Fluid evolution and hydrocarbon accumulation model of ultra-deep gas reservoirs in Permian Qixia Formation of northwest Sichuan Basin,SW China

The fluid evolution and reservoir formation model of the ultra-deep gas reservoirs in the Permian Qixia Formation of the northwestern Sichuan Basin are investigated by using thin section,cathodoluminescence,inclusion temperature and U-Pb isotopic dating,combined with gas source identification plates and reservoir formation evolution profiles established based on burial history,thermal history,reservoir formation history and diagenetic evolution sequence.The fluid evolution of the marine ultra-deep gas reservoirs in the Qixia Formation has undergone two stages of dolomitization and one phase of hydrothermal action,two stages of oil and gas charging and two stages of associated burial dissolution.The diagenetic fluids include ancient seawater,atmospheric freshwater,deep hydrothermal fluid and hydrocarbon fluids.The two stages of hydrocarbon charging happened in the Late Triassic and Late Jurassic–Early Cretaceous respectively,and the Middle to Late Cretaceous is the period when the crude oil cracked massively into gas.The gas reservoirs in deep marine Permian strata of northwest Sichuan feature multiple source rocks,composite transportation,differential accumulation and late finalization.The natural gas in the Permian is mainly cracked gas from Permian marine mixed hydrocarbon source rocks,with cracked gas from crude oil in the deeper Sinian strata in local parts.The scale development of paleo-hydrocarbon reservoirs and the stable and good preservation conditions are the keys to the forming large-scale gas reservoirs.

Sedimentary environments controlled by tectonics and induced differential subsidence:A perspective in the Permian Liangshan and Qixia Formations,northwestern Sichuan Basin,China

Based on field observation,core description and well logging analysis,the tectonic-sedimentary framework of the Liangshan and Qixia Formations in the northwestern Sichuan Basin,China is deeply discussed.Two long-term sequence cycles were identified,denoted as LSC1 and LSC2,respectively.The sequence stratigraphic framework was established,suggesting the Liangshan Formation to be not isochronously deposited.Paleogeomorphy before deposition of LSC1 was reconstructed by the impression method.LSC1 was featured by thin,low-energy shoal deposits in the high topography,and thick inter-shoal sea and open sea deposits in the low topography.Meanwhile,paleogeomorphy before deposition of LSC2 was reconstructed using the residual thickness method,which was demonstrated to have primary high-energy,thick shoal deposits in the high topography,and thin inter-shoal and open sea deposits in the low topography.The results show that differential tectonic subsidence has already taken place during the Qixia Period,and thus the Dongwu Movement should occur earlier than previously expected.Meanwhile,pre-depositional paleogeomorphy has obvious controlling effects on the sequence stratigraphic filling and sedimentary facies distribution.Results of this study were expected to provide practical guidance to fine characterization of the sedimentary evolution process and prediction of high-quality reservoir distribution.

The reservoir characteristics research of Devonian Jinbaoshi Formation,Northwest Sichuan Basin,SW China

A great breakthrough was achieved on the Middle Devonian's oil-gas exploration in the Longmenshan area in northwestern Sichuan.However,only the Guanwushan Formation was researched in detail.The underlying formation-Jinbaoshi Formation as a set of the potential well reservoir and its reservoir characteristics have not been discussed.Based on the section's fine description,thin section analysis,and core borehole logging,combined with petrophysical analysis,the reservoir characteristics,controlling factors,and evolution process of the Jinbaoshi Formation reservoir in the Longmenshan area are deeply studied in this paper.The results showed that the Jinbaoshi Formation has developed a set of sand-shale interbedding deposit of terrigenous clastic and carbonate rocks.The reservoir lithology is mainly quartz sandstone and calcareous quartz sandstone.The quartz sandstone reservoir has good physical properties,but the calcareous quartz sandstone has the characteristics of strong heterogeneity,low porosity,and permeability.Residual intergranular pores are mainly developed in the reservoir space.And the development of intercrystalline pores and intergranular dissolved pores can also be seen,but the development frequency is low,and the scale is small.Among them,the Devonian Jinbaoshi Formation quartz sandstone's average porosity is about 8%,and the highest is 18.43%.The main diagenesis types of the Jinbaoshi Formation are compaction,recrystalization,and dissolution.Compaction is the main reason for the destruction of original pores,and dissolution is the main driving force for later porosity and permeability improvement.Rock fragments,calcareous silty clasts,and bioclastic grains are the main dissolution objects.The formation of intergranular dissolved pores significantly improves the physical properties of the reservoir.Therefore,the reservoir development of the Jinbaoshi Formation is mainly controlled both by favourable sedimentary facies and diagenesis.Quartz sandstone and calcareous sandstone of the Jinbaoshi Formation were controlled by early sedimentary facies in the syngenetic rock stage and developed more early intergranular pores;in the early diagenesis stage,compaction-pressure solution and cementation resulted in residual intergranular pores.In the middle-late diagenesis stage,the calcareous cement is dissolved,and more pores were formed.

Genesis and characteristics of the dolomite reservoirs in Middle Devonian Guanwushan Formation, Northwest Sichuan Basin, SW China

A great breakthrough has been made on oil-gas exploration of the Middle Devonian Guanwushan Formation in Northwest Sichuan Basin.The further exploration shows that the dolomite reservoir is complicated with insufficient investigation.Taking the Middle Devonian Guanwushan Formation as an example,systematic study has been carried out on its reservoir character,mechanism and genesis of dolostone.The field and core data suggest that reservoir types of Guanwushan Formation consist of crystalline dolomite,breccia dolomite and reef dolomite,and reservoir space is characterized by intercrystal(dissolution)pores,residual pores among breccias,intragranular dissolution pores,pockets as well as fractures.Besides,pore structure is of good configuration,showing medium-low porosity and moderate permeability,with average porosity and permeability of 2.23%and 0.44mD respectively,which suggesting fracture-pore and fracture-cavity reservoir.Combined with the previous research,it is suggested that the reservoir of Guanwushan Formation was controlled by facies,dolomitization and two-step karstification,with reef-shoal facies being material base for reservoir development,early dolomitization being key factor for reservoir space preservation,polyphase karstification being foundation for reservoir development and tectogenesis finally finalizing the reservoir.

川西北下二叠统茅口组古构造演化与控藏作用

利用钻井、测井、岩心、野外剖面和地震等资料,开展川西北二叠系茅口组成藏期古构造恢复及控藏作用研究。研究表明:川西北茅口组台缘滩和台内滩发育,寒武系和二叠系烃源岩在区内分布较广;晚二叠世茅口组顶古构造整体呈“南高北低”格局,发育NW—SE向的低幅隆起;早中三叠世该古构造转变为“西高东低”格局,剑阁地区形成了面积较大的古构造圈闭;早侏罗世该古构转变为“东高西低”格局,构造高点向东迁移至九龙山地区,后经喜山期调整为盆地边缘高,中部地区凹陷的格局。流体包裹体均一温度的分析表明,茅口组存在4期油气运移。结合区域生烃演化史,研究认为:晚二叠世茅口组台缘带是原油运移的有利区,早中三叠世形成的剑阁地区古圈闭能够较好地捕获油气,晚三叠世天然气主要向NE方向的剑阁、九龙山和元坝地区形成的低幅度背斜圈闭运移,喜山期天然气进一步向高部位聚集并调整形成现今气藏。剑阁—柘坝场的台缘带与烃源岩和古构造的匹配关系好,具有较大的天然气勘探潜力。

川西北中泥盆统观雾山组储层特征及其主控因素

为明确川西北观雾山组储层特征及主控因素,通过野外剖面及岩心观察、铸体薄片鉴定、扫描电镜、阴极发光、微米CT扫描、孔渗及地球化学测试等对其进行了分析。研究表明:川西北观雾山组储层岩性主要为生物礁白云岩、生屑白云岩和角砾状细-中晶白云岩。主要储集空间为生物体腔孔、晶间孔和溶蚀孔洞。孔隙度平均值为2.58%,渗透率平均值为0.71×10^(-3)μm^(2)。储层发育主要受沉积相、白云石化及岩溶作用控制。台缘礁滩及台内高能滩是储层发育的有利相带。有序度、阴极发光、锶同位素和稀土元素特征表明,同生-准同生期白云石化作用形成储层基础。高频沉积旋回控制的准同生溶蚀和构造抬升控制的表生岩溶改造是储层形成的关键。埋藏成岩阶段烃类成熟释放的酸性流体对储层改造也有改善。

基于碳酸盐岩储层裂缝表征与产能描述的开发技术对策——以川西北双鱼石区块栖霞组气藏为例

针对碳酸盐岩气藏试采期开发技术对策研究中存在的问题,在剖析裂缝表征方法和扩展气井产能概念的基础上,探索和揭示了不同类型储层裂缝特征相对应的气井产能变化规律,形成了碳酸盐岩储层裂缝表征与产能描述技术。文中研究明确了裂缝-孔洞型、裂缝-孔隙型和孔隙型3类储层酸压改造后形成的裂缝搭配模式与试井双对数曲线的对应关系;通过建立复合地层渗流方程,实现了对气井产能以及影响产能的动态储量、平均渗透率的描述,揭示了纯气井和气水同产井在早期、过渡期、平稳期和变化期4个阶段的产能变化规律,以此为依据提出了井位平面部署、靶体位置优化、钻井及储层改造工艺、生产井制度优化4个方面的对策建议。通过实施开发技术对策,取得了单井产量的突破,生产井水侵速度得到一定程度的控制。文中研究成果指导了气藏开发技术对策的制定,为同类型碳酸盐岩气藏的高效勘探开发提供了技术参考。

川西北地区海相油气成藏物质基础——优质烃源岩

川西海相油气勘探程度低,油气成藏条件研究薄弱。通过区域地质、烃源岩形成环境、有机地化和有机岩石学等综合研究,重点探讨了龙门山构造带北段海相优质烃源岩发育情况。龙门山北段海相油气成藏的烃源条件好,主要有筇竹寺组、大隆组优质泥质烃源岩和栖霞组、茅口组优质碳酸盐岩烃源岩,而泥盆系烃源岩分布有限,奥陶纪—志留纪缺乏优质烃源岩形成条件。该区经历过大规模油气运移、聚集成藏和后期破坏过程,分析这一过程对川西海相油气勘探具有借鉴意义。预测龙门山逆冲推覆构造带和川西坳陷深处具有良好的海相油气勘探前景。

川西北广元地区海相层系油苗和沥青来源分析

川西北广元地区长江沟剖面寒武系—三叠系中固体沥青大量产出,油气苗丰富,经饱和烃、芳烃生物标志化合物绝对定量分析研究认为,下寒武统固体沥青、泥盆系和下二叠统茅口组油苗饱和烃生物标志化合物特征相似,显示早期有下寒武统烃源充注;三者之间芳烃生物标志化合物特征存在一定差异,除成熟度影响以外,可能后期有上古生界源岩充注。下三叠统飞仙关组油苗饱和烃、芳烃生物标志化合物特征与古生界沥青和油苗存在显著差异,而与上二叠统大隆组具有亲缘关系,也可能有下三叠统源岩的自身供给。

川西北跨度23a的原地应力实测数据特征及其地壳动力学意义分析

研究区位于龙门山断裂带北段的中央断裂带和前山断裂带之间,该区地质结构主要为准原地体系和逆冲推覆体系,岩性以志留系下统的泥岩、粉砂泥岩分布最广,遍及全区。为了满足该区一工程建设的需要,在研究范围内开展了4个钻孔的水压致裂原地应力测量工作,测试时间跨度达23 a。测试数据显示,虽然测试时间跨度达23 a,但是原地应力状态基本没有变化,研究区最大水平主应力方向的优势方向为N24.4°W,最大、最小水平主应力随深度线性增加的梯度分别为0.036和0.025。基于实测数据计算的特征参数kH max,kh min,m和R在23 a内没有变化。该区域位于龙门山断裂带中央断裂的下盘,为被动盘,断层活动性和地震活动性都极其微弱,这种特殊的区域地壳动力学条件决定了研究区稳定的区域应力场特征。通过与以往研究成果的对比分析可知,m较好地反映了该区域地壳的应力积累能力,即从应力积累的角度反映了区域断层的强度,这一研究与以往研究成果十分吻合。在未来的研究中,或许可以利用实测应力资料计算的m值,再结合区域断层和地震活动性的比较分析来评价特定区域的地震危险性。

川西北地区ST3井泥盆系油气地球化学特征及来源

对比ST3井泥盆系油气与相关源岩地球化学特征,结合地质研究,明确泥盆系油气来源。结果表明:ST3井泥盆系观雾山组沥青饱和烃分布呈现双峰特征,Pr/Ph=0.56;三环萜烷分布以C23为主峰,五环三萜烷以C30藿烷为主峰,Ts/Tm=0.82,C31~C35升藿烷系列分布齐全且近于呈正常降序分布,伽马蜡烷丰度高;孕甾烷和升孕甾烷含量丰富,规则甾烷中以C27甾烷占优势;ST3井泥盆系两份天然气都是干气,以烃类为主,甲烷含量高,体积分数分别为94.42%、96.96%,C2H6、C3H8含量低,干燥系数大,非烃气体含量低,H2S含量仅为0.01~0.022g/cm^3;甲乙烷碳同位素均值分别为-31.9‰、-28.5‰,乙烷碳同位素相对较轻,甲乙烷呈正碳同位素分布序列;甲烷氢同位素为-139‰、-138‰;对比综合显示ST3井泥盆系油气主要来源于筇竹寺组泥岩,同时下二叠统泥灰岩是重要补充。

川西北构造样式特征及其油气地质意义

川西北地区经历多期的构造运动,构造样式多种多样,构造特征复杂多变,对油气勘探有着非常重要的影响。对川西北地区地震资料、测井资料和露头资料进行综合分析与总结,结果表明:其构造样式主要包括基底冲断与滑覆叠加构造、叠瓦扇逆冲断层、断层相关褶皱、反冲断层和背斜构造。以构造样式形成时间可划分出3个构造变形阶段:(1)印支期逆冲推覆阶段;(2)燕山期逆冲推覆阶段;(3)喜马拉雅期逆冲推覆—滑覆阶段。结论认为:各大构造样式当中,断层相关褶皱和高陡背斜可以形成构造圈闭和岩性圈闭,是目前实际的勘探目标;反冲断层组成的构造三角带可以形成构造圈闭和岩性圈闭,是潜在的有利勘探区带。

川西北地区二叠系栖霞组超深层气藏流体演化过程与成藏模式

综合利用普通薄片、阴极发光、包裹体测温及U-Pb同位素定年等测试数据,结合埋藏史、热史、成藏史及成岩演化序列,利用气源识别图版及成藏演化剖面,研究四川盆地西北部二叠系栖霞组超深层气藏流体演化过程及成藏模式。栖霞组海相超深层气藏流体演化过程中发生了两期白云石化和1期热液作用、两期油气充注和伴生的两期埋藏溶蚀作用,成岩流体包括古海水、大气淡水、深部热液和烃类流体。两期油气充注时间分别为晚三叠世和晚侏罗世—早白垩世,中晚白垩世为原油大量裂解生气时间。川西北地区海相超深层气藏具“多元供烃、复式输导、差异成藏、晚期定型”的成藏模式,二叠系天然气主要为二叠系海相混合型烃源岩生成的原油裂解气,局部混合有来自深部震旦系原油裂解气的贡献。古油气藏的规模发育、稳定良好的保存条件是天然气规模成藏的关键。

构造叠加弱应变沉积岩地区的磁组构研究——以川西北盆地为例

磁组构是一种灵敏的应变指示计。单一方向应力作用下,在平行层缩短的初始阶段,磁线理与地层走向是一致的。然而,在构造叠加背景下弱变形的沉积岩地区,另一个(多个)不同方向的应力使得已经产生定向排列的磁性矿物发生旋转,表现为磁线理和与地层走向斜交。川西北盆地在新生代是一个典型的构造叠加区域,来自龙门山和米仓山的变形在此相互作用。本文在川西北盆地分3条剖面在18个采样点中采集了172个样品进行了磁组构研究。研究区内观察到3种弱变形的磁组构类型:沉积磁组构、初始变形磁组构和铅笔状磁组构。由于应变的叠加,由盆地内部向造山带前缘没有出现应变由弱到强的变化趋势,同时磁线理的方向也不一致。由盆地向造山带,来自米仓山的变形逐渐增强,磁线理从与地层走向一致转变成与地层走向斜交。

四川盆地川西北地区侏罗系自流井组大安寨段页岩气聚集条件

通过采用岩心观察、扫描电镜、地化参数分析等实验方法,研究了四川盆地川西北地区页岩的沉积相、厚度及分布、有机质类型及含量、成熟度、生烃史等页岩气成藏条件。川西北地区侏罗系自流井组大安寨段发育潮坪、沼泽及泻湖相,富有机质黑色泥页岩为主、单层厚度大,有机碳平均质量分数为2.0%,有机质类型以Ⅱ1、Ⅱ2、型为主的混合型,生烃潜力较大,热演化程度高,具备页岩气藏发育的良好地质条件。根据页岩气富集的多种因素分析,认为元坝—仪龙南部、达州—宣汉地区页岩气聚集条件较优越,是四川盆地川西北地区自流井组大安寨段页岩气勘探开发的有利区域。

龙门山山前复杂构造带双鱼石构造栖霞组超深层整装大气田的形成

以往在四川盆地西北部龙门山山前复杂构造带以冲断推覆带的勘探为主且主要集中在中深层,近期该区中二叠统天然气勘探取得重大突破,发现了双鱼石构造栖霞组超深层整装大气田,并且揭示出一个油气规模成藏的勘探新领域——冲断掩伏带与前缘背冲带原地构造超深层。为了给下一步油气勘探部署提供依据和参考,基于对生储盖组合以及圈闭等油气成藏要素的分析,总结了双鱼石构造栖霞组气藏的形成机制与模式。研究结果表明:(1)该区栖霞组储层受台地边缘滩微相的控制,叠合早成岩期岩溶与白云石化作用改造,形成以溶蚀晶间孔为主要储集空间的孔隙型储层;(2)栖霞组气藏天然气的来源包括下寒武统筇竹寺组泥页岩和中二叠统栖霞组、茅口组泥灰岩,该区规模发育下寒武统与中二叠统优质烃源岩,为气藏形成提供了充足的气源;(3)栖霞组储层与寒武系、二叠系烃源岩组成“下生上储”和“自生自储”的近源高效源储组合,烃源断层有效沟通源岩和储层,其上发育茅口组泥灰岩直接盖层和三叠系膏岩区域盖层,生、储、盖组合良好;(4)受龙门山推覆构造挤压作用以及双滑脱层夹持的影响,双鱼石构造栖霞组以层内原地背冲背斜构造为特征,与晶粒白云岩共同作用并形成了构造—岩性复合圈闭,不同构造高带上的钻井属于同一个压力系统,展现出整装气藏的特征,含气面积合计达到1900 km2。结论认为,较之于冲断推覆带,原地构造超深层构造变形弱,断层在沟通下部烃源岩的同时又未破坏圈闭的封盖性,油气早期成藏后得以稳定保存至今,这是双鱼石构造栖霞组天然气能够规模成藏的关键。

川西北地区下二叠统栖霞组滩相储层特征及其分布

四川盆地西北部下二叠统栖霞组白云岩储层为生物颗粒滩储层,目前对该套地层中的滩体类型及其特征研究较少。为此,在分析该区栖霞组储层特征的基础上,重点研究生物颗粒滩在纵向上的岩相组合、储集空间发育情况和物性特征,探讨滩体的储集性能与储层的平面分布。根据野外露头资料及钻井岩心的宏观及微观特征,结合物性分析结果,认为滩体形成时的古地理背景及经历的成岩作用不同,导致沉积的岩性组合、储集性能和分布差异极大。天井山—矿2井—西北乡一带的浅水高能生物滩位于栖霞组二段的中部,形成于龙门山古断裂上升盘的局部高地,由中—粗晶白云岩、生屑白云岩和云质"豹斑"石灰岩组成,累计厚度为60～90 m,滩体频繁暴露于水体之上,发生混合水云化作用和溶解作用,物性较好,是最有利的储层分布区;通口—水根头、余家沟—曾家山和鱼洞河—旺苍—巴中一带的深水低能生物滩发育于栖二段的顶部,形成于浅缓坡下部的浪基面附近,水体较深,能量较低,储集空间欠发育,为区内差—非储层分布区。

川西北九龙山构造须二段储层演化特征

川西北地区九龙山构造上三叠统须家河组须二段为致密储层,根据薄片、扫描电镜等分析资料研究认识了该储层的成岩作用特征,结合自生矿物包裹体均一温度、胶结物同位素地质温度和古地温梯度等建立了储层的成岩作用序列;根据储层在压实过程中的原生孔隙损失规律、成岩矿物形成时期及其对孔隙度破坏的定量化统计、次生孔隙的定量化研究等,剖析了储层致密化进程。结果认为:须二段储层在侏罗纪前具较好孔隙度;中侏罗世末期,储层孔渗性变差,但仍能满足天然气运移聚集的储集条件;储层的致密化发生在晚侏罗世。产水层高孔低渗是因早期绿泥石环边胶结,产气层低孔高渗则是因次生孔较发育,孔缝连为一体所致。

四川盆地西北部上古生界天然气勘探前景

近期,四川盆地西北部上古生界海相地层天然气勘探取得了重要的新进展,除证实中二叠统栖霞组孔隙型白云岩储层可能大面积连片分布外,还首次在井下发现了含气性较好的泥盆系厚层白云岩储层。最新研究成果表明:(1)区内沉积下寒武统巨厚优质烃源岩,烃源条件优越;(2)受加里东运动的影响,四川盆地西北部整体抬升,形成由南向北逐渐倾伏的西翼低陡东翼高缓的大型箱状隆起,构造顶部宽缓,为泥盆纪、石炭纪和二叠纪的继承性大规模台缘礁滩沉积和白云化作用奠定了基础;(3)上古生界存在多个不整合面,发生多期表生溶蚀作用,极大地改善了储层储渗性能;(4)龙门山推覆作用形成的构造形变特征为油气成藏创造了优越的烃源断裂及封盖条件,有利于大气田的形成。研究认为:该区(1)号隐伏断裂带以东的背冲背斜带具备形成大型构造—地层、构造—岩性复合圈闭气藏的有利条件,其中射箭河—中坝地区沉积古地貌地势相对较高、栖霞组白云化作用更强,加里东古隆起中轴线至东脊线附近是栖霞组气藏最有利的勘探区块,中轴线往西至(1)号隐伏断裂带是可同时兼探上古生界3套气层的最有利勘探区块。

四川盆地龙门山北段隐伏构造带特征及其油气勘探意义

2014年以来,四川盆地西北部(以下简称川西北)龙门山山前带双鱼石地区上古生界天然气勘探获得重大发现,先后在中二叠统栖霞组、中泥盆统观雾山组钻获多口工业气井。随着勘探工作的稳步推进,深入开展龙门山逆冲推覆构造前锋带—山前带构造特征研究,是认识该区上古生界气藏特征、拓展油气勘探领域的重要前提。为此,基于新部署的线束三维地震、重磁电资料以及ST9等井的实钻成果,解剖了龙门山逆冲推覆构造前锋带—山前带的构造特征,进而分析了该区隐伏构造带的构造特征、天然气成藏条件和勘探前景。结果表明:(1)龙门山逆冲推覆构造前锋带(1)号隐伏断裂之下发育大型隐伏构造带,其地层受挤压褶皱变形,发育下三叠统嘉陵江组以下的海相地层;(2)由南到北(1)号断裂底部滑脱层位由浅变深,从南部的寒武系滑脱,向北部逐渐转换为基底卷入,古生界及其以上地层整体抬升,越向北抬升幅度越大,断裂上下盘之间的位移距离、褶皱幅度也越大,北部相对南部上古生界构造整体抬升约1 500 m;(3)在剑阁以西—广元地区,(1)号断裂东侧整体表现出"三级台阶"的构造格局。结论认为:龙门山逆冲推覆构造前锋带(1)号断裂下盘隐伏构造带面积达1 800 km2,具有优越的天然气成藏条件,其中观雾山组和栖霞组储集条件、保存条件好,是川西北深层海相层系天然气勘探拓展寻找新突破的重要领域,具有现实的油气勘探意义。