致密含气砂岩核磁共振—声波速度联合实验

为研究致密含气砂岩有效储层划分、流体识别方法,选取了典型致密含气砂岩样品,开展核磁共振—声波速度联合实验。以核磁共振实验为基础,结合压汞曲线特征,研究了储层孔隙结构特征,分析了储层可储性;以岩石声学特性实验为基础,研究纵、横波速对储层含气性的敏感性;分析了核磁共振T2谱与横波速度对岩石孔隙特征的共性反映,得出了T2几何平均值(T2gm)与横波速度之间的关系,进而建立了核磁共振—声波速度联合含气性识别图版。研究表明,目标区致密砂岩储层有4种孔隙结构,孔隙发育尺度与粗—细小喉道交互配位关系,决定了4种孔隙结构储层的储集和渗透能力。致密含气砂岩纵波速度对含气性敏感,利用纵波时差与纵、横波速比交会识别含气性效果良好;核磁共振T2gm与横波速度呈幂函数关系,为利用核磁共振测井预测地层横波速度提供了帮助。进而将不同含气岩石纵波时差与核磁共振T2gm进行交会,显示该方法对致密砂岩储层含气性具有较好的识别效果。

Nuclear magnetic resonance-acoustic velocity joint experiment of tight gas sandstone

To study the effective reservoir division and fluid identification methods of tight gas sandstone, the samples of typical tight gas sandstone were selected to carry out Nuclear Magnetic Resonance(NMR)-acoustic velocity joint experiment. Based on NMR experiments in combination with the characteristics of mercury injection curves, the pore structure characteristics and reservoir reserving availability of reservoirs were studied and analyzed. The sensibility of v_p and v_s to reservoir gas-bearing ability was studied on a basis of rock acoustic characteristic experiments. The common reflection of rock pore characteristics by NMR T₂ spectrum and v_s was analyzed to obtain the relationship between T₂ geometric average (T_2gm) and v_s, based on which the NMR-acoustic velocity joint gas-bearing identification chart is established. Research results show that there are four kinds of pore structures in tight sandstone reservoirs of the target area, and the reserving and penetration abilities of such reservoirs is determined by the interacted coordination relationship between pore development scale and coarse-fine throat. The v_p of tight gas sandstone is sensitive to gas-bearing property, and the P-wave transit time versus v_p/v_s cross-plot works well in identifying the gas-bearing property. There is a power function relationship between NMR T_2gm and v_s, helpful to predict reservoir v_s with the use of NMR logging. Thus, P-wave transit time versus NMR T_2gm of different gas-bearing rocks is cross-plotted to prove the favorable identification effect of this method on gas-bearing property of tight sandstone reservoirs.