应力敏感性碳酸盐岩气藏斜井生产动态规律分析

Production performance analysis for slanted wells in stress-sensitive carbonate gas reservoirs

为解决高石梯—磨溪碳酸盐岩气藏应力敏感性强、斜井生产动态变化不明晰问题,开展岩石应力敏感性实验,分析渗透率变化规律并引入拟时间、拟压力函数描述,考虑孔、缝、洞发育及外边界封闭的储层特征,综合运用Laplace变换、Fourier变换及其反变换、点源函数叠加等方法,建立应力敏感各向异性碳酸盐岩气藏三重孔隙介质斜井渗流数学模型。应用Stehfest数值反演方法,结合气藏物质平衡方程,对模型进行求解;采用矿场实际储层、流体及生产数据,验证模型的有效性,分析应力敏感因数、井斜角与地层厚度等对生产动态的影响规律,绘制不同井斜角时地层厚度随井底流压变化关系图版。结果表明:储层应力敏感性越强,井底流压递减越快;井斜角越大,井底流压越高,但递减速率较为接近;地层厚度越大,井底流压递减速率越小,地层厚度与井斜角之间存在最佳匹配关系。该研究结果为矿场实际井斜角设计提供依据。

The formation in Gaoshiti-Moxi carbonate gas reservoir is strongly stress-sensitive,and currently the production performance for slanted wells cannot be predicted accurately.Therefore,experiments are conducted to study the rock stress-sensitive properties and identify the stress-sensitive exponent for natural fractures systems,and then the pseudo-time and pseudo-pressure are introduced to describe this effect.The formation contains many porous mediums,such as pores in matrix,fractures and vugs,provided that the outer boundary is closed,the Laplace transformation,the Fourier transformation and inversion and the point source superposition are used to derive the mathematical model for inclined well in stress-sensitive and anisotropic carbonate gas reservoirs with tripe porosity media.In combination with Material Balance Equation(MBE),the Stehfest numerical inversion method is utilized to solve the proposed model.The formation,fluids and production data in gas field are collected to verify the validity of this model.The effects of stress-sensitive exponents,inclined angles and formation thickness on production performance are analyzed,and the chart for bottom-hole pressure and formation thickness under different inclined angles is drawn.The results demonstrate that the stronger the formation stress-sensitivity is,the lower the bottom-hole pressure is,and the larger the decline rate is.The bottom-hole pressure with larger inclined angles is higher,however,the decline rate for different cases is almost the same.The drop rate of bottom-hole pressure decreases with the increase of formation thickness.There is an optimal correlation between formation thickness and inclined angles,which provides some theoretical basis for the design of inclined angles in practice.