Formation,evolution,reconstruction of black shales and their influence on shale oil and gas resource

Black shales are important products of material cycling and energy exchange among the lithosphere,atmosphere,hydrosphere,and biosphere.They are widely distributed throughout geological history and provide essential energy and mineral resources for the development of human society.They also record the evolution process of the earth and improve the understanding of the earth.This review focuses on the diagenesis and formation mechanisms of black shales sedimentation,composition,evolution,and reconstruction,which have had a significant impact on the formation and enrichment of shale oil and gas.In terms of sedimentary environment,black shales can be classified into three types:Marine,terrestrial,and marine-terrestrial transitional facies.The formation processes include mechanisms such as eolian input,hypopycnal flow,gravity-driven and offshore bottom currents.From a geological perspective,the formation of black shales is often closely related to global or regional major geological events.The enrichment of organic matter is generally the result of the interaction and coupling of several factors such as primary productivity,water redox condition,and sedimentation rate.In terms of evolution,black shales have undergone diagenetic evolution of inorganic minerals,thermal evolution of organic matter and hydrocarbon generation,interactions between organic matter and inorganic minerals,and pore evolution.In terms of reconstruction,the effects of fold deformation,uplift and erosion,and fracturing have changed the stress state of black shale reservoirs,thereby having a significant impact on the pore structure.Fluid activity promotes the formation of veins,and have changed the material composition,stress structure,and reservoir properties of black shales.Regarding resource effects,the deposition of black shales is fundamental for shale oil and gas resources,the evolution of black shales promotes the shale oil and gas formation and storage,and the reconstruction of black shales would have caused the heterogeneous distribution of oil and gas in shales.Exploring the formation mechanisms and interactions of black shales at different scales is a key to in-depth research on shale formation and evolution,as well as the key to revealing the mechanism controlling shale oil and gas accumulation.The present records can reveal how these processes worked in geological history,and improve our understanding of the coupling mechanisms among regional geological events,black shales evolution,and shale oil and gas formation and enrichment.

Evaluation of the oil and gas preservation conditions, source rocks, and hydrocarbongenerating potential of the Qiangtang Basin: New evidence from the scientific drilling project

The Qiangtang Basin of the Tibetan Plateau,located in the eastern Tethys tectonic domain,is the largest new marine petroliferous region for exploration in China.The scientific drilling project consisting primarily of well QK-1 and its supporting shallow boreholes for geological surveys(also referred to as the Project)completed in recent years contributes to a series of new discoveries and insights into the oil and gas preservation conditions and source rock evaluation of the Qiangtang Basin.These findings differ from previous views that the Qiangtang Basin has poor oil and gas preservation conditions and lacks high-quality source rocks.As revealed by well QK-1 and its supporting shallow boreholes in the Project,the Qiangtang Basin hosts two sets of high-quality regional seals,namely an anhydrite layer in the Quemo Co Formation and the gypsum-bearing mudstones in the Xiali Formation.Moreover,the Qiangtang Basin has favorable oil and gas preservation conditions,as verified by the comprehensive study of the sealing capacity of seals,basin structure,tectonic uplift,magmatic activity,and groundwater motion.Furthermore,the shallow boreholes have also revealed that the Qiangtang Basin has high-quality hydrocarbon source rocks in the Upper Triassic Bagong Formation,which are thick and widely distributed according to the geological and geophysical data.In addition,the petroleum geological conditions,such as the type,abundance,and thermal evolution of organic matter,indicate that the Qiangtang Basin has great hydrocarbon-generating potential.

Analysis of the world oil and gas exploration situation in 2021

The global exploration investment, new oil and gas discoveries, exploration business adjustment strategies of oil companies in 2021, and future favorable exploration domains are systematically analyzed using commercial databases such as IHS and public information of oil companies. It has been found that the world oil and gas exploration situation in 2021 has continued the downturn since the outbreak of COVID-19. The investment and drilling workload decreased slightly, but the success rate of exploration wells, especially deepwater exploration wells, increased significantly, and the newly discovered reserves increased slightly compared with last year. Deep waters of the passive continental margin basins are still the leading sites for discovering conventional large and medium-sized oil and gas fields. The conventional oil and gas exploration in deep formations of onshore petroliferous basins has been keeping a good state, with tight/shale oil and gas discoveries made in Saudi Arabia, Russia, and other countries. While strengthening the exploration and development of local resources, national, international, and independent oil companies have been focusing on major overseas frontiers using their advantages, including risk exploration in deep waters and natural gas. Future favorable exploration directions in the three major frontiers, the global deep waters, deep onshore formations, and unconventional resources, have been clarified. Four suggestions are put forward for the global exploration business of Chinese oil companies: first, a farm in global deepwater frontier basins in advance through bidding at a low cost and adopt the “dual exploration model” after making large-scale discoveries;second, enter new blocks of emerging hot basins in the world through farm-in and other ways, to find large oil and gas fields quickly;third, cooperate with national oil companies of the resource host countries in the form of joint research and actively participate exploration of deep onshore formations of petroliferous basins;fourth, track tight/shale oil and gas cooperation opportunities in a few countries such as Saudi Arabia and Russia, and take advantage of mature domestic theories and technologies to farm in at an appropriate time.

Geological characteristics of unconventional tight oil reservoir (10^(9) t): A case study of Upper Cretaceous Qingshankou Formation, northern Songliao Basin, NE China

The Daqing exploration area in the northern Songliao Basin has great potential for unconventional oil and gas resources,among which the total resources of tight oil alone exceed 109 t and is regarded as an important resource base of Daqing oilfield.After years of exploration in the Qijia area,Songliao Basin,NE China,tight oil has been found in the Upper Cretaceous Qingshankou Formation.To work out tight oil’s geological characteristics,taking tight oil in Gaotaizi oil layers of the Upper Cretaceous Qingshankou Formation in northern Songliao Basin as an example,this paper systematically analyzed the geological characteristics of unconventional tight oil in Gao3 and Gao4 layers of the Qijia area,based on the data of the geological survey,well drilling journey,well logging,and test.It is that three sets of hydrocarbon source rocks(K2qn1,K2qn2+3,and K2n1)develop in the examined area,and exhibit excellent type I and II kerogens,high organic matter abundance,and moderate maturity.The reservoir is generally composed of thin-bedded mudstone,siltstone,and sandstone,and presents poor porosity(average 8.5 vol.%)and air permeability(average 4 mD).The main reservoir space primarily includes intergranular pores,secondary soluble pores,and intergranular soluble pores.Three types of orifice throats were identified,namely fine throat,extra-fine throat,and micro-fine throat.The siltstone is generally oil-bearing,the reservoirs with slime and calcium become worse oil-bearing,and the mudstone has no obvious oil-bearing characteristics.The brittleness indices of the sandstone in the tight oil reservoir range from 40%to 60%,and those of the mudstone range from 40%to 45%,indicating a better brittleness of the tight oil reservoir.Based on the study of typical core hole data,this paper gives a comprehensive evaluation of the properties of the tight oil and establishes a tight oil single well composite bar chart as well as the initial evaluation system with the core of properties in the tight oil reservoir.This study has theoretical guiding significance and practical application value for tight oil exploration and evaluation in the Qijia area.

“Compression Dynamometamorphic Solid Bitmen” and Its Significance in Oil and Gas Exploration

There is natural occurrence of pressure-induced solid bitumen, here referred to as “compression dynamometamorphic solid bitumen”. It differs in physical properties and chemical structure from thermal metamorphic solid bitumen. Under a high pressure and moderate temperature, the solid bitumen forms crystals and its reflectance rises rapidly with increasing crystallization. Accordingly, its reflectance can reach a very high value without having been exposed to a high level of thermal stress. Laboratory simulation confirms the formation of pressure-induced solid bitumen at moderate temperatures. The revelation of this new bitumen type is very helpful in the accurate maturity determination of carbonate organic matter.

Exploration of Complicated Oil and Gas Fields

Complicated oil and gas fields occupy an important position in oil and gas exploration. In this paper, complicated oil and gas fields are grouped into four types: fault-block, lithologic, stratigraphic and fissure types. On the basis of the new theory of petroleum geological exploration in composite oil and gas accumulation areas within continental basins, a new exploration sequence suitable for complicated oil and gas fields has been established, which comprises four stages:(1) initial exploration;(2) preliminary exploration;(3) early step-by-step exploration and development: and(4) late step-by-step exploration and development. The idea of cybernetics has been taken to control various links of a systematic exploration project so as to fully, effectively and comprehensively utilize the new exploration techniques, eventually realizing the optimization of exploration with the aim of raising the efficiency of exploration of complicated oil and gas fields.

Research and Application of New Methods to Oil-Gas Geochemical Exploration

Based on the results of researches and applications for many years, it has been discovered that new methods and techniques for geochemical exploration of oil and gas such as δC, altered carbonate, Hg in absorption phase, Ks, Fe2+, δ13C, fluorescence in two and three dimensions, and N2 and O2 in heat release can give full play in the following five fields: (1) optimization of the favourable target or hollow zones and structural zones in a region; (2) evaluation of oil traps and delineation of prospective oil and gas areas; (3) prediction of deep-seated oil-bearing horizons; (4) evaluation of the genesis of oil and gas geochemical anomalies and determination of the types of oil and gas accumulations; (5) forecast of the burial depths of oil and gas pools.

Bohai Bay Oil and Gas Exploration Contract Signed

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Geological characteristics and co-exploration and co-production methods of Upper Permian Longtan coal measure gas in Yangmeishu Syncline, Western Guizhou Province, China

Coal measure gas(also known as coal-bearing unconventional gas)is the key field and development direction of unconventional natural gas in recent years.The exploration and evaluation of coal measure gas(coalbed methane,coal shale gas and coal measure tight sandstone gas)from single coalbed methane has greatly expanded the field and space of resource evaluation,which is of positive significance for realizing the comprehensive utilization of coal resources,maximizing the benefits and promoting the innovation of oil and gas geological theory and technological advances in exploration and development.For the first time,in Yangmeishu Syncline of Western Guizhou Province,the public welfare coalbed methane geological survey project of China Geological Survey has been carried out a systematic geological survey of coal measure gas for the Upper Permian Longtan Formation,identified the geological conditions of coal measure gas and found high quality resources.The total geological resource quantity of coalbed methane and coal shale gas is 51.423×109 m3 and the geological resource abundance is up to 566×106 m3/km2.In this area,the coal measures are characterized by many layers of minable coal seams,large total thickness,thin to the medium thickness of the single layer,good gas-bearing property of coal seams and coal measure mudstone and sandstone,good reservoir physical property and high-pressure coefficient.According to the principle of combination of high quality and similarity of key parameters of the coal reservoir,the most favorable intervals are No.5-2,No.7 and No.13-2 coal seam in Well YMC1.And the pilot tests are carried out on coal seams and roof silty mudstone,such as staged perforation,increasing hydraulic fracturing scale and"three gas"production.The high and stable industrial gas flow with a daily gas output of more than 4000 m3 has been obtained,which has realized the breakthrough in the geological survey of coal measure gas in Southwest China.Based on the above investigation results,the geological characteristics of coal measure gas in the multi-thin-coal-seam-developed area and the coexploration and co-production methods,such as the optimization method of favorable intervals,the highefficiency fracturing and reservoir reconstruction method of coal measures,and the"three gas"drainage and production system,are systematically summarized in this paper.It will provide a reference for efficient exploration and development of coal measure gas in similar geological conditions in China.

Petroleum geology and exploration direction of gas province in deepwater area of North Carnarvon Basin, Australia

North Carnarvon Basin is a gas province with minor oily sweet spots in deepwater area with water depth more than 500 m,which is one of the hot spots of global petroleum exploration for its series of giant hydrocarbon discoveries in recent years.However,the degree of oil and gas exploration in deepwater area is still low,and the conditions for oil and gas accumulation are not clear.Based on the current exploration situation and latest database of fields,applying multidisciplinary analysis of hydrocarbon geology,hydrocarbon accumulation elements and its exploration direction of North Carnarvon Basin in deepwater area are analyzed.The results show that there are three sets of main source rocks in deepwater area of North Carnarvon Basin,which are Triassic marine shale in Locker Formation and delta coal-bearing mudstone with thin carbonaceous mudstone in Mungaroo Formation,Lower–Middle Jurassic paralic carbargilite and coal measure strata in Athol Formation and Murat Formation,Cretaceous delta mudstone in Barrow Group and marine shale in Muderong Formation.Most source rock samples show gas-prone capability.The coarse sandstone of delta facies in Middle–Upper Triassic Mungaroo Formation is the most important reservoir in deepwater area,Lower Cretaceous Barrow Group deep-water gravity flow or underwater fan turbidite sandstone is the secondly main reservoir.Lower Cretaceous marine shale in Muderong Formation is most important regional caprock.Triassic mudstone in Mungaroo Formation is an important interlayer caprock in deepwater area.There are two main reservoir accumulation assemblages in deepwater area,one is Triassic structural-unconformity plane reservoir accumulation assemblage of Locker Formation to Mungaroo Formation,and the other is Lower–Middle Jurassic Athol Formation and Murat Formation–Lower Cretaceous stratigraphic lithology-structural reservoir accumulation assemblage of Barrow Group to Muderong Formation.There are three main control factors of hydrocarbon Accumulation:One is coupling of source and seal control hydrocarbon distribution area,the second is multi-stage large wave dominated deltas dominate accumulation zone,the third is direction of hydrocarbon migration and accumulation in hydrocarbon-rich generation depression was controlled by overpressure.The south of Exmouth platform in deepwater area is adjacent to hydrocarbon rich depression zone,reservoir assemblage is characterized by“near source rocks,excellent reservoir facies,high position and excellent caprocks”,which is the main battlefield of deepwater oil and gas exploration in North Carnarvon Basin at present.There are a lot of fault block traps in the northern structural belt of Exmouth platform,and the favorable sedimentary facies belt at the far end of delta plain in Mungaroo Formation is widely distributed,which is the next favorable exploration zone.The Lower Cretaceous,which is located at the concave edge uplift adjacent to the investigator depression and the Exmouth platform,also has a certain exploration prospect in northwest of deepwater area.

Oil-gas reservoir in the Mesozoic strata in the Chaoshan depression,northern South China Sea:a new insight from long off set seismic data

The Chaoshan depression,a Mesozoic basin in the Dongsha sea area,northern South China Sea,is characterized by well-preserved Mesozoic strata,being good conditions for oil-gas preservation,promising good prospects for oil-gas exploration.However,breakthrough in oil-gas exploration in the Mesozoic strata has not been achieved due to less seismic surveys.New long-off set seismic data were processed that acquired with dense grid with single source and single cable.In addition,the data were processed with 3D imaging method and fi ner processing was performed to highlight the target strata.Combining the new imaging result and other geological information,we conducted integrated interpretation and proposed an exploratory well A-1-1 for potential hydrocarbon.The result provides a reliable basis for achieving breakthroughs in oil and gas exploration in the Mesozoic strata in the northern South China Sea.