Theoretical Research For Horizontal Wells Productivity Analysis In Low Permeability Reservoir

Horizontal well's technique of mining has become an important means of enhancing oil recovery, digging old oilfield and developing new oil fields. It was more widely used in developing and designing oil field. Especially for the low permeability reservoir, it's hard to obtain good economic benefits with using normal vertical wells technique, but we can obtain some production capacity if we developed low permeability reservoir with horizontal wells. At present, the fruit of analysis and calculation to horizontal well's production is more on research reservoir engineering. The research of filtration theory was very rare in domestic and foreign, which was that apply branch wells, horizontal wells combining vertical wells to develop low permeability reservoir. It is at initial stage and it is a new research theme for reservoir workers. In view of the feature that filtration law was not Darcy law and starting pressure gradient was ubiquitous presence in low permeability reservoir, adopted fundamental principle such as dynamic of fluids through porous media, reservoir engineering and so on, filtration theory was systematically studied, it was that low permeability reservoir was developed by the combination of horizontal well, branch well and straight well. Established deliverability equation under the situation that hole pattern was jointly developed by the combination of horizontal well, branch well and straight well, this article mainly made such cognizance and result as follows:Single well development filtration theory of horizontal well in low permeability reservoir was studied under different boundary conditions and so did branch well development filtration theory. Used potential's principle of superimposition, conformal transformation and equivalent filtrational resistance, considered starting pressure gradient, established deliverability equation of horizontal well and branch well of low permeability reservoir. The equation was simple and it had more accuracy degree. The computational solution to horizontal well's deliverability of low permeability reservoir showed the equation was much close to actual horizontal well and branch well's deliverability of low permeability reservoir.Derived deliverability computational method under the situation that different hole pattern was jointly developed by the combination of horizontal well, branch well and straight well in low permeability reservoirs. The influence of various factors is analyzed. The computational result of the formula showed that with the increase of starting pressure gradient, well network's production of horizontal well and branch well decreased; with the increase of penetrated ratio, starting pressure gradient's degree of influence on different hole pattern of horizontal well and branch well decreased.Established non-stabilized flow mathematical model of horizontal well of low permeability reservoir, drew effective drive factor which included such as parameters: starting pressure gradient, pressure and radius and so on. From effective drive factor, starting pressure gradient and so on angles, we analyzed affecting factor on horizontal well's production. The result showed that with the increase of starting pressure gradient, horizontal well's production was gradually reducing; with the increase of effective drive factor, horizontal well's production gradually increase.The flow theory of oil-gas two-phase of horizontal well in low permeability reservoir was studied, established mathematical model oil-gas two-phase flow. By the calculation and analysis of analysis example, when BHFP was same, the smaller starting pressure gradient was, the higher the production was. We should decrease starting pressure gradient's influence for low permeability reservoir as far as possible.Horizontal well's inflow-out performance of low permeability reservoir was studied, selected bottom of a well as a node, horizontal well's reasonable production was given under different starting pressure gradient. This theory had some reference value for choosing reasonable working system and reasonable output of low permeability reservoir's development with application horizontal well on oil field.This paper's fruit focused on theory research about developed low permeability reservoir with horizontal well, especially deliverability calculation method was given. The method was developed by the combination of branch horizontal well and vertical well in low permeability reservoir. It has provided a new theory basis for low permeability reservoir's s development, at the same time, it has expanded theories and methods of horizontal well production forecast.