Multi-Factor Evaluation of Deep Karst Dolomite Reservoir Based on Paleogeomorphological Reconstruction, a Case Study From the 4th Member of the Dengying Formation in the Central Sichuan Basin, China

The evaluation of reservoirs is of great importance in exploration practices, and reservoir distribution is dependent on multiple geological factors. The carbonate platform of the fourth member (Z2dn4) of the Dengying Formation (Z2dn) in the Gaoshiti-Moxi area (GMA) was uplifted above sea level duri...

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Main Authors: Zikun Zhou, Xingzhi Wang, Xiyan Yang, Long Wen, Wenzhi Wang, Deming Zeng, Mingyang Wei, Shengyang Xie, Fei Huo
Format: Article
Language:English
Published: Frontiers Media S.A. 2022-06-01
Series:Frontiers in Earth Science
Subjects:
Online Access:https://www.frontiersin.org/articles/10.3389/feart.2022.930269/full
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author Zikun Zhou
Zikun Zhou
Xingzhi Wang
Xingzhi Wang
Xiyan Yang
Xiyan Yang
Long Wen
Wenzhi Wang
Deming Zeng
Deming Zeng
Mingyang Wei
Mingyang Wei
Shengyang Xie
Shengyang Xie
Fei Huo
Fei Huo
author_facet Zikun Zhou
Zikun Zhou
Xingzhi Wang
Xingzhi Wang
Xiyan Yang
Xiyan Yang
Long Wen
Wenzhi Wang
Deming Zeng
Deming Zeng
Mingyang Wei
Mingyang Wei
Shengyang Xie
Shengyang Xie
Fei Huo
Fei Huo
author_sort Zikun Zhou
collection DOAJ
description The evaluation of reservoirs is of great importance in exploration practices, and reservoir distribution is dependent on multiple geological factors. The carbonate platform of the fourth member (Z2dn4) of the Dengying Formation (Z2dn) in the Gaoshiti-Moxi area (GMA) was uplifted above sea level during episode II of the Tongwan movement and underwent prolonged karstification by meteoric freshwater in the terminal Sinian, leading to a strong heterogeneity in reservoirs. Paleogeomorphology reflects hydraulic gradients that can affect the intensities of surface karstification and may be approximated by terrain slope gradients. Karst products (especially solution vugs and caverns) exist prevailingly in the Z2dn4; their development mirrors the extents of internal dissolution. Based on paleogeomorphological reconstruction using the elevation method, the slope angles of single boreholes were calculated through the digital elevation model (DEM). In accordance with single-borewell Fullbore Formation MicroImager (FMI) logging data, four electrofacies (host rock, vug, fracture, and cave) were identified in boreholes possessing FMI data. The identified electrofacies were matched with corresponding conventional logging curves to obtain the training data. A model generalized for other boreholes without FMI data was established with the random forest algorithm and the thicknesses of the four electrofacies in each borehole were determined to characterize the extent of karstification. Slope gradients and electrofacies thicknesses, together with multiple physical parameters of reservoirs in boreholes, were utilized for factor analysis. Four factors were obtained and fused into one comprehensive score based on their ratios of variance proportions. The favorability of reservoirs was described by the comprehensive scores of each borehole. These analyses showed that the most advantageous reservoirs are distributed in the vicinity of the platform margin in the west of the GMA, where they enjoy several benefits. Deposition of porous mound-shoal complexes occurs predominantly in the platform margin where large-scale caves are more developed in the mixing karst zone of seawater and freshwater. Meanwhile, the transmeridional lateral migration of hydrocarbons from the regional hydrocarbon-generating center abutting the west of the GMA contributes to earlier entrapment and accumulation in the mound-shoal complexes in the platform margin.
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spelling doaj.art-de8a892467d84db8872d3428e33ded202022-12-22T00:23:10ZengFrontiers Media S.A.Frontiers in Earth Science2296-64632022-06-011010.3389/feart.2022.930269930269Multi-Factor Evaluation of Deep Karst Dolomite Reservoir Based on Paleogeomorphological Reconstruction, a Case Study From the 4th Member of the Dengying Formation in the Central Sichuan Basin, ChinaZikun Zhou0Zikun Zhou1Xingzhi Wang2Xingzhi Wang3Xiyan Yang4Xiyan Yang5Long Wen6Wenzhi Wang7Deming Zeng8Deming Zeng9Mingyang Wei10Mingyang Wei11Shengyang Xie12Shengyang Xie13Fei Huo14Fei Huo15School of Earth Science and Technology, Southwest Petroleum University, Chengdu, ChinaState Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu, ChinaSchool of Earth Science and Technology, Southwest Petroleum University, Chengdu, ChinaState Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu, ChinaSchool of Earth Science and Technology, Southwest Petroleum University, Chengdu, ChinaState Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu, ChinaExploration and Development Research Institute, PetroChina Southwest Oil and Gas Field Company, Chengdu, ChinaExploration and Development Research Institute, PetroChina Southwest Oil and Gas Field Company, Chengdu, ChinaSchool of Earth Science and Technology, Southwest Petroleum University, Chengdu, ChinaState Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu, ChinaSchool of Earth Science and Technology, Southwest Petroleum University, Chengdu, ChinaState Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu, ChinaSchool of Earth Science and Technology, Southwest Petroleum University, Chengdu, ChinaState Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu, ChinaSchool of Earth Science and Technology, Southwest Petroleum University, Chengdu, ChinaState Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu, ChinaThe evaluation of reservoirs is of great importance in exploration practices, and reservoir distribution is dependent on multiple geological factors. The carbonate platform of the fourth member (Z2dn4) of the Dengying Formation (Z2dn) in the Gaoshiti-Moxi area (GMA) was uplifted above sea level during episode II of the Tongwan movement and underwent prolonged karstification by meteoric freshwater in the terminal Sinian, leading to a strong heterogeneity in reservoirs. Paleogeomorphology reflects hydraulic gradients that can affect the intensities of surface karstification and may be approximated by terrain slope gradients. Karst products (especially solution vugs and caverns) exist prevailingly in the Z2dn4; their development mirrors the extents of internal dissolution. Based on paleogeomorphological reconstruction using the elevation method, the slope angles of single boreholes were calculated through the digital elevation model (DEM). In accordance with single-borewell Fullbore Formation MicroImager (FMI) logging data, four electrofacies (host rock, vug, fracture, and cave) were identified in boreholes possessing FMI data. The identified electrofacies were matched with corresponding conventional logging curves to obtain the training data. A model generalized for other boreholes without FMI data was established with the random forest algorithm and the thicknesses of the four electrofacies in each borehole were determined to characterize the extent of karstification. Slope gradients and electrofacies thicknesses, together with multiple physical parameters of reservoirs in boreholes, were utilized for factor analysis. Four factors were obtained and fused into one comprehensive score based on their ratios of variance proportions. The favorability of reservoirs was described by the comprehensive scores of each borehole. These analyses showed that the most advantageous reservoirs are distributed in the vicinity of the platform margin in the west of the GMA, where they enjoy several benefits. Deposition of porous mound-shoal complexes occurs predominantly in the platform margin where large-scale caves are more developed in the mixing karst zone of seawater and freshwater. Meanwhile, the transmeridional lateral migration of hydrocarbons from the regional hydrocarbon-generating center abutting the west of the GMA contributes to earlier entrapment and accumulation in the mound-shoal complexes in the platform margin.https://www.frontiersin.org/articles/10.3389/feart.2022.930269/fullreservoir evaluationpaleogeomorphological reconstructionrandom forest algorithmfactor analysisDeng memberGaoshiti-Moxi area
spellingShingle Zikun Zhou
Zikun Zhou
Xingzhi Wang
Xingzhi Wang
Xiyan Yang
Xiyan Yang
Long Wen
Wenzhi Wang
Deming Zeng
Deming Zeng
Mingyang Wei
Mingyang Wei
Shengyang Xie
Shengyang Xie
Fei Huo
Fei Huo
Multi-Factor Evaluation of Deep Karst Dolomite Reservoir Based on Paleogeomorphological Reconstruction, a Case Study From the 4th Member of the Dengying Formation in the Central Sichuan Basin, China
Frontiers in Earth Science
reservoir evaluation
paleogeomorphological reconstruction
random forest algorithm
factor analysis
Deng member
Gaoshiti-Moxi area
title Multi-Factor Evaluation of Deep Karst Dolomite Reservoir Based on Paleogeomorphological Reconstruction, a Case Study From the 4th Member of the Dengying Formation in the Central Sichuan Basin, China
title_full Multi-Factor Evaluation of Deep Karst Dolomite Reservoir Based on Paleogeomorphological Reconstruction, a Case Study From the 4th Member of the Dengying Formation in the Central Sichuan Basin, China
title_fullStr Multi-Factor Evaluation of Deep Karst Dolomite Reservoir Based on Paleogeomorphological Reconstruction, a Case Study From the 4th Member of the Dengying Formation in the Central Sichuan Basin, China
title_full_unstemmed Multi-Factor Evaluation of Deep Karst Dolomite Reservoir Based on Paleogeomorphological Reconstruction, a Case Study From the 4th Member of the Dengying Formation in the Central Sichuan Basin, China
title_short Multi-Factor Evaluation of Deep Karst Dolomite Reservoir Based on Paleogeomorphological Reconstruction, a Case Study From the 4th Member of the Dengying Formation in the Central Sichuan Basin, China
title_sort multi factor evaluation of deep karst dolomite reservoir based on paleogeomorphological reconstruction a case study from the 4th member of the dengying formation in the central sichuan basin china
topic reservoir evaluation
paleogeomorphological reconstruction
random forest algorithm
factor analysis
Deng member
Gaoshiti-Moxi area
url https://www.frontiersin.org/articles/10.3389/feart.2022.930269/full
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