Effect of low-concentration HCl on the mineralogy, physical and mechanical properties, and recovery factors of some shales

Samiha Morsy , C.J. Hetherington , J.J. Sheng
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引用次数: 29

Abstract

Oil and gas-bearing shale formations have received a great deal of interest in recent years because they could make a significant contribution to global hydrocarbon production. However, their development has been hindered by the complexity of drilling and completion strategies, which must be adapted in response to shale’s mineralogy and physical properties. Matrix acidizing is commonly used as a pre-flush to the hydraulic fracturing stimulation of shale formations. The process dissolves sediments and mud solids that inhibit the permeability of the rock, enlarging the natural pores of the reservoir and stimulating flow of hydrocarbons; in some plays it is used as the main stimulation technique (e.g. Monterey shale, California). The mineralogical, mechanical, and physical responses to matrix acidizing of several important North American shale formations have been evaluated, and the effect on their recovery factors are described. Samples of Eagle Ford, Mancos, Barnett, and Marcellus shale formations were exposed to 1, 2 and 3 wt% HCl. Mass loss, compositional analysis, and X-ray diffraction based mineral assemblage characterization and quantification, show samples lost as much as 16 wt% by mass when treated with 3 wt% HCl for 3 h. The majority of the mass loss was attributed to carbonate dissolution. Analysis of post-acid treated samples show increases in porosity relative to the starting materials, but the increases in porosity are not necessarily correlated with acid strength. Images of post-acid samples demonstrate the development of cracks and fractures in Mancos, Barnett, and Marcellus samples. In contrast, the Eagle Ford samples show a homogenously distributed decrease in density, which based on mineralogical and compositional characterization, is attributed to spatially near uniform dissolution of calcite. Eagle Ford samples showed the largest increase in oil recovery factors ranging from 38% to 71% with a significant reduction in Young’s modulus ranging from 25% to 82% when exposed to HCl solutions at 93 °C.

低浓度HCl对部分页岩矿物学、物理力学性质及采收率的影响
近年来,含油气页岩地层受到了人们的极大关注,因为它们可能对全球油气产量做出重大贡献。然而,钻井和完井策略的复杂性阻碍了它们的发展,这些策略必须根据页岩的矿物学和物理特性进行调整。基质酸化通常被用作页岩地层水力压裂增产的预冲洗。该过程溶解了抑制岩石渗透性的沉积物和泥浆固体,扩大了储层的天然孔隙,刺激了碳氢化合物的流动;在一些地区,它被用作主要的增产技术(如加利福尼亚州的Monterey页岩)。对北美几个重要页岩地层基质酸化的矿物学、力学和物理响应进行了评价,并描述了酸化对其采收率的影响。Eagle Ford、Mancos、Barnett和Marcellus页岩地层的样品暴露在1、2和3 wt%的HCl中。质量损失、成分分析和基于x射线衍射的矿物组合表征和定量表明,当用3wt %的HCl处理3小时时,样品的质量损失高达16wt %。大部分质量损失归因于碳酸盐溶解。酸处理后样品的分析表明,相对于起始材料,孔隙度增加,但孔隙度的增加不一定与酸强度相关。酸化后样品的图像显示了Mancos, Barnett和Marcellus样品中裂缝和裂缝的发展。相比之下,Eagle Ford样品的密度呈均匀分布的下降,根据矿物学和成分表征,这是由于方解石在空间上几乎均匀溶解。Eagle Ford样品显示,当暴露在93°C的HCl溶液中时,采收率提高幅度最大,从38%到71%,杨氏模量显著降低,从25%到82%。
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