Study On The Effect Of Fractures On The Water Flooding In Low Permeability Reservoir At Ansai Oilfield

As a result of the complex fractures in the low permeability reservoir, the water-oil displacement effect in the low permeability reservoir is not satisfactory. This dissertation analyzed the macro pore structure character of the fractured low permeability reservoirs. Combining with core displacement experiments and visual plane model experiments, the percolation flow law of the fractured low permeability reservoirs was studied. The effect of fractures on the water displacing oil in low permeability reservoirs was also analyzed. The main research results are as follows:Fractures make the great contributions to the improvement of permeability and lead to no strict correlation between permeability and porosity.Overflow pressure experiments on fractured low permeability sandstone cores show that under the higher confined pressure the overflow phenomenon is more obvious. The percolation flow curves of the single phase indicate that under the higher confined pressure the nonlinear percolation flow curve is similar to a straight line. The character of oil/water relative permeability was analyzed, a small range of two phase flow of oil and water, a high residual oil saturation, the water-phase relative permeability curve raising to the left.The cores from Chang 6 reservoir were studied by water displacement oil experiments, and the effect of the fractures on the water displacing oil law is also analyzed:(1) the fracture cause water channeling, and the final displacing efficiency is low; (2) the fracture has little effect on final displacement efficiency, but it decrease the non-water displacing efficiency; (3) the fracture make no effect on the water displacing oil.Based on the micro-models with small size and poor visibility, a new improved testing method of the visual plane models was established. The experimental results of the visual plane models including an injection well and a production well were consistent with the simulation results, showing that the visual plane model is effective and accurate. Using the visual plane model, the effect of fractures on the well pattern arrangement was studied. It indicates that the rhombic inverted nine-spot well pattern was more effective than the square inverted nine-spot well pattern. After applications of adjustment measures for the well pattern, the row well pattern was recommended for the development of fractured low permeability reservoirs.The equivalent fracture flow model was established based on the continuous medium theory. With the use of it, the steady-state productivity equation was set up in fractured low-permeability reservoirs. Through the application of the productivity equation for the example calculation and compared with the actual production data, the correctness and universal validity were confirmed. The influences of fracture characterization parameters on productivity were analyzed by using the model, which includes the fracture width, the fracture length and the fracture permeability.