煤层气水平井排采控制研究
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摘要
地面工程的制约与采收面积的需求,使水平井成为煤层气的主要开采方式和开发的发展趋势。然而,水平井在开采试验中产量低、衰减快,除了煤层气储层低含气饱和度、低储层压力、低渗透率等客观条件制约外,排采强度的不合理是影响煤层气产量的一个决定性因素。煤层气储层渗透率在排采过程处于动态变化,排采强度也需作相应的调整和优化。目前对煤层气水平井排采流体的动态变化特征仍认识不清,排采强度调整不当,导致产量不稳定、产能低。因此,通过研究煤层气水平井的渗流特征,制定合理的排采强度,为水平井的排采制度优化提供参考和依据,对于提高煤层气水平井,指导我国煤层气开采具有重要意义。
本文通过对煤层气储层特征及产出机理进行分析研究,从煤层气的产出机理与井中流体相态变化的三个阶段,分析不同排采阶段煤层气、水的渗流特征,推导了煤层气水平井排采二维势稳态分布,证实了其等势面为一簇以水平井两端点为焦点的椭圆面。建立了水平井不同排采阶段煤层气储层中水、气-水动态变化模型,采用模型化的方法分析不同阶段排水量对煤层气井产能的影响,同时,建立了饱和水单相流、非饱和单相流和气-水两相流阶段的排采强度模型。实例分析LL-01PW水平井不同排采阶段的排采特征,给出了不同排采阶段最优化排采强度。
研究结果认为总产水量和日产水量是地层供水能力和排采强度的综合反映,井底压力变化则是煤层气井排采的一个关键数据,是排采强度直接作用的结果,初步建立并验证了水平井不同排采阶段排采强度模型。提出了煤层气水平井开采中,需根据研究区煤层气储层特征,建立开采区的排采强度模型,通过模型分析不同排采阶段压力传递规律和井底压力变化特征,调整排采强度,控制井底压力的变化,增加采收面积,提高煤层气水平井的产能。
Horizontal wells have become a dominating recovery method and development tendency on CBM exploitation, because of restriction of surface engineering and demanding for harvesting area. However, horizontal wells have low production and fast attenuation in experiment, unreasonable production intensity is a determining factor, besids restriction of CBM reservoir from external condition of low gas saturation, low reservoir pressure, low permeability and so on. CBM reservoir permeability is a dynamic change in the production, so production intensity should be made corresponding adjustment and optimization.At present, there’s no clear understanding on the dynamic change characteristics of production fluid in CBM horizontal wells, and adjusting production intensity is unreasonable, which lead to unstable yield and low productivity. So the study on the restriction of fluid productivity based on reservoir characteristics is important to guide CBM exploitation and increase CBM exploitation benefit in our county.
According to the analyze and research of CBM reservoir characteristics and mechanism production, based on CBM mechanism production and three stages of a phase behavior change in a well, analysised of different stages of CBM production and water flow characteristics, and two-dimensional potential steady state distribution of horizontal CBM production wells is derived, and the equipotential surface are a cluster elliptic surface wich its focus is the horizontal well two endpoints has been proved. Established water and gas-water dynamics model at different stages of CMB horizontal well production, analysis the effect of CBM wells productivity at different stages displacement by using modeling method. At the same time, the production intensity model of single-phase flow saturated water, single-phase flow in unsaturated and gas-water two-phase flow are established. Example analysis of different production stages characteristics on LL-01PW horizontal well. And given the different stages optimized production intensity.
The results obtained indicated that daily water production and accumulative water production are the comprehensive reflection of stratigraphy water supply capacity and production intensity, and bottom hole pressure change is one key data to CBM horizontal wells production,and it is the result of direct effect of production intensity. Production intensity models have been initially established and validated on horizontal wells different production stages, acorrding to study area CBM reservoir characteristics and initially established. In the exploitation of horizontal CBM wells, improving the productivity of horizontal CBM wells by analyzing the pressure transfer law of different stages of production and variation of bottom hole pressure change with the model, regularizing the production intensity, controlling the changes in bottom hole pressure, increasing the harvesting area of horizontal CBM wells.
本文通过对煤层气储层特征及产出机理进行分析研究,从煤层气的产出机理与井中流体相态变化的三个阶段,分析不同排采阶段煤层气、水的渗流特征,推导了煤层气水平井排采二维势稳态分布,证实了其等势面为一簇以水平井两端点为焦点的椭圆面。建立了水平井不同排采阶段煤层气储层中水、气-水动态变化模型,采用模型化的方法分析不同阶段排水量对煤层气井产能的影响,同时,建立了饱和水单相流、非饱和单相流和气-水两相流阶段的排采强度模型。实例分析LL-01PW水平井不同排采阶段的排采特征,给出了不同排采阶段最优化排采强度。
研究结果认为总产水量和日产水量是地层供水能力和排采强度的综合反映,井底压力变化则是煤层气井排采的一个关键数据,是排采强度直接作用的结果,初步建立并验证了水平井不同排采阶段排采强度模型。提出了煤层气水平井开采中,需根据研究区煤层气储层特征,建立开采区的排采强度模型,通过模型分析不同排采阶段压力传递规律和井底压力变化特征,调整排采强度,控制井底压力的变化,增加采收面积,提高煤层气水平井的产能。
Horizontal wells have become a dominating recovery method and development tendency on CBM exploitation, because of restriction of surface engineering and demanding for harvesting area. However, horizontal wells have low production and fast attenuation in experiment, unreasonable production intensity is a determining factor, besids restriction of CBM reservoir from external condition of low gas saturation, low reservoir pressure, low permeability and so on. CBM reservoir permeability is a dynamic change in the production, so production intensity should be made corresponding adjustment and optimization.At present, there’s no clear understanding on the dynamic change characteristics of production fluid in CBM horizontal wells, and adjusting production intensity is unreasonable, which lead to unstable yield and low productivity. So the study on the restriction of fluid productivity based on reservoir characteristics is important to guide CBM exploitation and increase CBM exploitation benefit in our county.
According to the analyze and research of CBM reservoir characteristics and mechanism production, based on CBM mechanism production and three stages of a phase behavior change in a well, analysised of different stages of CBM production and water flow characteristics, and two-dimensional potential steady state distribution of horizontal CBM production wells is derived, and the equipotential surface are a cluster elliptic surface wich its focus is the horizontal well two endpoints has been proved. Established water and gas-water dynamics model at different stages of CMB horizontal well production, analysis the effect of CBM wells productivity at different stages displacement by using modeling method. At the same time, the production intensity model of single-phase flow saturated water, single-phase flow in unsaturated and gas-water two-phase flow are established. Example analysis of different production stages characteristics on LL-01PW horizontal well. And given the different stages optimized production intensity.
The results obtained indicated that daily water production and accumulative water production are the comprehensive reflection of stratigraphy water supply capacity and production intensity, and bottom hole pressure change is one key data to CBM horizontal wells production,and it is the result of direct effect of production intensity. Production intensity models have been initially established and validated on horizontal wells different production stages, acorrding to study area CBM reservoir characteristics and initially established. In the exploitation of horizontal CBM wells, improving the productivity of horizontal CBM wells by analyzing the pressure transfer law of different stages of production and variation of bottom hole pressure change with the model, regularizing the production intensity, controlling the changes in bottom hole pressure, increasing the harvesting area of horizontal CBM wells.
引文
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[11] Levine J R 1996.Model study of the influence of matrix shrinkage on absolute permeability of coalbed reservoirs[J].Geological Society Publication.(199):197-212
[12] Shi,J.Q.,Duruca,S.,2005:A model for changes in coalbed permeability during primary and enhanced methane recovery, SPE Reservoir Evaluation&Engineering August,291-299
[13] Sawyer W K, Paul G W.1990.Schraufnagle RA. Development and application of 3D coalbed simulator. Paper CIM/SPE,90-119
[14] Palmer I, Mansoori J.1998.How permeability depends upon stress and pore pressure in coal be:A new model [M],SPE BEE.539-544
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[22]张先敏.煤层气储层数值模拟及开采方式研究[D].东营:中国石油大学(华东),2007,4:14-17
[23]王起新,孙维吉等.煤层气运移双重介质气-水两相流数学模型及数值模拟[J].西安石油大学学报(自然科学版),2007,522(81)
[24]赵阳升,杨栋,胡耀青等.低渗透煤储层煤层气开采有效技术途径的研究[J].煤炭学报, 2001,26(5):455-458
[25]宋岩,张新民.煤层气成藏机制及经济开采理论基础[M].北京:科学出版社,2005
[26]薛改珍,金学锋等.沁水盆地煤层气安全钻井工艺[J].石油钻探技术,2007,35(5):65-67
[27]石书灿,李玉魁等.煤层气竖直压裂井与多分支水平井生产特征[J],西南石油大学学报(自然科学版)2009,31(1):48-52
[28]马东民.煤层气井采气机理分析[J].西安科技学院学报,2003,23(2):156-158
[29]王红岩,刘洪林,赵庆波等.煤层气富集成藏规律[M].北京:石油工业出版社,2005
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