Research On The Multiple Fracturing Mechanism Of Low Permeability Fractured Reservoir In Daqing Oilfield

There are many high water cut wells and breakthrough layers in the Daqing peripheral oilfields, most of those breakthrough layers are main formations. As peripheral oilfields put into production in fracturing way, fracturing water breakthrough and low recovery are common, and with the oilfield developing the number of high water cut wells increases year by year. For these wells, multiple fracturing and water plugging technology in the same well and layer are not good for remaining oil development of high aquifer, and measure effect is poor which resulting in high water cut wells shut-in finally. The shut-in of these wells not only affected the adjustments of injection-production strategy, but also caused large idle assets. In order to develop remaining oil further, we must explore remaining oil seeking technology adapt to the high water content wells. To operate in the peripheral low-permeability oil fields of Daqing at large scale, there are a range of issues need to be solved by field tests, such as the criteria of selecting well and layer, operation optimization and adaptability to other low permeability oil fields. If problems mentioned above can be solved by field test, it will provide technical support for low-permeability oilfield development during high water cut stage and it will be significant for improving the producing degree of peripheral "three low" reservoir and ensure the oilfield stable yield 40 million tons/a. All of these have long-term economic and social benefits.In this article, according to a large number of researches about reservoir multiple fracturing mechanism at home and abroad, based on the previous work, we studied the multiple fracturing mechanism of low permeability fractured reservoirs in Daqing. Based on the numerical simulation model, we analyzed the remaining oil distribution, according to the orthogonal design method and grey correlation method, we analyzed the sensitivity of reservoir stimulation, by means of breakeven analysis, and we got the fracturing economic limits and developed software. The economic limits resulted coincided to actual field. The main results of the article are as follows:We summarized the geological and development characteristics of fractured reservoirs. In order to study fracture steering, the mechanical model of the total stress field is established, the total stress field around the well 10C76-118 is calculated and the total stress field data after stress field superposition is solved. According to mechanical characteristics of the fractures, we discussed the multiple fracturing mechanics criteria.Based on the mechanical conditions of multiple fracturing for new fractures, we made mechanical analysis on the new fracture, thus the fracture initiation angle is determined under the condition of completely tensile failure and total shear destruction, further determined the condition fracture initiation angle should satisfied with:0°<θn< 45°.According to the stress analysis around the multiple fracturing fractures, we calculated the boundary stress influence coefficient, analyzed factors impacting on the multiple fracturing fractures, the stress field distribution after 1000 days in C55 blocks is simulated, and then we obtained the extension track of multiple fracturing fractures. The 3D geological model of block is built with Petrel software, the numerical simulation model is established with Eclipse software, and we corrected the production history, analyzed remaining oil distribution for the block. We found that the coincidence rate for earlier stage fitting is better than the later one. The coincidence rate of the whole region fitting is more than 90%, and the single well compliance rate is over 85%. The flooding radius after fracturing is larger than the one before fracturing, which is consistent with the field results.We made single factor analysis on cumulative oil production of block, and analyzed the sensitivity of factors affected fracturing combined with the orthogonal design theory and grey correlation method. According to breakeven analysis, the technical and economic limits of fracturing for different index are determined with the cost, revenue and tax formula, and we developed the software for it.