基于岩石纵波与横波测试及测井数据的页岩气藏脆性评价方法及应用

Brittleness evaluation method for shale gas reservoir based on acoustic P-wave and S-wave testing of rock samples and its logging application

作为一种清洁能源,页岩气的开发在中国得到了迅速的发展,中石化焦石坝和高邮凹陷区块是中国页岩气勘探区块比较成功的案例。相对于常规油气藏来说,页岩气的开发较为复杂,影响页岩气开发的因素较多,其中,储层的岩石物理性质是影响页岩气藏能否成功开发的关键因素之一。为了提示岩石物理性质对页岩气开发的影响规律,本文开展了系统的研究。首先,从页岩气层的岩心中钻出5个样品(直径2.5厘米,长度为4~6厘米),放入水中进行充分饱和,然后将饱和水的样品放入HR2500-2高速冷冻离心机中,分别使用8种速度进行脱水,得到不同含水饱和度的样品。其次,在模拟地层条件下,使用CTS-45非金属超声检测分析仪确定每个样品在不同含水饱和度下的纵波和横波速度,最后将实验数据与岩石力学参数的计算方法相结合,计算得到泊松比、杨模量、脆性指数等一系列关键参数。利用上述方法对高邮凹陷块5口井的岩样进行了分析,结果表明:杨氏模量越高,泊松比越低,脆性越高,可压性越高。并总结出了E1F4每个小层可压性,可以对各个小层的压裂设计进行科学的指导。

As a clean energy development technology of shale gas is relatively mature worldwide,and its research methods are also remarkably extensive.Research on rock physical properties of shale gas reservoirs is one of the key technologies.Considering Chinese shale gas exploration blocks,the Sinopec focal dam and Gaoyou sag block are markedly successful.This paper comprehensively analyzes the compressibility of this block based on P-wave and S-wave tests of rocks and logging data to guide the fracturing design of this block scientifically.First,five samples(diameter:2.5 cm;length:4-6 cm)are drilled from the cores in the laboratory(drilling is conducted in the shale gas layer).Second,the saturated water sample is placed into an HR2500-2 high-speed refrigerated centrifuge,and eight speeds are used to dehydrate simulation samples with different water saturations.Third,the samples are then placed under simulated developed conditions to determine their P-wave and S-wave velocities by using a CTS-45 nonmetal ultrasonic testing analyzer.Finally,combining experimental data with the calculation method for rock mechanics parameters,a series of parameters,such as Poisson’s ratio,Young’s modulus,and brittleness index,are obtained.Results obtained from applying these methods to five wells of the Gaoyou sag block show that a high Young’s modulus and a low Poisson’s ratio increase brittleness and strengthen fracturing performance.Overall,the E_(1)F_(4)interval of each small-layer fracturing level provides scientific guidance to the fracturing design.