P- and S-wave velocities and attenuations of Naparima Hill Formation mudstones at elevated pressures

IF 2.2 3区 地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY
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Abstract

Velocity and attenuation (the inverse of the Q factor, Q−1) are fundamental elastic wave attributes used to understand subsurface physical properties and characterize unconventional reservoirs. Mudstone, an abundant sedimentary rock, is commonly regarded as a source rock with great promise for unconventional exploration. Despite this, velocity and attenuation studies are lacking on mudstones and have failed to address the link between these elastic wave attributes and physical rock properties. In this study, we measured the P- and S-wave velocities (Vp and Vs) and Q factors (Qp and Qs) of the Naparima Hill organic-rich mudstone at effective pressures up to 130 MPa. The main aims are to investigate the effects of mineralogy, bulk density, porosity, and saturation on these elastic wave attributes and to evaluate if a relationship exists between velocity and attenuation. Vp and Vs were obtained using the trough transmission method, while the spectral-ratio and rise-time techniques were used to determine Qp and Qs in the frequency range of 0.8 to 1.7 MHz. The results show that the velocities and Q factors rose with increasing carbonate, bulk density, and effective pressure, and decreasing clay, silica, and porosity. The saturated mudstones have lower velocities and Q factors than the dry specimens. Strong, linear relationships (R2 > 0.85) were established between Vp and Vs under both dry and saturated conditions. Moderate to strong linear relationships (R2 > 0.5) were established between Qs and Qp, Qp and Vp, Qs and Vs, and Qs and Vp under saturated conditions. These relationships create a framework for predicting the elastic wave attributes (Vs, Qp, and Qs), from the readily extractable Vp in mudstones.

纳帕里马山地层泥岩在高压下的 P 波和 S 波速度及衰减情况
速度和衰减(Q 系数的倒数,Q-1)是弹性波的基本属性,用于了解地下物理性质和非常规储层的特征。泥岩是一种丰富的沉积岩,通常被认为是非常规勘探前景广阔的源岩。尽管如此,有关泥岩的速度和衰减研究却很缺乏,也未能解决这些弹性波属性与岩石物理性质之间的联系。在这项研究中,我们测量了纳帕里马山富含有机质泥岩在有效压力高达 130 兆帕时的 P 波和 S 波速度(Vp 和 Vs)以及 Q 系数(Qp 和 Qs)。主要目的是研究矿物学、体积密度、孔隙度和饱和度对这些弹性波属性的影响,并评估速度和衰减之间是否存在关系。采用波谷透射法获得了 Vp 和 Vs,同时采用频谱比和上升时间技术确定了 0.8 至 1.7 兆赫频率范围内的 Qp 和 Qs。结果表明,随着碳酸盐、体积密度和有效压力的增加,以及粘土、二氧化硅和孔隙度的降低,速度和 Q 因子都在上升。饱和泥岩的速度和 Q 系数低于干燥试样。在干燥和饱和条件下,Vp 和 Vs 之间都有很强的线性关系(R2 > 0.85)。在饱和条件下,Qs 与 Qp、Qp 与 Vp、Qs 与 Vs 以及 Qs 与 Vp 之间建立了中等到较强的线性关系(R2 > 0.5)。这些关系为从泥岩中易于提取的 Vp 预测弹性波属性(Vs、Qp 和 Qs)提供了框架。
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来源期刊
Journal of Applied Geophysics
Journal of Applied Geophysics 地学-地球科学综合
CiteScore
3.60
自引率
10.00%
发文量
274
审稿时长
4 months
期刊介绍: The Journal of Applied Geophysics with its key objective of responding to pertinent and timely needs, places particular emphasis on methodological developments and innovative applications of geophysical techniques for addressing environmental, engineering, and hydrological problems. Related topical research in exploration geophysics and in soil and rock physics is also covered by the Journal of Applied Geophysics.
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