自生“加大”含铁白云石胶结物特征及对致密砂岩储层的影响——以鄂尔多斯盆地陇东地区延长组4+5段为例

随着油气勘探的不断深入,致密砂岩储层越来越受到人们的关注,特别是关于致密化的成因及油气充注的时间。利用岩石学、岩石地球化学以及储层物性资料,综合分析鄂尔多斯盆地陇东地区延长组4+5段中含铁白云石胶结物产出特征、成因及其对储层质量的影响。研究表明：自生含铁白云石主要以白云岩岩屑的“次生加大边”形式出现,其形成与早成岩晚期碎屑白云岩的压溶和Fe质交代有关;少量含铁白云石交代长石颗粒。岩石粒度、黑云母碎屑含量、沉积微相控制含铁白云石胶结物的含量与分布,进而控制储层质量。在镇原和环县地区含铁白云石胶结物的含量高于华池和白豹地区;在水下分流河道中上部和河口坝中部,含铁白云石胶结物含量有增加的趋势。黑云母等碎屑的蚀变可能是最主要的Fe质来源。在水下分流河道底部砂体中,含铁白云石胶结物的含量一般小于3%,孔渗性整体较好;在水下分流河道顶部砂体中,这种胶结物的含量通常大于3%,储层质量一般较差。该研究成果将对相似地质条件下致密储层形成机理的分析提供一定的依据。     

Hydrocarbon accumulation period and geochemical discrimination of gas-bearing properties of deep tight sandstone in Kuqa depression,China

In order to clarify the hydrocarbon accumulation period of deep tight sandstone in Dabei-Keshen area of Kuqa depression, and to develop identification methods of reservoir fluid properties, a series of experiments were carried out. The results show that hydrocarbon inclusions are less distributed, and gaseous hydrocarbon is mainly methane. Hydrocarbon has been continuously charged since 12?Ma in Dabei gas field, and one main period of accumulation took place during 6–4?Ma for Keshen gas field. Late accumulation may limit the application of hydrocarbon inclusions abundance, rock soluble salt components to distinguish reservoir fluid properties. Carbon isotope composition of carbonate cement in tight sandstone is an effective indicator for gas-bearing properties. For gas layer, the carbon isotope is lighter than ?1.5‰ and ?2.5‰ for Dabei and Keshen gas field receptively.     

龙门山前侏罗系沙溪庙组致密砂岩储层叠前地震预测

龙门山前侏罗系沙溪庙组致密砂岩横向变化快、非均质性强、孔隙结构复杂,储层与围岩阻抗差异小,岩石物理规律不清,且地震叠前道集资料品质差、测井横波资料匮乏,优质储层预测困难。针对以上问题,通过叠前反褶积、阿尔法滤波、剔除拟合振幅补偿优化处理了叠前CRP道集,采用改进的Xu-White模型预测了横波,并通过贝叶斯稀疏脉冲反演获得了叠前弹性参数VP/VS,预测了砂体边界,最后在砂体边界控制下,利用蒙特卡罗—贝叶斯分类方法反演了孔隙度,预测了致密砂岩有利储层发育区。研究表明：贝叶斯稀疏脉冲反演简化了稀疏脉冲反演过程,求解更稳定,砂岩边界控制下的孔隙度反演排除了泥岩影响,提高了孔隙度预测精度,该技术在龙门山前侏罗系沙溪庙组致密砂岩有利储层预测中取得了较好的效果,具有一定的推广应用价值。     

海上中高渗透率砂岩油藏油水相渗曲线合理性综合分析技术

为解决相渗曲线合理性分析的技术难题,从渤海油田大量的相渗曲线基础资料出发,通过分析相渗曲线的曲线形态,统计油相指数和水相指数分布范围,开展相渗曲线端点值与空气渗透率变化规律研究,并建立一套由"曲线形态分析法"、"油相指数和水相指数分析法"、"端点值分析法"组成的海上油田中高渗透率砂岩油藏相渗曲线合理性综合分析技术。应用结果表明,该项技术能够指导矿场技术人员分析相渗曲线的合理性,可确保油藏研究成果的可靠性,具有较好的推广应用价值。     

致密砂岩气藏井网加密优化

采用物理模拟实验与数学评价方法相结合,系统研究了井控范围从500 m逐步加密至100 m(相当于井距从1 000 m加密至200 m）过程中不同渗透率砂岩储层在不同含水饱和度条件时的储量采出程度,揭示了井网加密对提高储量采出程度作用,以采出程度提高5%~10%和大于10%为依据,建立井网加密可行性判识图表,为气藏井网部署和加密方案优化提供了参考依据。实验岩心常规空气渗透率分别为1.63×10^-3 μm²、0.58×10^-3 μm²、0.175×10^-3 μm²、0.063×10^-3 μm²,含水饱和度介于30.3%~71.1%之间。研究结果表明：渗透率为1.63×10^-3 μm²的储层,采出程度总体均较高,除了在含水饱和度高达69.9%时的采出程度与井控范围有关外,其余含水饱和度条件下,采出程度与井控范围关系不大,可以采用大井距开发;渗透率为0.58×10^-3 μm²的储层,采出程度与含水饱和度和井控范围关系密切,随含水饱和度降低、井控范围加密而增加;渗透率为0.175×10^-3 μm²的储层,采出程度受含水饱和度的影响十分显著,只有在含水饱和度≤52.3%时,井网加密优化可提高储量采出程度,当含水饱和度>52.3%时,储量采出程度均较低,一般≤10%,即使井控范围加密至100 m,也难以得到提高;渗透率为0.063×10^-3 μm²的储层,总体上采出程度非常低,即使含水饱和度仅有31.6%,井控范围加密至100 m,其采出程度最高也只有2.3%,因此,该类储层依靠井网加密难以得到有效动用。     

致密砂岩气藏地层水可动性及其影响因素研究

为研究致密砂岩气藏储层物性参数与地层水可动能力间的关系,明确不同物性储层的地层水可动性,通过核磁共振方法测量岩心孔隙大小分布,进行了X射线全岩衍射分析,提出了一种采用离心法与核磁共振相结合方式划分地层水可动程度的新方法,并分析了孔隙度、渗透率、孔隙结构、岩石矿物组成与地层水可动性之间的关系。结果表明,地层水可动或不可动无绝对界限,储层孔隙结构决定地层水可动性;矿物组成对地层水可动性影响不大。研究认为,地层水根据可动性可分为束缚水、可动束缚水、可动水,但束缚水饱和度、可动束缚水饱和度、可动水饱和度的划分不是绝对的,通过实验方法可得到其近似值。研究结果对致密砂岩气藏划分开发层系,减小地层产水可能性具有指导意义。     

鄂尔多斯盆地定边油田长7 致密砂岩储层成岩作用及孔隙演化规律

鄂尔多斯盆地定边油田延长组长7储层石油地质储量丰富,但砂体致密、非均质性强等因素严重制约了油气的有效勘探开发。综合运用铸体薄片、扫描电镜等资料,深入分析研究区储层的岩石组分、孔隙类型、物性特征及成岩作用,将成岩演化事件与地质响应有机匹配建立研究区孔隙演化模型,厘清储层成岩演化及孔隙演化规律,同时对比不同深度成岩作用对孔隙演化规律的影响程度。结果表明,研究区长7储层以长石砂岩为主,主要发育黏土、碳酸盐等胶结物,有效孔隙类型以残余粒间孔、次生溶孔及晶间微孔为主,为典型的特低孔、超低渗透致密砂岩储层。成岩演化过程先后经历快速压实—早期胶结、胶结—早期溶蚀、溶蚀增孔、压实—晚期胶结等阶段,目前处于中成岩A期。压实作用是导致孔隙减小、储层致密的主控因素,平均减孔量为20.40%;胶结作用平均减孔量为14.02%,其中晚期胶结是储层致密的关键因素;溶蚀作用平均增孔量为5.87%,可延缓储层致密过程。长7^1油层段底部与长7^2油层段中部储层压实、胶结作用减孔量相对较弱,溶蚀增孔量相对较大,可作为研究区勘探开发的首要目标。     

致密砂岩油藏能量补充方式评价及优化

针对致密砂岩油藏大规模体积压裂开发后能量补充困难的问题,利用自主设计制作的大型人造三维岩心物理模型和物理模拟实验舱,开展致密砂岩油藏能量补充方式优化研究。实验结果表明:致密砂岩油藏压裂开发过程中,地层能量损耗严重,采取注水或注气的方式可有效进行能量补充;地层中裂缝规模越大,越有利于原油渗流,后续补充能量的传播范围越广,有助于进一步提高原油采收率;从提高驱油效率和扩大波及系数方面优选吞吐渗吸介质,CO₂均优于活性水,CO₂吞吐开发在矿场试验中取得了显著的增油效果,因此,CO₂吞吐作为一种有效的能量补充方式在致密油开发中展现了良好的应用前景。该文分析了致密砂岩储层水平井压裂开发的渗流规律,优选出致密砂岩储层大规模压裂开发后最佳渗吸介质,可为致密砂岩油藏开发设计提供重要的理论依据。     

Initial and residual trapping of hydrogen and nitrogen in Fontainebleau sandstone using nuclear magnetic resonance core flooding

Hydrogen is among a few promising energy carriers of the future mainly due to its zero-emission combustion nature. It also plays an important role in the transition from fossil fuel to renewable. Hydrogen technology is relatively immature and serious knowledge gaps do exist in its production, transport, storage, and utilization. Although the economical generation of hydrogen to the scale required for such transition is still the biggest technical and environmental challenge, unlocking the large-scale but safe storage is similarly important. It is difficult to store hydrogen in solid and liquid states and storing it in the gaseous phase requires a huge volume which is just available in subsurface porous media. Sandstone is the most abundant and favourable medium for such storage as carbonate rock might not be suitable due to potential geochemical reactions.It is well established in the literature that interaction of the host rock-fluid and injected gas plays a crucial role in fluid flow, residual trapping, withdrawal, and more generally storing capacity. Such data for the hydrogen system is extremely rare and are generally limited to contact angle measurements, while being not representative of the reality of rock-brine-hydrogen interaction(s). Therefore, we have conducted, for the first time, a series of core flooding experiments using Nuclear Magnetic Resonance (NMR) to monitor hydrogen (H₂) and Nitrogen (N₂) gas saturations during the drainage and imbibition stages under pressure and temperature that represent shallow reservoirs. To avoid any geochemical reaction during the test, we selected a clean sandstone core plug of 99.8% quartz (Fontainebleau with a gas porosity of 9.7% and a permeability of 190 mD).Results show significantly low initial and residual H₂ saturations in comparison with N₂, regardless of whether the injection flow rate or capillary number were the same or not. For instance, when the same injection flow rate was used, H₂ saturation during primary drainage was 4% and it was <2% after imbibition. On other hand, N₂ saturation during the primary drainage was 26% and it was 17% after imbibition. However, when the same capillary number of H₂ was utilised for the N₂ experiment, the N₂ saturation values were ～15% for initial gas saturation and 8% for residual gas saturation. Our results promisingly support the idea of hydrogen underground storage; however, we should emphasise that more sandstone rocks of different clay mineralogy should be investigated before reaching a conclusive outcome.     

白云岩与砂岩致密储集体质量的差异性

白云岩与砂岩致密储集体质量参数为随机分布的连续谱系，孔隙结构、物理参数复杂多变，表征难度较大。基于铸体薄片、压汞、核磁共振、孔隙度和渗透率等测试技术，结合大量天然气勘探开发实际资料，采用统计分析对比方法，重点讨论了储层质量宏观与微观参数特征。结果表明，白云岩与砂岩致密储集体质量参数具有正态分布特征，是一种金字塔数据结构，常规储层比例一般为15%~20%，是砂岩或白云岩致密储层的“甜点”；致密砂岩储层微观孔隙发育，孔、喉连通性较好，分布比较均匀，储层孔、渗关系较好，表现为相对高孔和低渗；白云岩致密储层质量尽管具有孔、喉连通性差和孔、渗关系较差的不利因素，但也具有相对高渗、低束缚水饱和度、低排驱压力及裂缝网络发育等有利因素，天然气渗流能力较好，勘探开发潜力较大。我国发育碳酸盐岩沉积，应加强致密白云岩气藏成藏条件研究与勘探。