Research on Pore Structure and Fractal Characteristics of Tight Sandstone Reservoir Based on High-Pressure Mercury Injection Method

Pore structure is the key element of tight sandstone reservoir, which restricts the accumulation and flow of oil and gas in the reservoir. At present, reservoir pore structure is the focus and difficulty of unconventional oil and gas exploration and development research. The tight sandstone reservoir in the Chang 4 + 5 member of the Upper Triassic Yanchang Formation is the main reservoir for oil and gas exploration in G area. At present, there is little research on its pore structure and fractal characteristics, which to some extent affects the progress of exploration and development. This paper selects the tight core samples of the Chang 4 + 5 member in the southern edge of the Ordos Basin, and based on the high-pressure mercury intrusion experiment, uses fractal theory to study the pore structure and fractal characteristics of the reservoir in the study area, thus providing theoretical basis for the evaluation and exploration and development of the Chang 4 + 5 tight reservoir in the G area. The research results show that the lithology of the Chang 4 + 5 tight sandstone reservoir in the southern edge of the Ordos Basin is mainly feldspathic sandstone, with the highest feldspar content, followed by quartz, and the clay mineral is mainly chlorite. The reservoir has poor physical properties and strong heterogeneity. There are three main fractal characteristics in Chang 4 + 5 reservoir in G area: the fractal curve of Type I reservoir sample is in two segments, the relatively large pore has certain fractal characteristics, the pore structure is relatively regular, and the heterogeneity is weak;Relatively small pores have no fractal characteristics and pore structure is irregular. The fractal curve of Type II reservoir samples shows a three-segment pattern, and each pore size range has certain fractal characteristics, and it gradually gets better with the increase of pore size. The fractal curve of Type III reservoir samples presents a similar one-segment pattern, and the fractal dimension exceeds the upper limit of 3. It is considered that the full pore size of this type of reservoir does not have fractal characteristics, the pore throat is completely irregular or the surface is rough, and the heterogeneity is very strong.

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.

An Integrated Rock Typing Approach for Unraveling the Reservoir Heterogeneity of Tight Sands in the Whicher Range Field of Perth Basin, Western Australia

Tight gas sands in Whicher Range Field of Perth Basin show large heterogeneity in reservoir characteristics and production behavior related to depositional and diagenetic features. Diagenetic events (compaction and cementation) have severely affected the pore system. In order to investigate the petrophysical characteristics, reservoir sandstone facies were correlated with core porosity and permeability and their equivalent well log responses to describe hydraulic flow units and electrofacies, respectively. Thus, very tight, tight, and sub-tight sands were differentiated. To reveal the relationship between pore system properties and depositional and diagenetic characteristics in each sand type, reservoir rock types were extracted. The identified reservoir rock types are in fact a reflection of internal reservoir heterogeneity related to pore system properties. All reservoir rock types are characterized by a compacted fabric and cemented framework. But distribution and dominance of diagenetic products in each of them depend on primary depositional composition and texture. The results show that reservoir rock typing based on three aspects of reservoir sandstones (depositional properties, diagenetic features and petrophysical characteristics) is a suitable technique for depiction of reservoir heterogeneity, recognition of reservoir units and identifying factors controlling reservoir quality of tight sandstones. This methodology can be used for the other tight reservoirs.

Tight gas production model considering TPG as a function of pore pressure,permeability and water saturation

Threshold pressure gradient has great importance in efficient tight gas field development as well as for research and laboratory experiments.This experimental study is carried out to investigate the threshold pressure gradient in detail.Experiments are carried out with and without back pressure so that the effect of pore pressure on threshold pressure gradient may be observed.The trend of increasing or decreasing the threshold pressure gradient is totally opposite in the cases of considering and not considering the pore pressure.The results demonstrate that the pore pressure of tight gas reservoirs has great influence on threshold pressure gradient.The effects of other parameters like permeability and water saturation,in the presence of pore pressure,on threshold pressure gradient are also examined which show that the threshold pressure gradient increases with either a decrease in permeability or an increase in water saturation.Two new correlations of threshold pressure gradient on the basis of pore pressure and permeability,and pore pressure and water saturation,are also introduced.Based on these equations,new models for tight gas production are proposed.The gas slip correction factor is also considered during derivation of this proposed tight gas production models.Inflow performance relationship curves based on these proposed models show that production rates and absolute open flow potential are always be overestimated while ignoring the threshold pressure gradients.

致密砂岩砂-泥结构发育特征及其对储集空间的控制作用——以渤海湾盆地临南洼陷古近系沙河街组三段下亚段为例

在陆相含油气沉积盆地中,沉积水体变化快,砂岩和泥岩频繁交互。不同的砂-泥互层形式导致砂岩储层的储集空间差异性明显。以渤海湾盆地惠民凹陷临南洼陷古近系沙河街组三段下亚段(沙三下亚段)为例,基于砂岩和泥岩在空间上的组合形式及其单层厚度分析,利用铸体薄片观察、物性测试和微米CT技术,系统分析不同砂-泥结构下砂岩储层的物性特征、孔隙类型和孔隙结构特征。结果表明,研究区沙三下亚段发育厚泥岩夹薄砂岩、中泥岩夹薄砂岩、厚泥岩夹中砂岩、薄砂岩-薄泥岩互层、中砂岩-中泥岩互层、厚砂岩-厚泥岩互层、中砂岩夹薄泥岩、厚砂岩夹中泥岩和厚砂岩夹薄泥岩9种砂-泥结构类型。砂岩和泥岩之间的离子交互关系,导致不同砂-泥结构砂岩储层储集能力具有较强的非均质性。对于砂/地比较小的砂-泥结构,泥岩能够为砂岩提供充足的CO_(3)^(2-),Ca^(2+),Fe^(2+)和Mg^(2+)离子。砂岩被胶结物完全充填,储层变得极为致密。随着砂/地比增大,泥岩无法为砂岩提供充足的CO_(3)^(2-),Ca^(2+),Fe^(2+)和Mg^(2+)离子。砂-泥界面附近砂岩中碳酸盐胶结作用较强,储层极为致密;而砂岩内部碳酸盐胶结作用较弱,发育少量的原生孔隙。同时,砂岩厚度比较大的砂-泥结构,有利于有机酸的注入,形成大量的粒间溶蚀孔,改善储层质量。基于砂-泥结构的差异性,揭示了砂-泥结构控制下砂岩储层储集空间演化路径和模式,对指导致密储层的甜点预测具有重要意义。

裂缝性致密砂岩气藏剩余气分布预测及开发优化建议:以川西坳陷新场地区须家河组二段为例

裂缝性致密砂岩气藏具有储层基质致密低渗、裂缝非均质发育、气水界面不统一等特点,导致天然气资源动用程度低,气井产能差异大,开发形势整体不乐观。为明确气藏的剩余气分布规律及动用对策,以新场地区须家河组二段气藏为例,根据产能主控因素分析,形成了一套适用于裂缝性致密砂岩气藏的数值模拟技术流程,定量表征了剩余气分布特征,提出了开发优化建议。结果表明:综合考虑构造裂缝和基质砂体岩性对产能的控制作用,对动态模型采用“分井区、分砂组、分介质、分岩性”的方式精细划分流动单元,保证了数值模拟的高效和精度。剩余气分布整体在构造起伏约束下,受基质岩性、断裂裂缝和井控程度影响。建议布井潜力区应具备构造高部位、基质砂体连续、断裂裂缝发育、剩余气富集等条件,进一步根据井间干扰程度和地层能量利用率优化布井位置。

库车坳陷下侏罗统致密砂岩孔隙结构差异研究

为了明确库车坳陷迪北地区下侏罗统阳霞组、阿合组的储层孔隙微观结构差异及其对致密砂岩气富集的控制作用,通过激光共聚焦图像分析、压汞实验和束缚水饱和度测试等方法对这2套储层的物性、孔隙类型及孔隙微观结构等进行了对比分析。研究结果表明,阿合组储层的孔隙微观结构比阳霞组储层好,更有利于致密砂岩气的聚集成藏。

杭锦旗地区致密气藏石英砂替代陶粒可行性实验研究

为了满足鄂尔多斯盆地杭锦旗地区低成本压裂改造的需要,根据杭锦旗地区不同区块闭合压力特点,开展了不同岩板对长期导流能力的影响、不同粒径对长期导流能力的影响、石英砂铺砂浓度的界定以及石英砂替代陶粒导流能力分析等实验研究工作。结果表明:1)在相同的闭合压力加载条件下,长期导流能力大小与石英砂所占支撑剂比例呈负相关;2)随着闭合压力加载时间的延长,支撑剂破碎和嵌入程度逐渐严重,30 h以后,人工裂缝导流能力损失明显;3)石英砂与陶粒的混合比例为2∶8,3∶7和4∶6时,其导流能力均满足闭合压力为35~50 MPa的要求,能够实现用石英砂替代陶粒而达到降低压裂成本的目的。以上成果认识,对杭锦旗地区石英砂替代陶粒压裂改造及实现低成本战略具有一定指导意义。

德惠断陷致密气产能主控因素分析与压裂技术优化

德惠断陷致密气藏储集层埋藏深、纵向跨度大、孔喉连通性差,高密度完井体积压裂技术虽实现了效益开发,但存在不同井间压后产能效果差异性大,稳产时间短的难题。通过对已施工井优质储集层厚度、铺砂强度、裂缝复杂程度和水锁伤害等因素与产能关系的分析,明确影响单井产能的主控因素,形成差异性射孔+“三段式”先成缝后成网+多级暂堵转向、防水锁压裂液体系等一系列压裂技术对策。经现场DS80-2井试验,压后第二天见气,见气返排率3.8%,日产气8.5×104 m 3,无阻流量19.2×104 m 3,为同区块同厚度气藏产量最高,见气返排率最低井;较设计产能提产20%,降本19%,达到提产控投的目的,为实现致密气藏高效勘探、效益开发提供了技术支撑。

致密气有效砂体预测技术及应用效果——以苏里格A区块盒8下段为例

苏里格气田是目前我国陆上探明储量规模最大的整装致密气田,A区块是气田重要的致密气资源产出区,研究区盒8下段主要为辫状河沉积,有效砂体厚度较薄,展布规律不清晰,通过常规地震反演技术无法对研究区有效砂体进行有效区分及准确预测。故本文在盒8下段沉积特征的基础上,通过使用不同频率的雷克子波,开展精细的层位标定,有效划分地层;利用Xu~White模型进行横波预测,建立了岩性、物性以及孔隙流体弹性参数与地震响应特征之间的联系。通过弹性敏感参数分析,利用纵横波速度比对泥岩、基质砂体及有效砂体进行区分;最终利用孔渗参数联合地质统计学反演结果,对苏里格气田A区块盒8下段有效砂体的展布特征进行预测及刻画。结果显示:有效砂体厚度为4~17.8m,整体上呈现南北向条带状展布,连通性较强,主要分布于研究区中北部及南部,预测结果与钻井符合率为86.3%,表明了该方法的可靠性,为苏里格气田及其他地区致密气开发提供了相关技术手段。

致密砂岩气藏压裂砂堵原因分析及对策

东胜气田属于典型致密气藏,通过水力压裂获得了效益开发,但压裂过程中频繁砂堵和较高的首段砂堵率导致施工周期和成本增加。针对上述问题,通过对压裂现场工况分析将砂堵原因分为地层可压性弱、地层滤失、液体性能差、设备故障和现场指挥失误5个方面,从施工参数和岩石力学参数对裂缝参数的影响探究了造成压裂砂堵的根本原因,并对压裂曲线特征进行了因素归纳,在此基础上提出了适应工区不同工况的防控措施,为东胜气田提高压裂施工成功率和快速释放气井产能提供了技术支撑。

基于深度全连接神经网络的储层有效砂体厚度预测

河道砂是重要的油气储集体之一,实现砂体厚度的定量预测是提高油气开发效率的关键。随着目标储层非匀质性的增强,地震属性与储层岩性、物性、孔隙流体之间的关系更趋复杂。如何在地质信息有限的情况下实现高效且智能的复杂储层定量预测是目前储层预测领域的热点和难点。为了实现对致密砂岩储层的高精度智能化预测,本文提出基于深度全连接神经网络的储层有效砂体厚度预测方法。该方法通过构建多层堆叠的全连接神经网络逐层优化针对储层有效砂体厚度预测的地震属性,并将优化后的属性直接映射为砂体厚度。首先针对模型数据分析了训练样本对全连接神经网络建模的影响,然后在小样本情况下分别对比了该网络的深、浅层形态在网络规模大于训练样本数目及网络规模小于训练样本数目时的表现差异,发现当训练样本为小样本时,深层网络表现优于浅层网络,前提是训练样本数目大于网络规模。最后,我们将深度全连接神经网络用于胜利油田某区实际数据的有效砂体厚度预测,应用效果显示该方法对致密砂岩储层中4 m左右的砂体实现了有效识别,体现了该端到端智能建模方法从地震属性中挖掘潜藏地质信息的能力,证实了其在储层定量预测中的有效性。

成岩作用对致密砂岩储层物性的影响——以川中地区上三叠统须四段气藏为例

川中地区上三叠统须家河组四段砂岩是四川盆地内的天然气储层之一,该碎屑岩储层具有低孔隙度、低渗透率的特点。在对该区上三叠统须家河组气藏宏观沉积特征研究的基础上,采用岩石薄片、铸体薄片、扫描电镜及X射线衍射等方法,对该气藏储层的成岩作用及其对储集物性的影响进行了探讨,建立了该区致密砂岩成岩作用序列以及孔隙演化模式。研究结论如下:①随压实作用的不断增强,孔隙度呈持续下降的趋势;②成岩作用对致密砂岩储集层的影响具有双重性,压实作用、胶结作用使得砂岩孔隙度降低,而溶蚀作用则增加了孔隙度;③该区的孔隙构成主要是环边绿泥石剩余原生粒间孔以及溶蚀形成的长石、岩屑粒内溶孔,泥质杂基溶蚀粒间孔,伊利石黏土中微孔以及由压实压裂、压实滑动和构造动力所形成的微裂缝孔;④勘探中既要注意机械压实作用、压溶作用对储层的负面影响,同时也要重视成岩早期环边绿泥石胶结物形成、碎屑(主要是长石)及其填隙物溶蚀作用等有利因素。

川西新场气田沙二段致密砂岩储层岩石力学性质

对川西新场地区侏罗系沙溪庙组二段致密储层样品所进行的岩石力学实验结果表明,岩石抗张及抗压强度随着岩石密度的增加而增大、岩石孔隙度的增加而减小,且随着岩石粒度的增加,抗张强度减小、抗压强度增大;砂岩的弹性模量明显高于泥岩,且随着岩石密度的增加而增加、孔隙度的增加而减小。与常温常压下相比,模拟地层条件下沙溪庙组泥岩饱和介质为气体时,抗压强度高3.2倍,弹性模量低2.35倍,泊松比高2倍;当砂岩饱和介质为水时,与饱和气体介质的砂岩相比,强度及弹性模量均降低,泊松比增大。这说明水介质对岩石有"软化效应"。进而在实验研究的基础上,应用测井、压裂资料计算了地层的岩石力学参数,通过对三种方法所得结果的对比分析,评价了地层条件下岩石力学参数,由此获得了较为合理、可信的地层岩石力学参数剖面。

低渗透致密砂岩储层成岩相类型及测井识别方法——以鄂尔多斯盆地苏里格气田下石盒子组8段为例

鄂尔多斯盆地苏里格气田是低渗透致密砂岩气藏的典型代表,根据碎屑成分、成岩矿物组合、填隙物成分、成岩作用类型等特征,将苏里格气田盒8段储层划分为粒间孔+火山物质强溶蚀相、晶间孔+火山物质溶蚀相、晶间孔+岩屑溶蚀相、晶间孔+石英加大胶结相、水云母胶结+岩屑微溶蚀相和压实胶结致密成岩相6种成岩相类型,分析了不同成岩作用对测井响应的影响。在此基础上,通过自然伽马、声波时差、密度及深侧向测井等参数与成岩相的对应关系,建立了连续定量识别储层成岩相的方法。利用该方法对Z65井测井资料进行了处理,通过与薄片鉴定及压汞结果对比,验证了方法的准确性。利用单井成岩相判别结果划分苏里格气田盒8段成岩相展布,其中气田中部主要以粒间孔+火山物质强溶蚀相和晶间孔+火山物质溶蚀相为主,是有利的成岩相带。

基于岩石电阻率参数研究致密砂岩孔隙结构

低孔低渗致密砂岩储层孔隙结构特征是影响其油气储集能力和采收率的重要因素,故对其孔隙结构特征进行研究具有重要的意义。文章主要探讨了利用电阻率参数开展该类储层孔隙结构特征研究的方法。基于铸体薄片和压汞实验数据反映出的此类储层孔隙结构的特征,选取毛细管束模型推导并建立了致密砂岩储层孔隙结构特征参数计算模型,并结合岩电实验数据对模型进行了验证。结果表明:从电阻率参数计算得到的岩石孔隙结构参数能较好地反映岩石的孔隙结构特征,利用电阻率计算得到的岩石孔隙结构参数是随含水饱和度变化而变化的量,其变化量及变化的速率能够反映出储集层开采过程中油气藏内部流体的分布变化;利用井下不同时刻实测电阻率参数计算得到的岩石的孔喉半径,仅代表测井时刻地层内导电流体所占据的孔隙空间的半径,而计算得到的岩石迂曲度也只反映了当前状态下导电流体的分布状况。

鄂尔多斯盆地中西部长9储层差异化成岩与烃类充注过程研究

储层非均质性极大地影响储层内流体的流动和分布,在油气运移成藏和提高采收率研究中广受关注。储层内发生的差异化成岩作用是层内非均质性的重要成因,与烃类充注事件的相互关系也是致密砂岩油气成藏机理研究的核心内容。本文以鄂尔多斯盆地中西部上三叠统延长组长9储层为例,研究储层内砂岩所表现出的差异化成岩作用及其影响下的流体活动过程。系统的显微观察发现,长9储层主要由机械压实致密型砂岩、钙质胶结致密型砂岩、含水砂岩和含油砂岩等四类岩石组成。利用显微岩相学、紫外荧光光谱、包裹体均一温度测试、盆地模拟等技术综合分析表明,机械压实致密型砂岩在早成岩期即在压实作用影响下强烈塑性变形致密化;钙质胶结致密型砂岩在早成岩期就发生强烈的碳酸盐胶结作用而致密化。这两类砂岩在成岩中后期基本不能为流体活动提供孔隙空间。含水砂岩和含油砂岩均经历了复杂的差异化成岩过程,含油砂岩内可以辨识出至少三期沥青,含水砂岩则未见沥青残留。以含油砂岩中沥青质所对应的烃类充注为标志,重建了长9储层的成岩序列,划分出三期流体流动过程,烃类充注与成岩作用交替进行。含水砂岩大致可划分出相似的成岩过程,但未发生烃类充注。

美国致密砂岩气藏开发与启示

美国是目前致密砂岩天然气产量最多的国家,历经40年逐步形成了气藏描述、井网加密、增产改造及钻井完井等系列配套技术,其成功的开发实践将为我国致密砂岩气藏开发提供宝贵的经验。在系统调研并分析美国致密砂岩气藏储层特征、开发特征与关键技术的基础上,借鉴美国致密砂岩气田的开发经验,得到以下几点启示:①三维地震技术可以有效地提高开发井成功率;②井网加密可以有效提高多层、透镜状气藏的采收率;③直井分层压裂是致密气藏开发的主体增产工艺技术;④综合应用小井眼、快速钻井、地面优化简化等技术来降低成本。上述分析研究结论将对我国低渗透砂岩气藏合理开发起到积极的推动作用。

从模拟实验看致密砂岩储层的石油成藏条件

通过不同系列物理模拟实验,对致密砂岩储层中油水倒置成藏的临界地质条件进行了研究。模拟实验结果表明,对于密度约为0.8g/cm^3的原油,材质相同的各种毛细玻璃管孔喉半径为1.8 mm时,或砂柱中砂体粒径小于0.35～0.40 mm时,即能够产生稳定的油水倒置现象。油水倒置现象的产生与流体浮力和毛细管力之间的力平衡有关,油的密度在油水倒置关系的形成过程中起着比表面张力更为重要的作用。因此,致密砂岩储层油水倒置油藏形成的临界地质条件,主要取决于储油砂层的孔喉半径及其与原油密度之间的关系。

致密砂岩油藏体积压裂裂缝扩展数值模拟研究

体积压裂是提高致密砂岩油藏产量的关键技术。应用有限元和离散元的混合方法建立了体积压裂扩展模型,对长庆油田长7致密砂岩油藏水平井多簇压裂进行了裂缝扩展模拟研究。结果表明,应力差小于4 MPa时有利于体积裂缝形成,高于5 MPa时主要形成平面裂缝;天然裂缝密度仅在较低应力差条件下对体积压裂改造效果影响显著;在应力差为3 MPa时,增加射孔簇数、降低簇间距,改造面积增加并不显著,簇间裂缝干扰严重,局部裂缝出现合并现象;应力差为5 MPa时,簇间裂缝干扰相对较弱,增加射孔簇利于沟通天然裂缝,提高体积裂缝发育程度和扩大改造面积。