煤层气井液氮压裂技术研究

发布时间：2018-03-28 05:04

本文选题：煤层气　切入点：液氮压裂　出处：《西南石油大学》2015年硕士论文

【摘要】：水力压裂是煤层气储层增产改造的重要措施。我国的煤层气增产改造技术是建立在中、低阶煤层气开发理论、经验基础之上,对高阶煤层气储层的适应性较差,导致开发过程常面临单井产量低的难题。高阶煤层气储层孔渗性差,增产改造过程需增加煤层破碎程度,提高煤层气解吸和渗流能力,才能大幅提高单井产量。基于提高煤层破碎程度的理念,本文提出了煤层气井液氮压裂技术。在前人关于液氮压裂增产机理和工艺研究的基础上,通过实验、模拟、理论计算等手段对液氮压裂过程中温度场,液氮注入对煤层岩石渗透率、岩石力学性质、地应力及应力敏感性等方面的影响进行了研究,主要得到以下成果： (1)调研分析了沁水盆地南部高阶煤层气储层特征、液氮压裂技术优势及液氮作为压裂液的经济适用性,得出液氮压裂技术具有可行性,并提出了液氮压裂的工艺流程及液氮注入导致煤层破坏的五种模式。 (2)建立了油管注液氮、油套环空注氮气的井筒温度场计算模型,通过编制Matlab程序计算了不同条件下井筒内液氮的温度分布。采用COMSOL Multiphysics软件建立了考虑近井多裂缝、割理及地层流体相变的流热耦合温度场模型,计算得到了不同条件下近井和近缝地带储层的温度分布。 (3)实验得到了不同冻融温度范围条件下,干燥与饱和水煤岩样冻融前后渗透率的变化规律。冻结时间不变的条件下,冻融温度范围越大,煤岩样渗透率升高幅度越大；饱和水煤岩样渗透率升高幅度高于干燥煤岩样。 (4)实验得到了饱和水煤岩样在不同冻结温度下的抗拉强度及不同冻融温度范围下冻融前后抗拉强度；还得到了不同冻融温度范围下饱和水煤岩样冻融前后的杨氏模量、泊松比。冻结导致饱和水煤岩样抗拉强度升高,温度越低,抗拉强度越高；冻融导致煤岩样杨氏模量降低、泊松比升高,抗拉强度降低,且冻融温度范围越大,抗拉强度降低越多。 (5)基于现有地应力计算模式,建立了考虑温度和一次冻融影响的地应力计算模式,计算得到了不同冻结温度和不同冻融温度范围条件下煤层水平地应力的大小。温度降低,煤层最大水平主应力先减小后增大,最小水平主应力减小,水平应力差增大；低温引起的水平地应力变化能够使煤层割理发生剪切破坏。冻融导致煤层最大、最小水平主应力升高,最小水平主应力升高幅度更大。冻融导致煤岩应力敏感性增强,且应力敏感性随冻融温度范围增大而增强。 (6)针对目前缺乏液氮压裂现场试验的问题,根据论文的研究成果对现有的煤层气井液氮压裂增产工艺提出了改进建议。
[Abstract]:Hydraulic fracturing is an important measure to increase the production of coalbed methane reservoir. The technology of increasing production of coalbed methane in our country is based on the theory and experience of developing coal bed methane of middle and low order, and its adaptability to high order coalbed methane reservoir is poor. As a result, the development process often faces the problem of low production rate of single well. The porosity and permeability of high order coalbed methane reservoir is poor, and the degree of coal seam fragmentation and the ability of desorption and percolation of coal bed gas should be increased in the process of increasing production and reforming. Based on the idea of increasing the degree of coal seam breakage, this paper puts forward the liquid nitrogen fracturing technology for coalbed methane wells. Based on the previous researches on the mechanism and technology of liquid nitrogen fracturing, through experiments, simulation, The effects of temperature field and liquid nitrogen injection on permeability, rock mechanical properties, in-situ stress and stress sensitivity during liquid nitrogen fracturing are studied by means of theoretical calculation. The main results are as follows:. The characteristics of high-order coalbed methane reservoirs in the southern Qinshui Basin, the advantages of liquid nitrogen fracturing technology and the economic applicability of liquid nitrogen as fracturing fluid are investigated and analyzed, and the feasibility of liquid nitrogen fracturing technology is obtained. The process flow of liquid nitrogen fracturing and five modes of coal seam failure caused by liquid nitrogen injection are put forward. (2) the wellbore temperature field calculation model for tubing injection of liquid nitrogen and oil ring air nitrogen injection is established, and the temperature distribution of liquid nitrogen in wellbore under different conditions is calculated by compiling Matlab program. COMSOL Multiphysics software is used to establish a multi-fracture model for near well. The fluid-heat coupled temperature field model of cleat and phase transition of formation fluid is used to calculate the temperature distribution of the reservoirs in the near well and near fracture zone under different conditions. The permeability of dry and saturated water coal samples before and after freezing and thawing is obtained under different freezing and thawing temperature ranges. The larger the freezing and thawing temperature range is, the greater the permeability of coal and rock samples is under the condition of constant freezing time. The permeability of saturated coal samples is higher than that of dry coal samples. The tensile strength of saturated water-coal samples at different freezing temperatures and the tensile strength before and after freezing and thawing at different freezing and thawing temperatures were obtained by experiments, and the Young's modulus of saturated water-coal samples before and after freezing and thawing were obtained under different freezing and thawing temperatures. Poisson's ratio. Freezing causes the tensile strength of saturated coal and rock samples to increase, and the lower the temperature, the higher the tensile strength. Freezing and thawing cause the Young's modulus of coal and rock samples to decrease, Poisson's ratio to increase, tensile strength to decrease, and the range of freezing and thawing temperature to increase. The more the tensile strength decreases. 5) based on the existing calculation model of in-situ stress, a calculation model of in-situ stress considering the influence of temperature and primary freezing and thawing is established, and the horizontal ground stress of coal seam under different freezing temperature and different freezing and thawing temperature range is calculated. The maximum horizontal principal stress of coal seam decreases first and then increases, the minimum horizontal principal stress decreases and the horizontal stress difference increases, the variation of horizontal ground stress caused by low temperature can cause shear failure of coal seam cleats, and freezing and thawing results in the largest coal seam. The minimum horizontal principal stress increases and the minimum horizontal principal stress increases more. Freezing and thawing increase the stress sensitivity of coal and rock, and the stress sensitivity increases with the increase of freezing and thawing temperature. (6) in view of the lack of liquid nitrogen fracturing field test at present, according to the research results of the paper, some suggestions for improving the existing liquid nitrogen fracturing technology of coalbed gas wells are put forward.
【学位授予单位】：西南石油大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TE357

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