广安气田须六段气藏低渗透高含水砂岩储层单相气体渗流特征

广安气田须六段气藏的砂岩储层表现出典型的高含水、低渗透特征,气藏渗透率为0.1mD的岩样占60%,且平均孔隙度仅有8.97%,平均含水饱和度达55%,与常规气藏相比较,该气藏储层的气体渗流特征具有特殊性。为了深入认识该气藏渗流特征和关键性的影响因素,掌握其生产动态特征,需用岩心开展针对性的渗流机理实验研究,同时,应用渗流效应系统分析方法诊断该气藏存在的特殊渗流形式。研究表明:广安气田须六段气藏岩样随着压力梯度增大单相气体渗流存在阈压效应、滑脱效应、达西渗流效应及高速非达西渗流效应4种渗流形式;物性越差、含水饱和度越高的岩样非线性渗流效应越明显。该研究成果不仅为认识该气藏的渗流特征提供了直接理论依据,而且也有利于掌握其生产动态的特殊规律。

Characteristics of single phase gas seepage in sandstone gas reservoirs with low-permeability and high water saturation in the sixth member of the Xujiahe Formation,Guang'an Gas Field

The gas reservoir in the sixth member of the Xujiahe Formation in the Guang'an Gas Field is a typical high water saturation and low permeability sandstone gas reservoir, with an average permeability of 0.1 mD (accounting for 60% of the tested samples), an average porosity of only 8.97% and an average water saturation of 55%. The characteristics of gas seepage in this reservoir are different from that in the conventional gas reservoirs. In order to understand the seepage characteristics and their key influencing factors, as well as the dynamic production performance, an experimental study of seepage mechanism is performed on cores sampled from this gas reservoir. The unique seepage patterns of this gas reservoir are identified through a systematic analysis of seepage effects. Along with the increasing of pressure gradient, single phase gas seepage in cores sampled from this gas reservoir show four kinds of effects, including threshold pressure effect, slippage effect, Darcy seepage effect and high speed non Darcy seepage effect. The non linear seepage effect of core samples gets stronger with the worsening of physical properties and the increasing of water saturation. These study results not only provide a direct theoretical basis for in depth understanding of seepage characteristics of this gas reservoir, but also help recognize the unique pattern of production performance.