串珠状缝洞型碳酸盐岩气藏压力变化特征研究

缝洞型碳酸盐岩储层目前的模型建立主要以渗流、管流或渗—管流结合等理论为基础,但是当储层内具有大尺度溶洞时,渗流理论不能准确表征宏观缝洞储集体；当储层内具有大开度裂缝时,其内部流体流动特征与平板流特征更为接近。因此,需要建立以裂缝平板流与宏观非均质性理论为基础的储层模型。根据气体物质守恒方程与流体力学方程,推导了更接近于真实大型裂缝中气体流动特征的平板流动模型,建立了串珠状缝洞型碳酸盐岩气藏储层的宏观非均质数学模型,并通过数值方法求解出该模型定产量生产时井底压力与各溶洞压力数据。绘制出溶洞压力导数半对数曲线和井底压力双对数曲线,发现压力导数双对数曲线可以分为4段:井筒储集反应段、裂缝反应阶段、溶洞反应阶段和边界反应阶段。随后,分别研究了各类缝洞参数对压力导数双对数曲线形态特征的影响。研究表明,不同的缝洞参数会影响压力导数双对数曲线上相应阶段的形态特征。

Pressure variation characters in bead-like fractured-vuggy carbonate gas reservoir

Current model for fractured-vuggy carbonate reservoir is established on the theories of seepage, pipe flow or combination of seepage and pipe flow.However, seepage theory could not accurately characterize macroscopic fractured-vuggy reservoir when there are large vugs. Inner fluid flow characters are similar to flat flow characters when the fracture is large in the reservoir.Therefore, it is necessary to set a reservoir model based on the theory of fracture flat flow and the theory of macroscopic heterogeneity.According to gas mass conservation equation and fluid mechanical equation, we deduced a flat flow model more close to gas flow characters in actual large fractures, and established a macroscopic mathematic model for bead-like fractured-vuggy carbonate gas reservoir, and acquired the data of bottom hole pressure and pressure of all vugs through numerical methods.We drew the semi-logarithmic curve of pressure derivatives and the double logarithmic curve of bottom hole pressure, and discovered that the double logarithmic curve of pressure derivatives could be classified into four stages:wellbore storage effect reaction stage, fracture reaction stage, vug reaction stage and boundary reaction stage.Then, we probed into the effect of various fractured-vuggy parameters on the morphology of the double logarithmic curve of pressure derivatives.It was revealed that different fracture-vuggy parameters affect the morphology of double logarithmic curves of pressure derivatives at different stages.