Table of Content

10 February 2025, Volume 47 Issue 1

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A Special Issue on Deep Sea Oil and Gas Exploration and Development Geology

High Efficient Development Strategies and Key Technologies for Turbidite Sandstone Reservoirs in Deep-water

WANG Guangfu, ZHANG Wenbiao, LI Fayou, LU Wenming, LI Meng

2025, 47(1):  1-15.  DOI: 10.11885/j.issn.1674-5086.2024.08.31.04

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In response to the challenges of high investment in deepwater turbidite sandstone oilfield development, limited available data for project planning, high requirements for the success rate of the one-time well network, and striving for maximum oil recovery through high-speed oil production, researches have been conducted on reservoir characteristics of turbidite sandstone, geophysical prediction, geomodeling and numerical simulation integration, and efficient development strategies. It has been revealed that deep-water turbidite sandstone channels can be subdivided into composite channels, single channels, branch channels, and submarine fans as microfacies. Key geophysical technologies have been developed including seismic point identification of turbidite channel reservoirs' original oil-gas interface; amplitude attribute characterization of the extension distribution and oscillation range of turbidite channels, division of multi-stage channel cutting relationships on seismic profiles, prediction of sandstone thickness through wave impedance inversion, characterization of changes in water drive front using 4D seismic monitoring techniques. Technologies of development indicators and production parameters optimization for reservoir-well-pipeline-network-FPSO integration have been established. Development strategies for turbidite channel sandstone reservoirs such as irregular well networks deployment, economic limit of single well controlled recoverable reserves, early water injection at the edge with a large well space have been summarized. The above key technologies and models have been applied to the development of P Oilfield in Block 18 of Angola, achieving the goals of fewer wells and high production, high investment and high return, making possible the efficient development of the deep-water marginal reserves that have not been utilized for more than 10 years, and providing reference for the development of similar reservoirs.

Quantitative Characterization of Deep-sea Channel Continuity Under Architecture Model Constraints

LIU Fei, ZHAO Xiaoming, FENG Xiaofei, CAO Shuchun, BU Fanqing

2025, 47(1):  16-26.  DOI: 10.11885/j.issn.1674-5086.2024.08.28.01

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Deep-sea channels are important transportation channels and deposition sites for sedimentary debris to deep-sea basins, and they are the main types of reservoirs in deep-sea sedimentary environments. Aiming at the problems of unclear structural pattern and distribution pattern of sand body inside the channel, and the difficulty of predicting reservoir continuity, we have carried out a research on quantitative characterization method of reservoir continuity in deep-sea channel type. The study takes the deep-sea waterway configuration pattern and characterization results as the constraints, takes the inverse of the product of the lateral and vertical stacking ratio of the sand body as the continuity coefficient, and synthesizes the coupling relationship between the continuity and curvature to realize the quantitative evaluation of the distribution pattern of the continuity of the reservoirs in the deep-sea channel. The study achieves the following insights, the single channel configurations in the study area are divided into three types: isolated (Type Ⅰ), contact (Type Ⅱ), and embedded (Type Ⅲ), corresponding to lateral stacking ratios of >1.00, 0.85~1.00 and <0.85, and vertical stacking ratios of >1.00, 0.80~1.00 and <0.80, and continuity coefficients of 0.96~1.34, 1.37~1.67 and 1.67~2.56, type Ⅰ curvature distribution intervals of 1.00~1.11, type Ⅱ distribution intervals of 1.02~1.28, and type Ⅲ distribution intervals of 1.10~2.28, with continuity decreasing with increasing curvature. The study quantifies the continuity coefficients and curvature distribution ranges of different configuration styles, quantitatively characterizes the stacking relationship between single channel sands, and is of great significance as a geological guide for the efficient production and fine development of deep-sea channel reservoirs.

Migration Patterns and Genetic Mechanisms of Deep-sea Channels

LIANG Shiqin, WU Wei, XIANG Wei, ZHAO Zhonghui, SUI Yaping

2025, 47(1):  27-41.  DOI: 10.11885/j.issn.1674-5086.2024.08.31.02

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The deep-sea channel is one of the important conduits for the transport of terrestrial clastic sediments to deep-water basins, and it is also the main depositional site for sand sedimentation in deep-water basins.This study summarizes previous research to clarify the migration and formation mechanisms of deep-sea channels, yielding the following findings: based on the migration mode, deep-sea channels can be categorized into unidirectional migration channels (upstream migration type/downstream migration type) and multidirectional migration channels (downstream migration type/lateral migration type/obstacle migration type). The migration characteristics of the channels can be characterized based on the changes in the channel thalweg, unidirectional migration channels are accompanied by overall changes in the thalweg line, while multidirectional migration channels primarily exhibit local changes. The interaction between bottom currents and gravity currents controls the sedimentary construction of unidirectional migration channels. In addition, self-circulation and upwelling currents also affect the sedimentary evolution of the channels. Multidirectional migration channels, on the other hand, are controlled by multiple factors such as sea level changes, sediment supply, tectonic movements, paleo-topography, and the sedimentary action of the channels themselves. The formation of unidirectional migration channels is mainly controlled by the interaction between gravity flows and contour currents, the self-circulation of flows, and upwelling flows, while multidirectional migration channels are mainly influenced by sea-level changes, sediment supply, tectonic movements, paleotopography, and the self-deposition of channels. The future research and development directions of deep-sea channel migration patterns mainly include three aspects: 1) actively conducting multi-scale quantitative research; 2) exploring the coupling mechanisms of various dynamic factors related to channel migration; 3) strengthening the research on the relationship between channel migration patterns and reservoir development.

Evolutionary Model of Hydrochemical Lobes in the ABL Block of Campos Basin

YIN Guofeng

2025, 47(1):  42-55.  DOI: 10.11885/j.issn.1674-5086.2024.09.04.01

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As the major components of submarine fan systems, submarine channels and lobes receive much attention from the sedimentological community. However, studies about the“channel-lobe transitional zone”and the associated channelized lobes are still not enough. This study takes the Block ABL in deep-water areas of Campos Basin of Brazil as the example and recognizes different depositional elements of sandy channels, muddy channels, and sheet lobes, which suggests that channelized lobes are widely developed within the study area. We then characterize the overall deposition and internal architecture of channelized lobes, analyze the associated controlling factors, and establish the evolution model. The results suggest that the overall deposition of channelized lobes show significant variations between different locations; compared with the deposition in southern and downdip area, lobes in northern and proximal areas are more channelized. About the internal architecture, the channelized lobes could be divided into 3 lobe elements, which developed from north to south in terms of sequence. Lobe element 1 was mainly controlled by the source from north, which developed lots of distributaries and was more channelized. Controlled by the main source, Lobe element 2 was oriented along the major feeder channel; due to the gradual decreasing of topographic gradient, the degree of channelization of Lobe element 2 decreased. Lobe element 3 was mainly controlled by the behavior of gravity flow in the major feeder channel; around the bend of major feeder channel, gravity flows were stripped and deposited rapidly, which caused the formation of Lobe element 3 with relatively weak degree of channelization.

Sedimentary Model and Reservoir Characteristics of the “Three Group” Channel System in the North Sea of UK

BU Fanqing, YANG Li, CAO Shuchun, YANG Baoquan, Lü Wenrui

2025, 47(1):  56-66.  DOI: 10.11885/j.issn.1674-5086.2024.09.02.05

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There are significant differences in the sedimentary reservoir characteristics of different types of deep-water turbidite channel systems. Taking the restricted deep-water turbidite channel system of the P oil formation in the North Sea G Oilfield in the UK as an example, seismic geomorphology methods, drilling and core data were used to characterize the distribution characteristics of the internal reservoirs in the turbidite channel system, and to clarify the impact of diagenesis on reservoirs in North Sea through thin section and electron microscopy observation. Research indicats that: 1) the P oil formation developed within a restricted U-shaped canyon, forming a typical "three group" sedimentary pattern vertically; 2) the bottom A and B sand formation is composed of coarse-grained sediments. At the bottom, the A sand body is not developed and does not deposit, and is in unconformable contact with the underlying strata; the B sand group is a mud debris flow mixed with plastic flow; the central C sand formation covers the entire canyon and has the best reservoir quality; the top D sand formation is a late stage sedimentation, mainly composed of natural mud embankments; 3) the upper and lower oil groups do not have good physical properties but the middle group does. This study not only has significant theoretical implications for the development of deep-water sedimentology, but also has important practical significance for the exploration and development of similar oil fields.

Developmental Characteristics and Genesis Mechanisms of Submarine Canyons in the Rovuma Basin, East Africa

MA Hongxia, ZHU Yueyue, XU Xiaoyong, HE Yunlong, WANG Hongping

2025, 47(1):  67-79.  DOI: 10.11885/j.issn.1674-5086.2024.08.28.07

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The external morphological characteristics, internal filling structure and genetic mechanism of submarine canyons in the Rovuma Basin are not fully understood. We make a study on the external morphological characteristics, internal filling structure and genetic mechanism of submarine canyons by using three-dimensional seismic data, combined with the relevant theories of deep-water sedimentology and previous research results. The results indicate that there are 10 canyons in the Rovuma Basin, trending east-west, with a V-shaped narrow upstream and U-shaped gentle downstream profile vertically, and showing an isolated-merged-dispersed pattern on the horizontal plane. The internal filling sediment types in the canyons include basal lags, slides and MTDs. Outside the canyons, sediment drifts and pockmarks are observed. Considering the developmental background of submarine canyons in the study area, it is believed that there may be two genesis mechanisms at play. One involves the escape of natural gas from the underlying strata, leading to the formation of pockmarks and subsequent erosion of weak layers, with interconnected pockmarks forming the initial shape of the canyon, gradually evolving under the influence of sediment-laden fluid flow and erosion. The second mechanism involves destabilization of sediment on the lower slope due to the activity of large-scale faults, resulting in gravity flow events and subsequent erosion leading to canyon formation.

Hydrodynamic of the Lower Eocene in the Ruvuma Basin, East Africa

ZHAO Wenkai, XU Xiaoyong, TIAN Dongmei, ZHANG Ying, WU Jianan

2025, 47(1):  80-94.  DOI: 10.11885/j.issn.1674-5086.2024.09.03.03

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The interaction between gravity flow and underflow can form an asymmetric unidirectional migration channel. The evolution model of unidirectional migration channel has been established by predecessors, but the hydrodynamic mechanism of the interaction between gravity flow and underflow is relatively weak. In this study, the sedimentary hydrodynamic numerical simulation of the interaction between gravity flow and underflow under different conditions in the early and late Lower Eocene in the Ruvuma Basin, East Africa was carried out. The results of the study are as follows: in the early Lower Eocene of the Ruvuma Basin, the restrictive effect of the channel is strong, and the sedimentation of gravity flow is the main effect; in the late period, Under the interaction of gravity flow and bottom current, the fine sediment at the top of gravity flow in the channel drifts northward, forming an asymmetric natural dike on the north side of the channel. Under the action of the crosswise fluid caused by the bottom current, the fine sediment at the top of the gravity flow is transported northward. As sediments gradually accumulate on the north side to form drift deposits, lateral sedimentation steepens the north side of the channel. The two opposite fluids collide in the south side of the channel, the erosion effect is enhanced, in the south side of the strong erosion, the restrictive action is weakened and a new negative terrain is formed. This asymmetric sedimentation pattern gradually migrates the sewers to the south for a long time. By revealing the depositional hydrodynamic processes of the interaction between gravity flow and bottom current in different periods of the Lower Eocene in the Ruvuma Basin, this study elucidates the sediment-erosion mechanism of the fluid structure on the channel and analyzes the genetic mechanism of the asymmetric unidirectional migration channel from the perspective of fluid dynamics.

Development and Evolution of Deep-sea Channels in Salt Diapir Typed Microbasins

MU Boyu, ZHAO Xiaoming, QI Kun, LIU Fei, LI Fayou

2025, 47(1):  95-106.  DOI: 10.11885/j.issn.1674-5086.2024.08.28.05

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The unclear development and evolution characteristics of deep-sea channels in salt diapir typed microbasins hinders the exploration and development of deep-sea oil and gas and increases the difficulty of deep-sea oil and gas exploration and development. To solve such problems we made a case study on a Miocene salt diapir typed microbasin in the deep-water area of the continental margin of Angola, based on 3D seismic data and using RGB color blending technique, and analyzed the development and evolution characteristics and evolution model of channels in the basin. The study shows that the structural development of the microbasin controls the development and evolution of the deep-water channel. The channels C1, C2 and C3 developed along the short axis of the microbasin mainly develop the model of overflowing the microbasin, while channels C4 and C5 developed along the long axis of the basin mainly developed the model of filling microbasins. Whether the channel fills or overflows in the microbasin is mainly related to the relationship between the active period of the salt structure and the formation and evolution of the channel, the relative magnitude of the erosion ability of the gravity flow in the channel to the active rate of the salt structure, the structural development characteristics of the microbasin and the angle between channel flow direction and tectonic trend. The channels C4 and C5 flow along the bottom of the structure under the action of gravity flow. With the increase of the accommodation space, the end of the channel gradually begins to lobe and form leaf deposits.

Deepsea Turbidite Channel Barrier and Interlayer Geomodeling: A Case Study from G Oilfied, Lower Congo Basin, West Africa

XU Rui, LI Fayou, ZHANG Wenbiao, LU Wenming, YUAN Shujin

2025, 47(1):  107-118.  DOI: 10.11885/j.issn.1674-5086.2024.09.02.03

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As a significant component of turbidite deposition system, turbidite channel has been proven challenging due to its complicated sedimentary hierarchy and strong heterogeneity. Currently, the quantitative research on deep-water turbidite channels mostly focuses on channel reservoirs, but less attention is paid to barrier and interlayer. In the later stage of high water cut development, the influence of interlayer in a single channel on the prediction of remaining oil cannot be ignored, and it is necessary to study the interlayer. In this study, a set of characterization and modeling approach are formed for the barrier and interlayer. First of all, based on core, logging and geophysical techniques, the three-level interlayer architecture levels and models within the reservoir are formed. Then, through the pre-stack shale inversion, the mud interlayer identification data body is formed, and on this basis, the geometric characteristics and scale of the interlayer are quantitatively studied. Finally, a multi-level nested method based on target simulation-sequential indicator simulation-multi-point statistics was used to establish a sedimentary microfacies model of different levels of interlayer in a single turbidite channel, and the quantitative simulation of single sand body level of deep-water turbidite under sparse well pattern conditions was realized. After comparison and verification of posterior wells, the model predicts that the lithology coincidence rate of interlayers is 87%. This modeling approach realizes the quantitative characterization of the interlayer of single sand body, which greatly improves the characterization accuracy of turbidite reservoir, and provides important guidance for remaining oil prediction and production.

A Study on the Sedimentary Characteristics and Evolution of Mud-rich Deepwater Turbidite Reservoir

Lü Wenrui, CAO Shuchun, BU Fanqing, GUAN Hong, XIAO Peng

2025, 47(1):  119-129.  DOI: 10.11885/j.issn.1674-5086.2024.09.02.01

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Located in the southern West African Basin, Z Oilfield has low net pay and low net-to-gross ratios, belonging to the mud-rich deep-water gravity-flow deposits. Based on the well penetrations, seismic attributes and production data, the facies types, sedimentary configuration boundaries of the Z Oilfield were identified. The facies distribution characteristics and sedimentary evolution of Z Oilfield were summarized, leading to the following conclusions: 1) the Z Oilfield has developed main channel, levee, main lobe, lobe fringe, shale and slump; 2) channel and lobe configuration boundaries were identified through changes in seismic axis strength, seismic amplitude attributes, and RGB frequency division attributes; 3) for Z Oilfield, the bottom oil group developed unconfined channel-lobe system, dominated by lobes, transitioning upwards to confined channel systems, with strong vertical stacking of channels, and on the top oil groups weakly confined channel systems have developed, with stronger lateral migration, and smaller scales of individual channels.

Petroleum Geological Characteristics of Transformation-extensional Continental Margin Basins in East Africa

FAN Yuhai, QU Hongjun, ZHU Nan

2025, 47(1):  130-146.  DOI: 10.11885/j.issn.1674-5086.2024.08.29.01

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In recent years, a series of large gas fields have been discovered in the deepwater areas of the Rovuma Basin and Tanzania Basin on the transform-extensional passive continental margin of East Africa, with recoverable reserves reaching 3.8$\times$10$^{12}$ m$^3$. However, the resource discovery rate in this region is merely 13.1%, indicating a vast potential for undiscovered resources. Based on the comprehensive research achievements of passive continental margin basins in East Africa, this paper summarizes the geological conditions such as source rocks, reservoirs, traps, and migration within the area, and explores the combination patterns of source-reservoir-cap rocks. The results reveal that: 1) The main source rocks in the transform-extensional passive continental margin basins of East Africa are mainly the lagoon facies and restricted marine shale or limestone of the Middle-Upper Jurassic-Cretaceous & the main reservoir rocks are the marine clastic rocks of the Middle-Upper Jurassic-Cretaceous-Neogene. 2) Hydrocarbons are charged into the reservoirs through "vertical charging" or "lateral charging" along faults, and "lateral charging" along unconformities or reservoirs; controlled by the complex tectonic evolution of East Africa, trap types dominated by structures and stratigraphic lithologies have formed. 3) The conditions for hydrocarbon accumulation are most favorable in the Rovuma and Tanzania basins, and the favorable exploration horizons are the sandstone reservoirs of the Cretaceous-Neogene. The Triassic Calub Formation sandstone in the Somali Basin holds promising exploration prospects. With the advancement of exploration degrees and technical levels, significant breakthroughs are expected in the oil and gas exploration of other basins.

Quantitative Characterization of Evolution and Controlling Factors of Paleo-Rajang Delta in the Zengmu Basin

TANG Zhiyi, XIE Xinong, XU Junjie, WU Jianan, CHEN Beichen

2025, 47(1):  147-162.  DOI: 10.11885/j.issn.1674-5086.2024.08.28.04

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To clarify the development and evolutionary processes of the large delta complex and slope system on the southern margin of the South China Sea, this paper, based on the interpretation of 2D seismic profile from the region, quantitatively describes the evolution of the Paleo-Rajang Delta in the Zengmu Basin. Key parameters such as the clinoform migration angle $\alpha$, clinoform accretion thickness to clinoform accretion distance ratio $\sigma$, pro-delta width $l$ and pro-delta slope angle $\beta$ are selected to describe the evolution process of the delta. The study explores the controlling effects of various factors on this process. The main body of the delta has undergone five stages of evolution: 1) the early stage of continental shelf delta, forming an oblique prograding clinoforms; 2) the rapid advance stage. when the delta evolved to the marginal shelf delta, and the inflection point trajectory of the prograding clinoforms rose at a medium-high angle while $l$ was small but $\beta$ was large; 3) the stable accretion stage. when the depositional center moved to the slope, and the inflection point of the prograding clinoforms rose at a medium angle while the front of $l$ and $\beta$ were unchanged; 4) the stage of slow progradation. when the inflection point of the prograding clinoforms presented a low angle of progradation while $l$ and $\beta$ gradually decreased; 5) late stage of shelf delta progradation. when climatic conditions coupled with source supply and sea level change affected the rate of change of accommodation $A$ and the rate of sediment supply $S$ and ultimately jointly controled the evolution of the deltaic system and its slope migration.

Palaeoclimatic and Palaeofloral Evolution and Their Influences on Organic Matter Enrichment of the Early Oligocene-Early Miocene Marine Shales in the Qiongdongnan Basin

DING Wenjing, LI Youchuang, LAN Lei, YANG Shuchun, LIU Haiyu

2025, 47(1):  163-180.  DOI: 10.11885/j.issn.1674-5086.2024.09.12.02

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Natural gases in the northern South China Sea are predominantly derived from the Late Oligocene-Early Miocene marine shales. The organic matter enrichment and its controlling factors are key points for the natural gas exploration in the Qiongdongnan Basin. The organic matter enrichment from the Oligocene to the Early Miocene marine shales from fifteen wells in the Qiongdongnan Basin was found using the data of total organic carbon measurement and Rock-Eval pyrolysis. During the early Oligocene, the Middle Yacheng Formation shales are enriched in terrigenous organic matter, which was thought to be caused by the flourished tropical/subtropical plants in the more humid environment. During the Late Oligocene-Early Miocene, there is also a terrigenous organic matter enrichment. Analyses of plant-derived biomarkers, palynogical records in shales in combination with regional global climate variations suggest the terrigenous organic matter enrichment was in association with warming and humid climate in the Late Oligocene-Early Miocene, during which higher plants flourished and the East Asian summer monsoon coupled with annual precipitation intensified. The significant extra precipitation brought by intensified East Asian summer monsoon was beneficial for the large amount of scattered plant organic matter enrichment and hence the terrigenously-enriched marine shales were more widely deposited in shallow marine environment. The finding of terrigenous organic matter enrichment in the Late Oligocene-Early Miocene marine source rocks was beneficial for the deep-water natural gas exploration in the deeply buried Ledong Sag and the Lingshui Sag in the Qiongdongnan Basin.