and 0.5% defoaming agent. Because of the double efficacy of plasticizing and toughening, the slurry system had good mechanical deformation capacity and the flexural strength reached 48.9 MPa. This can completely met the plugging strength requirements in the field. This system has good application prospect in the old seam plugging of oil well in the fractured reservoir.