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首页> 外文会议>SPWLA Annual Logging Symposium;Society of Petrophysicists and Well Log Analysts, inc >EFFECT OF CLAY AND ORGANIC MATTER ON NITROGEN ADSORPTION SPECIFIC SURFACE AREA AND CATION EXCHANGE CAPACITY IN SHALES (MUDROCKS)
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EFFECT OF CLAY AND ORGANIC MATTER ON NITROGEN ADSORPTION SPECIFIC SURFACE AREA AND CATION EXCHANGE CAPACITY IN SHALES (MUDROCKS)

机译：泥土和有机质对页岩（泥岩）氮吸附比表面积和阳离子交换能力的影响

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Resisitivity log is one of the most important tools to find oil and gas saturated intervals. In unconventional oil and gas producing rocks, however, this tool is affected by many factors and not considered very reliable. Shale reservoir rocks usually have high total specific surface area (TSSA) due to high clay and total organic content (TOC) and nano-scale pores. Resistivity values are rather low and usually not indicative of reservoir zones in high TSSA rocks. We measured the TSSA using nitrogen adsorption and cation exchange capacity (CEC) techniques. Clays and organic matter (OM) affect the measured TSSA using either technique. To more accurately calculate the water saturation using available models this effect must be taken into account. We investigate here the mineralogical associations of CEC and TSSA and their effects on resistivity in shale reservoirs.We have studied samples from oil and gas producing reservoirs such as Bakken, Haynesville, European Silurian, Niobrara, and Monterey formations. We measured CEC using Co(Ⅲ)-hexamine~(3+) with the spectrophotometric technique and calculated the equivalent TSSA (CEC-TSSA). We also measured the specific surface area using sub-critical Nitrogen gas adsorption technique (N2-SSA). Rock mineralogy, organic matter properties and scanning electron microscope (SEM) images were used to further analyze the data.We find that CEC values are directly correlated with the clay type and content regardless of the OM content or level of thermal maturity. Smectite and illite (when negligible smectite is present) dominate the CEC value in shales. N2-SSA correlates with clay content, especially smectite and illite, but is less sensitive to clay type as CEC. This correlation between N2-SSA and clay content was observed in Bakken (no organic matter), thermally mature (gas window) Haynesville, and low TOC (<2.67 wt%) Niobrara (oil window) samples. We also find that OM significantly affects N2-SSA in two different ways: (1) Blockage of pores and throats by bituminous kerogen, which limits the accessibility of nitrogen to clay surfaces. This effect was observed in thermally immature (oil window) Niobrara (TOC>2.6 wt%) and Monterey shales. (2) Development of nano-scale OM-hosted pores with high surface area mostly for thermally mature (gas window) shales as observed in high TOC (> 1.5 wt %) Silurian shales. Correlation with N2-SSA and CEC values revealed that the average charge density for most of the shales in this study varies between 3-5 em2 and for some high TOC Niobrara samples can be as high as 32. Relatively higher charge density is due to underestimation of the TSSA by nitrogen adsorption technique. Our results aid in understanding the low electrical resistivity response and in establishing correlations to calculate the CEC and specific surface area for resistivity models.
机译：电阻率日志是查找油气饱和间隔的最重要工具之一。但是，在非常规油气生产岩石中，该工具受许多因素的影响，并不十分可靠。页岩储层岩石通常具有较高的总比表面积（TSSA），这是由于粘土和总有机物含量（TOC）和纳米级孔隙较高。电阻率值很低，通常不能指示高TSSA岩石中的储层带。我们使用氮吸附和阳离子交换容量（CEC）技术测量了TSSA。粘土和有机物（OM）会影响使用任何一种技术测得的TSSA。为了使用可用的模型更准确地计算水饱和度，必须考虑此影响。我们在这里研究CEC和TSSA的矿物学联系及其对页岩储层电阻率的影响。 我们已经研究了来自石油和天然气生产储层的样品，例如Bakken，Haynesville，欧洲志留系，Niobrara和Monterey地层。我们使用分光光度法使用Co（Ⅲ）-六胺〜（3+）测量了CEC，并计算了等效的TSSA（CEC-TSSA）。我们还使用亚临界氮气吸附技术（N2-SSA）测量了比表面积。岩石矿物学，有机质特性和扫描电子显微镜（SEM）图像用于进一步分析数据。 我们发现CEC值与粘土类型和含量直接相关，而与OM含量或热成熟度无关。蒙脱石和伊利石（当蒙脱石含量可忽略不计时）在页岩中的CEC值占主导地位。 N2-SSA与粘土含量有关，尤其是绿土和伊利石，但对粘土类型的敏感性不如CEC。在Bakken（无有机物），热成熟（气窗）Haynesville和低TOC（<2.67 wt％）Niobrara（油窗）样品中观察到N2-SSA与粘土含量之间的相关性。我们还发现，OM以两种不同方式显着影响N2-SSA：（1）沥青干酪根堵塞了孔和喉咙，这限制了氮对粘土表面的可及性。在未成熟的热（油窗）Niobrara（TOC> 2.6 wt％）和蒙特利页岩中观察到了这种影响。 （2）在高TOC（> 1.5 wt％）志留纪页岩中观察到，主要用于热成熟（气窗）页岩的具有大表面积的纳米级OM孔隙的发展。与N2-SSA和CEC值的相关性表明，本研究中大多数页岩的平均电荷密度在3-5 e / nm2之间变化，对于某些高TOC Niobrara样品，其平均电荷密度可能高达32。相对较高的电荷密度是由于用氮吸附技术低估了TSSA。我们的结果有助于理解低电阻率响应，并建立相关性以计算电阻率模型的CEC和比表面积。

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