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Results
Prediction of petrophysical classes and reservoir beds through microfacies and pore types characterization, Tahe Ordovician naturally fractured vuggy carbonates
Issoufou Aboubacar, Mahaman Salifou (Université Dan Dicko Dankoulodo de Maradi, China University of Geosciences) | Heng, Zhang (China University of Geosciences, China University of Geosciences) | Li, Jie (China University of Geosciences, China University of Geosciences) | Ousmane, Boukari Issoufou (Université Abdou Moumouni) | Cai, Zhongxian (China University of Geosciences, China University of Geosciences)
Abstract Carbonates commonly present a stacking-pattern architecture determined by the depositional processes despite the diagenetic modifications. This study integrates spectral cyclostratigraphy and petrophysical analysis to locate prolific reservoir beds to optimize reservoir development. This involves subdividing the reservoir succession into different hierarchical units to understand the variation of microfacies and pore-structure types. The variation trends and discontinuity surfaces (chronostratigraphic and lithostratigraphic boundaries) are determined by conjointly interpreting the prediction error filter analysis (PEFA) and integrated PEFA (INPEFA) and synthetic seismic trace and seismogram. We define the rock texture types (microfacies) through self-consistent approximation based on the INPEFA log while considering the variation of depositional sequence and grain size, core/thin-section petrography, and borehole electrical image interpretation. We establish lithology-depth and petrophysical classes-depth profiles using largely well-log data and present new petrophysical classes for naturally fractured vuggy reservoirs. We predict porosity and permeability from the distribution of high-frequency cycles and lithofacies while considering the implications of diagenesis. The results indicate that the depositional processes and diagenesis largely control the quality of the reservoir beds in response to the relative sea-level variations. The reservoir beds comprise the reservoir units with connected-vugs- and fractures-dominated pore systems and the horizons with microporosity-dominated pore systems that are candidates for secondary recovery processes. The study proposes a total porosity variation model that describes an external cardiac compression-like depth profile, revealing alternation between low/tight and high-porosity horizons, with the highly porous intervals associated with the solution-enlarged porosity zones. Permeability varies with the pore type mixing and rock texture type rather than the total porosity. The method well applies to distinguish flow conduits from baffles and barriers in complex carbonate reservoirs.
- North America > United States > Texas (1.00)
- Asia > Middle East (1.00)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock (1.00)
- Geology > Geological Subdiscipline > Stratigraphy (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock (0.69)
- (3 more...)
- Geophysics > Seismic Surveying > Seismic Processing (1.00)
- Geophysics > Borehole Geophysics (1.00)
- North America > United States > Texas > Permian Basin > Yeso Formation (0.99)
- North America > United States > Texas > Permian Basin > Yates Formation (0.99)
- North America > United States > Texas > Permian Basin > Wolfcamp Formation (0.99)
- (36 more...)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Carbonate reservoirs (1.00)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- (5 more...)
- Information Technology > Artificial Intelligence (0.67)
- Information Technology > Sensing and Signal Processing > Image Processing (0.66)
- Information Technology > Data Science (0.46)
Summary Several dual‐ and triple‐porosity models have been proposed for quantifying the porosity exponent (m) in multiporosity reservoirs. Total porosity (ϕ) is usually portioned into the matrix (ϕb) and vuggy porosity, which includes separate vugs (SVGs) and connected vugs (CVGs). As a result, in their majority, the existing petrophysical models were developed and applied mostly without any distinction between the various types of CVGs despite their specific pore geometries, which critically determine the properties of the rock/fluid systems. For instance, unlike otherwise CVGs, natural fractures (NFs) and microcracks that have low pore‐aspect‐ratio values are highly compressible; this can cause their closure and lead to increasing m values. In this paper, we proposed a quadruple‐porosity model that accounts for NFs (ϕ2 or ϕf) and CVGs (ϕc), in addition to ϕb and SVGs (ϕnc) separately, as distinct input variables to ensure accurate determination of m in composite reservoirs. The approach was based on the volume‐model method and rules of electric‐resistance networks in porous media. Computed water‐saturation values used to validate the model show significant improvement and close agreement with the laboratory measurements, demonstrating the applicability of the proposed model for accurate prediction of m in naturally fractured vuggy reservoirs. New correlations that consider the pore‐type diversity were generated using a plot of ϕ vs. m, obtained with the proposed quadruple‐porosity model. The procedure involved sorting the ϕ/m scattering points using pore‐type mixing and relative abundance of specific porosity. It allowed defining consistent ϕ/m relationships, with determination coefficients of 0.7 to 0.9. This suggests that m varies with the pore‐structure types; this was further demonstrated with a rock‐frame flexibility factor (γ) used as a proxy to cluster the scattering points. The established correlations can alternatively be applied to reasonably predict m using detailed prior knowledge of pore‐type description.
- North America > United States > Texas (1.00)
- Europe (1.00)
- Asia > Middle East (1.00)
- (2 more...)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock (1.00)
- Geology > Geological Subdiscipline (1.00)
- Geophysics > Borehole Geophysics (1.00)
- Geophysics > Seismic Surveying > Seismic Modeling (0.46)
- Energy > Oil & Gas > Upstream (1.00)
- Government > Regional Government > North America Government > United States Government (0.67)
- South America > Brazil > Campos Basin (0.99)
- North America > United States > Texas > Permian Basin > Yeso Formation (0.99)
- North America > United States > Texas > Permian Basin > Yates Formation (0.99)
- (32 more...)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Naturally-fractured reservoirs (1.00)
- Reservoir Description and Dynamics > Reservoir Simulation (1.00)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (1.00)
- (3 more...)