摘要
沁水盆地南部煤岩储层天然裂缝普遍发育,天然裂缝有效性是决定煤岩储层渗流能力、影响煤层气井能否高产的重要因素。综合利用野外露头、岩心和扫描电镜等资料,在分析沁水盆地南部上古生界煤岩储层天然裂缝类型和发育特征的基础上,对裂缝有效性及其主控因素开展研究,并结合单井生产动态资料,探讨了裂缝有效性对煤层气开发的影响。结果表明:沁水盆地南部煤岩储层主要发育割理和构造裂缝,其中割理包括面割理和端割理,构造裂缝包括剪切裂缝和张性裂缝。受多种地质因素影响,不同类型裂缝的有效性存在明显差异。割理形成于煤化作用阶段,多被方解石和粘土矿物等全充填或半充填,整体上其裂缝有效性较差。构造裂缝多未被矿物充填,其有效性主要受控于裂缝规模、倾角、储层埋深及与现今地应力最大主应力方向夹角。构造裂缝开度大、延伸较远,裂缝有效性好;高角度构造裂缝有效性好于斜交缝;受地应力状态变化影响,随储层埋深的增加,裂缝有效性依次表现为较差、较好、较差;NE-SW向裂缝有效性最好,其次为近EW向和近NS向裂缝,NW-SE向裂缝有效性最差。相比于割理,构造裂缝在规模和裂缝有效性方面均好于前者,可作为煤层主要的渗流和产出通道,对煤层气的开发具有明显积极作用。然而,过大规模尺度的构造裂缝,尤其当构造裂缝穿过煤层在顶底板发育时,不仅会造成煤岩储层内煤层气散失和储层压力降低,同时还将导致外来地层水对煤层的补充,不利于煤层气的保存和有效开采。
Natural fractures were well developed in coalbed mathane(CBM)reservoirs in the southern Qinshui Basin,and their effectiveness is an important factor affecting the seepage ability of CBM reservoirs and the high production of CBM wells.In this study,the types and development characteristics of natural fractures in the Upper Paleozoic CBM re-servoirs,southern Qinshui Basin,are investigated by using outcrop,core and scanning electron microscopy(SEM)data.Then,the fracture effectiveness and its main controlling factors are analyzed.Finally,the influence of effective fractures on CBM development is discussed in combination with single-well dynamic production performance.The results show that cleats and tectonic fractures were mainly developed in the study area.The cleats include face and butt cleats,and the tectonic fractures include shear and tension fractures.There are marked differences in the fracture effectiveness of various types under the influence of multiple geological factors.The cleats were formed at the stage of coalification and mostly filled or semi-filled by calcites and clay minerals,resulting in poor effectiveness of fractures.Most tectonic fractures were not filled with minerals,and their effectiveness is mainly controlled by fracture size,dip angle,reservoir depth and their included angle with the direction of the in-situ maximum principal stress at present.The tectonic fractures feature large aperture,longer propagation and good fracture effectiveness.High-angle tectonic fractures are more effective than oblique fractures.Affected by the change of in-situ stress state,the fracture effectiveness varies systematically with the increasing burial depth,i.e.,from fair to good and then fair again.The NE-SW-trending fractures are the most effective,followed by nearly EW-trending and nearly NS-trending fractures,and the NW-SE-trending fractures coming at last.The tectonic fractures,better in terms of both scale and fracture effectiveness compared with the cleats,are the main seepage and production channels of coalbeds,and play a positive role in the CBM development.However,over-sized tectonic fractures,especially when cutting through the coal seam and extending into the roof and floor,will result in the loss of CBM,the decrease of reservoir pressure,and the incursion of external formation water.Therefore,it is not conducive to the preservation and effective exploitation of CBM.
作者
史今雄
曾联波
谭青松
王继鹏
张云钊
李宏为
Shi Jinxiong;Zeng Lianbo;Tan Qingsong;Wang Jipeng;Zhang Yunzhao;Li Hongwei(State Key Laboratory of Petroleum Resources and Prospecting,China University of Petroleum(Beijing),Beijing 102249,China;College of Geosciences,China University of Petroleum(Beijing),Beijing 102249,China;Huabei Oilfield Branch Company Ltd.,PetroChina,Renqiu,Hebei 062552,China;Changqing Oilfield Branch Company Ltd.,PetroChina,Xi’an,Shaanxi 710018,China)
出处
《石油与天然气地质》
EI
CAS
CSCD
北大核心
2020年第3期617-626,共10页
Oil & Gas Geology
关键词
天然裂缝
有效性
煤岩储层
煤层气开发
上古生界
沁水盆地
natural fracture
effectiveness
CBM reservoir
CBM development
Upper Paleozoic
Qinshui Basin