鄂尔多斯盆地东缘康宁地区二叠系致密储层成岩作用与孔隙度演化
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摘要
鄂尔多斯盆地东缘康宁地区具有广阔的天然气勘探前景,是我国致密气勘探开发的重点区域之一。为研究其储层成岩作用及致密化机理,开展了铸体薄片鉴定、扫描电镜分析、X射线衍射测试、粒度分析等研究,对二叠系致密储层的岩石成分、孔隙类型和成岩演化等进行了深入探讨。结果表明:①岩石类型以细—中粒长石岩屑砂岩和岩屑砂岩为主,石英体积分数平均49%,岩屑体积分数平均36%,长石体积分数平均15%;②储层物性以低孔-特低渗型为主,平均孔隙度为7%,平均渗透率为0.46 mD,为典型致密储层;孔径小,喉道细,分选差,以次生溶蚀孔隙为主;③二叠系砂岩经历了压实作用、胶结作用、溶蚀-交代作用,成岩阶段为中成岩A—B期。④压实作用是导致储层致密的主要因素,使得初始孔隙度减少了16.39%,碳酸盐胶结作用和黏土矿物的充填作用次之,使孔隙度减少了约12.30%,后期溶蚀作用使孔隙度增加了6.01%,这一结论与现今实测平均孔隙度平均值7.46%较为吻合。上述研究成果对研究区致密气藏勘探中寻找次生溶蚀"甜点"具有一定的参考价值。
Giant natural gas potential exists in Kangning area in the eastern margin of Ordos Basin which is one of the tight sands gas targets in China. To investigate the diagenesis characteristics and genesis of densification,based on the data of thin sections,scanning electron microscope(SEM),X-ray diffraction,particle size analysis,the rock composition,pore type and diagenesis-porosity evolution process of Permian reservoirs were analyzed.The results show that reservoirs are dominated by fine-medium feldspathic lithic sandstone and lithic sandstone.The average content of quartz is 49%. Rock fragment and feldspar content is in average values of 36% and 15%respectively. The reservoirs are typical low porosity and extra-low permeability tight sandstone,with an average porosity of 7% and an average permeability of 0.46 m D. The pore diameter is small with fine throat and poor sorting. Additionally,secondary dissolved pore dominates the main pore system. The Permian sandstone reservoirs have experienced compaction,cementation and dissolution-replacement,which are divided into middle A-B diagenetic stage. Compaction is the key to cause the formation of tight reservoirs,resulting in a porosity loss of16.39%. Second leading factor is carbonate cementation and clay mineral filling,which reduces porosity by12.30%,whereas later dissolution increases porosity by 6.01%. The calculated porosity is almost equivalent to the measured average porosity of 7.46%. The above research results have a certain reference value for searching for secondary dissolution sweet spot in exploration of tight gas reservoirs in the study area.
Giant natural gas potential exists in Kangning area in the eastern margin of Ordos Basin which is one of the tight sands gas targets in China. To investigate the diagenesis characteristics and genesis of densification,based on the data of thin sections,scanning electron microscope(SEM),X-ray diffraction,particle size analysis,the rock composition,pore type and diagenesis-porosity evolution process of Permian reservoirs were analyzed.The results show that reservoirs are dominated by fine-medium feldspathic lithic sandstone and lithic sandstone.The average content of quartz is 49%. Rock fragment and feldspar content is in average values of 36% and 15%respectively. The reservoirs are typical low porosity and extra-low permeability tight sandstone,with an average porosity of 7% and an average permeability of 0.46 m D. The pore diameter is small with fine throat and poor sorting. Additionally,secondary dissolved pore dominates the main pore system. The Permian sandstone reservoirs have experienced compaction,cementation and dissolution-replacement,which are divided into middle A-B diagenetic stage. Compaction is the key to cause the formation of tight reservoirs,resulting in a porosity loss of16.39%. Second leading factor is carbonate cementation and clay mineral filling,which reduces porosity by12.30%,whereas later dissolution increases porosity by 6.01%. The calculated porosity is almost equivalent to the measured average porosity of 7.46%. The above research results have a certain reference value for searching for secondary dissolution sweet spot in exploration of tight gas reservoirs in the study area.
引文
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[9]郝杰,周立发,袁义东,等.断陷湖盆致密砂砾岩储层成岩作用及其对孔隙演化的影响.石油实验地质,2018,40(5):635.HAO J,ZHOU L F,YUAN Y D,et al. Diagenetic characteristics and their control on porosity of sandy conglomerate reservoirs in faulted basins. Petroleum Geology&Experiment,2018,40(5):635.
[10]汪洋,李树同,牟炜卫,等.姬塬西部地区长81致密储层特征及孔隙度演化分析.岩性油气藏,2016,28(4):62-63.WANG Y,LI S T,MOU W W,et al. Tight reservoir characteristics and porosity evolution of Chang 81in western Jiyuan area.Lithologic Reservoirs,2016,28(4):62-63.
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[12]冯旭,刘洛夫,李朝玮,等.碎屑岩孔隙演化定量计算方法的改进和应用.石油与天然气地质,2017,38(6):1199.FENG X,LIU L F,LI C W,et al. Improvement and application of quantitative calculation of porosity evolution of clastic rock.Oil&Gas Geology,2017,38(6):1199.
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[14] DOWEY P J,HODGSON D M,WORDEN R H. Pre-requisites,processes,and prediction of chlorite grain coatings in petroleum reservoirs:a review of subsurface example. Marine and Petroleum Geology,2012,32(1):73.
[15]吴陈冰洁,朱筱敏,魏巍,等.查干凹陷下白垩统巴二段储层特征及孔隙演化.岩性油气藏,2017,29(1):75.WU-CHEN B J,ZHU X M,WEI W,et al. Reservoir characteristics and pore evolution of the second member of the Lower Cretaceous Bayingebi Formation in Chagan Depression. Lithologic Reservoirs,2017,29(1):75.
[16]范萌萌,李文厚,袁珍.鄂尔多斯盆地东南部长6成岩作用及其对孔隙的影响.地质通报,2016,35(2/3):449.FAN M M,LI W H,YUAN Z. Diagenesis and its influence on porosity of Chang 6 reservoir in southeast Ordos Basin. Geological Bulletin of China,2016,35(2/3):449.
[17]刘再振,刘玉明,李洋冰,等.鄂尔多斯盆地神府地区太原组致密砂岩储层特征及成岩演化.岩性油气藏,2017,29(6):55.LIU Z Z,LIU Y M,LI Y B,et al. Tight sandstone reservoir characteristics and diagenesis evolution of Taiyuan Formation in Shenmu-Fugu area,Ordos Basin. Lithologic Reservoirs,2017,29(6):55.
[18]任战利,于强,崔军平,等.鄂尔多斯盆地热演化史及其对油气的控制作用.地学前缘,2017,24(3):138-139.REN Z L,YU Q,CUI J P,et al. Thermal history and its controls on oil and gas of the Orods Basin. Earth Science Frontiers,2017,24(3):138-139.
[19]赵孟为.磷灰石裂变径迹分析在恢复盆地沉降抬升史中的应用:以鄂尔多斯盆地为例.地球物理学报,1996,39(增刊1):241-242.ZHAO M W. The application of apatite fission track analysis to the reconstruction of the subsidence and uplift history of sedimentary basins:a case study from the Ordos Basin. Acta Geophysica Sinica,1996,39(Suppl 1):241-242.
[20]于强.鄂尔多斯盆地中东部地区古生界热演化史与天然气成藏.西安:西北大学,2012.YU Q. The Paleozoic thermal evolution history and natural gas accumulation of the central and eastern parts of Ordos Basin.Xi'an:Northwestern University,2012.
[21] BEARD D C,WEYL P K. Influence of texture on porosity and permeability of unconsolidated sand. AAPG Bulletin,1973,57(2):352.
[22] SCLATER J G,CHRISTIE P A F. Continental stretching:an exploration of the post-mid-Cretaceous subsidence of the central North Sea Basin. Journal of Geophysical Research,1980,85(B7):3732.
[2]魏新善,胡爱平,赵会涛,等.致密砂岩气地质认识新进展.岩性油气藏,2017,29(1):12.WEI X S,HU A P,ZHAO H T,et al. New geological understanding of tight sandstone gas. Lithologic Reservoirs,2017,29(1):12.
[3]傅宁,杨树春,贺清,等.鄂尔多斯盆地东缘临兴—神府区块致密砂岩气高效成藏条件.石油学报,2016,37(增刊1):111.FU N,YANG S C,HE Q,et al. High-efficiency reservoir formation conditions of tight sandstone gas in Linxing-Shenfu blocks on the east margin of Ordos Basin. Acta Petrolei Sinica,2016,37(Suppl 1):111.
[4]赵达,许浩,汤达祯,等.临兴地区下石盒子组致密砂岩储层成岩作用及有利成岩相研究.科技通报,2016,32(7):31.ZHAO D,XU H,TANG D Z,et al. Diagenesis and favorable diageneticfacies analysis on the tight sand stone reservoirs of the Lower Shihezi Formation in Linxing area. Bulletin of Science and Technology,2016,32(7):31.
[5] ATHY L F. Density,porosity and compaction of sedimentary rocks. AAPG Bulletin,1930,14(1):13.
[6] MAXWELL J C. Influence of depth,temperature and geologic age on porosity of quartz sandstone. AAPG Bulletin,1964,48(5):707.
[7] SCHERER M. Parameters influencing porosity in sandstones:a model for sandstone porosity prediction. AAPG Bulletin,1987,71(5):486.
[8]王瑞飞,陈明强.储层沉积-成岩过程中孔隙度参数演化的定量分析:以鄂尔多斯盆地沿25区块、庄40区块为例.地质学报,2007,81(10):1435.WANG R F,CHEN M Q. Quantitative analysis of porosity evolution during the reservoir sedimentation-diagenesis:Taking the Yan 25 and Zhuang 40 areas in the Ordos Basin as examples.Acta Geologica Sinica,2007,81(10):1435.
[9]郝杰,周立发,袁义东,等.断陷湖盆致密砂砾岩储层成岩作用及其对孔隙演化的影响.石油实验地质,2018,40(5):635.HAO J,ZHOU L F,YUAN Y D,et al. Diagenetic characteristics and their control on porosity of sandy conglomerate reservoirs in faulted basins. Petroleum Geology&Experiment,2018,40(5):635.
[10]汪洋,李树同,牟炜卫,等.姬塬西部地区长81致密储层特征及孔隙度演化分析.岩性油气藏,2016,28(4):62-63.WANG Y,LI S T,MOU W W,et al. Tight reservoir characteristics and porosity evolution of Chang 81in western Jiyuan area.Lithologic Reservoirs,2016,28(4):62-63.
[11] ZOU C N,ZHU R K,LIU K Y,et al. Tight gas sandstone reservoirs in China:Characteristics and recognition criteria. Journal of Petroleum Science and Engineering,2012,83:82-89.
[12]冯旭,刘洛夫,李朝玮,等.碎屑岩孔隙演化定量计算方法的改进和应用.石油与天然气地质,2017,38(6):1199.FENG X,LIU L F,LI C W,et al. Improvement and application of quantitative calculation of porosity evolution of clastic rock.Oil&Gas Geology,2017,38(6):1199.
[13]武文慧.鄂尔多斯盆地上古生界储层砂岩特征及成岩作用研究.成都:成都理工大学,2011.WU W H. Research on the characteristics and diagenesis of sandstone in the Upper Paleozoic reservoir in Ordos Basin.Chengdu:Chengdu University of Technology,2011.
[14] DOWEY P J,HODGSON D M,WORDEN R H. Pre-requisites,processes,and prediction of chlorite grain coatings in petroleum reservoirs:a review of subsurface example. Marine and Petroleum Geology,2012,32(1):73.
[15]吴陈冰洁,朱筱敏,魏巍,等.查干凹陷下白垩统巴二段储层特征及孔隙演化.岩性油气藏,2017,29(1):75.WU-CHEN B J,ZHU X M,WEI W,et al. Reservoir characteristics and pore evolution of the second member of the Lower Cretaceous Bayingebi Formation in Chagan Depression. Lithologic Reservoirs,2017,29(1):75.
[16]范萌萌,李文厚,袁珍.鄂尔多斯盆地东南部长6成岩作用及其对孔隙的影响.地质通报,2016,35(2/3):449.FAN M M,LI W H,YUAN Z. Diagenesis and its influence on porosity of Chang 6 reservoir in southeast Ordos Basin. Geological Bulletin of China,2016,35(2/3):449.
[17]刘再振,刘玉明,李洋冰,等.鄂尔多斯盆地神府地区太原组致密砂岩储层特征及成岩演化.岩性油气藏,2017,29(6):55.LIU Z Z,LIU Y M,LI Y B,et al. Tight sandstone reservoir characteristics and diagenesis evolution of Taiyuan Formation in Shenmu-Fugu area,Ordos Basin. Lithologic Reservoirs,2017,29(6):55.
[18]任战利,于强,崔军平,等.鄂尔多斯盆地热演化史及其对油气的控制作用.地学前缘,2017,24(3):138-139.REN Z L,YU Q,CUI J P,et al. Thermal history and its controls on oil and gas of the Orods Basin. Earth Science Frontiers,2017,24(3):138-139.
[19]赵孟为.磷灰石裂变径迹分析在恢复盆地沉降抬升史中的应用:以鄂尔多斯盆地为例.地球物理学报,1996,39(增刊1):241-242.ZHAO M W. The application of apatite fission track analysis to the reconstruction of the subsidence and uplift history of sedimentary basins:a case study from the Ordos Basin. Acta Geophysica Sinica,1996,39(Suppl 1):241-242.
[20]于强.鄂尔多斯盆地中东部地区古生界热演化史与天然气成藏.西安:西北大学,2012.YU Q. The Paleozoic thermal evolution history and natural gas accumulation of the central and eastern parts of Ordos Basin.Xi'an:Northwestern University,2012.
[21] BEARD D C,WEYL P K. Influence of texture on porosity and permeability of unconsolidated sand. AAPG Bulletin,1973,57(2):352.
[22] SCLATER J G,CHRISTIE P A F. Continental stretching:an exploration of the post-mid-Cretaceous subsidence of the central North Sea Basin. Journal of Geophysical Research,1980,85(B7):3732.