裂缝性致密砂岩储层声波测井数值模拟响应特性研究

Research on Numerical Simulation Response Characteristics of Acoustic Logging for Fractured Tight Sandstone Reservoirs

由于裂缝性致密砂岩储层的裂缝宽度小于100μm,因此常规测井和成像测井等方法难以对微裂缝进行有效识别,且目前关于裂缝性致密砂岩的储层研究相对较少。斯通利波具有频散性,其速度和能量的空间分布随频率的改变而改变,低频时斯通利波转变为管波,管波能量的消耗使井眼流体流入和流出地层,因此斯通利波对微裂缝非常敏感。为此,开展了裂缝性致密砂岩储层声波测井数值模拟响应特性研究。针对单条水平裂缝,确定了裂缝宽度对斯通利波识别微裂缝的影响:裂缝宽度越大,斯通利波波形振幅越小;裂缝宽度较小(小于100μm,即微裂缝)时,波形振幅递减较快,波形振幅衰减更明显;20μm裂缝宽度与0μm裂缝宽度时的斯通利波波形振幅基本相同,说明在数值模拟Z方向网格最小设为20μm的条件下,斯通利波识别微裂缝的最小分辨率,即利用斯通利波能够识别微裂缝的最小裂缝宽度也为20μm;并与等价实验条件下的单条水平裂缝物理模型试验结果进行了对比,符合度较高,说明利用声波全波列测井资料评价裂缝性致密砂岩微裂缝的精确度较高。

The fracture width of fractured tight sandstone reservoir was less than 100 μ m , conventional logging and imaging logging methods were difficult to be used for recognizing microfractures , and the researches of fractured tight sandstone reservoir were relatively less.Stoneley wave was dispersive , the spatial distribution of velocity and energy of Stoneley wave was changed along with the change of frequency , Stoneley wave was changed into a tube wave in low frequency , the energy consumption of tube wave made the borehole fluid flowing in and out of the formation , thus it was sensitive to microfractures.Therefore , the research of numerical simulation response characteristics of acoustic logging was carried out for fractured tight sandstone reservoirs.For a single horizontal fracture , the impact of fratureswidth on identification of microfracture of Stoneley wave was determined , the bigger the width of fracture was , the smaller the amplitude of Stoneley wave was.When the fracture width was smaller ( the width of fracture was less than 100 μ m , that was a microfracture ), the amplitude of Stoneley wave was reduced quickly , the attenuation of Stoneley wave was more obvious.The amplitude of Stoneley wave of 20 μ m is the same with that of 0 μ m , when grid in Zdirection is set to 20 μ m , the minimum resolution of Stoneley wave is for microfracture recognition , the smallest width of microfracture is 20 μ m when Stoneley wave is used for recognition of it ; and the result is compared with the experimental results of physical mode for a single fracture under the equivalent condition , the conformity is higher , it shows that the accuracy is higher for using acoustic full wave train logging data to evaluate the micro cracks of fractured tight sandstone.