考虑时变效应的致密气井产能评价——以延安气田为例

Productivity evaluation of tight gas well with time-dependent mechanism:a case study of Yan’an gasfield

在致密气井的生产过程中,压裂裂缝导流能力、储层流体分布和气水相渗都会不断发生变化,具有时变效应,而传统的产能评价往往忽略了这种效应。针对这一问题,通过建立考虑裂缝导流能力时变效应和储层气水相渗时变效应的渗流数学模型,评价了时变效应对气井产能的影响。研究结果显示:压裂裂缝导流能力的时变效应增加了流体流动阻力,缩短了气井的稳产期;气井生产过程中,除了流体和岩石本身的膨胀能外,气水相渗的时变效应能够减小束缚水饱和度,使得部分束缚水转化为可动水,增大了水相渗透率,减小了气相渗透率,加快气井见水并增大气井产水量,促使气井递减提早出现。延安气田的实际气井生产表明,不考虑时变效应预测的稳产期偏长,预测的产水量远低于实际气井的产水量,时变效应对气井生产的影响不可忽略,结合延安气田开发实际还需进一步研究在立体井网开发模式下考虑时变效应的气井产能模型。

In the production process of tight gas wells,the fracture conductivity,reservoir fluid distribution and gas-water relative permeability will vary with time.However,the traditional models always ignore these effects.Based on this,the time-dependent factors,including fracture conductivity and relative permeability are introduced to construct the seepage model for gas production.Subsequently,the simulations are conducted to analyze the effects of time-dependent mechanisms on gas well productivity.Results show that time-dependent fracture conductivity will accelerate the gas production decline because the fluid flow towards the wellbore will consume more energy.In the production process,besides the expansion of rock and fluids,the pressure gradient can decrease the irreducible water saturation and promote the migration of irreducible water,resulting in the increase of water permeability and the decrease of gas permeability.This effect will reduce the period of stable gas production and increase the water production.The production of a gas well in Yan’an gasfield indicated that ignoring the time-dependent effects will severely underestimate the water production and overrate the period of table gas production.Finally,according to the development mode of Yan’an gasfield,the gas well productivity model with considering the time-dependent factors for stereoscopic well pattern should be further studied.