The primary controlling parameters of porosity, permeability,and seepage capability of tight gas reservoirs:a case study on Upper Paleozoic Formation in the eastern Ordos Basin,Northern China

Tight sandstone gas(hereafter"tight gas")has become a subject of unconventional gas exploration globally.The large-scale development and use of tight gas resources in the USA,in particular,facilitated the rapid rebound of natural gas production in the USA,in addition to driving the rapid development of tight gas worldwide.In the eastern Ordos Basin,the Upper Paleozoic feature includes multiple layers of gas,a shallow depth,and notable potential for exploration and development.However,the reservoirs in the area are relatively tight,exhibit strong heterogeneity,and possess a complex micropore structure,thus restricting the eff ective economic development of oil and gas.Thus,research on the primary parameters controlling pore throat structure and the seepage capability of low-permeability reservoirs will be beneficial for the effcient exploration and development of natural gas in the eastern Ordos Basin.The parameters of reservoir porosity and percolation ability,as well as permeability,were analyzed using systematic sampling of the of the Upper Paleozoic Benxi,Taiyuan,and Shanxi Formations in the eastern Ordos Basin,constant-rate mercury injection experiments,nuclear magnetic resonance analysis,and gas–water-phase experimental studies.The results indicate that reservoir porosity is controlled by the effective pore volume and number,whereas permeability is controlled by the largest throat radius,rather than the average.The effective pore volume controls the movable fluid saturation,while reservoir percolation capability is controlled by the effective pore volume,irreducible water saturation,and size of the gas–water two-phase seepage zone.

The coupling of dynamics and permeability in the hydrocarbon accumulation period controls the oil-bearing potential of low permeability reservoirs:a case study of the low permeability turbidite reservoirs in the middle part of the third member of Shahejie

The relationships between permeability and dynamics in hydrocarbon accumulation determine oil- bearing potential （the potential oil charge） of low perme- ability reservoirs. The evolution of porosity and permeability of low permeability turbidite reservoirs of the middle part of the third member of the Shahejie Formation in the Dongying Sag has been investigated by detailed core descriptions, thin section analyses, fluid inclusion analyses, carbon and oxygen isotope analyses, mercury injection, porosity and permeability testing, and basin modeling. The cutoff values for the permeability of the reservoirs in the accumulation period were calculated after detailing the accumulation dynamics and reservoir pore structures, then the distribution pattern of the oil-bearing potential of reservoirs controlled by the matching relationship between dynamics and permeability during the accumulation period were summarized. On the basis of the observed diagenetic features and with regard to the paragenetic sequences, the reservoirs can be subdivided into four types of diagenetic facies. The reservoirs experienced two periods of hydro- carbon accumulation. In the early accumulation period, the reservoirs except for diagenetic facies A had middle to high permeability ranging from 10 × 10-3 gm2 to 4207 × 10-3 lain2. In the later accumulation period, the reservoirs except for diagenetic facies C had low permeability ranging from 0.015 × 10-3 gm2 to 62× 10-3 -3m2. In the early accumulation period, the fluid pressure increased by the hydrocarbon generation was 1.4-11.3 MPa with an average value of 5.1 MPa, and a surplus pressure of 1.8-12.6 MPa with an average value of 6.3 MPa. In the later accumulation period, the fluid pressure increased by the hydrocarbon generation process was 0.7-12.7 MPa with an average value of 5.36 MPa and a surplus pressure of 1.3-16.2 MPa with an average value of 6.5 MPa. Even though different types of reservoirs exist, all can form hydrocarbon accumulations in the early accumulation per- iod. Such types of reservoirs can form hydrocarbon accumulation with high accumulation dynamics; however, reservoirs with diagenetic facies A and diagenetic facies B do not develop accumulation conditions with low accumu- lation dynamics in the late accumulation period for very low permeability. At more than 3000 m burial depth, a larger proportion of turbidite reservoirs are oil charged due to the proximity to the source rock, Also at these depths, lenticular sand bodies can accumulate hydrocarbons. At shallower depths, only the reservoirs with oil-source fault development can accumulate hydrocarbons. For flat surfaces, hydrocarbons have always been accumulated in the reservoirs around the oil-source faults and areas near the center of subsags with high accumulation dynamics.

Development of the theory and technology for low permeability reservoirs in China

The development theories of low-permeability oil and gas reservoirs are refined, the key development technologies are summarized, and the prospect and technical direction of sustainable development are discussed based on the understanding and research on developed low-permeability oil and gas resources in China. The main achievements include:(1) the theories of low-permeability reservoir seepage, dual-medium seepage, relative homogeneity, etc.(2) the well location optimization technology combining favorable area of reservoir with gas-bearing prediction and combining pre-stack with post-stack;(3) oriented perforating multi-fracture, multistage sand adding, multistage temporary plugging, vertical well multilayer, horizontal and other fracturing techniques to improve productivity of single well;(4) the technology of increasing injection and keeping pressure, such as overall decreasing pressure, local pressurization, shaped charge stamping and plugging removal, fine separate injection, mild advanced water injection and so on;(5) enhanced recovery technology of optimization of injection-production well network in horizontal wells. To continue to develop low-permeability reserves economically and effectively, there are three aspects of work to be done well:(1) depending on technical improvement, continue to innovate new technologies and methods, establish a new mode of low quality reservoir development economically, determine the main technical boundaries and form replacement technology reserves of advanced development;(2) adhering to the management system of low cost technology & low cost, set up a complete set of low-cost dual integration innovation system through continuous innovation in technology and management;(3) striving for national preferential policies.

Porosity Calculation of Tight Sand Gas Reservoirs with GA-CM Hybrid Optimization Log Interpretation Method

Tight sand gas reservoirs are our country’s fairly rich unconventional natural gas resources, and their exploration and development is of prime importance. Sulige Gas Field which located in the northern Ordos Basin is tight sand gas reservoirs. It is typically featured by low porosity and low permeability, and the error of porosity calculation by traditional methods is larger. Multicomponent explanation model is built by analyzing the thin slice data, and the objective function is got according to the concept of optimization log interpretation method. This paper puts the Genetic Algorithm and the Complex Algorithm together to form the GA-CM Hybrid Algorithm for searching the optimal solution of the objective function, getting the porosity of tight sandstone gas reservoirs. The deviation got by this method is lesser compared with the core porosity, with a high reliability.

Advances in enhanced oil recovery technologies for low permeability reservoirs

Low permeability oil and gas resources are rich and have great potential all over the world, which has gradually become the main goal of oil and gas development. However, after traditional primary and secondary exploitation, there is still a large amount of remaining oil that has not been recovered.Therefore, in recent years, enhanced oil recovery(EOR) technologies for low permeability reservoirs have been greatly developed to further improve crude oil production. This study presents a comprehensive review of EOR technologies in low permeability reservoirs with an emphasis on gas flooding, surfactant flooding, nanofluid flooding and imbibition EOR technologies. In addition, two kinds of gel systems are introduced for conformance control in low permeability reservoirs with channeling problems. Finally,the technical challenges, directions and outlooks of EOR in low permeability reservoirs are addressed.

Geologic characteristics, controlling factors and hydrocarbon accumulation mechanisms of China’s Large Gas Provinces of low porosity and permeability

Based on the analysis of the geological characteristics and controlling factors, we analyzed the formation mechanism of different types of gas reservoirs. The main characteristics of gas provinces with low porosity and permeability are mainly as follows: large area, low abundance, small gas pools and large gas provinces; widely distributed excellent hydrocarbon source rocks with closely contacted source-reservoir-cap association; development mainly in large continental depressions or in paralic shallow-river delta systems; many kinds of traps coexisting in large areas, dominantly para-layered lithologic, digenetic and capillary pressure traps; double fluid flow mechanisms of Darcy flow and non-Darcy flow; complicated gas and water relations; and having the resource distribution of highly productive "sweet spots", banding concentration, and macroscopically large areas integrated. The main controlling factors of large sandstone gas provinces with low porosity and permeability are stable dynamic backgrounds and gentle structural frameworks which control the extensive distribution of alternate (interbedded) sandstones and mudstones; weak hydropower of large gentle lake basins controlling the formation of discontinuous, low porosity and permeability reservoirs in shallow-water deltas; regionally differential diagenesis and no homogeneous digenetic facies controlling the development of favorable reservoirs and digenetic traps; and weak and dispersive reservoir-forming dynamic forces leading to the widely distributed small traps with low abundance. Low porosity and permeability gas provinces with different trap types have different formation mechanisms which include fluid diversion pressure difference interactive mechanism of lithologic-trap gas accumulations, separated differential collection mechanism of digenetic-trap gas accumulations, and the Non-Darcy flow mechanism of capillary-pressure gas accumulations.

二连盆地阿南凹陷白垩系凝灰岩类储层特征及有利区分布

阿南凹陷白垩系腾一下亚段凝灰岩类储层是近年来二连盆地致密油勘探的重点领域。通过岩心观察、薄片鉴定、储层物性分析及X-衍射分析等,采用高压压汞、氮气吸附、场发射电镜、CT扫描等实验方法,分析了二连盆地阿南凹陷白垩系凝灰岩类储层的岩性、物性、储集空间类型和孔隙结构特征,结合有利储层形成机制预测了有利储层发育区。研究结果表明:①二连盆地阿南凹陷白垩系腾一下亚段发育凝灰岩、沉凝灰岩、凝灰质泥岩、凝灰质(粉)砂岩4种凝灰岩类。②研究区凝灰岩类储层物性变化范围较大,平均孔隙度为4.88%,其中超低孔、特低孔的样品数占比为83.6%,平均渗透率为0.067 mD,整体属于超低孔、超低渗储层。凝灰岩主要发育溶蚀孔和脱玻化孔,呈“立体”网络孔隙结构,以介孔、宏孔为主,储层物性最好;凝灰质(粉)砂岩主要发育溶蚀孔和粒间孔,具有微细孔—微喉孔隙结构,介孔发育,储层物性较好;沉凝灰岩和凝灰质泥岩主要发育溶蚀孔、晶间孔和微裂缝,多发育孤立型孔隙结构,以介孔为主,储层物性较差。③研究区凝灰岩类优质储层受沉积作用、成岩作用和构造作用共同控制,沉积作用为优质储层形成提供了物质基础,控制了储层的形成和分布;压实作用和胶结作用降低了储层物性,白云岩化和脱玻化作用改善了储集性能;溶蚀作用是有效储层形成的关键,对物性改善具有积极作用。④研究区发育Ⅰ,Ⅱ,Ⅲ类凝灰岩类储层,Ⅰ类储层集中分布在洼槽区,Ⅱ类储层沿西部缓坡呈条带状分布,Ⅲ类储层分布范围最广。其中A43东、A27北、H16西和A11西南等区块发育的Ⅰ类储层是下一步凝灰岩类致密油勘探的有利区带。

Seismic wave equations in tight oil/gas sandstone media

Tight oil/gas medium is a special porous medium,which plays a significant role in oil and gas exploration.This paper is devoted to the derivation of wave equations in such a media,which take a much simpler form compared to the general equations in the poroelasticity theory and can be employed for parameter inversion from seismic data.We start with the fluid and solid motion equations at a pore scale,and deduce the complete Biot’s equations by applying the volume averaging technique.The underlying assumptions are carefully clarified.Moreover,time dependence of the permeability in tight oil/gas media is discussed based on available results from rock physical experiments.Leveraging the Kozeny-Carman equation,time dependence of the porosity is theoretically investigated.We derive the wave equations in tight oil/gas media based on the complete Biot’s equations under some reasonable assumptions on the media.The derived wave equations have the similar form as the diffusiveviscous wave equations.A comparison of the two sets of wave equations reveals explicit relations between the coefficients in diffusive-viscous wave equations and the measurable parameters for the tight oil/gas media.The derived equations are validated by numerical results.Based on the derived equations,reflection and transmission properties for a single tight interlayer are investigated.The numerical results demonstrate that the reflection and transmission of the seismic waves are affected by the thickness and attenuation of the interlayer,which is of great significance for the exploration of oil and gas.

低渗稠油高压降黏驱高黏阻滞带形成机制与主控因素——以胜利油田王152油藏为例

化学降黏剂驱已在胜利油田深层低渗稠油中开展了初步先导试验,但试验表明井间存在高黏阻滞带,降低了地层渗流能力。因此,借助降黏剂驱岩心流动实验,结合必要的测试分析,剖析低渗稠油降黏驱高黏阻滞带形成机制与主控因素。结果表明,大排量高压注入降黏剂会在驱替前缘形成高黏阻滞带,影响驱替压力传导、降低驱油效果。该高黏阻滞带形成核心机制在于:(1)高压注入增加低孔压区域有效应力,地层孔喉受到挤压损害渗流能力;(2)高压快速降黏剂驱时,轻质组分优先流出,重质组分滞留、堆积、压实从而堵塞细小孔隙,形成高黏稠油沉聚的高饱和度油墙;(3)高压注入降黏剂会加剧其指进窜流,驱替前缘易形成W/O乳状液,增大混合流体的黏度。由此,对于低渗稠油油藏降黏驱开发,应采取多轮次温和注入降黏剂的开发模式,渐进式建立注采井间稠油整体驱动,进而有效规避稠油高黏阻滞带的形成,提高降黏剂驱油效果。

柴达木盆地英雄岭地区古近系油气成藏过程及其演化特征

通过构造演化特征研究,结合烃类包裹体分析和典型油气藏精细解剖,阐述了柴达木盆地英雄岭地区古近系下干柴沟组上段油气藏的形成和演化过程。研究结果表明:(1)英雄岭地区古近系下干柴沟组上段形成于半咸化—咸化湖泊—盐湖环境,发育以纹层状灰云岩为储集层、富含有机质、广覆式分布的源储一体型油气藏;(2)研究区下干柴沟组上段共经历3期油气充注,第Ⅰ期烃类包裹体为单一液相油包裹体,反映了早期低熟原油的运移和充注;第Ⅱ期烃类包裹体为单一液相油包裹体,反映了一幕中等成熟原油的运移和充注;第Ⅲ期烃类包裹体为气液两相油包裹体,反映了一幕高成熟原油的充注。(3)研究区油气具有3期成藏的特征:上干柴沟组沉积中晚期,在下干柴沟组上段形成了低饱和度-低熟油藏;上油砂山组沉积期,低熟—成熟油气向盐间储集层和高渗带聚集形成了油气高产区;狮子沟组—七个泉组沉积期,成熟—高熟油通过双层断裂接力输导运移至干柴沟组上段及以上地层运聚形成构造油气藏。

低孔低渗稠油油藏注水增能效果影响因素

吐哈盆地鲁克沁油田二叠系发育低孔低渗砂砾岩稠油油藏,由于储集层物性差,非均质性强,自然产能低,压裂投产后,注水开发效果较差。为了解决平面矛盾突出、见效率低、欠注区域不见效的开发矛盾,实施注水增能提高单井产量,但单井增产效果差异较大。为此,通过室内物理模拟实验,对储集层润湿性和注水增能过程进行了研究。结果表明,吐哈盆地鲁克沁油田二叠系储集层具亲水性,压裂有利于裂缝与储集层基质发生渗吸作用,可有效补充地层能量,从而提高单井产量;注入速度越快,地层能量恢复越快;焖井压力越高,增油量越高。通过数值模拟,并结合现场情况,优化注入参数,注水增能效果较好,措施有效率达88%。

华池地区长8段致密油储层品质定量评价方法

鄂尔多斯盆地华池地区长8段属于低孔隙度低渗透率致密油储层,其复杂的孔隙结构使得储层参数计算精度低,定性的储层品质分类方法不能满足精细解释需求,需要开展储层品质定量评价,提高致密油储层解释符合率。通过岩石物理实验资料与试油资料建立储层品质分类标准,基于岩石物理实验资料与核磁共振测井资料建立孔隙度、渗透率、中值孔喉半径、排驱压力、分选系数、孔喉半径均值的测井解释模型,采用主成分分析法确定测井解释参数的权重系数,经归一化处理后构建储层品质综合评价指数。应用结果表明,该方法能够定量评价致密油储层品质级别,储层品质定量计算结果与试油产量吻合,具有一定的推广应用价值。

二氧化氯复合解堵技术在W油田S油区的应用

针对W油田S油区因油层污染/堵塞而低产低效情况较普遍的问题,分析储层损害的主要因素。基于近年油井常用解堵方式的作用机理、优缺点及适用范围,重点介绍二氧化氯解堵技术机理和工艺流程。二氧化氯复合解堵技术在W油田S油区的现场应用实践(工艺试验)表明,该工艺方法简单、适应性较强,可有效解除聚合物、微生物及其代谢产物、铁硫化物造成的油井油层污染/堵塞,增注增产效果显著,具有较好的推广应用前景。

低孔渗油气富集区优质储层形成条件及相关问题

低孔低渗 (孔隙度一般小于 1 2 % ,渗透率大多在 1× 1 0 - 3μm2左右 )性质的碎屑岩作为储层的油气藏是我国中西部地区稳定克拉通盆地或者叠合盆地中最主要的油气藏类型。但是 ,通过近几年的勘探实践发现 ,在低孔低渗含油气区中 ,仍有具优质储集层的高产油气藏存在。从优质储层的构造、沉积和成岩等几个方面讨论了这些优质储层的形成条件、阐述了描述和识别优势储层的原则和方法基础。认为储层的原始物质组成和结构是影响其物性特征的最关键因素、先天母质条件是优质储层之本源 。

天然气充注成藏与深部砂岩储集层的形成--以塔里木盆地库车坳陷为例

在塔里木盆地库车坳陷深层天然气成藏条件分析的基础上,阐明深部有效储集层的形成机制。研究表明,天然气充注成藏过程与深部砂岩有效储集层的形成具有密切关系:早期曾捕获到油气的储集层,后期深埋后储集层性能较好;若早期未能捕获到油气,深埋后储集层则比较致密。深埋压实作用对孔、缝的保存影响较大。在储集层深埋致密化之前发生的油气充注过程,抑制了岩石的机械压实和裂缝闭合,阻碍了致密化进程,使储集层的有效孔、缝得以保存。库车深层煤系气源充沛,高演化侏罗系烃源岩成气潜力依然较大,深部砂岩储集层发育次生孔隙和微裂隙,膏盐盖层分布广,厚度大,生储盖空间配置好;以断裂为主构成的输导体系发育,排烃效率高,运聚系数大,油气被高效捕获成藏;盐构造下的深部和超深部圈闭发育。因而,库车坳陷深层和超深层成藏条件好,勘探潜力巨大。

低孔低渗储集层岩石物理分类方法的讨论

为了在储集层孔隙结构和岩石物理特征基本相同的情况下建立测井解释岩电参数模型,需要按岩石物理特征对储集层进行分类。通过实际资料和理论分析,对比地层流动带指数与储集层品质指数两种宏观物性参数的差异,研究储集层岩石物理分类的有效方法和反映微观孔隙结构变化的特征参数。利用两种指数对松辽盆地大情字井地区和鄂尔多斯盆地姬塬地区典型低孔低渗储集层60块岩心的压汞实验资料进行了分类,结果表明,按照储集层品质指数对储集层进行分类能更准确地反映储集层的孔隙结构和岩石物理特征。理论分析亦证明,储集层品质指数与孔隙结构之间呈单调函数关系,而地层流动带指数与储集层孔隙结构之间并不是简单的单调函数关系,储集层品质指数比地层流动带指数能更准确地反映储集层孔隙结构和岩石物理性质的变化。

川中公山庙油田沙一段油藏储层特征研究

公山庙油田沙一段油藏是在川中侏罗系沙溪庙组低孔低渗储层背景下发现的构造岩性复合油藏,其储层的研究对川中侏罗系砂岩油藏勘探具有重要指导意义。文章通过地层及岩性、物性、储集空间及储集类型等方面的系统研究,认为尽管储层基质孔隙度、渗透率均很低,但孔隙结构好,完全具备储渗能力。并在此基础上结合动态测试资料分析指出其储集类型仍属裂缝-孔隙型,首次明确在此低孔低渗储集条件下裂缝-孔隙型砂岩油藏的存在,拓展了川中侏罗系砂岩油藏的勘探思路。

基于BP神经网络技术的储层流动单元研究

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