Gas-Water Production of a Continental Tight-Sandstone Gas Reservoir under Different Fracturing Conditions

A numerical model of hydraulic fracture propagation is introduced for a representative reservoir(Yuanba continental tight sandstone gas reservoir in Northeast Sichuan).Different parameters are considered,i.e.,the interlayer stress difference,the fracturing discharge rate and the fracturing fluid viscosity.The results show that these factors affect the gas and water production by influencing the fracture size.The interlayer stress difference can effectively control the fracture height.The greater the stress difference,the smaller the dimensionless reconstruction volume of the reservoir,while the flowback rate and gas production are lower.A large displacement fracturing construction increases the fracture-forming efficiency and expands the fracture size.The larger the displacement of fracturing construction,the larger the dimensionless reconstruction volume of the reservoir,and the higher the fracture-forming efficiency of fracturing fluid,the flowback rate,and the gas production.Low viscosity fracturing fluid is suitable for long fractures,while high viscosity fracturing fluid is suitable for wide fractures.With an increase in the fracturing fluid viscosity,the dimensionless reconstruction volume and flowback rate of the reservoir display a non-monotonic behavior,however,their changes are relatively small.

Distribution patterns of tight sandstone gas and shale gas

Based on an elaboration of the resource potential and annual production of tight sandstone gas and shale gas in the United States and China,this paper reviews the researches on the distribution of tight sandstone gas and shale gas reservoirs,and analyzes the distribution characteristics and genetic types of tight sandstone gas reservoirs.In the United States,the proportion of tight sandstone gas in the total gas production declined from 20%-35%in 2008 to about 8%in 2023,and the shale gas production was 8310×10^(8)m^(3)in 2023,about 80%of the total gas production,in contrast to the range of 5%-17%during 2000-2008.In China,the proportion of tight sandstone gas in the total gas production increased from 16%in 2010 to 28%or higher in 2023.China began to produce shale gas in 2012,with the production reaching 250×10^(8)m^(3)in 2023,about 11%of the total gas production of the country.The distribution of shale gas reservoirs is continuous.According to the fault presence,fault displacement and gas layer thickness,the continuous shale gas reservoirs can be divided into two types:continuity and intermittency.Most previous studies believed that both tight sandstone gas reservoirs and shale gas reservoirs are continuous,but this paper holds that the distribution of tight sandstone gas reservoirs is not continuous.According to the trap types,tight sandstone gas reservoirs can be divided into lithologic,anticlinal,and synclinal reservoirs.The tight sandstone gas is coal-derived in typical basins in China and Egypt,but oil-type gas in typical basins in the United States and Oman.

Quantitative characterization of tight gas sandstone reservoirs using seismic data via an integrated rock-physics-based framework

Seismic characterizing of tight gas sandstone (TGS) reservoirs is essential for identifying promising gas-bearing regions. However, exploring the petrophysical significance of seismic-inverted elastic properties is challenging due to the complex microstructures in TGSs. Meanwhile, interbedded structures of sandstone and mudstone intensify the difficulty in accurately extracting the crucial tight sandstone properties. An integrated rock-physics-based framework is proposed to estimate the reservoir quality of TGSs from seismic data. TGSs with complex pore structures are modeled using the double-porosity model, providing a practical tool to compute rock physics templates for reservoir parameter estimation. The VP/VS ratio is utilized to predict the cumulative thickness of the TGS reservoirs within the target range via the threshold value evaluated from wireline logs for lithology discrimination. This approach also facilitates better capturing the elastic properties of the TGSs for quantitative seismic interpretation. Total porosity is estimated from P-wave impedance using the correlation obtained based on wireline log analysis. After that, the three-dimensional rock-physics templates integrated with the estimated total porosity are constructed to interpret microfracture porosity and gas saturation from velocity ratio and bulk modulus. The integrated framework can optimally estimate the parameters dominating the reservoir quality. The results of the indicator proposed based on the obtained parameters are in good agreement with the gas productions and can be utilized to predict promising TGS reservoirs. Moreover, the results suggest that considering microfracture porosity allows a more accurate prediction of high-quality reservoirs, further validating the applicability of the proposed method in the studied region.

Analysis of Reservoir Forming Conditions and Prediction of Continuous Tight Gas Reservoirs for the Deep Jurassic in the Eastern Kuqa Depression,Tarim Basin

The exploration targets in the Kuqa Depression at present are mainly structure traps in Cretaceous-Tertiary.Due to the complexity of mountain distribution and reservoir forming conditions, the exploration of Jurassic in the eastern Kuqa Depression has been in a state of semi-stagnation since the discovery of the Yinan-2 gas reservoir.According to the concept and theory of 'continuous petroleum reservoirs' and the re-analysis of the forming conditions of the Yinan-2 gas reservoir and regional natural gas in the eastern Kuqa Depression,it is believed that the deep Jurassic has good natural gas accumulation conditions as well as geological conditions for forming continuous tight gas reservoirs.The boundary of the Yinan-2 gas reservoir is not controlled by a structural spillpoint.The downdip part of the structure is dominated by gas,while the hanging wall of the fault is filled by water and forming obvious inverted gas and water.The gas reservoir has the normal temperature and ultrahigh pressure which formed in the near source or inner-source.All of these characteristics indicate that the Yinan-2 gas reservoir is different from conventional gas reservoirs.The deep Jurassic in the eastern Kuqa Depression has multisets of source-reservoir-cap assemblages,which comprise interbedded sandstones and mudstones.These assemblages are characterized by a self-generation,self-preserving and self-coverage model.Reservoir sandstones and coal measure mudstones are interbedded with each other at a large scale.As the source rocks,Triassic-Jurassic coal measure mudstones distribute continuously at a large scale and can generate and expel hydrocarbon.Source rocks contact intimately with the overlying sandstone reservoirs.During the late stage of hydrocarbon expulsion,natural gas charged continuously and directly into the neighboring reservoirs.Petroleum migrated mainly in a vertical direction over short distances.With ultra-high pressure and strong charging intensity,natural gas accumulated continuously.Reservoirs are dominated by sandstones of braided delta facies.The sand bodies distribute continuously horizontal.With low porosity and low permeability,the reservoirs are featured by strong heterogeneity.It is hypothesized that the sandstones of the interior depression tend to be relatively tight with increasing depth and structure stress weakness.Thus,it is predicted that continuous tight gas reservoirs of ultra-high pressure may exist in the deep formations of the eastern and even the whole Kuqa Depression.So,it is worth evaluating the exploration potential.

Geological characteristics and accumulation mechanisms of the "continuous" tight gas reservoirs of the Xu2 Member in the middle-south transition region,Sichuan Basin,China

＂Continuous＂ tight gas reservoirs are those reservoirs which develop in widespread tight sandstones with a continuous distribution of natural gas. In this paper, we summarize the geological features of the source rocks and ＂＇continuous＂ tight gas reservoirs in the Xujiahe Formation of the middle- south transition region, Sichuan Basin. The source rocks of the Xul Member and reservoir rocks of the Xu2 Member are thick （Xul Member： 40 m, Xu2 Member： 120 m） and are distributed continuously in this study area. The results of drilled wells show that the widespread sandstone reservoirs of the Xu2 Member are charged with natural gas. Therefore, the natural gas reservoirs of the Xu2 Member in the middle-south transition region are ＂continuous＂ tight gas reservoirs. The accumulation of ＂continuous＂ tight gas reservoirs is controlled by an adequate driving force of the pressure differences between source rocks and reservoirs, which is demonstrated by a ＂one-dimensional＂ physical simulation experiment. In this simulation, the natural gas of＂continuous＂ tight gas reservoirs moves tbrward with no preferential petroleum migration pathways （PPMP）, and the natural gas saturation of＂continuous＂ tight gas reservoirs is higher than that of conventional reservoirs.

Types and genesis of sweet spots in the tight sandstone gas reservoirs:Insights from the Xujiahe Formation,northern Sichuan Basin,China

Through comprehensively applying geological and geophysical data,as well as core and thin section observation,the characteristics of reservoirs and fractures in the second member of the Xujiahe Formation(hereinafter referred to as Xu2 Member)in the Yuanba area,northern Sichuan Basin,were studied.Combined with the analysis of the main controlling factors of production capacity,the types and characteristics of the sweet spots in the tight sandstone gas reservoir were determined.The evaluation standards and geological models of the sweet spots were established.The results are as follows:(1)There are bedding-parallel fracture-,fault-induced fracture-,and pore-dominated sweet spots in the tight sandstone gas reservoirs of the Xu2 Member.(2)The bedding parallel fracture-dominated sweet spots have developed in quartz sandstones with well-developed horizontal fractures and micro-fractures.They are characterized by high permeability and high gas output during production tests.This kind of sweet spots is thin and shows a limited distribution.Their logging responses show extremely low gamma-ray(GR)values and medium-high AC values.Moreover,the bedding parallel fracture-dominated sweet spots can be mapped using seismic methods.(3)The fault-induced fracture-dominated sweet spots have welldeveloped medium-and high-angle shear fractures.Their logging responses show an increase in peaks of AC values and total hydrocarbon content and a decrease in resistivity.Seismically,the areas with welldeveloped fault-induced fracture-dominated sweet spots can be effectively mapped using the properties such as seismic entropy and maximum likelihood.(4)The pore-dominated sweet spots are developed in medium-grained feldspathic litharenites with good reservoir properties.They are thick and widely distributed.(5)These three types of sweet spots are mainly determined by sedimentation,diagenesis,and tectonism.The bedding parallel fracture-dominated sweet spots are distributed in beachbar quartz sandstones on the top of the 1st sand layer group in the Xu2 Member,which develops in a shore-shallow lake environment.The fault-induced fracture-dominated sweet spots mainly occur near faults.They are increasingly developed in areas closer to faults.The pore-dominated sweet spots are primarily distributed in the 2nd and 3rd sand layer groups,which lie in the development areas of distributary channels near provenances at western Yuanba area.Based on the geological and seismic data,a comprehensive evaluation standard for these three types of sweet spots of the tight sandstone reservoirs in the Xu2 Member has been established,which,on the one hand,lays the foundation for the development and evaluation of the gas reservoir,and on the other hand,deepens the understanding of sweet spot in the tight sandstone gas reservoirs.

Production forecasting methods for different types of gas reservoirs

Hydrocarbon production in oil and gas fields generally progresses through stages of production ramp-up,plateau(peak),and decline during field development,with the whole process primarily modeled and forecasted using lifecycle models.SINOPEC's conventional gas reservoirs are dominated by carbonates,low-permeability tight sandstone,condensate,volcanic rocks,and medium-to-high-permeability sandstone.This study identifies the optimal production forecasting models by comparing the fitting coefficients of different models and calculating the relative errors in technically recoverable reserves.To improve forecast precision,it suggests substituting exponential smoothing method-derived predictions for anomalous data caused by subjective influences like market dynamics and maintenance activities.The preferred models for carbonate gas reservoir production forecasts are the generalized Weng's,Beta,Class-I generalized mathematical,and Hu-Chen models.The Vapor pressure and Beta models are optimal for forecasting the annual productivity of wells(APW)from gas-bearing low-permeability tight sandstone reservoirs.The Wang-Li,Beta,and Yu QT tb models are apt for moderate-to-small-reserves,single low-permeability tight sandstone gas reservoirs.The Rayleigh,Hu-Chen,and generalized Weng's models are suitable for condensate gas reservoirs.For medium-to-high-permeability sandstone gas reservoirs,the lognormal,generalized gamma,and Beta models are recommended.

Tight sandstone gas accumulation mechanism and development models

Tight sandstone gas serves as an important unconventional hydrocarbon resource, and outstanding results have been obtained through its discovery both in China and abroad given its great resource potential. However, heated debates and gaps still remain regarding classification standards of tight sandstone gas, and critical controlling factors, accumulation mechanisms, and devel- opment modes of tight sandstone reservoirs are not deter- mined. Tight sandstone gas reservoirs in China are generally characterized by tight strata, widespread distri- bution areas, coal strata supplying gas, complex gas-water relations, and abnormally low gas reservoir pressure. Water and gas reversal patterns have been detected via glass tube and quartz sand modeling, and the presence of critical geological conditions without buoyancy-driven mecha- nisms can thus be assumed. According to the timing of gas charging and reservoir tightening phases, the following three tight sandstone gas reservoir types have been identified： （a） ＂accumulation-densification＂ （AD）, or the conventional tight type, （b） ＂densification-accumulation＂ （DA）, or the deep tight type, and （c） the composite tight type. For the AD type, gas charging occurs prior to reser- voir densification, accumulating in higher positions under buoyancy-controlled mechanisms with critical controlling factors such as source kitchens （S）, regional overlaying cap rocks （C）, gas reservoirs, （D） and low fluid potential areas （P）. For the DA type, reservoir densification prior to the gas charging period （GCP） leads to accumulation in depres- sions and slopes largely due to hydrocarbon expansive forces without buoyancy, and critical controlling factors are effective source rocks （S）, widely distributed reservoirs （D）, stable tectonic settings （W） and universal densification of reservoirs （L）. The composite type includes features of the AD type and DA type, and before and after reservoir densification period （RDP）, gas charging and accumulation is controlled by early buoyancy and later molecular expansive force respectively. It is widely distributed in anticlinal zones, deep sag areas and slopes, and is con- trolled by source kitchens （S）, reservoirs （D）, cap rocks （C）, stable tectonic settings （W）, low fluid potential areas （P）, and universal reservoir densification （L）. Tight gas resources with great resource potential are widely dis- tributed worldwide, and tight gas in China that presents advantageous reservoir-forming conditions is primarily found in the Ordos, Sichuan, Tarim, Junggar, and Turpan- Hami basins of central-western China. Tight gas has served as the primary impetus for global unconventional natural gas exploration and production under existing technical conditions.

A Volumetric Model for Evaluating Tight Sandstone Gas Reserves in the Permian Sulige Gas Field,Ordos Basin,Central China

To accurately measure and evaluate reserves is critical for ensuring successful production of unconventional oil and gas. This work proposes a volumetric model to evaluate the tight sandstone gas reserves of the Permian Sulige gas field in the Ordos Basin. The reserves can be determined by four major parameters of reservoir cutoffs, net pay, gas-bearing area and compression factor Z, which are controlled by reservoir characteristics and sedimentation. Well logging, seismic analysis, core analysis and gas testing, as well as thin section identification and SEM analysis were used to analyze the pore evolution and pore-throat structure. The porosity and permeability cutoffs are determined by distribution function curve,empirical statistics and intersection plot. Net pay and gas-bearing area are determined based on the cutoffs, gas testing and sand body distribution, and the compression factor Z is obtained by gas component. The results demonstrate that the reservoir in the Sulige gas field is characterized by ultralow porosity and permeability, and the cutoffs of porosity and permeability are 5% and 0.15×10^(–3) μm^2, respectively. The net pay and gas-bearing area are mainly affected by the sedimentary facies, sand body types and distribution. The gas component is dominated by methane which accounts for more than 90%, and the compression factor Z of H_8(P_2h_8) and S_1(P_1s_1) are 0.98 and 0.985, respectively. The distributary channels stacked and overlapped, forming a wide and thick sand body with good developed intergranular pores and intercrystalline pores. The upper part of channel sand with good porosity and permeability can be sweet spot for gas exploration. The complete set of calculation systems proposed for tight gas reserve calculation has proved to be effective based on application and feedback. This model provides a new concept and consideration for reserve prediction and calculation in other areas.

A new model for predicting irreducible water saturation in tight gas reservoirs

The irreducible water saturation(Swir) is a significant parameter for relative permeability prediction and initial hydrocarbon reserves estimation.However,the complex pore structures of the tight rocks and multiple factors of the formation conditions make the parameter difficult to be accurately predicted by the conventional methods in tight gas reservoirs.In this study,a new model was derived to calculate Swir based on the capillary model and the fractal theory.The model incorporated different types of immobile water and considered the stress effect.The dead or stationary water(DSW) was considered in this model,which described the phenomena of water trapped in the dead-end pores due to detour flow and complex pore structures.The water film,stress effect and formation temperature were also considered in the proposed model.The results calculated by the proposed model are in a good agreement with the experimental data.This proves that for tight sandstone gas reservoirs the Swir calculated from the new model is more accurate.The irreducible water saturation calculated from the new model reveals that Swir is controlled by the critical capillary radius,DSW coefficient,effective stress and formation temperature.

Hydrocarbon detections using multi-attributes based quantum neural networks in a tight sandstone gas reservoir in the Sichuan Basin, China

A direct hydrocarbon detection is performed by using multi-attributes based quantum neural networks with gas fields.The proposed multi-attributes based quantum neural networks for hydrocarbon detection use data clustering and local wave decomposition based seismic attenuation characteristics,relative wave impedance features of prestack seismic data as the selected multiple attributes for one tight sandstone gas reservoir and further employ principal component analysis combined with quantum neural networks for giving the distinguishing results of the weak responses of the gas reservoir,which is hard to detect by using the conventional technologies.For the seismic data from a tight sandstone gas reservoir in the Sichuan basin,China,we found that multiattributes based quantum neural networks can effectively capture the weak seismic responses features associated with gas saturation in the gas reservoir.This study is hoped to be useful as an aid for hydrocarbon detections for the gas reservoir with the characteristics of the weak seismic responses by the complement of the multiattributes based quantum neural networks.

致密砂岩气藏与页岩气藏展布模式

在阐述美国和中国致密砂岩气和页岩气资源潜力和年产量的基础上,系统梳理致密砂岩气藏与页岩气藏展布的研究沿革,分析页岩气藏、致密砂岩气藏展布特征及致密砂岩气成因类型。研究表明:(1)美国致密砂岩气在天然气总产量中占比由2008年的35%降至2023年的8%左右;美国页岩气2023年产量为8310×10^(8)m^(3),在天然气总产量中占比由2000—2008年的5%~17%升至2023年的70%以上。(2)中国致密砂岩气占天然气总产量比例由2010年的16%升至2023年的28%以上;2012年中国开始生产页岩气,2023年产量达250×10^(8)m^(3),约占天然气全国总产量的11%。(3)页岩气藏展布模式为连续型,根据页岩气藏是否有断层切割及断距与气层厚度的关系,连续型页岩气藏可分为连续式和断续式两种。(4)与以往大部分学者认为致密砂岩气藏展布模式为连续型的认识不同,致密砂岩气藏展布模式不是连续型;根据圈闭类型,致密砂岩气藏可分为岩性型、背斜型和向斜型3种。(5)中国3大克拉通盆地和埃及Obavied次盆的致密砂岩气为煤成气,美国阿巴拉契亚盆地和阿曼迦巴盐盆地的致密砂岩气为油型气。

A Comprehensive Porosity Prediction Model for the Upper Paleozoic Tight Sandstone Reservoir in the Daniudi Gas Field, Ordos Basin

This paper investigated the porosity controlling factors for tight sandstone reservoir in the Daniudi gas field, Ordos Basin based on an integrated petrographic, petrophysical and geostatistical analyses, and proposed a comprehensive prediction model for reservoir porosity. Compaction was found to be a key factor for causing reservoir densification. The degree of sandstone compaction appears to be affected by grain sizes and sorting. Under normal compaction conditions（e.g., cement content less than 6%, and with no dissolution）, the variation in reservoir porosity with burial depth can be well correlated with grain compositions, grain sizes, and sorting. Based on qualitative examination of the controlling factors for reservoir porosities, geostatistics were used to quantify the effects of various geological parameters on reservoir porosities. A statistical model for comprehensive prediction of porosity was then established, on the assumption that the present reservoir porosity directly relates to both normal compaction and diagenesis. This model is easy to use, and has been validated with measured porosity data. The porosity controlling factors and the comprehensive porosity prediction can be used to quantify effects of the main controlling factors and their interaction on reservoir property evolution, and may provide a reference model for log interpretation.

Formation condition of deep gas reservoirs in tight sandstones in Kuqa Foreland Basin

Due to the high expense of deep oil and gas exploration,prediction of gas-bearing properties before drilling is crucial for deep gas reservoir of tight sandstone.Deep tight sandstone gas fields in Kuqa Foreland Basin are characterized by high abundance,high gas saturation,high pressure,high and stable yield,which belong to high-efficiency tight gas reservoir.Based on theoretical analysis of controlling factors and mechanisms of gas-bearing properties for tight sandstone gas reservoir,and taking tight sandstone gas fields with high effectiveness such as Dibei,Keshen and Dibei gas fields in Kuqa Foreland Basin as examples,formation condition and mechanism of high-efficiency tight sandstone gas reservoir in Kuqa area are studied through a comparative analysis of typical tight sandstone gas reservoir in Sichuan Basin and Ordos Basin.The results show that the formation condition of deep gas reservoir of tight sandstone in Kuqa foreland basin includes four factors:i.e.,overpressure gas charging,fracture development,“early-oil and late-gas”accumulation process and favorable preservation condition.The overpressure gas charging and fracture development are the most important factors for formation of high-efficiency tight gas reservoirs in Kuqa Foreland Basin.High-quality source rocks,high sourcereservoir pressure difference,and overpressure filling induced thereby are preconditions for formation of tight sandstone with high gas saturation.The fracture development controls gas migration,accumulation,and high yield of tight sandstone gas reservoir.The reservoir wettability changed by the early oil charging is beneficial to late natural gas charging,and the preservation condition of high-quality gypsum cap rocks is the key factor for gas reservoirs to maintain overpressure and high gas saturation.Matching of above four favorable factors leads to the tight sandstone gas reservoir with high abundance,high gas saturation and high gas production in Kuqa Foreland Basin,which is very different from other basins.Under the condition of little difference in physical property of tight sandstone reservoir,excessive source-reservoir pressure difference,facture development,preservation condition and current formation overpressure are the most significant factors to be considered in exploration and evaluation of deep tight sandstone gas.

Predicting gas-bearing distribution using DNN based on multi-component seismic data: Quality evaluation using structural and fracture factors

The tight-fractured gas reservoir of the Upper Triassic Xujiahe Formation in the Western Sichuan Depression has low porosity and permeability. This study presents a DNN-based method for identifying gas-bearing strata in tight sandstone. First, multi-component composite seismic attributes are obtained.The strong nonlinear relationships between multi-component composite attributes and gas-bearing reservoirs can be constrained through a DNN. Therefore, we identify and predict the gas-bearing strata using a DNN. Then, sample data are fed into the DNN for training and testing. After optimized network parameters are determined by the performance curves and empirical formulas, the best deep learning gas-bearing prediction model is determined. The composite seismic attributes can then be fed into the model to extrapolate the hydrocarbon-bearing characteristics from known drilling areas to the entire region for predicting the gas reservoir distribution. Finally, we assess the proposed method in terms of the structure and fracture characteristics and predict favorable exploration areas for identifying gas reservoirs.

Sichuan super gas basin in southwest China

A sedimentary basin is classified as a super basin when its cumulative production exceeds 5 billion barrels of oil equivalent(6.82×10^(8) t of oil or 7931.66×10^(8) m^(3) of gas)and its remaining recoverable resources are at least 5 billion barrels of oil equivalent.By the end of 2019,the total output of oil and gas in Sichuan Basin had been 6569×10^(8) m^(3),the ratio of gas to oil was 80:1,and the total remaining recoverable resources reached 136404×10^(8) m^(3),which makes it as a second-tier super basin.Because the output is mainly gas,it is a super gas basin.The reason why the Sichuan Basin is a super gas basin is that it has four advantages:(1)The advantage of gas source rocks:it has the most gas source rocks(9 sets)among all the basins in China.(2)The advantage of resource quantity:it has the most total remaining recoverable resources among all the basins in China(136404×10^(8) m^(3)).(3)The advantage of large gas fields:it has the most large gas fields(27)among all the basins in China.(4)The advantage of total production:by the end of 2019,the total gas production had been 6487.8×10^(8) m^(3),which ranked the first among all the basins in China.There are four major breakthroughs in natural gas exploration in Sichuan Basin:(1)Breakthrough in shale gas:shale gas was firstly found in the Ordovician Wufeng-Silurian Longmaxi formations in China.(2)Breakthrough in tight sandstone gas:the Triassic Xu2 Member gas reservoir in Zhongba gas field is the first high recovery tight sandstone gas reservoir in China.(3)Breakthrough in giant carbonate gas fields.(4)Breakthrough in ultra-deep gas reservoir.These breakthroughs have led to important progress in different basins across the country.Super basins are classified according to three criteria:accumulative oil and gas production,remaining recoverable resources,tectonic attributes of the basin and the proportion of oil and gas in accumulative oil and gas production.

“连续型”油气藏及其在全球的重要性:成藏、分布与评价

分析国内外各种油气藏勘探和研究现状,基于油气分布共性本质特征的认识,阐述"连续型"非常规圈闭油气藏内涵与成藏特征。"连续型"油气藏指在大范围非常规储集体系中油气连续分布的非常规圈闭油气藏,其地质特征是:在盆地中心、斜坡等大面积"连续"分布,且局部富集;以大规模非常规储集层为主;非常规圈闭,储集空间大,圈闭边界模糊;自生自储为主;多为一次运移;主要靠扩散方式聚集,浮力作用受限;非达西渗流为主;流体分异差,饱和度差异较大,油、气、水与干层易共存,无统一油气水界面与压力系统;资源丰度较低,储量主要按井控区块计算;开采工艺特殊,需针对性技术。论述了湖盆中心砂质碎屑流成因及其"连续型"油藏、大型浅水三角洲低—特低孔渗及致密砂岩油气藏、煤层气以及泥页岩裂缝型油气藏等典型实例。

鄂尔多斯盆地长6油层组准连续型致密砂岩油藏形成机理

鄂尔多斯盆地陕北斜坡延长组长6油藏为典型的准连续型致密砂岩非常规油藏,主要具有以下7个特点:(1)长6油藏形成和分布对圈闭无严格要求,石油大面积连片分布,油藏分布范围不受圈闭限制;(2)区域相对稳定的大地构造背景条件,以及大面积复合连片分布的致密储集体是长6准连续型致密砂岩油藏形成的外部因素;(3)长7油层组成熟烃源岩大面积连续分布,高强度生、排烃是长6准连续型致密砂岩油藏形成的前提;(4)长6油藏的形成主要是初次运移和短距离二次运移的结果,垂向裂缝和侧向连通砂体有效组合为石油优势运移通道,石油就近运移聚集成藏;(5)石油运移的动力主要是生烃作用产生的异常压力,浮力作用弱,对油藏的形成和分布不起主要作用;(6)长6油藏油水分布规律复杂,无纯油层,油水层、水层、干层共存,无统一的油水界面和压力系统,油藏非均质性强,含油饱和度不均一,储量丰度较低,存在甜点富集区;(7)在石油大规模生成运移时,长6储层已经致密化或同步致密,为形成长6准连续型致密砂岩油藏创造了条件。

苏里格气田上古生界连续型致密气形成过程

苏里格气田上古生界致密砂岩储层叠置连片分布、多层位普遍含气,是典型的连续型致密砂岩大气区.利用生排烃物理模拟、数值模拟、岩矿观察、流体包裹体和碳氧同位素等手段,共同约束验证,综合分析相关成藏要素,探索恢复盆地大面积致密砂岩气形成的动态过程.研究发现,苏里格气田具有稳定平缓构造面貌（晚侏罗世至今,苏里格地区古构造坡降速一般为3-6 m/km）、高成熟煤系源岩广布式生排烃气和大面积致密砂岩储层叠置分布的成藏地质背景（生气强度大于1 600 kg/m2、砂体厚度大于15m的源储接触面积可达2.35×104km2,占苏里格气田面积的78%）;在晚侏罗世至早白垩世早期,苏里格气田具有规模充注和连续聚集的成藏特征;早白垩世晚期以后,其成藏特征缓慢调整,最终形成大面积连续型致密砂岩大气区.成岩成藏耦合关系和源储共生紧密接触,共同决定了苏里格气田近源连续聚集的成藏模式.近生气中心区的致密储集砂体是天然气勘探开发的有利区.

准连续型致密砂岩气藏地质条件和成藏特征——以鄂尔多斯盆地中部上古生界山西组为例

通过大量钻井、测井、录井以及试气资料,结合岩心观察和薄片鉴定,对鄂尔多斯盆地上古生界山西组准连续型致密砂岩储层的岩石学特征、成岩作用、物性特征和孔候特征进行综合分析,并对山西组的成藏特征从烃源岩特征、储层特征、储盖组合特征以及成藏模式4个方面进行研究.结果表明:鄂尔多斯盆地上古生界山西组属于准连续型致密砂岩气藏,烃源岩在早白垩世末大量生气,具有近源成藏、砂体大面积准连续分布、储层致密、成岩作用类型多、孔喉结构复杂、物性普遍较差、烃源岩类型好等特征.山西组下部主要广覆式发育优质烃源岩,上部主要为致密储层,天然气通过微裂缝进入致密储层中进而成藏,在地层中呈准连续分布.综合分析鄂尔多斯盆地上古生界山西组准连续型致密砂岩气资源潜力大,具有广阔的勘探前景.