裂缝性致密砂岩储层声波测井物理模型试验

The Physical Model Experiment of Sonic Logging in Fractured Tight Sandstone Reservoirs

摘要: 低孔、低渗致密砂岩油气藏等复杂油气藏是当前及今后相当长时间内油气勘探的主体。因此，低孔、低渗致密砂岩的精细评价成为测井专业的发展趋势和核心任务。为此，开展了裂缝性致密砂岩储层声波测井物理模型试验研究。该次研究包括模型井试验和小岩心试验两部分：模型井试验用100倍带光源读数显微镜(刻度1DIV/0.02 mm)来刻度裂缝宽度(100 µm~14 mm)，再用声波测井换能器来测量不同裂缝宽度时的波形；小岩心试验针对不同孔隙度(3.7%~7.5%)、不同裂缝宽度(30~500 µm)下，纵波、横波同一时刻的波峰幅度进行纵向对比，得到声波幅度的变化趋势。试验结果表明：随着裂缝宽度的增加，纵波和横波幅度都呈明显的衰减趋势；与纵波幅度的变化情况相比，横波的衰减情况更严重；裂缝宽度越大，纵波、横波衰减系数越大。综合物理模型试验测量结果及已研究的数值模拟计算结果认为，当裂缝宽度小于100 μm时，波形幅度随裂缝宽度的变化非常敏感，递减幅度非常快，不能定量确定裂缝宽度。

Abstract: Tight sandstone reservoir with low porosity and low permeability has been the major location for oil and gas exploration at present and in the years to come. Therefore, the fine evaluation of tight sandstone reservoirs with low porosity and low permeability was a development trend and core task for well logging. For this purpose, the research and experiment of sonic logging physical model were carried out in fractured tight sandstone reservoirs. The research included modeling wells and small core experiments. The modeling wells experiment was carried out by using 100 time light readout microscope (scale 1DIV/0.02 mm) to scale the fracture width (100 µm - 14 mm), and acoustic logging transducer was applied to measure the waveforms at different fracture widths. In the small core experiment, different porosities (3.7% - 7.5%) and different fissure widths (30 - 500 µm) were taken into consideration, the P-wave and S-wave amplitudes were longitudinally compared in the experiment at the same time and the variation trend of wave amplitude was obtained from the experiment. The experiment results showed that diminishing trend of P-wave and S-wave amplitude attenuation was more obvious with the increase of fracture width. Compared with the changes of the P-wave amplitude, attenuation of S-wave was more obvious. The greater the fracture width was, the larger the attenuation coefficient of P-wave and S-wave was. The results of physical model and numerical simulation show that waveform amplitude is very sensitive and diminishes rapidly with the change of fracture width when the fracture width is less than 100 μm. Therefore fracture width cannot be determined quantitatively.