页岩气井组分比例变化规律研究

SENSITIVITY STUDY OF FLOWING GAS COMPOSITION FOR WELLS IN SHALE GAS RESERVOIR

页岩气开发过程中,生产井产出气的组分比例会随时间发生变化.本文基于组分模型数值模拟研究了生产井中甲烷组分比例变化的规律.研究表明,吸附气、渗透率与孔隙度影响页岩气组分比例的瞬态响应特征.吸附气显著影响组分比例的变化规律,吸附量的大小决定组分比例的变化值及组分比例导数曲线的上下位置.渗透率影响组分比例初期变化规律,但在后期,不同渗透率对瞬态组分比例规律的影响基本一致.孔隙度对组分比例变化及其导数曲线的影响与吸附气的影响类似,但在生产初期,孔隙度对组分比例的影响要小于吸附气对组分比例的影响.本文的研究提供了一种进行页岩地层参数评价的新方法.

Because of the ultra-low permeability of the shale-gas reservoir, the transient flow in these reservoirs can last many years and radial flow is very difficult to reach, which makes the pressure transient analysis impractical. Transientrate-analysis methods as a substitute for pressure transient analysis to determine reservoir parameters have become very popular in recent years. However, due to the absence of the flowing well pressure and low-frequency, low-resolution production data, diagnosis of production data suffers from uniqueness and uncertainty. Composition of different gas components change with time has been reported in the gas-condensate reservoirs and the shale-gas reservoirs. In this paper we use a compositional model incorporating extended Langmuir isotherm and apparent permeability to study flowing composition transient response. First, a dry gas compositional model is established to model flow of components in the shale-gas reservoirs. Then, fully implicit linearization of the equation system is employed to solve the nonlinear equation system based on unstructured gridding. Numerical simulation shows that adsorption gas content, porosity and permeability affect the characteristics of flowing composition, composition change and composition derivative. Adsorption gas content determines drop speed of composition, the value of composition change and composition derivative for CH4 component. Permeability affects composition transient response during early stage. However, during the medium and late stages, different permeabilities have the same influence on the composition transient response. The effects of porosity and adsorption gas content on composition change and composition derivative are similar. However, small difference exists for the effects of porosity and adsorption gas content on composition change with time at early stage. The findings in this paper would provide a new way to interpret the shale-gas reservoir parameters.