Do CO2-charged fluids contribute to secondary porosity creation in deeply buried carbonates?

Biehl, Bianca Coline; Reuning, Lars; Schoenherr, Johannes; Lewin, Anna; Leupold, Maike; Kukla, Peter A.

doi:10.1016/j.marpetgeo.2016.05.005

Cited by 16 publications

(6 citation statements)

References 31 publications

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“…The reaction stoichiometry was calculated with average porosities of dolomite (16.9%) and calcite (3.8%) for the Zechstein-2-Carbonates in NW Germany as determined by Biehl et al [2]. The resulting reaction stoichiometry is equal to about 2 : 1.…”

Section: Case Study: Zechstein-2-carbonatesmentioning

confidence: 99%

“…Reservoir quality is mainly controlled by mineralogy. Where the mineralogy is dominated by dolomite, reservoir quality is predicted to be moderate to good and poor where the mineralogy is mainly calcitic [1][2][3]. Early studies suggested that the vast majority of this calcite is not of primary origin but rather formed due to dedolomitization [4,5].…”

Section: Introductionmentioning

confidence: 99%

“…In contrast, dedolomites with similar macro-and microfabrics have been described in other parts of the Southern Permian Basin from timeequivalent Zechstein-2-Carbonates, ranging from eastern Poland to the NE coast of England, sometimes affecting carbonate with hundreds of meters of thickness [2,3,9,[19][20][21][22][23].…”

Section: Introductionmentioning

confidence: 99%

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Dedolomitization Potential of Fluids from Gypsum-to-Anhydrite Conversion: Mass Balance Constraints from the Late Permian Zechstein-2-Carbonates in NW Germany

2018

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The Zechstein-2-Carbonates represent one of the most prolific hydrocarbon systems of Central Europe. Carbonate reservoir quality is primarily controlled by mineralogy, with dolomite representing moderate-to-good porosities and calcite commonly representing low porosities. Current models suggest that this calcite is the result of a basin-wide phase of dedolomitization. The calcium (Ca) source for the dedolomites is thought to be derived from the fluids liberated during gypsum-to-anhydrite conversion. We present an easy-to-use and generally applicable template to estimate the dedolomitization potential of these fluids. Depending on reaction stoichiometry, salinity, and temperature, we estimate that between 2.8 * 10 −3 m 3 and 6.2 * 10 −3 m 3 of calcite may replace dolomite for each m 3 of anhydrite created. Within the constraints dictated by the environment of the late Permian Zechstein basin, we estimate that about 5 * 10 −3 m 3 of dedolomite is created for each m 3 of anhydrite. Mass balance constraints indicate that fluids derived from gypsum-to-anhydrite conversion account for less than 1% of the observed dedolomite in most of the studied industry wells from northern Germany.

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Section: Case Study: Zechstein-2-carbonatesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Dedolomitization Potential of Fluids from Gypsum-to-Anhydrite Conversion: Mass Balance Constraints from the Late Permian Zechstein-2-Carbonates in NW Germany

2018

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“…Evidence for external hydrothermal fluids with temperatures up to 380°derived from deeper presalt strata, which entered the intrasalt carbonates during times of basement activity, as observed by Schoenherr et al [5] for the A3C interval, are not indicated by bitumen reflectance measurements measured within this study (Figure 7). Late diagenetic porosity formation that can be associated with hydrothermal processes in evaporate-associated carbonates [42,71] is also absent from the studied reservoirs.…”

Section: Diagenetic Processes and Fluid Composition During Deepmentioning

confidence: 92%

Diagenetic Processes and Reservoir Heterogeneity in Salt-Encased Microbial Carbonate Reservoirs (Late Neoproterozoic, Oman)

et al. 2019

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A common problem in dolomite reservoirs is the heterogeneous distribution of porosity-reducing diagenetic phases. The intrasalt carbonates of the Ediacaran-Early Cambrian Ara Group in the South Oman Salt Basin represent a self-sourcing petroleum system. Depositional facies and carbonate/evaporite platform architecture are well understood, but original reservoir properties have been modified by diagenesis. Some of the carbonate reservoirs failed to produce hydrocarbons at acceptable rates, which triggered this study. The extent of primary porosity reduction by diagenetic phases was quantified using point counting. To visualize the distribution of diagenetic phases on a field scale, we constructed 2D interpolation diagenesis maps to identify patterns in cementation. The relative timing of diagenetic events was constrained based on thin-section observations and stable isotope analyses. Near-surface diagenesis is dominated by reflux-related processes, leading to porosity inversion in initial highly porous facies and a patchy distribution of early cements. This strong diagenetic overprint of primary and early diagenetic porosity by reflux-related cements leads to a reduction of stratigraphic and facies control on porosity. Calcite was identified as a burial-related cement phase that leads to an almost complete loss of intercrystalline porosity and permeability. Bitumen is an important pore-occluding phase and time marker of the deep-burial realm. The stratigraphic position of the dolomite reservoirs embedded at the base of a salt diapir had a strong impact on its diagenetic development. The salt isolated the dolomites from external fluids, leading to a closed system diagenesis and the buildup of near lithostatic fluid pressures. In combination, these processes decreased the impact of further burial diagenetic processes. The study highlights that cement distribution in salt-encased carbonate reservoirs is mainly related to early diagenetic processes but can be very heterogeneous on a field scale. Further work is needed to implement these heterogeneities in an integrated numerical reservoir model.

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“…Organic acids should not be the cause of vug pores in the Lower Qiulitage Group. In recent years, many scholars have paid attention to the influence of CO 2 in hydrothermal fluid on carbonate reservoirs (Biehl et al, 2016).…”

Section: Burial Dissolutionmentioning

confidence: 99%

Characteristics and dolomitization of the Lower Qiulitage Group reservoir in Bachu Uplift, Tarim Basin, China

Xia

Peng

et al. 2019

Earth sci. res. j.

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The characteristics of the Lower Qiulitage Group in Bachu uplift, which originated in the Upper Cambrian period, are not clear. Based on four core observations, identification of 40 thin sections, and geochemical analysis of samples, this study concludes that crystal dolomite reservoirs developed in the Lower Qiulitage Group in Bachu uplift. Intercrystalline pores and dissolved pores formed the main reservoir space, while dissolution pores and fractures were developed in the middle and bottom part of the formation. The reservoir features low porosity and low permeability, and the fine-medium crystalline dolomite reservoir has the best pore structure. According to a petrochemical analysis, the Lower Qiulitage Group reservoir experienced intense dolomitization, with slightly higher content of trace elements Mn and Sr and negative oxygen isotropy. Tectonic hydrothermal dolomitization developed locally under the influence of base faults, and vug pores were filled with saddle dolomites and siliceous filling. The presence of rare earth elements Ce and Eu presented positive anomaly characteristics. It suggested that the CO2 acid dissolution caused by hydrothermal fluids may be a new mechanism for the increase in pores in deeply buried reservoirs, which is worth further study.

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Do CO2-charged fluids contribute to secondary porosity creation in deeply buried carbonates?

Cited by 16 publications

References 31 publications

Dedolomitization Potential of Fluids from Gypsum-to-Anhydrite Conversion: Mass Balance Constraints from the Late Permian Zechstein-2-Carbonates in NW Germany

Dedolomitization Potential of Fluids from Gypsum-to-Anhydrite Conversion: Mass Balance Constraints from the Late Permian Zechstein-2-Carbonates in NW Germany

Diagenetic Processes and Reservoir Heterogeneity in Salt-Encased Microbial Carbonate Reservoirs (Late Neoproterozoic, Oman)

Characteristics and dolomitization of the Lower Qiulitage Group reservoir in Bachu Uplift, Tarim Basin, China

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