未固结砂岩中的井孔声场传播特征研究

We often encounter unconsolidated sands in porous granular marine sediments. The ocean sediment is often modeled as fluid and elastic solid composed of mineral grain. The method of calculating elastic parameters of unconsolidated sandstone was considered to be thinking about not only the normal stress between grain to grain , but also the shear forces between grain to grain. The energy loss of elastic wave propagation contains not only the viscosity loss of pore fluid movement relative skeleton but also the loss produced by stress mechanism friction of grain to grain. Due to stress mechanism of unconsolidated sand matrix is different from consolidation sands, when the elastic wave propagation in the unconsolidated sands, its propagation mechanism is different with the porous medium in the traditional Biot theory. This study was based on effective medium model of unconsolidated sandstone, focus on acoustic propagation characteristics of unconsolidated sandstone well logging. According to the borehole of the sound field theory using numerical simulation, study on the propagation characteristics of acoustic wave in unconsolidated sand borehole. Get the relationship between the variety of sub-wave and guided wave and reservoir parameters.

在海洋沉积中经常会遇到未固结砂岩，它是由矿物颗粒组成的岩石骨架和孔隙流体组成。其组成岩石骨架的矿物颗粒和颗粒之间是非胶结的。未固结砂岩弹性参数的计算不但要考虑固体颗粒和颗粒之间存在的正应力，还要考虑颗粒和颗粒之间存在的剪切力。弹性波传播时，能量损失不但包括孔隙中流体相对骨架运动产生的粘滞性损耗，还包括固体颗粒与颗粒之间接触应力机制产生的摩擦损失。由于未固结砂岩与固结砂岩岩石骨架的应力机制不同，当弹性波在其中传播时，其传播机制与传统的Biot理论中的等效孔隙介质不同。本研究拟根据未固结砂岩的等效介质模型，对未固结砂岩井中声场的传播特征展开研究。根据井中声场理论利用数值模拟研究未固结砂岩井中声波的传播特征，获取各种分波和导波与未固结砂岩颗粒组成、储层参数之间的关系。

本项目主要研究内容包括三个方面，一是研究了未固结砂岩的岩石物理特征和有效介质模型；二是利用Biot-Stoll的孔隙介质声场传播方程推导了未固结砂岩中的井中声场的解析解，并获得了井中声场的传播特征；利用低频极限的剪切模量 、体变模量高低频极限差 ，体积弛豫频率 和剪切弛豫频率 ，计算出了未固结砂岩的体积模量和剪切模量。以Biot-Stoll的孔隙介质声场传播方程为基础计算出了未固结砂岩中快纵波、慢纵波、横波的平面波表达形式。计算了声源函数、声源频谱，并根据井孔边界条件建立了井中声场方程,推导了其井中声场解的表达式。三是根据准弹性介质应力边界条件,利用时间域交错网格有限差分数值模拟了井内外声场的传播，进一步研究了声场传播的速度、幅度与岩石的颗粒特征之间关系，获得了未固结砂岩中孔隙度和配位数、接触关系、颗粒大小和形状对井孔中纵横波传播速度的影响。