Hydrogeochemical and isotopic evidence for trans-formational flow in a sedimentary basin: Implications for CO2 storage

doi:10.1016/j.apgeochem.2012.08.024

Applied Geochemistry

Volume 30, March 2013, Pages 4-15

https://doi.org/10.1016/j.apgeochem.2012.08.024 Get rights and content

Abstract

Deep saline aquifers are considered as the most promising option for geologic disposal of CO₂. One of the main concerns, however, is the integrity of the caprocks between and above the storage formations. Here, a hydrogeochemical and isotopic investigation is presented, using ionic chemistry, stable isotopes (δ¹⁸O, δ²H and ⁸⁷Sr/⁸⁶Sr) and radiocarbon dating, on five saline aquifers on a regional scale, namely: Neogene Minghuazhen, Guantao, Ordivician, Cambrian and Precambrian, all found in the Bohai Bay Basin (BBB) in North China. Groundwater recharge, flow pattern, age and mixing processes in the saline aquifers show that the Neogene Guantao Formation (Ng) in the Jizhong and Huanghua Depressions on both of the west and east sides of the Cangxian Uplift is a prospective reservoir for CO₂ sequestration, with a well confined regional seal above, which is the clayey layers in the Neogene Minghuazhen Formation (Nm). However, this is not the case in the Cangxian Uplift, where the Ng is missing where structural high and fault zones are developed, creating strong hydraulic connections and trans-formational flow to the Nm aquifer. Comparing storage capacity and long-term security between the various hydrogeologic units, the depressions are better candidate sites for CO₂ sequestration in the BBB.

Highlights

► We make a hydrogeochemical study on integrity of caprocks at regional scale. ► Groundwater origin, flow pattern, age and mixing processes are investigated. ► Good regional seal and trans-formational flow through caprocks are identified. ► Integrity of caprocks indicates suitability of saline aquifers for CO₂ storage.

Introduction

Deep saline aquifers are promising geological formations for long term sequestration of large quantities of CO₂ as a means of climate change mitigation (IPCC, 2005), since they offer the largest storage volume among all kinds of underground spaces for geological CO₂ sequestration and are widely distributed in sedimentary basins throughout the world (Koide et al., 1993). It is proposed that CO₂ be injected at depths greater than 800 m to be kept in supercritical state (Bachu, 2003). When injected into the formation, CO₂ spreads in the porous medium, displacing formation water and occupying an increasing portion of the flow domain (Pruess and Garcia, 2002), then being trapped through coupled physical and chemical mechanisms, including geological trapping (IPCC, 2005), hydrodynamic trapping (Bachu et al., 2007) and geochemical trapping (Gunter et al., 1997).

One of the major concerns for the sequestration is leakage of CO₂ from the reservoir. On a regional scale, the saline aquifer should be capped by an extensive aquitard or aquiclude to ensure CO₂ sequestration and to prevent it from escaping into adjacent formations or to the surface (Bachu, 2000). Crucial factors in determining the effectiveness of the caprocks include lithology, thickness, diagenesis, ductility, and local and regional continuity (Ho et al., 2005). There are several large Cenozoic–Mesozoic Basins in eastern China, such as the Songliao Baisin, BBB, Subei–Southern Yellow Sea Basin, East China Sea Basin and Pearl River Mouth Basin. These basins are characterized by high porosity and permeability, with good CO₂ source-sink matches and are potential areas for deployment of large scale CCS (Li et al., 2009, Pang et al., 2012), thus it is necessary to evaluate the confinement effectiveness of the saline aquifers in these basins.

In this study, Tianjin is taken as an example to carry out a primary characterization of the caprocks of the saline aquifers by examining the hydrodynamic regime of formation waters based on hydrogeochemical and isotopic data.

Section snippets

Geologic and hydrogeologic settings

Tianjin lies in the eastern part of the North China Plain, bordered by Beijing to the west, the Yanshan Mountains in Hebei province to the north and the Bohai Sea to the east with an area of 11,900 km² (Fig. 1). Tectonically, Tianjin is located at the northeastern part of the North China block, and is separated by the Baodi Fault into two sub-tectonic units (Fig. 1), the northern unit belonging to the Yanshan Folded Belt and the southern unit belonging to the BBB, both of which are developed on

Sampling and analysis

Altogether chemical data on 170 samples are considered, among which 29 were collected from the geothermal production wells sunk in the Neogene aquifers in the Huanghua Depression and the Ordovician, Cambrian and Precambrian aquifers in the Cangxian Uplift during two sampling campaigns in December, 2009 and March, 2010, respectively. Analyses of water were conducted at the Analytical Laboratory, Beijing Research Institute of Uranium Geology, where anions ( $F^{-}, {Cl}^{-}, {SO}_{4}^{2 -}, {NO}_{3}^{-}$ ) were measured with a

Water isotopes and origin

Stable isotopes in the water samples from Tianjin are shown in Fig. 4. It is noted that all the samples plot to the right of the Global Meteoric Water Line (GMWL) and the Local Meteoric Water Line (Pang, 2000). Groundwaters from the Nm and Ng aquifers show relatively high δ²H values with respect to those from the pre-Cenozoic aquifers, which may indicate a higher recharge elevation of the pre-Cenozoic aquifers. Using the relationship between isotopic composition and elevation for eastern China (

Conclusions

Based on their hydrogeological and geochemical characteristics, the suitability of the saline aquifers in Tianjin was examined primarily from the circulation of the formation waters. The saline waters in the Neogene and pre-Cenozoic formations are recharged in the Yanshan Mountains to the north and the Taihangshan Mountains to the NW, with ages between 8.4–24.0 and 5.7–18.2 ka B.P., respectively, and flows from the north to the south.

The Cangdong, Haihe and Baitangkou Faults are water

Acknowledgement

Funding for this work was provided by China National High-Tech R&D (863) Program (Grant 2008AA062303), which is gratefully acknowledged.

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Hydrogeochemical and isotopic evidence for trans-formational flow in a sedimentary basin: Implications for CO2 storage

Abstract

Highlights

Introduction

Section snippets

Geologic and hydrogeologic settings

Sampling and analysis

Water isotopes and origin

Conclusions

Acknowledgement

Mar. Petrol. Geol.

Energy Convers. Manage.

Int. J. Greenh. Gas Control

Phys. Earth Planet. Int.

Energy Convers. Manage.

Energy Procedia

Geothermics.

Appl. Geochem.

Mar. Petrol. Geol.

Chem. Geol.

Atmos. Environ.

Int. J. Greenh. Gas Control

Screening and ranking of sedimentary basins for sequestration of CO2 in geological media in response to climate change

Environ. Geol.

Paleoclimatic interpretation of the past 30 ka from isotopic studies of the deep confined aquifer of the North China plain

Appl. Geochem.

Analysis of causes and recharge–discharge of Ordovician geothermal fluid in Tianjin area

Global Geol.

Mesozoic tectonic evolution of the Yanshan fold and thrust belt, with emphasis on Hebei and Liaoning Provinces, northern China

Geol. Soc. Am. Mem.

A review: pyrite oxidation mechanisms and acid mine drainage prevention

Crit. Rev. Environ. Sci. Technol.

Hydrogeochemical and isotopic evidence for trans-formational flow in a sedimentary basin: Implications for CO₂ storage

Screening and ranking of sedimentary basins for sequestration of CO₂ in geological media in response to climate change