渝东南地区下古生界页岩含气性差异关键控制因素

焦伟伟1,2,3,方光建1,2,3,汪生秀1,2,3,张志平1,2,3,余 川1,2,3

(1.页岩气勘探开发国家地方联合工程研究中心(重庆地质矿产研究院),重庆 401120; 2.国土资源部页岩气资源勘查重点实验室(重庆地质矿产研究院),重庆 401120; 3.油气资源与探测国家重点实验室重庆页岩气研究中心,重庆 401120)

摘 要:渝东南地区紧邻涪陵页岩气田,区内的下寒武统牛蹄塘组和上奥陶统五峰组—下志留统龙马溪组是目前页岩气勘探开发的2套重点层位,相比于涪陵焦石坝地区,改造强度更强,演化程度更高,勘探效果也差别较大,已有研究证明构造运动是盆内与盆外页岩气差异富集的关键控制作用。而对于同样经历了强改造和高演化的渝东南地区下古生界的2套页岩层位来说,2者均具有优质的物质基础,但含气性却差异十分显著。从现场含气量解吸和室内等温吸附实验出发,通过动静态指标对比和相关性研究,分析含气性的关键控制因素。结果表明:下寒武统牛蹄塘组页岩吸附能力较强,但现场解吸气却表现为“高氮、低烃、微含气”的特征;上奥陶统五峰组—下志留统龙马溪组页岩吸附能力略逊于下寒武统牛蹄塘组,但含气性却明显好于牛蹄塘组,多口井的解吸气量达到工业下限,气体成分以烃类气体为主。有机质的孔隙结构和富有机质页岩层系底板的封闭性是导致这2套层位含气性差异显著的关键因素。下寒武统牛蹄塘组页岩有机质孔欠发育,致使储集物性较差,而其底板发育不整合面并伴随流体活动,导致气藏遭到破坏,是其含气性差的关键。上奥陶统五峰组—下志留统龙马溪组页岩中呈蜂窝状密集发育的有机质孔大大增加了页岩气赋存的空间,加之顶底板的封闭性较好,为页岩气富集提供了良好的条件。通过单井解剖总结建立了渝东南地区下古生界两种典型的页岩气保存散失模型:敛聚保存型聚集模式和底板冲刷破坏散失模式。针对2套目的层的含气性关键控制因素的差异,建议对于下寒武统牛蹄塘组应进一步加强选区指标的研究;上奥陶统五峰组—下志留统龙马溪组应进一步加强选带方法的研究。

关键词:渝东南;富有机质页岩;含气性;有机质孔;封闭性;氮气

与渝东南地区仅有一条深大断裂之隔的涪陵页岩气田在上奥陶统五峰组—下志留统龙马溪组页岩层获重大突破,成为北美以外第1个实现商业化开发的千亿方级整装气田,是我国页岩气勘探开发的一面旗帜[1-3]。而紧邻的渝东南地区页岩气勘探开发步伐却愈渐迟缓,上奥陶统五峰组—下志留统龙马溪组页岩在前期实现部分点上突破后,目前并未有新进展;而其下部富有机质页岩厚度更大、有机碳含量更高的下寒武统牛蹄塘组勘探更是难以推进[4-5]。那么上奥陶统五峰组—下志留统龙马溪组页岩的有利勘探目标区究竟在哪,下步勘探如何部署?下寒武统牛蹄塘组是否有必要进一步勘探,勘探风险如果降低?这些是目前困扰勘探企业的瓶颈问题。近年来,针对中国南方志留系海相页岩开展的研究较多[6-10],而针对下寒武统的相对较少,且多集中在页岩气富集地质条件的评价方面[11-14],缺乏对含气性及富集规律方面的系统研究[15],周文等对四川盆地及周缘下古生界的2套页岩进行了对比研究,指出2者含气量差异的关键影响因素是桐湾期形成的不整合面[16]。桐湾期的这套不整合面是否影响了改造更强、演化更高的盆地外缘的页岩气富集?那么对于目前勘探前景有待进一步证实的渝东南地区下古生界2套页岩层位的含气性差异是否还有其他因素影响?该类研究鲜有报道。含气量是页岩含气性最准确也是最直接的反映,是页岩气勘探开发过程中选区、选层、选段的关键参数,而掌握含气性的关键控制因素是准确把握有利勘探目标区的先决条件,对于勘探的成败具有重大影响[17-18]。因此本次研究聚焦热点地区的重点问题,通过动静态指标的对比分析,结合典型井解剖,寻找下寒武统牛蹄塘组和上奥陶统五峰组—下志留统龙马溪组2套页岩层位含气性差异显著的关键控制因素,以期为勘探企业部署和规划提供理论参考。

1 地质背景

渝东南地区位于七曜山基底断裂南东部,属于四川盆地东部盆缘的高陡构造带(图1),在大地构造上属于扬子准地台上扬子台坳的一个Ⅳ级构造单元,面积约1.82万km2。渝东南地区经历了晋宁、澄江、加里东、印支、燕山和喜山等多期构造运动叠加,表现为快速沉降—缓慢隆升剥蚀—快速隆升剥蚀的演化过程,形成沿南东—北西方向,隔槽式褶皱—城垛式褶皱—隔挡式褶皱依次发育的构造格局,从而导致不同构造部位保存条件的显著差异,使渝东南地区的油气聚集条件更加复杂。背斜和断裂主要形成于中生代的燕山期,受燕山期北西—南东向强烈挤压应力影响,现今呈现北北东向山脉与小型山间盆地相间的地貌特征。

图1 渝东南地区位置及构造纲要
Fig.1 Structure and location of southeast Chongqing

渝东南地区出露地层以古生界为主,其次为中生界三叠系和少量侏罗系,缺失白垩系和古近系地层。渝东南地区广泛发育下古生界海相页岩,目前的重点勘探层位有两套:下寒武统牛蹄塘组(∈1n)和上奥陶统五峰组—下志留统龙马溪组(O3w—S1l),具有发育广、厚度大、埋深浅、有机质丰度高、成熟度高等特点[19]。五峰组—龙马溪组页岩有机碳含量平均为1.61%,有机质成熟度2.56%。页岩厚度一般为35~120 m,底界埋深500~4 000 m。五峰组—龙马溪组由下至上分为3个亚段,其中第1亚段是页岩气富集的最有利部位,厚度为10~36 m;下寒武统牛蹄塘组页岩有机碳含量平均为3.43%,有机质成熟度3.0%以上,已达到过成熟。页岩厚度50~140 m,主体埋深3 500~5 500 m。牛蹄塘组自下至上分为2个亚段,其中第2亚段富有机质页岩全区沉积稳定、分布广泛、厚度较大,但含气性上第1亚段略好,较上部龙马溪组页岩气富集规律更复杂。

重庆市最新的页岩气资源评价结果显示,渝东南地区两套目的层页岩气地质资源量总计11 937.8×108 m3,其中下寒武统牛蹄塘组页岩气地质资源丰度为1.58×108 m3/km2,五峰组—龙马溪组为2.62×108 m3/km2。目前上奥陶统五峰组—下志留统龙马溪组页岩层勘探程度相对较高,而且重庆永川、彭水、黔江、尤其涪陵地区在该层位已经取得了页岩气勘探的重大突破,充分证明了该层位良好的勘探潜力。而牛蹄塘组已完钻参数井7口,地温解吸气量多在0.5 m3/t以下,为微含气,且氮气含量非常高。处于相同构造背景下的2套页岩,含气性差异为何如此显著,是一个值得关注的问题。

2 含气性特征

目前对于页岩含气性评价的最直接和有效的方法为含气量现场解吸实验,可直接获得页岩单位体积的含气量;现场解吸实验可采集气体样品,进一步针对气样开展实验,掌握气体组成、同位素等特征;实验室中开展等温吸附实验,评价页岩的吸附能力,可初步估算页岩的吸附气含量[20]

2.1 等温吸附含气性对比

等温吸附实验主要采用容量法和磁悬浮天平重量法,对2套目的层51个页岩岩芯样品开展实验研究。并收集渝东北地区下寒武统页岩等温吸附实验数据进行整体对比研究。

30 ℃下等温吸附实验发现,渝东南下寒武统牛蹄塘组页岩的甲烷吸附能力在1.57~8.45 m3/t,平均值为4.96 m3/t。吸附能力强于渝东南五峰组—龙马溪组页岩(0.37~8.59 m3/t,平均值为2.8 m3/t);与渝东北地区同层位对比发现,渝东北下寒武统鲁家坪组页岩的甲烷吸附能力在1.61~5.87 m3/t,平均值为2.96 m3/t,渝东南下寒武统牛蹄塘组页岩的甲烷吸附能力最强(图2)。

图2 重庆地区下古生界富有机质页岩甲烷吸附能力
Fig.2 CH4 adsorption capacity of organic-rich shale from the Lower Paleozoic in Chongqing

2.2 现场解吸含气性对比

钻井岩芯解吸是获取页岩含气量最直接可靠的手段[21]。采用所在单位自主研发的页岩气全自动现场解吸仪对2套目的层587个页岩岩芯样品进行了现场解吸实验(其中下寒武统牛蹄塘组页岩4口井129个,五峰组—龙马溪组页岩8口井458个)。

下寒武统牛蹄塘组富有机质页岩层段(TOC含量>2%)现场解吸含气量统计表明,其解吸气量绝大多数在0.5 m3/t以下,整体含气性较差,仅秀山地区的N4井牛蹄塘组下部个别样品解吸气量大于1.0 m3/t(表1)。平面上未发现明显规律,纵向上下部含气性好于上部。五峰组—龙马溪组富有机质页岩层段(TOC含量>2%)含气性明显好于牛蹄塘组,8口井中有4口在其富有机质页岩层段解吸气量达到了工业下限1.0 m3/t,最高单井解吸气量达2.7 m3/t(表1)。平面上,沿南东向北西方向含气性逐渐变好,研究区构造运动沿该方向逐渐变弱,说明构造运动强度对五峰组—龙马溪组页岩的含气性有明显的控制作用。

表1 渝东南地区下古生界富有机质页岩段现场解吸含气量
Table 1 Desorbed gas contents of organic-rich shale from the Lower Paleozoic in southeast Chongqing

编号层位区间值/(m3·t-1)平均值/(m3·t-1)样品个数N1∈1n0.047 0~0.144 00.08619N2∈1n0.040 0~0.422 00.1789N3∈1n0.006 0~0.255 00.1288N4∈1n0.094 0~2.220 01.1572L1O3w—S1l0.640 0~1.630 01.1306L2O3w—S1l0.584 0~5.315 01.70015L3O3w—S1l0.020 8~0.335 40.1808L4O3w—S1l0.900 0~1.520 01.19010L5O3w—S1l0.960 0~2.700 01.62034L6O3w—S1l0.053 0~0.690 00.06024L7O3w—S1l0.010 0~0.190 00.04039L8O3w—S1l0.002 0~0.220 00.11011

2.3 页岩气气体组成对比

下寒武统牛蹄塘组页岩气主要组分为N2,CH4,CO2及少量C2H6。牛蹄塘组页岩气中氮气含量普遍较高,除N4井有一个样品N2含量小于50%以外,其他样品N2含量均在90%以上,平均93.8%;烃类普遍偏低,CH4含量最大为7.46%,绝大部分在0.5%~4.0%,平均2.72%;含微量C2H6,在0.04%~0.08%;CO2含量在0.5%~5.5%,平均2.75%。干燥系数均在0.97以上,指示了高演化程度,具有典型的干气特征[22]

五峰组—龙马溪组页岩气以烃类气体为主(含量达98%以上),主要为CH4,含量在94.33%~98.96%,平均含量97.77%;含少量C2H6(0.15%~0.77%),其他烃类气体很少;非烃类气体含量较低,主要为N2和CO2,其中N2含量在0.22%~1.69%,CO2含量在0.17%~4.08%。干燥系数在0.98以上,也呈现出高热演化程度和典型干气特征。

对比发现,二者均表现为典型干气特征,五峰组—龙马溪组含气性远好于牛蹄塘组。下寒武统牛蹄塘组页岩气以氮气为主,烃类含量不足3%,指示了气藏形成过程中可能遭受破坏,导致烃类气体散失,氮气充注。而五峰组—龙马溪组页岩气以甲烷气体为主,其他气体总含量不足3%,仅个别样品含少量氮气,指示了较好的保存条件[23]

3 含气性差异关键控制因素

我国页岩气资源类型多,构造演化、沉积环境、热演化过程复杂,使不同地区页岩气形成、富集存在较大差异[24-25]。对比发现,下寒武统牛蹄塘组页岩吸附能力大于五峰组—龙马溪组,但现场解吸气量却差很多;气体成分对比证实,保存条件较差可能是2者含气性差异的一个关键影响因素。

沉积构造背景分析证实,两套层位沉积时期,渝东南地区基本处于深水陆棚相,为页岩气富集高产提供了良好的物质基础[26];渝东南地区的强烈构造改造期为燕山期,两套层位的主要生排烃期都在强烈改造之前,有利于页岩气富集和保存。在证实所处沉积构造背景相似的条件下,通过详细对比2套层位的生烃条件、储集条件、保存条件、资源丰度、勘探现状等5个方面18个指标来讨论导致其含气性差异显著的关键因素(表2)。

对比研究发现,两套层位烃源岩分布广、厚度大、有机碳含量高、有机质类型好,为页岩气生成提供了良好的物质基础;二者主要的差异在于显微组分类型、有机质孔发育程度和底板封闭性等3个方面,可能是导致含气性差异的关键因素。

(1)烃源岩条件对比发现,牛蹄塘组页岩有机碳含量高于五峰组—龙马溪组页岩,但生烃潜力后者高出前者近30%;牛蹄塘组页岩显微组分为原沥青,五峰组—龙马溪组页岩显微组分为笔石表皮体。LUO等经过统计发现,笔石表皮体占到岩石中分散有机质体积的20%~93%,认为笔石表皮体对埋藏有机碳具有重要贡献[27]。四川盆地志留系龙马溪组和鄂尔多斯盆地奥陶系平凉组页岩高TOC含量层段均与高丰度笔石层段对应发育,也说明了笔石有机质对埋藏有机碳的重要贡献[28-29]。本次通过对L6井岩芯观察也证实富含笔石的层段,其现场解吸气含量也较高。因此认为笔石表皮体应该是二者生烃潜力差异的关键。

(2)储集条件对比发现,二者的主要差异在于有机质孔的发育程度。牛蹄塘组页岩有机质孔约占12.8%,呈簇状发育,连通性较差(图3);五峰组—龙马溪组页岩优势孔隙为有机质孔,占近40%,呈蜂窝状发育(图4),大大提高了储层的吸附能力和连通性[30]。通过聚焦离子束扫描电镜证实,在牛塘组页岩中有机质孔隙度贡献率不足0.01%,而五峰组—龙马溪组页岩中有机质孔隙度贡献率达到18.4%。所以有机质孔的发育程度可能是两套层位含气性差异的关键因素之一。

表2 渝东南地区两套重点层位页岩气聚集条件对比
Table 2 Accumulation condition comparison of the two important horizons in southeast Chongqing

层位O3w—S1l∈1n厚度(TOC含量>2%)/m10~6010~50TOC含量/%1.494.25烃源条件Ro/%2.56>3.0有机质类型Ⅰ型Ⅰ型显微组分笔石表皮体原沥青生烃潜力/(108 m3·km-2)8060空间类型有机质孔、粒内孔、粒间孔、微裂缝粒内孔、粒间孔、有机质孔、微裂缝有机质孔3~100 nm(蜂窝状)10~35 nm(针孔状)储集条件溶蚀孔不发育发育(多微米级)孔径规模几十纳米80%孔隙<10 nm连通性较好较差物性孔隙度1.25%,渗透率0.031 9×10-15 m2孔隙度0.71%,渗透率0.009 3×10-15 m2埋深/m500~4 000500~7 000保存条件上覆地层厚层泥岩(170 m)页岩夹石英砂岩下伏地层连续沉积灰岩(40 m)白云岩(溶孔)断裂较发育较发育资源丰度/(108 m3·km-2)2.621.58勘探现状获得突破(彭水、黔江)尚未突破(解吸气量普遍未达工业下限1 m3/t)

图3 渝东南地区牛蹄塘组页岩孔隙结构特征
Fig.3 Pore structure of the Lower Cambrian Formation in southeast Chongqing

图4 渝东南地区五峰组—龙马溪组页岩孔隙结构特征
Fig.4 Pore structure of the Upper Ordovician Wufeng Formation and the Lower Silurian Longmaxi Formation in southeast Chongqing

(3)保存条件对比发现,二者的差异主要在下覆地层的封闭性。渝东南地区五峰组—龙马溪组页岩底板为宝塔组致密灰岩,顶板为新滩组大套厚层沉积泥岩夹粉砂岩,顶底板封闭性较好,为页岩气聚集提供了较好的条件;牛蹄塘组埋藏深、上覆地层厚度大,但底部发育有滑脱层,底板存在风化壳(图5),且被多条深大断裂切穿,是高氮低烃的关键,这一观点笔者已有研究证实[31]

图5 岩芯及野外露头中的溶蚀、充填及顺层滑脱现象
Fig.5 Corrosion,fill and decollement in cores or field outcrop

3.1 有机质孔隙结构对含气性的关键控制作用

相关性统计分析证实,页岩的吸附气量、解吸气量与页岩的有机碳含量均呈现较好的正相关关系(图6,7),说明有机碳含量是控制页岩尤其是页岩中吸附气含量的主要地质因素。其原因前人已有研究证明,在高过成熟阶段,丰富的有机质能够发育大量的有机微孔隙,是页岩气的主要赋存的位置[32-34]。通过有机碳含量与孔隙度的相关性分析证明,矿物基质孔的孔隙度基本在1%以下,有机质孔是页岩高孔隙度的主要贡献者,有机质孔对于页岩孔隙度的贡献大于基质孔隙(图8)[35]。所以结合上文,下寒武统牛蹄塘组相对五峰组—龙马溪组有机质孔欠发育,从而导致其孔隙度低,连通性差,气体储集空间有限,是其含气性差的关键影响因素之一。

图6 重庆地区泥页岩有机碳含量与吸附气量关系
Fig.6 Relationship between total organic content (TOC) and adsorbed gas content in Chongqing

图7 渝东南地区两套页岩有机碳含量与现场解吸气量相关关系
Fig.7 Relationship between total organic content (TOC) and desorbed gas content in southeast Chongqing

图8 L10井五峰组—龙马溪组页岩有机碳含量与孔隙度相关关系(据文献[35])
Fig.8 Relationship between total organic content (TOC)and porosity of O3w—S1l shale from Well L10(from References[35])

3.2 底板封闭性对含气性的关键控制作用

通过单井解剖和牛蹄塘组页岩气高氮低烃的专项研究证明,造成2套层位含气性差异的另外一个关键因素是底板的封闭性,并由此总结建立了渝东南地区下古生界两种典型的页岩气保存散失模型。

图9为针对渝东南五峰组—龙马溪组页岩的敛聚保存型聚集模式,其页岩气层段通常埋深适中(大于1 500 m),顶底板封存能力较好,构造形态为平缓向斜,深大断裂不发育,利于页岩气保存,地层压力表现为常压-微超压。典型井为位于濯河坝向斜西翼的L9井,完钻井深2 676 m。目的层五峰组—龙马溪组页岩层底板为中奥陶统宝塔组灰岩,结构致密,溶蚀孔洞不发育;顶板为中上志留统致密砂岩,厚度在1 400~1 600 m。所在构造为蝶形平缓向斜,倾角20°左右,核部三叠系出露地表,向斜内无大型逆冲断层发育,整体保存条件较好,使得页岩气得以保存聚集(图9)。L9井单井最高解吸气量达4.42 m3/t,平均1.04 m3/t。底部富有机质页岩段平均含气量2.15 m3/t。

图9 渝东南地区页岩气敛聚保存聚集模式
Fig.9 Accumulation mode of shale gas in southeast Chongqing

优越的顶底板条件是页岩气层具有良好保存条件的基础,能够使页岩气在大量生成时尽可能的保留在页岩层中。但若顶底板条件不佳,与页岩气层之间存在不整合面,或者顶底板条件本身物性较好,为良好的储集层,在此条件下,页岩气在主要生烃期,由于烃浓度的差异,将会向页岩气层外发生运移,另外,如果底板遭到水洗,气体将会散失。典型实例为下寒武统页岩气层,如渝东南地区N4井,该井下寒武统牛蹄塘组与震旦系灯影组之间为桐湾运动造成的不整合面,灯影组白云岩岩溶孔洞发育,另外在牛蹄塘组底部发育滑脱层,页岩气向下或沿着不整合面与滑脱层构成的通道发生大规模散失;另外这条气体散失通道也是地下水体活动的通道,使气藏进一步遭受冲刷破坏,导致牛蹄塘组页岩含气量较低,且解吸气基本为氮气(>90%)(图10),这一观点笔者已另有研究证实[31]

图10 渝东南地区页岩气底板冲刷破坏散失模式
Fig.10 Dissipation mode of shale gas in southeast Chongqing

4 结 论

(1)渝东南地区2套富有机质页岩层:下寒武统牛蹄塘组和上奥陶统五峰组—下志留统龙马溪组同处于盆缘复杂的构造环境,且均具有良好的物质基础,但2者含气性差异显著。

(2)下寒武统牛蹄塘组页岩吸附能力较强,但普遍微含气,现场解吸气表现为“高氮、低烃”的特征,氮气含量高达93%以上;上奥陶统五峰组—下志留统龙马溪组页岩吸附能力低于下寒武统牛蹄塘组,但页岩含气性明显好于牛蹄塘组,多口井解吸气量达到工业下限,部分井压裂获工业气流,气体成分以烃类气体为主,非烃类气体不足3%。

(3)通过动静态指标对比及相关性分析证明,有机质孔隙结构和富有机质页岩层系底板封闭性是导致2套层位含气性差异显著的关键因素。下寒武统牛蹄塘组页岩有机质孔欠发育,致使储集物性较差,而其底板发育不整合面并伴随流体活动,导致气藏遭到破坏,是其“高氮、低烃、微含气”的关键。上奥陶统五峰组—下志留统龙马溪组页岩中呈蜂窝状密集发育的有机质孔大大增加了页岩气赋存的空间,加之顶底板的封闭性较好,为页岩气富集提供了良好的条件。

(4)针对2套目的层的含气性关键控制因素的差异,建议对于下寒武统牛蹄塘组应进一步加强选区指标的研究;上奥陶统五峰组—下志留统龙马溪组应进一步加强选带方法的研究。

参考文献:

[1] 郭彤楼,刘若冰.复杂构造区高演化程度海相页岩气勘探突破的启示——以四川盆地东部盆缘JY1井为例[J].天然气地球科学,2013,24(4):643-651.

GUO Tonglou,LIU Ruobing.Implications from marine shale gas exploration breakthrough in complicated structural area at high thermal stage:Taking Longmaxi Formation in well JY1 as an example[J].Natural Gas Geoscience,2013,24(4):643-651.

[2] 郭旭升,胡东风,文治东,等.四川盆地及周缘下古生界海相页岩气富集高产主控因素——以焦石坝地区五峰组-龙马溪组为例[J].中国地质,2014,41(3):893-901.

GUO Xusheng,HU Dongfeng,WEN Zhidong,et al.Major factors controlling the accumulation and high productivity in marine shale gas in the Lower Paleozoic of Sichuan Basin and its periphery:A case study of Wufeng-Longmaxi Formation of Jiaoshiba area[J].Geology in China,2014,41(3):893-901.

[3] 罗健,戴鸿鸣,邵隆坎,等.四川盆地下古生界页岩气资源前景预测[J].岩性油气藏,2012,24(4):70-74,9.

LUO Jian,DAI Hongming,SHAO Longkan,et al.Prospect prediction for shale gas resources of the Lower Paleozoic in Sichuan Basin[J].Lithologic Reservoirs,2012,24(4):70-74,9.

[4] 张小龙,张同伟,李艳芳,等.页岩气勘探和开发进展综述[J].岩性油气藏,2013,25(2):116-122.

ZHANG Xiaolong,ZHANG Tongwei,LI Yanfang,et al.Research advance in exploration and development of shale gas[J].Lithologic Reservoirs,2013,25(2):116-122.

[5] 胡明毅,邓庆杰,胡忠贵.上扬子地区下寒武统牛蹄塘组页岩气成藏条件[J].石油与天然气地质,2014,35(2):272-279.

HU Mingyi,DENG Qingjie,HU Zhonggui.Shale gas accumulation conditions of the Lower Cambrian Niutitang Formation in Upper Yangtze region[J].Oil & Gas Geology,2014,35(2):272-279.

[6] 张金川,聂海宽,徐波,等.四川盆地页岩气成藏地质条件[J].天然气工业,2008,28(2):151-156,180.

ZHANG Jinchuan NIE Haikuan,XU Bo,et al.Geological condition of shale gas accumulation in Sichuan Basin[J].Natural Gas Industry,2008,28(2):151-156,180.

[7] 郭旭升.南方海相页岩气“二元富集”规律——四川盆地及周缘龙马溪组页岩气勘探实践认识[J].地质学报,2014,88(7):1209-1218.

GUO Xusheng.Rules of two-factor enrichment for marine shale gas in Southern China—Understanding from the Longmaxi formation shale gas in Sichuan Basin and its surrounding area[J].Acta Geologica Sinica,2014,88(7):1209-1218.

[8] 韩双彪,张金川,邢雅文,等.渝东南下志留统龙马溪组页岩气聚集条件与资源潜力[J].煤炭学报,2013,38(S1):168-173.

HAN Shuangbiao,ZHANG Jinchuan,XING Yawen,et al.Shale gas accumulation conditions and resource potential of the Lower Silurian Longmaxi Formation in southeast Chongqing[J].Journal of China Coal Society,2013,38(S1):168-173.

[9] 李可,王兴志,张馨艺,等.四川盆地东部下志留统龙马溪组页岩储层特征及影响因素[J].岩性油气藏,2016,28(5):52-58.

LI Ke,WANG Xingzhi,ZHANG Xinyi,et al.Shale gas accumulation conditions of the Lower Cambrian Niutitang Formation in Upper Yangtze region[J].Lithologic Reservoirs,2016,28(5):52-58.

[10] 李辛子,王运海,姜昭琛,等.深部煤层气勘探开发进展与研究[J].煤炭学报,2016,41(1):24-31.

LI Xinzi,WANG Yunhai,JIANG Zhaochen,et al.Progress and study on exploration and production for deep coalbed methane[J].Journal of China Coal Society,2016,41(1):24-31.

[11] 程俊,徐晓飞,张文峰,等.上扬子西北缘宁强湾牛蹄塘组有机地球化学特征[J].岩性油气藏,2017,29(1):21-26.

CHENG Jun,XU Xiaofei,ZHANG Wenfeng,et al.Organic geochemical characteristics of Niutitang Formation in Ningqiang Bay,the northwestern margin of Upper Yangtze platform[J].Lithologic Reservoirs,2017,29(1):21-26.

[12] 程克明,王世谦,董大忠,等.上扬子区下寒武统筇竹寺组页岩气成藏条件[J].天然气工业,2009,29(5):40-44,137.

CHENG Keming,WANG Shiqian,DONG Dazhong,et al.Accumulation conditions of shale gas reservoirs in the Lower Cambrian Qiongzhusi Formation,the Upper Yangtze region[J].Natural Gas Industry,2009,29(5):40-44,137.

[13] 聂海宽,张金川,李玉喜.四川盆地及其周缘下寒武统页岩气聚集条件[J].石油学报,2011,32(6):959-967.

NIE Haikuan,ZHANG Jinchuan,LI Yuxi.Accumulation conditions of the Lower Cambrian shale gas in the Sichuan Basin and its periphery[J].Acta Petrolei Sinica,2011,32(6):959-967.

[14] 吴陈君,张明峰,马万云,等.渝东南牛蹄塘组页岩有机质特征及沉积环境研究[J].天然气地球科学,2014,25(8):1267-1274.

WU Chenjun,ZHANG Mingfeng,MA Wanyun,et al.Organic matter characteristic and sedimentary environment of the Lower Camnrian Niutitang shale in southeastern Chongqing[J].Natural Gas Geoscience,2014,25(8):1267-1274.

[15] 黄俨然,杨荣丰,肖正辉,等.湘西北下寒武统牛蹄塘组页岩含气性影响因素分析[J].岩性油气藏,2015,27(4):11-16.

HUANG Yanran,YANG Rongfeng,XIAO Zhenghui,et al.Influencing factors of shale gas-bearing property of Lower Cambrian Niutitang Formation in northwestern Hunan[J].Lithologic Reservoirs,2015,27(4):11-16.

[16] 周文,徐浩,余谦,等.四川盆地及其周缘五峰组—龙马溪组与筇竹寺组页岩含气性差异及成因[J].岩性油气藏,2016,28(5):18-25.

ZHOU Wen,XU Hao,YU Qian,et al.Shale gas-bearing property differences and their genesis between Wufeng-Longmaxi Formation and Qiongzhusi Formation in Sichuan Basin and surrounding areas[J].Lithologic Reservoirs,2016,28(5):18-25.

[17] 秦勇,申建,沈玉林.叠置含气系统共采兼容性——煤系“三气”及深部煤层气开采中的共性地质问题[J].煤炭学报,2016,41(1):14-23.

QIN Yong,SHEN Jian,SHEN Yulin.Joint mining compatibility of superposed gas-bearing systems:A general geological problem for extraction of three natural gases and deep CBM in coal series[J].Journal of China Coal Society,2016,41(1):14-23.

[18] 于炳松.页岩气储层的特殊性及其评价思路和内容[J].地学前缘,2012,19(3):252-258.

YU Bingsong.Particularity of shale gas reservoir and its evaluation[J].Earth Science Frontiers,2012,19(3):252-258.

[19] 龙鹏宇,张金川,唐玄,等.泥页岩裂缝发育特征及其对页岩气勘探和开发的影响[J].天然气地球科学,2011,22(3):525-532.

LONG Pengyu,ZHANG Jinchuan,TANG Xuan,et al.Feature of muddy shale fissure and its effect for shale gas exploration and development[J].Natural Gas Geoscience,2011,22(3):525-532.

[20] 朱亮亮.页岩含气量实验方法与评价技术[D].北京:中国地质大学(北京),2013:26-37.

ZHU Lliangliang.The research in labototial methodologies and analytical assessment to shale gas content[D].Beijing:China University of Geosciences(Beijing),2013:26-37.

[21] 魏强,晏波,肖贤明.页岩气解吸方法研究进展[J].天然气地球科学,2015,26(9):1657-1665.

WEI Qiang,YAN Bo,XIAO Xianming.Research progress on the desorption methods of shale gas[J].Natural Gas Geoscience,2015,26(9):1657-1665.

[22] 戴金星,宋岩,程坤芳,等.中国含油气盆地有机烷烃气碳同位素特征[J].石油学报,1993,14(2):23-31.

DAI Jinxing,SONG Yan,CHENG Kunfang,et al.Characteristics of carbons topes of organic alkane gases in petroliferous basins of China[J].Acta Petrolei Sinica,1993,14(2):23-31.

[23] 陈安定.氮气对于海相地层油气保存的指示作用[J].石油实验地质,2005,27(1):85-89.

CHEN Anding.Nitrogen as an index of oil-gas preservation conditions in marine strata[J].Petroleum Geology & Experiment,2005,27(1):85-89.

[24] 朱炎铭,陈尚斌,方俊华,等.四川地区志留系页岩气成藏的地质背景[J].煤炭学报,2010,35(7):1160-1164.

ZHU Yanming,CHEN Shangbin,FANG Junhua,et al.The geologic background of the Siluric shale-gas reservoiring in Szechwan,China[J].Journal of China Coal Society,2010,35(7):1160-1164.

[25] 邹才能,董大忠,王社教,等.中国页岩气形成机理、地质特征及资源潜力[J].石油勘探与开发,2010,37(6):641-653.

ZOU Caineng,DONG Dazhong,WANG Shejiao,et al.Geological characteristics,formation mechanism and resource potential of shale gas in China[J].Petroleum Exploration and Development,2010,37(6):641-653.

[26] 王鹏万,李昌,张磊,等.五峰组—龙马溪组储层特征及甜点层段评价——以昭通页岩气示范区A 井为例[J].煤炭学报,2017,42(11):2925-2935.

WANG Pengwan,LI Chang,ZHANG Lei,et al.Characteristic of the shale gas reservoirs and evaluation of sweet spotin Wufeng-Longmaxi Formation:A case from the A well in Zhaotong shale gas demonsration zone[J].Journal of China Coal Society,2017,42(11):2925-2935.

[27] LUO Qingyong,ZHONG Ningning,DAI Na,et al.Graptolite-derived organic matter in the Wufeng-Longmaxi Formationg(Upper Ordovician-Lower Silurian)of southeastern Chongqing,China:Implications for gas shale evaluation[J].International Journal of Coal Geology,2016,153:87-98.

[28] 朱炎铭,张寒,亢韦,等.中上扬子地区龙马溪组,筇竹寺组页岩有机质微孔缝特征:生物发育与孔隙网络[J].天然气地球科学,2015,26(8):1507-1515.

ZHU Yanming,ZHANG Han,KANG Wei,et al.Organic nanopores of Longmaxi and Qiongzhusi Formations in the Upper Yangtze:Biological precursor and pore network[J].Nature Gas Geoscience,2015,26(8):1507-1515.

[29] 邓昆,周文,周立发,等.鄂尔多斯盆地奥陶系平凉组笔石页岩微孔隙特征及其影响因素[J].石油勘探与开发,2016,43(3):378-385.

DENG Kun,ZHOU Wen,ZHOU Lifa,et al.Influencing factors of micropores in the graptolite shale of Ordovician Pingliang Formation in Ordos Basin,China[J].Petroleum Exploration and Development,2016,43(3):378-385.

[30] HOU Peng,JU Yang,GAO Feng,et al.Simulation and visualization of the displacement between CO2 and formation fluids at pore-scale levels and its application to the recovery of shale gas[J].International Journal of Coal Science & Technology,2016,3(4):351-369.

[31] 焦伟伟,汪生秀,程礼军,等.渝东南地区下寒武统页岩气高氮低烃成因[J].天然气地球科学,2017,28(12):1882-1890.

JIAO Weiwei,WANG Shengxiu,CHENG Lijun,et al.The reason of high nitrogen content and low hydrocarbon content of shale gas from the Lower Cambrian Niutitang Formation in southeast Chongqing[J].Natural Gas Geoscience,2017,28(12):1882-1890.

[32] 梁峰,朱炎铭,马超,等.湘西北地区牛蹄塘组页岩气储层沉积展布及储集特征[J].煤炭学报,2015,40(12):2884-2892.

LIANG Feng,ZHU Yanming,MA Chao,et al.Sedimentary distribution and reservoir characteristics of shale gas reservoir of Niutitang Formation in Northwestern Hunan[J].Journal of China Coal Society,2015,40(12):2884-2892.

[33] 陈尚斌,朱炎铭,王红岩,等.川南龙马溪组页岩气储层纳米孔隙结构特征及其成藏意义[J].煤炭学报,2012,37(3):438-444.

CHEN Shangbin,ZHU Yanming,WANG Hongyan,et al.Structure characteristics and accumulation significance of nanopores in Longmaxi shale gas reservoir in the southern Sichuan Basin[J].Journal of China Coal Society,2012,37(3):438-444.

[34] 王哲,李贤庆,周宝刚,等.川南地区下古生界页岩气储层微观孔隙结构表征及其对含气性的影响[J].煤炭学报,2016,41(9):2287-2297.

WANG Zhe,LI Xianqing,ZHOU Baogang,et al.Characterization of microscopic pore structure and its influence on gas content of shale gas reservoirs from the Lower Paleozoic in southern Sichuan Basin[J].Journal of China Coal Society,2016,41(9):2287-2297.

[35] MA Yong,ZHONG Ningning,CHENG Lijun,et al.Pore structure of the graptolite-derived OM in the Longmaxi shale,southeastern upper Yangtze region,China[J].Marine and Petroleum Geology,2016,72,1-11.

Key control factor for the gas-bearing properties difference of lower Paleozoic shale in southeast Chongqing

JIAO Weiwei1,2,3,FANG Guangjian1,2,3,WANG Shengxiu1,2,3,ZHANG Zhiping1,2,3,YU Chuan1,2,3

(1.National and Local Joint Engineering Research Center of Shale Gas Exploration and Development,Chongqing Institute of Geology and Mineral Resources,Chongqing 401120,China; 2.Key Laboratory of Shale Gas Exploration,Ministry of Land and Resources,Chongqing Institute of Geology and Mineral Resources,Chongqing 401120,China; 3.Chongqing Shale Gas Research Center of State Key Laboratory of Petroleum Resource and Prospecting,Chongqing 401120,China)

Abstract:Southeast Chongqing is close to Fuling shale gasfield.Niutitang Formation and Wufeng- Longmaxi Formation are its two major explorative formations.Compared with Jiaoshiba area,the two formations experienced stronger reformation and had higher thermal maturity,and their explorative results differed obviously,which was caused by tectonic movement.The two formations in Southeast Chongqing have same material resource,but the gas-bearing properties has significant difference.Based on field desorption and isothermal adsorption experiment,according to the comparative study of static and dynamic indexes,the key control factors were discovered.Adsorption capacity of Niutitang Formation was stronger,but its gas-bearing properties was poor that shown the characteristics of low hydrocarbon content and high nitrogen content.Adsorption capacity of Wufeng-Silurian Longmaxi Formation was weaker,but its gas-bearing properties was better than Niutitang Formation.There were several wells whose desorbed gas content reached industrial limit,and its gas composition was mainly hydrocarbon.It was proved that the organic pore structure and floor sealing ability of organic-rich shale were the main control factors for the gas-bearing properties difference of the two shale formations from the Lower Paleozoic in Southeast Chongqing.Organic pores of Niutitang Formation are underdeveloped,resulting in poor reservoir properties,and the unconformity of the bottom is accompanied by fluid activities,resulting in the destruction of gas reservoirs,which is the key to poor gas-bearing properties.Organic pores like honeycomb of Wufeng-Silurian Longmaxi Formation have greatly increased the space of shale gas accumulation,and the sealing of the above and under formation is better,which provides better accumulation conditions for shale gas.Then two typical models of shale gas accumulation for the Lower Paleozoic in the southeastern Chongqing were established including accumulation-preservation model and washing-destruction model.In view of the differences in the key gas-controlling factors of the two formations,it is suggested that the optimal indicators of favorable area should be further researched for Niutitang Formation,and the selection belt method for Wufeng-Silurian Longmaxi Formation should be further researched.

Key words:southeast Chongqing;organic-rich shale;gas-bearing properties;pore structure;sealing ability

中图分类号:P618.13

文献标志码:A

文章编号:0253-9993(2019)06-1786-09

移动阅读

焦伟伟,方光建,汪生秀,等.渝东南地区下古生界页岩含气性差异关键控制因素[J].煤炭学报,2019,44(6):1786-1794.doi:10.13225/j.cnki.jccs.2018.0944

JIAO Weiwei,FANG Guangjian,WANG Shengxiu,et al.Key control factor for the gas-bearing properties difference of lower Paleozoic shale in southeast Chongqing[J].Journal of China Coal Society,2019,44(6):1786-1794.doi:10.13225/j.cnki.jccs.2018.0944

收稿日期:2018-07-16

修回日期:2018-12-14

责任编辑:韩晋平

基金项目:重庆市重点产业共性关键技术创新专项基金资助项目(cstc2016zdcy-zd90001);重庆市科研院所绩效激励引导专项基金资助项目(cstc2017jxjl90009);国家科技重大专项资助项目(2016ZX05034003-001)

作者简介:焦伟伟(1981—),女,河北承德人,正高级工程师,博士。Tel:023-81925886,E-mail:jiaoweiw-210@163.com