Relationship between sandstone reservoirs densification and hydrocarbon charging in the Paleogene Huagang Formation of Xihu Depression, East China Sea Basin
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摘要: 东海盆地西湖凹陷致密砂岩气资源丰富,近年来古近系花港组成为勘探热点层位,但储层的致密化及与油气充注关系不明制约着花港组致密砂岩气的有效勘探和经济开发。在花港组储层特征的基础上,划分及厘定储层成岩作用类型与演化序列,恢复并揭示储层致密化过程及与油气充注的匹配关系。研究表明,西湖凹陷花港组储层砂岩主要经历压实、胶结和溶蚀3种成岩作用,压实作用是导致花港组储层孔隙损失和致密化的根本原因;并经历同生阶段、早成岩阶段(A、B期)和中成岩阶段(A、B期)共3阶段5期次的成岩演化过程;在中成岩阶段A2期时成岩环境开始由酸性向碱性发生转变,并伴随着晚期碳酸盐、硅质等胶结作用发育以及机械压实作用持续增强,储层逐渐趋于致密化;结合与油气主成藏期(7~0 Ma)的耦合关系将研究区花港组储层划分为3种类型:成藏未致密型储层、成藏同步致密型储层、成藏已致密型储层。研究梳理了西湖凹陷花港组储层特征、成岩演化序列、储层致密化及与油气充注的耦合关系,为下一步研究区致密砂岩气的勘探提供理论支持。Abstract: The tight sandstone gas resources in Xihu Depression of the East China Sea Basin are abundant. In recent years, the Paleogene Huagang Formation is a hot spot for exploration. However, the unclear densification of the reservoir and the matching relationship with the oil and gas charge restrict the effective exploration and economic development of the tight sandstone gas of the Huagang Formation. This study reveals the reservoir densification process and its relationship with hydrocarbon charging based on the analysis of sandstone reservoir characteristics, the classification and evolution of diagenesis type and evolution sequence.The study shows that the reservoir sandstone mainly undergoes three diagenesis processes: compaction, cementation and dissolution. Compaction is the root cause of sandstone pore loss and densification in the Huagang Formation reservoir during burial diagenesis. The formation experienced a total of three stages and five periods of diagenetic evolution, including the syngenetic stage, the early diagenetic stage (A, B period) and the middle diagenetic stage (A, B period). At the A2 period of the middle diagenetic stage, the diagenetic environment began to change from acidic to alkaline, accompanied by cementation of late carbonate and siliceous. When the strength of mechanical compaction continued to increase, the reservoir gradually became denser. Combined with the coupling relationship between oil and gas accumulation period (7-0 Ma), the Huagang Formation reservoirs in the study area are divided into three types: accumulated reservoir, synchronous dense reservoir, accumulated dense reservoir. The study combs the reservoir characteristics, diagenetic evolution sequence, reservoir densification and coupling relationship with hydrocarbon charging in the Huagang Formation of Xihu Depression, providing theoretical support for the exploration of tight sandstone gas in the next study area.
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图 2 西湖凹陷花港组储层砂岩压实作用特征
a.云母弯曲变形, 保留少量原生粒间孔, 线-凹凸接触, MN5井, 4 036 m,(-);b.变质岩屑塑性变形,保留少量原生粒间孔, 线-凹凸接, WS1井, 5 106.2 m, (-);c.云母弯曲变形呈定向排列, 泥岩岩屑呈假杂基充填粒间孔, MS1井, 3 728 m, (-);d.石英压裂缝,线接触,4 337.9 m, WS1井, (-);e.石英颗粒间压溶呈缝合线接触, MS1井, 3 931.7 m, (-);f.碎屑颗粒压实紧密呈线接触, MS1井, 3 931.1 m, (-)
Figure 2. Sandstone compaction characteristics of Huagang Formation reservoir in Xihu Depression
图 3 西湖凹陷花港组储层砂岩胶结作用特征
a.早期无铁方解石(亮黄色)基底式胶结,WS1井,4 325.5 m;b.晚期铁方解石和铁白云石充填细小残余粒间孔,WS1井, 5 114.7 m,(-);c.粒间孔或溶蚀孔中充填自生高岭石,并且富含高岭石晶间孔,MN5井,3 126.5 m,(-);d.书页状自生高岭石充填长石溶蚀孔,MN5井,3 122 m;e.石英加大边发育,MS4井,3 719.32 m,(+);f.粒间溶蚀扩大孔隙被锥状自生石英晶体充填,WS1井,4 324.2 m
Figure 3. Sandstone cementation characteristics of Huagang Formation reservoir in Xihu Depression
图 4 西湖凹陷花港组储层砂岩酸性溶蚀作用特征
a.长石溶蚀形成粒内孔和铸模孔,MS2井,3 308.3 m,(-);b.长石溶蚀形成铸模孔,WS6井,3 995.78 m;c.粒间溶蚀孔,MN5井,2 725 m,(-);d.火成岩岩屑溶蚀形成粒内溶孔,WS6,3 995.78 m;e.长石沿解理缝溶蚀,MN1井,3 857 m,(-);f.长石溶孔充填鳞片状自生高岭石,MN5井,3 200 m,(-)
Figure 4. Acidic dissolution characteristics of Huagang Formation reservoir sandstone in Xihu Depression
图 7 中央反转带中北部(a)、中央反转带中南部(b)、春晓-天外天构造带(c)和西次凹(d)花港组成岩-孔隙演化与油气充注耦合关系模式图
Figure 7. Schematic diagram of the coupling relationship between diagenetic-pore evolution and hydrocarbon charging of Huagang Formation in the north central part (a) and the south central part (b) of the central inversion belt, the Chunxiao-Tianwaitian structural belt (c) and the west sub-depression (d)
表 1 西湖凹陷部分钻井花港组储层砂岩的黏土矿物相对质量分数检测数据
Table 1. Clay mineral content detection data in Huagang Formation reservoirs of some wells in Xihu Depression
构造带 井号 井深/m 层位 黏土矿物相对质量分数/% K C 伊/蒙混层中S所占比例 I I/S 中央反转带中南部 MS8 2 888.29 H 37.76 18.18 15 30.04 14.02 2 888.98 H 51.58 22.74 15 13.37 12.31 2 889.38 H 58.09 25.05 15 10.46 6.40 2 889.50 H 28.21 34.01 15 32.33 5.45 MS5 3 563.50 H 7.96 7.42 25 73.11 11.50 3 537.50 H 51.16 9.81 20 14.81 24.22 3 418.00 H 45.74 6.99 23 19.59 27.68 3 462.50 H 28.08 14.28 25 31.89 25.75 3 325.00 H 47.59 13.86 22 16.70 21.84 3 325.50 H 42.56 9.26 22 21.29 26.90 3 323.50 H 12.70 13.91 25 31.05 42.34 3 313.00 H 15.48 14.14 22 38.29 32.09 3 312.50 H 10.09 9.98 22 38.61 41.32 中央反转带中北部 MN7 3 121.00 H1 47 17 20 7 29 3 223.00 H2 7 27 20 14 52 3 627.00 H3 9 47 15 22 22 3 819.70 H4 4 25 20 48 23 MN1 3 188.00 H1 25 16 25 15 44 3 581.00 H2 10 52 25 10 28 3 627.00 H3 6 40 15 27 27 3 791.00 H3 10 82 10 4 4 3 941.00 H4 6 37 15 20 37 西次凹 WS6 3 703.00 H5 46 20 20 14 20 3 737.00 H5 41 23 20 17 19 3 773.00 H5 56 25 20 7 12 3 792.00 H5 52 12 20 13 23 注:K.高岭石;C.绿泥石;I.伊利石;I/S.伊/蒙混层; S.蒙皂石;H.花港组;H1~H5.花港组第1~5小层 表 2 西湖凹陷花港组储层砂岩次生孔隙演化定量恢复计算结果
Table 2. Quantitative restoration calculation results of secondary porosity evolution of Huagang Formation reservoir sandstone in Xihu Depression
构造带 井号 φ1/% φ2/% φ3/% 压实减孔率/% 胶结减孔率/% 样品数量 西次凹 WS1 36.69 7.87 2.59 78.64 14.29 7 WS2 38.89 3.58 1.97 90.80 4.16 23 WS3 35.68 3.82 2.43 89.32 3.91 10 WS8 35.89 6.49 1.75 81.92 13.20 31 WS10 36.53 4.90 2.36 86.56 6.98 85 WS6 35.06 4.30 1.77 87.62 7.27 63 平均值 36.23 4.86 2.07 86.53 7.75 中央反转带中北部 MN5 32.94 11.66 3.08 86.12 8.17 12 MN1 33.09 8.15 3.00 86.53 7.75 16 MN3 30.09 3.63 1.57 87.98 8.61 33 MN4 37.36 4.38 1.88 88.00 7.60 48 MN7 36.08 5.26 2.87 85.26 6.69 104 MN9 37.24 7.96 4.13 78.62 10.29 6 平均值 34.79 5.48 2.36 83.60 9.54 中央反转带中南部 MS4 37.38 4.99 1.21 86.64 10.12 25 MS1 37.53 6.78 2.72 81.94 10.81 30 MS3 37.77 6.40 0.54 83.05 15.53 7 MS5 34.00 9.81 2.18 71.13 22.46 11 MS6 34.01 18.90 11.66 43.92 21.56 9 平均值 36.91 7.94 2.98 77.85 13.75 春晓-天外天 S1 32.83 12.67 4.98 61.41 23.41 7 S2 32.83 9.13 4.51 72.19 14.08 14 S5 32.83 7.20 2.49 78.06 14.37 6 平均值 32.83 9.62 4.18 70.70 16.56 注:φ1.原始孔隙度;φ2.受压实作用后孔隙度;φ3.胶结交代作用后孔隙度 表 3 西湖凹陷花港组油气充注期次与含烃包裹体赋存矿物关系
Table 3. Relationship between hydrocarbon filling period and authigenic mineral reserved hydrocarbon bearing inclusions of Huagang Formation in Xihu Depression
油气充注期次 第1期 第2期 第3期 赋存矿物类型 Ⅰ期方解石胶结物 Ⅰ期、Ⅱ期、Ⅲ期石英次生加大边 Ⅱ期方解石胶结物 含烃包裹体丰度 GOI小于1% GOI为1%~3% GOI为3%~4%,局部约为40% 包裹体岩相学特征
黄灰色含烃盐水包裹体于方解石胶结物内成群分布(MN-1井,3 752.2 m,H3)
褐色液烃及黄灰色含烃盐水包裹体沿石英加大边呈带状分布(MN-1井,3 695.0 m,H3)
褐色液烃及深灰色气烃包裹体于方解石胶结物内成群分布(MN-1井,3 739 m,H3)均一温度区间/℃ 96~105 118~150 135~155 油气充注时间/Ma 19~17 17~9 7~0 油气充注期次划分 注:GOI.含油流体包裹体丰度;O1D.东海群;N2s.三潭组;N13l.柳浪组;N12y.玉泉组;E3h.花港组;H1~H5.花港组第1~5小层 -
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