An overview of types and characterization of hot fluids associated with reservoir formation in petroliferous basins

Abstract

Increasing petroleum explorations indicate that the formation of many reservoirs is in close association with deep hot fluids, which can be subdivided into three groups including crust-derived hot fluid, hydrocarbon-related hot fluid, and mantle-derived hot fluid. The crustderived hot fluid mainly originates from deep old rocks or crystalline basement. It usually has higher temperature than the surrounding rocks and is characterized by hydrothermal mineral assemblages (e.g. fluorite, hydrothermal dolomite, and barite), positive Eu anomaly, low d 18 O value, and high 87 Sr/ 86 Sr ratio. Cambrian and Ordovician carbonate reservoirs in the central Tarim Basin, northwestern China serve as typical examples. The hydrocarbon-related hot fluid is rich in acidic components formed during the generation of hydrocarbons, such as organic acid and CO 2 , and has strong ability to dissolve alkaline minerals (e.g. calcite, dolomite, and alkaline feldspar). Extremely 13 C-depleted carbonate cements are indicative of the activities of such fluids. The activities of hydrocarbon-related hot fluids are distinct in the Eocene Wilcox Group of the Texas Gulf Coast, and the Permian Lucaogou Formation of the Jimusaer Sag and the Triassic Baikouquan Formation of the Mahu Sag in the Junggar Basin. The mantle-derived hot fluid comes from the upper mantle. The activities of mantle-derived hot fluids are common in the rift basins in eastern China, showing a close spatial relationship with deep faults. This type of hot fluid is

Volcanic events‐related hydrothermal dolomitisation and silicification controlled by intra‐cratonic strike‐slip fault systems: Insights from the northern slope of the Tazhong Uplift, Tarim Basin, China

“…Nonmagmatic hydrothermal fluids systems, including ‘basinal’, ‘crustal’, and ‘deep‐seated’ brine, possess variable REE + Y concentrations (Michard, 1989) but are consistently characterised by positive Eu anomalies (Hu et al., 2018). In today's marine environments, high‐temperature fluids, such as those typically found in back‐arc spreading centres and midocean ridges, unanimously possess positive Eu anomalies (Alexander et al., 2008; Cole et al., 2014; Mills & Elderfield, 1995).…”

“…The missing of REE + Y ratios for seawater (La N /La N * ≥ 1, Pr N /Yb N < 1), similar Y/Ho ratios (22.63-38.67) to volcanic rocks and the presence of positive europium anomalies (averaging 1.245; with only two exceptions of lower than 1; Table S2) together point to the addition of hydrothermal fluids (Brengman & Fedo, 2018 and references therein). Nonmagmatic hydrothermal fluids systems, including 'basinal', 'crustal', and 'deep-seated' brine, possess variable REE + Y concentrations (Michard, 1989) but are consistently characterised by positive Eu anomalies (Hu et al, 2018). In today's marine environments, high-temperature fluids, such as those typically found in back-arc spreading centres and midocean ridges, unanimously possess positive Eu anomalies (Alexander et al, 2008;Cole et al, 2014;Mills & Elderfield, 1995).…”

“…Tectonic events directly contributing to dolomitisation and silicification are poorly constrained. For instance, some authors advocated that the Permian volcanic activities led to the formation of strongly silicified limestones (Chen et al., 2015; Li et al., 2015), whereas some others argued that reactivation of strike‐slip faults in the Devonian was responsible for silicification (Lu et al., 2017); (b) Deep fluids have various types, including hydrothermal, formation, and remnant marine fluids, among which hydrothermal fluids can be subdivided into hydrocarbon‐related, crust‐derived, and mantle‐derived hot flows (Hu et al., 2018). The nature and source of fluids for dolomitisation and silicification, especially whether magmatic fluids were added, remain contentious in the study area.…”

Testing the preservation potential of early diagenetic dolomites as geochemical archives

“…The subsequent Dol 4 and Dol 5 phases are characterized by fluid inclusion homogenization temperatures up to 250°C (medians of 215°C and 235°C, respectively; Fig. B, D and E) suggesting burial depths in excess of some thousands of metres (Davies & Smith, ; Hu et al ., ). Elevated fluid inclusion salinities (17 to 20 wt.% NaCl typical for basinal or continental basement brines; Frape et al ., ) distinguished Dol 4 and Dol 5 from paragenetically‐older zebra saddle dolomite formed at shallower burial depths (Fig.…”

The basin and range systems and their evolution of the northwestern margin of Junggar Basin, China: Implications for the hydrocarbon accumulation

“…Due to the strongest activities of boundary faults, the deep Mahu Depression were generated in the Late Carboniferous to Early Permian and deposit deep-water facies mudstones in the Fengcheng and Wuerhe formations of Permian. Exploration testified that the thickness of widely distributed source rocks in this area reaches thousands of meters (Chang et al., 2019; Chen et al., 2016; Hu et al., 2018). These source rocks will provide abundant oil and gas source for the potential traps.…”