A study on the temperature sensitivity of NMR porosity in porous media based on the intensity of magnetization Dedicated to the special issue “Magnetic Resonance in Porous Media”

The measurement of nuclear magnetic resonance(NMR)porosity is affected by temperature.Without considering the impact of NMR logging tools,this phenomenon is mainly caused by variations in magnetization intensity of the measured system due to temperature fluctuations and difference between the temperature of the porous medium and calibration sample.In this study,the effect of temperature was explained based on the thermodynamic theory,and the rules of NMR porosity responses to temperature changes were identified through core physics experiments.In addition,a method for correcting the influence of temperature on NMR porosity measurement was proposed,and the possible factors that may affect its application were also discussed.

Formation conditions and reservoir-forming models of the Ordovician buried hill reservoirs in the Jizhong depression

The buried hill in the Jizhong depression contains abundant petroleum reserves and are important production areas.The Ordovician buried hill has restricted the discovery of new oil and gas exploration targets because of its strong reservoir heterogeneity and complex reservoir-controlling factors.Based on a large volume of core,thin section,logging,seismic,and geochemical data and numerous geological analyses,the reservoir-forming conditions and modes were systematically analyzed to guide the exploration and achieve important breakthroughs in the Yangshuiwu and Wen an slope buried hills.The study revealed that three sets of source rocks of the third and fourth members of the Shahejie Formation from the Paleogene and Carboniferous-Permian were developed in the Jizhong depression,providing sufficient material basis for the formation of buried hill oil and gas reservoirs.The reservoir control mechanism involving the three major factors of“cloud-karst-fault”was clarified,and karst cave,fracture fissure-pore,and cloud pore type reservoir models were established,thereby expanding the exploration potential.Controlled by the superposition of multi-stage tectonic processes during the Indosinian,Yanshanian,and Himalayan,two genetic buried hill trap types of uplift-depression and depression-uplift were formed.Based on the analysis of reservoir-forming factors of the Ordovician buried hill,three buried hill oil and gas reservoir-forming models were identified:low-level tectonic-lithologic composite quasi-layered buried hill,medium-level paleo-storage paleo-block buried hill,and high-level paleo-storage new-block buried hill.Comprehensive evaluations indicate that the reservoir-forming conditions of the low-level tectonic-lithologic composite quasi-layered buried hill in the northern portion of the Jizhong depression are the most favorable and that the Sicundian and Xinzhen buried hills are favorable areas for future exploration.

Petroleum geological features and hydrocarbon enrichment of Linhe Depression in Hetao Basin, NW China

Based on paleogeomorphology, drilling and seismic data, this paper systematically studies the structural and sedimentary evolution, source rock characteristics, reservoir characteristics and formation mechanism, hydrocarbon accumulation model and enrichment law in the Linhe Depression of the Hetao Basin, NW China. The Hetao Basin mainly experienced three stages of evolution, namely, weak extensional fault depression, strong extensional fault depression and strike-slip transformation, giving rise to four positive structural belts(Jilantai, Shabu, Nalinhu and Xinglong), which are favorable areas for oil and gas accumulation. The two main saline lacustrine source rocks, Lower Cretaceous Guyang Formation and Oligocene Linhe Formation, are characterized by high sulfur content, rich algae, early maturity, early expulsion, and wide oil generation window. The large structural transition belt in the intermountain area around the Hetao Basin controls the formation of large-scale braided river delta deposits, which are characterized by high quartz content(50%-76%), long-term shallow burial and weak compaction, low cement content, and good reservoir properties in delta front sandbody. The burial depth of the effective Paleogene reservoirs is predicted to reach 8000 m. Three hydrocarbon accumulation models, nose-uplift near sag, buried hill surrounding sag, fault nose near source rock, are constructed. The law of hydrocarbon accumulation in the Linhe Depression is finally clarified as follows: near-source around the depression is the foundation, high-quality thick reservoir is the premise, good tectonic setting and trap conditions are the key.

Rock thin-section analysis and identification based on artificial intelligent technique

Rock thin-section identification is an indispensable geological exploration tool for understanding and recognizing the composition of the earth.It is also an important evaluation method for oil and gas exploration and development.It can be used to identify the petrological characteristics of reservoirs,determine the type of diagenesis,and distinguish the characteristics of reservoir space and pore structure.It is necessary to understand the physical properties and sedimentary environment of the reservoir,obtain the relevant parameters of the reservoir,formulate the oil and gas development plan,and reserve calculation.The traditional thin-section identification method has a history of more than one hundred years,which mainly depends on the geological experts'visual observation with the optical microscope,and is bothered by the problems of strong subjectivity,high dependence on experience,heavy workload,long identification cycle,and incapability to achieve complete and accurate quantification.In this paper,the models of particle segmentation,mineralogy identification,and pore type intelligent identification are constructed by using deep learning,computer vision,and other technologies,and the intelligent thinsection identification is realized.This paper overcomes the problem of multi-target recognition in the image sequence,constructs a fine-grained classification network under the multi-mode and multi-light source,and proposes a modeling scheme of data annotation while building models,forming a scientific,quantitative and efficient slice identification method.The experimental results and practical application results show that the thin-section intelligent identification technology proposed in this paper does not only greatly improves the identification efficiency,but also realizes the intuitive,accurate and quantitative identification results,which is a subversive innovation and change to the traditional thin-section identification practice.

碳酸盐岩气藏水侵模拟与剩余气分布的核磁共振实验研究（英文）

边底水活跃气藏发生水侵是一种常见现象。研究区为碳酸盐岩气藏,因储层非均质性强、生产任务重,气藏发生严重水侵,影响开发效果,并将导致气藏采收率低。本文采用岩心驱替实验和核磁共振技术相结合的方法,研究了碳酸盐岩气藏水侵过程和注气复产过程中,气液两相渗流规律以及剩余气微观分布规律。研究结果表明,在水侵过程中,裂缝型岩心较孔隙型岩心的液相相对渗透率高、共渗区窄;在不同水侵速度下,裂缝型岩心的采收率最低。在注气复产过程中,注气对裂缝型岩心降低含水饱和度、恢复部分气相相对渗透率的效果突出。剩余气量及其分布与岩心物性相关,水侵速度对裂缝型岩心剩余气的分布影响较大,但对孔隙型岩心的影响小。研究结果进一步提高了对碳酸盐岩气藏水侵机理、注气复产以及剩余气分布的认识,为提高该类型气藏采收率提供依据。

Reservoir controlling differences between consequent faults and antithetic faults in slope area outside of source: A case study of the south-central Wenan slope of Jizhong Depression, Bohai Bay Basin, East China

The control effects of different occurrence faults on oil and gas accumulation and distribution in the outer slope area of oil and gas reservoirs were studied taking the south-central Wen’an slope of the Jizhong depression in the Bohai Bay Basin as an example.Based on 3D seismic data and the distribution of oil and water,the controlling differences between consequent fault and antithetic fault were analyzed and compared from the formation and evolution rule of faults and the formation mechanism of fault traps,including development positions of the consequent fault traps and antithetic fault traps,oil and gas distribution horizon adjusted by fault and formation period of fault traps.The differences between consequent faults and antithetic faults in controlling reservoirs have three main aspects:(1)Consequent fault traps and antithetic fault traps are in different positions,the consequent fault traps are at the segmented growing point in the hanging wall of"hard-linkage"faults,while the antithetic fault traps are developed in the position with the largest throw in the footwall because of tilting action;(2)The two kinds of faults result in different oil and gas distribution vertically,oil and gas adjusted by consequent faults is distributed in a single layer or multi-layers,while oil and gas adjusted by antithetic faults occur in single layers;(3)The two kinds of fault traps are formed in different periods,the consequent fault traps are formed at the time when the related faults enter the stage of"hard-linkage",while the antithetic fault traps are formed at the beginning of the fault active period.

Uncertainty Analysis Method of Casing Extrusion Load for Ultra-Deep Wells

With the consideration of the randomness of complex geologic parameters for ultra-deep wells,an uncertainty analysis method is presented for the extrusion load on casing in ultra-deep wells through complex formation at a certain confidence level.Based on the extrusion load model for casing in ultra-deep wells and the prerequisite of integrity of formation-cement ring-casing,the probability and statistics theory are introduced and the sensitivity analysis on the uncertainty of extrusion load on casing is conducted.The distribution types of each formation parameters are determined statistically.The distribution type and distribution function of the extrusion load on casing are derived.Then,the uncertainty analysis of the extrusion load on casing is carried out on several ultra-deep wells in Shanqian block as case study.Several conclusions are made regarding to the field trial result.The randomness of formation elasticity modulus and formation Poisson’s ratio are the main influence factors.The equivalent density profile of extrusion load on casing in ultra-deep wells is a confidence interval with a certain confidence level,rather than a single curve;the higher the confidence level is,the larger the bandwidth of the confidence interval of equivalent density profile becomes,and the larger the range of uncertainty interval becomes.Compared with the result of uncertainty analysis,an error exists in the result of traditional single valued calculation method.The error varies with different casing program and can be either positive or negative.The application of uncertainty analysis of extrusion load on casing provides proof for the accurate determination of casing collapse safety factor.Thus,the over engineering design or under engineering design as a result of tradition casing design will be avoided.

The Formation and Evolution Mechanism of Tight Oil and Gas in Lacustrine Carbonate Rocks in the Bohai Bay Basin

Tight oil, a kind of unconventional oil accumulation that accumulates in source rocks in a free or adsorbed status in low or ultra-low porous sandstones or carbonates rocks which are interbedded with or adjacent to source rocks.

Geological Modeling on the Reservoir of Oil Sand in Estuary

1 Introduction Pore is the major oil and gas reservoir, and its volume and structure determines the gas capacity of shale and the occurrence mode of gas. The development of shale porosity is mainly affected by the content and diagenesis of quartz, clay and some other minerals, the content and maturity of TOC, the strength and time of tectonic activities etc., besides the study ofpore＇s character of shale reservoir is an important prerequisite to exploration and production of shale hydrocarbon and guarantee and improvement of hydrocarbon reserves. Among pores, the organic pores include organic matter pores and biological fossil pores.

Rules of Formation of Lithostratigraphic Oil and Gas Reservoirs in the Southern Part of Songliao Basin

Oil and gas exploration in most areas and major horizons of Songliao Basin have reached a stage of high maturity.Presently,there are few structural trap reservoirs remaining to be drilled in the basin,and major targets

Blueprint for Energy Reserves

The government is drafting a strategic reserve blueprint to ensure energy security-the move coming close on the heels of the construction of four oil reserve bases, according to Ma Fucai, deputy director of the Office of the National Energy Leading Group. 'The blueprint will focus on building strategic reserves for key resources ranging from natural gas and coal to uranium, but the top priority is to build strategic oil reserves, which are almost complete,' Ma told the news media in mid-March, adding that 'the reserve system will then be expanded to other key energies.'

Characterization of Microscopic Pore Structures in Shale Gas Reservoirs of the Southeast Chongqing

Unlike traditional resources, mud shale has the characteristics of low porosity, low permeability, small pore structure, nanoscale pore as the main body. The microscopic pore structures of mud shale can not only influence the occurrence state of shale gas and gas content, but also influence the hydrocarbon expulsion efficiency of source rocks, which makes the study of shale gas reservoir necessary.

Critical tectonic events and their geological controls on deep buried coalbed methane accumulation in Daning-Jixian Block, eastern Ordos Basin

Commercial exploration and development of deep buried coalbed methane (CBM) in Daning-Jixian Block, eastern margin of Ordos Basin, have rapidly increased in recent decades. Gas content, saturation and well productivity show significant heterogeneity in this area. To better understand the geological controlling mechanism on gas distribution heterogeneity, the burial history, hydrocarbon generation history and tectonic evolution history were studied by numerical simulation and experimental simulation, which could provide guidance for further development of CBM in this area. The burial history of coal reservoir can be classified into six stages, i.e., shallowly buried stage, deeply burial stage, uplifting stage, short-term tectonic subsidence stage, large-scale uplifting stage, sustaining uplifting and structural inversion stage. The organic matter in coal reservoir experienced twice hydrocarbon generation. Primary and secondary hydrocarbon generation processes were formed by the Early and Middle Triassic plutonic metamorphism and Early Cretaceous regional magmatic thermal metamorphism, respectively. Five critical tectonic events of the Indosinian, Yanshanian and Himalayan orogenies affect different stages of the CBM reservoir accumulation process. The Indosinian orogeny mainly controls the primary CBM generation. The Yanshanian Orogeny dominates the second gas generation and migration processes. The Himalayan orogeny mainly affects the gas dissipation process and current CBM distribution heterogeneity.

Comparison of Formation Conditions of Source Rocks of Fengcheng and Lucaogou Formations in the Junggar Basin,NW China:Implications for Organic Matter Enrichment and Hydrocarbon Potential

Shales in the Carboniferous–Permian Fengcheng(FC) and Lucaogou(LCG) formations in Junggar Basin are important organic rich rocks containing significant oil resources.To evaluate the difference in sedimentary environment conditions and hydrocarbon-generating potential between the FC and LCG formations.Total organic carbon(TOC),Rock-Eval pyrolysis,solvent extraction,column fractionation,stable carbon isotope,gas chromatography-mass spectrometry(GC-MS) of saturated hydrocarbons and organic petrology from the source rocks of FC and LCG formations.were analyzed.The biomarker composition indicates that during the deposition of FC,LCG-1 to LCG-2,the sedimentary environment for the source rock formations changed with gradual decrease of salinity,from anoxic to dyoxic/suboxic in redox conditions,and from strong stratification to weakened stratification of water.The FC Formation source rock,with main telalginite(planktonic green algae),archaebacteria and minor terrestrial organic matter,deposited in the environment characterized by high salinity and strongly reducing condition.Its TOC content is relatively low with a high original hydrocarbongenerating potential of unit organic material.The LCG Formation source rock deposited in the environment with low salinity and large variations,the organic matter is mainly sourced from telalginite(planktonic green algae),lamalginite,bacteria and higher plants,resulting in strong heterogeneity of the source rock.The abundance of TOC is high,but the original hydrocarbon generation potential of unit organic matter is lower than that of FC Formation.The results provide a geochemical basis for further study of saline-brackish water sedimentary environment shales in the Junggar Basin.

Pore structure characteristics of low-rank coal reservoirs with different ash yields and their implications for recoverability of coalbed methane—a case study from the Erlian Basin, northeastern China

Pores are the main accumulation sites and migration pathways for coalbed methane(also referred to as CBM).Pore structure restricts the content and recoverability of CBM from coal reservoirs.In this study,12 representative coal samples with different ash yields that have similar tectonic characteristics and burial depths were collected from different mining areas in the Jiergalangtu and Huolinhe depressions in the Erlian Basin.These samples were used to study the restrictions of ash yield on the characteristics of coal pore structures and the recoverability of CBM through macroscopic and microscopic structure observation,scanning electron microscope observations,vitrinite reflectance tests,low-temperature N2 adsorption,nuclear magnetic resonance(NMR),and micro-computed tomography.The results show that coal reservoirs in the study area vary greatly in ash yield,based on which they can be divided into three types,i.e.,low-ash-content,ash-bearing,and high-ash-content coal reservoirs.In addition,the ash yield has a certain impact on the development of coal pores;coal samples with lower ash yields indicate the presence of well-developed medium-large pores and better connectivity.Ash yield also has a certain impact on the brittleness of coal wherein a lower ash yield implies the development of brittle coal that is more liable to fracture as compared to less brittle samples at the same pressure.Absorbed gas content also varies significantly with ash yield;a low ash yield impacts the gas saturation of coal.Overall,for coal reservoirs in the study area,their porosity,pore diameter,movable fluid porosity,adsorbed gas amount,and recoverability decrease as the ash yield increases.

Multi-stage gas diffusion and its implications for the productivity of coalbed methane in the southern Qinshui Basin, north China

The behavior of coalbed methane(CBM)diffusion considerably influences gas productivity.Based on the multi-porous diffusion model and on-site CBM desorption data of coal cores,the behavior of CBM diffusion and its implications on the gas productivity of No.3 coal seam in the southern Qinshui Basin(SQB)were elaborately analyzed.Results indicate that CBM diffusion of No.3 coal seam demonstrates noticeable three-stage characteristics,including the fast diffusion,transitional diffusion,and slow diffusion stages.During the gas diffusion process,the gas content and/or the degree of developed pores and fractures/cleats in coal seams can affect the desorption of CBM and the amount of diffused CBM by influencing the changes in gas pressure in pores,thus controlling the behavior of gas diffusion in different stages.Because gas content and the developed degree of pores and fractures/cleats are closely associated with the deformation degree of the coal seams,variably deformed coal seams exhibit unique characteristics of gas diffusion.The low-deformation degree of the coal seams have a relatively uniform distribution of gas production over the history of a well.By contrast,the moderate-deformation degree of the coal seams have a relatively high rate and amount of gas diffusion in the fast and transitional diffusion stages,producing most of the gas in the early-to-intermediate stages of the wells.Finally,the high-deformation degree of the coal seams has a high rate and amount in the fast diffusion stage,indicating that most of the production stage occurs during the early stage of the gas production history of a well.In summary,the behavior of gas diffusion can be used for predicting gas production potential.

Geochemical characteristics of produced fluids from CBM wells and their indicative significance for gas accumulation in Daning-Jixian block,Ordos Basin

The Daning-Jixian block,the eastern edge of the Ordos Basin,is one of the most potential areas for CO_(2)geological storage,enhanced coalbed methane recovery(ECBM)exploration and production in China in recent decades.The ionic composition and total dissolved solids(TDS)of the produced water,coal organic matter maturity,molecular composition and carbon isotope characteristics of the produced gas were utilized to analyze the hydrogeological condition,CBM generation and migration characteristics in this area.The CBM enrichment patterns and the geological impacts on gas well production characteristics were revealed.The optimal area for CBM development and CO_(2)geological storage in the study area were also proposed.Dominated by the Xueguan reverse fault zone,the hydraulic unit in this area can be divided into two parts(i.e.,the recharge-runoff zone in the east and the weak runoff-stagnation zone in the west).The thermogenic gas is dominating CBM genesis in this area.Secondary biogenic gas replenishment is only distributed in the eastern margin area,where theδ13C1 value is less than the thermal simulation results as an influence of hydrodynamic fractionation.Finally,two models of CBM formation and accumulation were proposed,1)thermogenic CBM migrated by hydrodynamic and resorbed for preservation at impermeable fault boundaries;2)thermogenic CBM trapped by fault and accumulated by hydrodynamic in slope zone.The gas production performance,generally increased from east to west,is mainly dominated by hydrogeological conditions.Generally,the west side of the fault zone is the enrichment and high-yield area for ECBM development and CO_(2)geological storage in the study area.

3-D geologic architecture of Xiong＇an New Area： Constraints from seismic reflection data

Studying the geologic architecture of the Xiong'an New Area will provide important basis for the evaluation of crustal stability, urban planning and infrastructural projects in this region, and it is also of great significance in exploring the occurrence of oil and gas, geothermal, hot dry rock and other resources. The stratigraphic system of the study area is established by using latest high quality seismic reflection and deep borehole data. Characteristics of the major faults developed in the study area are finely depicted with the method of structural analysis. Tectonic evolution of Xiong'an and adjacent areas is reconstructed by using balanced geological cross-section technique. The tectonic activity of the study area is discussed on the basis of the development of secondary faults and the distribution of active earthquakes across the region. This study demonstrates that Xiong'an New Area is located at the transfer zone of the central and northern Jizhong Depression. There are three regional unconformities developed in this area, by which four structural layers are sub-divided. Controlled by the Taihang Mountain piedmont fault, the Daxing fault, the Rongcheng fault and the Niudong fault, the structural framework of the study area is characterized by intervening highs with sags. This structural pattern has an important controlling over the reservoir characteristics, hydrocarbon accumulation and the distribution of geothermal resources and hot dry rock within this region. Rifting in this area began in the early Paleogene, exhibiting typical episodic character and became inactive in Neogene. The development feature of secondary faults along with the distribution of active earthquakes indicate that Xiong'an New Area has been in a relatively stable tectonic setting since the Neogene, while the Baxian Sag and other structural units to the east of it have obviously been in a rather active environment.

Genesis and Implications of the Composition and Sedimentary Structure of Fine-Grained Carbonate Rocks in the Shulu Sag

Fine-grained carbonate rocks, which extensively occur in the Eocene strata in the Shulu sag, Bohai Bay Basin, North China, represent an unconventional, fine-grained carbonate reservoir. However, previous studies have ignored the complexity of the lithofacies components and their formation mechanisms. Fine-grained carbonate rocks are typical reservoirs in which hydrocarbons form and gather. A better understanding of the nature of these rocks is extremely important for evaluating the quality of unconventional, fine-grained carbonate reservoirs. Various lithofacies components were discriminated in this study with a combination of petrographic observations and carbon isotope analyses. These finegrained carbonate rocks comprise terrigenous, biogenic and diagenetic materials. Terrigenous input and biologically induced precipitation are the main sources of the materials in the lake. Five lithofacies were identified based on the observations of sedimentary features（core and thin section） and mineralogical data：（1） varve-like laminated calcilutite,（2） graded laminated calcilutite,（3） interlaminated calcisiltitecalcilutite,（4） massive calcilutite, and（5） massive calcisiltite-calcarenite. Their origins were recorded by various lithofacies components, which are controlled by the interactions of physical, chemical and biological processes. This study indicated that the lithology of the bedrocks was the key factor controlling carbonate accumulation. The tectonics and climate can influence the weathering and types of lithofacies. Primary productivity controlled the precipitation of the endogenic calcite. These factors jointly determined the abundant fine-grained carbonate rocks that have accumulated in the Shulu sag.

Coevality of the sea-level fall and main mass extinction in the Permian-Triassic transition in Xiushui, Jiangxi Province, southern China

A continuous Permian-Triassic boundary （PTB） section has been found and studied for the first time in Xiushui, Jiangxi Province, South China. Evidence for a large sealevel fall has been found in the horizon of 0.8 m below the PTB, from the beginning of Hindeodus changxingensis zone （correlatable to Hindeodus typicalis Zone of the Meishan section）. Sedimentary record indicates that the sea level kept at Iowstand, or occasionally rose slowly during the whole Hindeodus parvus zone, except another substantial sea-level fall in early H. parvus zone. It began a quick rise from the beginning of Isarcicella staeschei zone, kept rising for the whole/, staeschei zone, and probably caused the stagnation of sea water. The first severe change in the biota, marked by the sudden disappearance of all steno- tropic organisms such as fusulinids and dasycladacians, happened at the same time as the first sea-level fall, and is regarded as the first and main episode of the end-Permian mass extinction in this area. A microbe-dominated biota followed the first extinction, and spanned the late H. changxingensis zone and the whole H. parvus zone. All the microbes and some other eurytropic organisms including gastropods and ostracods disappeared at the end of the H. parvus zone, and the following biota in the/. staeschei zone is very simple. The coevality of the main sea-level fall and the main extinction episode might be causal： both of them might be caused by a drastic climatic cooling.