As oil and gas exploration expands into new frontiers such as deep water and deep strata where drilling is sparse, conventional well-log-constrained acoustic impedance inversion faces significant challenges. Developing well-free inversion techniques that reliably estimate absolute acoustic impedance from seismic data and other available information—without relying on well logs—is of great importance for reducing exploration risks and enabling early reservoir evaluation. From the perspective of the information source and core mechanism of low-frequency compensation, this paper constructs a systematic taxonomy of well-free acoustic impedance inversion methods covering four technical pathways: (1) methods based purely on seismic data (using traveltime information, sparse priors, or wave equation to recover low frequencies); (2) methods based on integration of multi-geophysical-field data (using gravity, magnetic, electromagnetic data to provide ultra-low-frequency structural framework); (3) methods based on geological and statistical prior modeling (using pseudo-wells, geological frameworks, or geostatistical simulation to introduce prior knowledge); and (4) data-driven and artificial intelligence methods (using deep learning to implicitly learn the complex mapping from seismic data to acoustic impedance). The paper elaborates the principles, low-frequency recovery mechanisms, advantages, and limitations of each method. Through comparative tables and a case study in a deep-water well-free area, it reveals the evolutionary trend from single information sources to multi-mechanism integration. The study shows that no single technical pathway can independently overcome the strong non-uniqueness challenge of well-free inversion. Promoting deep integration of physics-based modeling and data-driven intelligence, along with synergistic utilization of multi-source information and multi-method approaches, is the key to narrowing the current technical gap and enhancing the reliability of well-free inversion. This paper aims to provide a clear theoretical framework and practical guidance for quantitative reservoir evaluation and risk decision-making in the early exploration of well-free areas.

With the deepening of oil and gas exploration in recent years, exploration targets have gradually shifted from structural reservoirs to lithologic reservoirs dominated by thin interbed reservoirs. The tunable effect of thin layer inhibits reflection energy of seismic wave at relatively high frequency and decreases the resolution of seismic data. The thinner the stratum is, the weaker the amplitude of the received seismic wave is. meanwhile, seismic waveforms will merge with each other, which further increases the difficulty of thin layer prediction. In this paper, a multi-scale iterative inversion technique is introduced to construct initial inversion model by introducing logging information from outside. Continuous wavelet transform is used to divide the frequency of logging and seismic data, and corresponding large, medium and small-scale signal components are obtained respectively. The constraint model of each scale is constructed by inverse distance weighting method. In the inversion process, Bayesian theory is introduced to modify the regularization parameters, and relationship between resolution and stability is adjusted adaptively to achieve the best balance of inversion results. The multi-scale iterative inversion technique improves initial model accuracy of the relative thin layer step by step on the premise of accuracy of thick layer inversion, and finally meets the purpose of weakening tuning effect, improving inversion resolution and effectively identifying thin layer. The technique has achieved good results in thin reservoir prediction in the slope zone of the Oriente Basin, Ecuador, with an average prediction accuracy of 87

In oil sands or heavy oil reservoirs, the chemical compositions and physical properties of fluids often exhibit significant vertical variations within the oil column. These variable properties pose significant challenges for predicting and developing hydrocarbon resources. In this study, the chemical compositions of bitumen at varying biodegradation levels within the oil column of the McMurray Formation in Mackay River area, Athabasca (Canada), were analyzed using extraction of organic matter and fraction separation, gas chromatography-mass spectrometry, elemental analysis, nuclear magnetic resonance hydrogen spectra, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy experiments, to construct bitumen cluster molecular models. The results indicate that with increasing depth of the oil column, the proportion of saturated hydrocarbons decreases, while the resin and asphaltene fractions increase. Compounds with weak biodegradation resistance are largely depleted. Predominantly, the saturated hydrocarbons include terpanes, hopanes, and pregnanes, whereas the aromatic hydrocarbons are rich in methylphenanthrenes, methylchrysenes, and triaromatic steroids. Biodegradation leads to a reduction in the proportion of carbon and hydrogen elements and an increase in heteroatoms within asphaltenes. The chemical structure of asphaltenes is primarily aliphatic, with increasing biodegradation levels, there is an increase in the proportion of H alpha and H beta, while H gamma decreases. The degree of condensation and oxygen substitution increases, while the number and length of branched chains, the number of rings per unit structure, and the hydrogen-to-carbon ratio decrease. Biodegradation primarily targets C-H bonds and methylene groups in alkanes and naphthenes, followed by functional groups such as hydroxyl, alcohol, and heteroatoms. This study not only deepens our understanding of the effects of biodegradation on the chemical composition of hydrocarbons but also offers a rapid and cost-effective method for predicting the physical and chemical properties of hydrocarbons.

During the deep-water hydrocarbon exploration along the passive continental margin, stratigraphic records of various types of basic igneous bodies are frequently encountered. The offshore deep-water basins in Brazil provide an outstanding natural laboratory for investigating basic igneous processes. This study utilizes drilling cuttings and three-dimensional high-quality seismic data obtained during deep-water hydrocarbon exploration to conduct sedimentary basin analysis. It helps to enhance the understanding of the spatial and temporal process of basic magma in ancient sedimentary basins and provides geological basis for hydrocarbon exploration. However, few studies have been conducted to document the spatial distribution, emplacement process, and impact on sedimentary architecture of these basic igneous bodies. Therefore, this study attempts to unravel the emplacement process of basaltic magma and discuss the coupling relationship between magmatic activity and sedimentary architecture. 3D seismic data acquired from the offshore Brazil shows that a series of intrusive dykes, sills, laccoliths, and extrusive lavas are founded in the post-salt sedimentary stratigraphy. Petrographic analysis indicates that these features originate from mafic magmatism, recording the entire lifecycle of basic magma from its intrusion to eventual eruption. The intrusion pressure and compression of mafic magma induced folds, small-scale faults, and deformation of the pre-existing sedimentary strata, furthermore, subsequently altering the filling characteristics of the overlying sedimentary strata. On the basis of the law of cross-cutting relationships, it is indicated that the magmatic activity reached its peak during the Santonian and Campanian Age. The interplay between basic igneous rocks within the sedimentary basins and their host sedimentary rocks suggests a four-stage evolutionary process. Initially, the pre-thinning of salt layers and formation of salt-walled basin. This is followed by a period of continuous basin subsidence, sedimentary infill, and the growth of salt walls. Subsequently, the intrusion and extrusion of basic magma, along with localized volcanic eruptions, force folds in the sedimentary strata. Finally, the lateral migration of the subsidence center within the salt-walled basins is observed, followed by overlapping sedimentary filling and the formation of drape structures. This comprehensive study sheds light on the genesis and evolution of basic magma in sedimentary basins, outlining the spatial distribution pattern of basic igneous bodies, and their impact on sedimentary strata deformation. The insights gained possess significant implications for petroleum geological research and exploration assessments.

The X Block in Peru is situated within the El Alto Uplift in the north-eastern T Basin of the South American fore-arc rift. It is a centurial oil field with a high degree of exploration. The deep Paleogene sandstone serves as the target oil reservoir for the field. The thin thickness and extensive lateral variability of the reservoir pose as a challenge for reservoir prediction. The present study focuses on medium-deep Paleogene sandstone reservoirs in the X Block. To achieve this, a combination of techniques is employed, including sandstone sedimentary facies analysis, dynamic cluster analysis of seismic waveforms, and the construction of Bayesian inversion frameworks for different seismic facies. The aim is to apply frequency fusion technology to perform facies controlled waveform indicator inversion. The inversion results demonstrate that the seismic waveform indicator inversion has enhanced the vertical and horizontal resolutions of the inversion results, and the identification accuracy of thin interbedded sandstone can be 5 m. The inversion results exhibit an 80

The Paleozoic (Carboniferous) Amotape Formation in a metamorphic-rock buried hill in the Talara Basin, Peru is an important regional exploration target, where a series of oil and gas reservoirs have been discovered. The daily oil production of Well EA2311 located in the La Guna buried hill in Block X, Peru is 2,890 barrels per day, and the cumulative oil production of Well EA2294 is 1.1 million barrels, indicating that this region has broad exploration prospects. Paleozoic metamorphic-rock buried hills have complex reservoir conditions, and the types and controlling factors of reservoirs in the buried hill remain unknown. These factors restrict oil and gas exploration in this region. Based on paleogeomorphology analysis and by making full use of data such as core data, thin-section analysis data, scanning electron microscopy (SEM) data, well log data, and seismic data, this paper analyzes the conditions for the formation of Paleozoic (Carboniferous) metamorphic-rock buried-hill reservoirs in the Talara Basin, Peru, determines the types of reservoirs, and reveals the main factors controlling the development of fractures in such reservoirs. The results of this study show that the main types of rocks in the Carboniferous Amotape Formation are quartzite and slate, and gneiss and phyllite have developed locally in this formation; the reservoirs are fractured and porous, which can be classified into weathering crusts and inner reservoirs in the vertical direction; the level of development of fractures is related to the thickness and purity of quartzite and the transformation by paleo-tectonic stresses. This understanding provides valuable guidance for the selection of favorable exploration zones in buried hills and the search for the subsequent exploration direction.

Low-amplitude structure refers to a kind of geological body with relatively gentle structure and low closure amplitude. Generally, the structure amplitude is about 10 m. The low-amplitude structure in seismic profile shows that the reflection event is straight and the variation amplitude is small, which is not easy to identify. Due to the impact of structure setting on the plane, it is difficult for conventional mapping methods to display low-amplitude structural features, which is not conducive to the identification of oil and gas sweet spots. The residual structure analysis technique can decompose the trend and local details of the plane data of structure travel time, which can highlight the low-amplitude structure features. In this paper, two methods of residual structure analysis are developed, namely, trend decomposition method and wavelet transform method. The two methods weaken the influence of regional structure from different angles, eliminate the interference of different regional backgrounds on low-amplitude structure, highlight local detail changes, and make the shape of low-amplitude structure more accurate and clearer. The application of the two techniques in the slope zone of the Oriente Basin has significantly improved the identification accuracy and evaluation efficiency of low-amplitude structures in the study area, and the rapid deployment of multiple horizontal wells has achieved good results.

The Lower Cretaceous Manville Group of Upper Mc Murray Formation is one of the main bitumen reservoirs in Athabasca. In this study, the relationship between reservoirs heterogeneity and bitumen geochemical characteristics were analyzed through core and microscopic observation, lab analysis, petrophysics and logging data. Based on the sedimentology framework, the formation environment of high-quality oil sand reservoirs and their significance for development were discussed. The results indicate that four types lithofacies were recognized in the Upper Mc Murray Formation based on their depositional characteristics. Each lithofacies reservoirs has unique physical properties, and is subject to varying degrees of degradation, resulting in diversity of bitumen content and geochemical composition. The tidal bar(TB) or tidal channel(TC) facies reservoir have excellent physical properties, which are evaluated as gas or water intervals due to strong degradation. The reservoir of sand bar(SB) facies was evaluated as oil intervals, due to its poor physical properties and weak degradation. The reservoir of mixed flat(MF) facies is composed of sand intercalated with laminated shale, which is evaluated as poor oil intervals due to its poor connectivity. The shale content in oil sand reservoir is very important for the reservoir physical properties and bitumen degradation degree. In the context of regional biodegradation, oil sand reservoirs with good physical properties will suffer from strong degradation, while oil sand reservoirs with relatively poor physical properties are more conducive to the bitumen preservation.

The Santos Basin is a globally hydrocarbon exploration hotspot. In the past decade, a large number of major discoveries have been made in pre-salt plays in ultra-deepwater areas of the Santos Basin. The current drilling and seismic data in the Santos Basin record at least five stages of magmatic activity, forming two types of basic igneous rocks, namely, flooding facies basalt and intrusive facies diabase. Three periods of magmatic eruption activities during the early Cretaceous were recorded in the pre-salt lacustrine strata. According to the spatial development characteristics of volcanic rocks, two types of volcanic edifices can be identified, namely, fissure-type and central-type. Among them, fissure-type volcanic edifices are distributed along faults with a wide range of distribution, which are the main types of volcanic edifices in the basin. While the central-type volcanic edifices are characterized by small-scale volcanic conduit facies. According to the depositional environment, it can be further divided into subaqueous effusive facies (the second stage of igneous rocks, such as the basalt developed in the same period of the deposition of the Itapema Formation in the northeast oil field of the East High), subaerial effusive facies (the third stage of basalt during the period of deposition of the Barra Velha Formation of the third stage in the southwest basin, which is mainly formed in the Central High inside the Central Sag) and transitional effusive facies. According to the integrated interpretation of gravity, magnetic and seismic data, it is pointed out that strike-slip faults and extensional faults control the spatial distribution of pre-salt igneous rocks in the Santos Basin, while the large-scale volcanic edifices control the tectonic framework of the basin. The volcanic rocks developed on a large scale in the first and third stages have significant constructive effects on the paleogeomorphology of carbonate build-up at the end of the rift stage and sag stage, and ultimately control the distribution of favorable reservoir facies belts of lacustrine carbonate rocks.

In response to the problems of unclear distribution of deep-water pre-salt carbonate reservoirs and formation conditions of large oil fields in the Santos passive continental margin basin, based on comprehensive utilization of geological, seismic, and core data, and reconstruction of Early Cretaceous prototype basin and lithofacies paleogeography, it is proposed for the first time that the construction of pre-salt carbonate build-ups was controlled by two types of isolated platforms: inter-depression fault-uplift and intra-depression fault-high. The inter-depression fault-uplift isolated platforms are distributed on the present-day pre-salt uplifted zones between depressions, and are built on half- and fault-horst blocks that were inherited and developed in the early intra-continental and inter-continental rift stages. The late intra-continental rift coquinas of the ITP Formation and the early inter-continental rift microbial limestones of the BVE Formation are continuously constructed; intra-depression fault-high isolated platforms are distributed in the current pre-salt depression zones, built on the uplifted zones formed by volcanic rock build-ups in the early prototype stage of intra-continental rifts, and only the BVE microbial limestones are developed. Both types of limestones formed into mound-shoal bodies, that have the characteristics of large reservoir thickness and good physical properties. Based on the dissection of large pre-salt oil fields discovered in the Santos Basin, it has been found that both types of platforms could form large-scale combined structural-stratigraphic traps, surrounded by high-quality lacustrine and lagoon source rocks at the periphery, and efficiently sealed by thick high-quality evaporite rocks above, forming the optimal combination of source, reservoir and cap in the form of “lower generation, middle storage, and upper cap”, with a high degree of oil and gas enrichment. It has been found that the large oil fields are all bottom water massive oil fields with a unified pressure system, and they are all filled to the spill-point. The future exploration is recommended to focus on the inter-depression fault-uplift isolated platforms in the western uplift zone and the southern section of eastern uplift zones, as well as intra-depression fault-high isolated platforms in the central depression zone. The result not only provides an important basis for the advanced selection of potential play fairways, bidding of new blocks, and deployment of awarded exploration blocks in the Santos Basin, but also provides a reference for the global selection of deep-water exploration blocks in passive continental margin basins.

The Andean fold-thrust belt in the northwest of the Madre de Dios Basin in Peru is a geologic structure where multidirectional tectonic stresses converge, and its structural complexity is higher than that of other areas of the basin. The Permian gas reservoirs in the basin are controlled by this fold-thrust belt, and the distribution of gas reservoirs varies greatly in different tectonic belts. By investigating the structural characteristics of the fold-thrust belt and the characteristics of faults in the fold-thrust belt and the distribution of the fold-thrust belt, this paper identifies the mode of tectonic evolution of the fold-thrust belt and summarizes the formation mechanism of the fold-thrust belt. The results of this study shows that three thrust belts have formed in the north, middle and south under compressional stresses in the southwest and south directions. Due to differences in the directions and magnitudes of tectonic stresses acting on the three belts, these belts trend NW-SE in the north, nearly E-W in the middle, and E-W in the south. The traps discovered in the study area exhibit a trend of increase in both number and area from south to north. This understanding provides valuable guidance on the optimal selection of favorable exploration targets and the search for the subsequent exploration direction.

According to the characteristics of the Pacific plate subduction plate boundary, the geometric variations of the Andes arc and back-arc foreland basin system, the Andean foreland basin system is generally divided into three tectonic domains. Based on the analysis of the tectonic-sedimentary evolution of typical sedimentary basins in the eastern piedmont of the Andes in South America, the tectonic evolution process of basins in different tectonic domains and the sedimentary filling characteristics of tectono-stratigraphy are summarized. The northern basins focus on the analysis of the Oriente Basin in Ecuador, which is composed of three tectono-sequences upwards, namely, the rift tectono-sequence, the continental margin tectono-sequence, and the retroarc foreland tectono-sequence. The foreland tectono-sequence has only one depozone characterized by the foredeep. The central basins focus on the analysis of the Ucayali Basin in Peru, which developed three types of prototype basins, namely rift basin, craton marginal basin and back-arc foreland basin. The tectonic compression at the end of the Cretaceous led to the activation and inversion of early normal faults. The shallow structural reservoirs in the basin are mostly related to the deep fault inversion at the foreland stage. This type of foreland basin is divided into four depozones in the east-west direction, namely, wedge-top, foredeep, forebulge and backbulge. The southern basins focus on the analysis of the Neuquén Basin in Argentina. The structural deformation style is basement-involved type, which has undergone tectonic evolution of rift, post-rift and foreland. The foreland basin of this type can be divided into five tectono-sedimentary units in the east-west direction: wedge-top, foredeep, forelimb, basement-involved uplift and backlimb. According to the comparative analysis of the tectonic styles and sedimentary filling characteristics of the Andean foreland system in South America, the sedimentary filling patterns of the Andean foreland basin can be divided into three types, namely, the foreland basin with a single foredeep, the classical foreland basin and the broken foreland basin. The above analysis of Andean foreland basin will be helpful to the evaluation of oil & gas exploration and the optimization of new overseas exploration projects in this area.

With the depletion of world energy resources, unconventional energy sources such as heavy oil and oil sand are attracting widespread attention. The Lower Cretaceous McMurray Formation in Athabasca has abundant oil sand resources, and the relationship between reservoir characteristics and bitumen heterogeneity has always been a research hotspot. However, the effect of interstitial material (matrix) in oil sand on the distribution and properties of bitumen is often overlooked. In this study, thin-section petrography, fluorescence microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), porosity and permeability gas measurements, organic matter extraction and separation of group components, and gas chromatography-mass spectrometry (GC-MS) were used to investigate the oil sands of a well in the Mackay River area. The results indicate that the matrix has a significant influence on the physical properties, support mode, and storage space of oil sands. The oil sands can be identified into three types according to the matrix content and texture: arenite (<15% matrix content), grain support, and predominantly intergranular pores; L-wackes (15–25% matrix content), grain support, dominated by intergranular pores and matrix micropores; H-wackes (>25% matrix content), matrix support, matrix micropores and micro-fractures as the main storage space. Geochemical surveys and biodegradation evaluation, indicate that arenites have good connectivity, but are vulnerable to formation water and microbial degradation, with most of the hydrocarbons being consumed by serious biodegradation. The tight matrix layers in H-wackes limit initial oil charging, resulting in poor oil interval. L-wackes contain an appropriate amount of matrix, which does not limit initial oil charging, and the matrix can absorb and protect hydrocarbons, reducing the degree of biodegradation. Therefore, considering matrix can further consummate the formation mechanism of water, oil, and poor oil interval in oil sand reservoir, provide more comprehensive information for predicting the distribution and quality of bitumen, and optimize well-site deployment and bitumen recovery.

Block M, Peru is located in the northwestern margin of the Madre de Dios Basin, at the front of the sub-Andean fold-thrust belt. Permian carbonate gas reservoirs are controlled by both carbonate sedimentary facies and thrust fault zones. The distribution of oil and gas in different structural belts varies greatly. In this paper, taking the Permian carbonate gas reservoir as the research object in Block M, Peru, on the basis of the analysis of the accumulation conditions, the structure and sedimentary research was carried out, and the favorable traps and the dominant facies belt of the carbonate were clarified. Through the coupling analysis of sedimentary and structure, the distribution characteristics of gas reservoirs in different thrust fault belts are summarized, that is, the accumulation conditions of the northern structural belt are better than those of the central and southern structural belts. The west side of the northern structural belt is better than the east side; the east side of the central structural belt is better than the west side; and the southern structural belt is less favorable due to the erosion of the caprock. The research results are helpful for the understanding of oil and gas accumulation laws and the selection of favorable exploration zones, and could provide guidance for the exploration of Permian carbonate gas reservoirs.

根据岩心薄片、分析化验、测井和地震等资料,利用地质和地球物理相结合的研究方法,对巴西桑托斯盆地火成岩期次、岩性岩相、地球物理特征、火山机构特征及Eastern油田火成岩发育特征等进行了研究.研究结果表明:①桑托斯盆地发育瓦兰今-欧特里夫期喷发岩、巴列姆-阿普特早期喷发岩、阿普特期喷发岩、坎潘期侵入岩及始新世侵入岩和喷发岩 5 期岩浆活动,具有陆上喷发和水下喷发 2 种模式,发育裂隙式和中心式火山机构,可划分为火山通道相、火山颈相、溢流相、碎裂相、次火山岩相、火山沉积相等 6 种岩相.②按照火山机构"定区"、火山通道"定源"、地震反射特征"定相"、多重属性"定性"、叠前反演"定量"的火成岩预测方法,实现了Eastern油田火成岩的分布预测,侵入岩主要分布于研究区中部,喷发岩主要分布于研究区西北部和东部,经钻井证实,预测结果符合率达 95%.③含火成岩的盆地中,其油气成藏与火成岩的形成演化密切相关,火成岩对油气成藏具有建设性和破坏性的双重影响,对油气勘探具有重要意义.

The sedimentary period of the Early Permian Fengcheng Formation in Mahu Depression of NW Junggar Basin is the key period for the formation of lacustrine organic-rich shale. The main objective of this paper is to use various spectral analysis methods to construct a tuned floating astronomical chronological time scale for the fine-grained sedimentary rocks of Fengcheng Formation. In this study, we provide astronomical constraints for the relationship between the fine-grained deposition of Fengcheng Formation and regional geological events in Junggar basin. High-resolution stratigraphic frameworks are critical for understanding the nature and patterns of major geological events. A detailed time series analysis of fine-grained sedimentary rocks of the Fengcheng Formation dominated by deep lacustrine shales was carried out in Borehole MY01. The results show that in the early Permian, driven by the long-eccentricity (413 kyr), short-eccentricity (100 kyr), obliquity (43.9 kyr and 34.9 kyr), precession (21.0 kyr and 17.6 kyr), the periodic variation wavelengths are 62.5 m, 14.71 m, 6.41 m, 5.24 m, 3.22 m and 2.75 m respectively. According to the published biostratigraphic division and U-Pb zircon age constraints, the stable 413 kyr tuned floating astrochronology time scale in the Early Permian shows that the deposition duration of the Fengcheng Formation shales is about 3.34 myr and the sedimentation rate is about 15 cm/kyr. In the future work, the systematic study of the absolute age of volcanic rocks will further help to more accurately constrain the sedimentary age of the Fengcheng Formation in Mahu Depression, NW Junggar Basin.

桑托斯盆地裂陷初期岩浆活动与储层发育关系密切.本文以盆地L区块火成岩-介壳灰岩复合体为研究对象,通过对火成岩岩石学、年代学测试及钻井、测井资料分析等,首次明确了桑托斯盆地裂陷初期岩浆活动特征及其对介壳灰岩沉积过程的控制,并指出介壳灰岩储层的分布特征.L区块内火成岩分属晚白垩世Santonian期—Campanian期和早白垩世Aptian两期岩浆活动产物,并以Aptian期为主,至少经历了 7次不连续喷发和3次侵入过程,形成了块状玄武岩、杏仁状玄武岩和玻基斑状玄武岩(含再沉积玻基斑状玄武岩)等喷发相火成岩和以辉绿岩(局部属粗玄岩)、煌斑岩形式产出的侵入相火成岩.Aptian期岩浆多期活动重塑了古地貌,形成了局部构造凸起,促成并控制了下白垩统Itapema组至少6期介壳灰岩沉积,最终形成了～620 m厚火成岩-介壳灰岩复合体.介壳灰岩储层呈透镜体形状,以"散点式"不连续分布在Aptian期盆内古隆、古断阶(坡)等区域,横向连续性差,垂向连通性受限,其发育规模和质量受古地貌及水深条件等影响.