| The multilateral well technology can increase the drainage area and the productivity as well as reducing the cost of development. From the low permeability reservoir, heavy or thin oil reservoir and the fractured reservoir, the application extends to the high permeability reservoir. It becomes one of the major achievements and key technology in today’s top oil industry. How to correctly predict the productivity and establish the reasonable development scheme has been a hot and difficult topic in recent years.Due to the multifarious characteristics of reservoir and types of well, even the well structure and the interaction with fluid is much more complex, it’s very difficult to establish the real physical model, only to employ the electric simulation experiment. Based on the analytic formulas of horizontal well and the radial branch well, as well as the herringbone well, according to the similitude principle, this paper has implemented the electrical experiment regarding to a field in Iraq, studying the influence of the branch length, the branch number, the branch angle, the main hole length and other parameters on productivity. In addition, for the first time, this paper has designed the stacked electrical simulation experiment, through which it discusses the influence of interlayer interference and interlayer parameter differences on the productivity.The qualitative relationship between shape of the equipotential line and the branch number is obtained. The optimal production formula for the target reservoir is obtained by contrasting after converting experimental results into actual productivity through the similarity coefficient. Combined with the test data, for the radial branch well, the branch length, branch number and well diameter are optimized. For the herringbone well, the morphological parameters (branch angle, branch number, branch length and the spacing) and the distribution parameter (the symmetry, the branch points and the distribution) are optimized. The effect of well position in layered reservoir on productivity is discussed. The stacked electrical simulation experiment is designed for the first time. The results of this study are as follows:(1)Through the equipotential lines description for radial wells with 3 or 4 branches and herringbone wells with 2 or 5 branches, it can be seen that they are relatively concentrated at the end of the branch, where the pressure gradient is larger. Then, the drainage area is increased with more branches. Moreover, the whole equipotential lines approximate concentric clusters.(2)According to the similarity coefficient, formulas for horizontal well from Merkulovb, Borisov, Giger, Joshi, Renard and Enhong Dou are verified. Result shows that the accuracy of Giger’s formula is the highest, the relative error is only 9.41%. On the contrary, the relative error of Enhong Dou’s formula is as high as 60%, and others remained at about 20%. For the radial wells, formulas from Ta6akoB, Songlin Cheng and Tingxue Jiang are validated, and Songlin Cheng’s formula is of the highest accuracy, its relative error is only 7.07%. There are two calculation formulas for herringbone well, both are deduced by Chunlan Li, and it’s found that their relative error is lower than 10%. If the branches are distributed uniformly, formula deduced before is more suitable, otherwise, the formula in 2010 is more accurate. And both formulas can also be applied to symmetrical or ipsilateral herringbone well.(3)The sensitivity analysis shows that the significance level of parameters’impact on productivity is:branch length> branch number> wellbore diameter. And for herringbone well, the result is:branch number> branch length> the distribution> branch angle. In addition, when the branch is located at both ends of the main wellbore, the productivity is higher than it locates in the middle, meanwhile, the top point’s productivity is much higher than others. When branches are located at the same side, the productivity is slightly lower than other two patterns.(4)About the layered connected reservoir, the influence of well’s location on productivity is discussed. It’s concluded that if the permeability of each layer is vertically random distributed and varies slightly, the position of well has no effect on the yield, whereas the effect is significant, besides, the productivity is much higher than the corresponding single reservoir. If the permeability decreases with depth, well locates in the top layer is of the highest yield. About the layered disconnected reservoir, for the first time, the electrical simulation experiment studying on the productivity law of double stacked multi-lateral well is established. It’s found that reducing the resistance from confluence to the ground or increasing it between layers can greatly improve the problem of interlayer interference. If the pressure of layer A and B is close, the difference of permeability between them has no effect on the yield, otherwise the productivity can be increased by raising the permeability of the higher pressure layer, and the more the difference of pressure, the more significant the stimulation effect. In addition, the well productivity increases with the increase of branch length, and the thinner the reservoir, the growth is more significant. |
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