Structural diagenesis and reservoir control analysis of tight sandstone in the strike-slip fault zones of the Chang 8 to Chang 6 Members in the Jinghe Oilfield
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摘要:
泾河油田长8-长6段致密砂岩“甜点”储层受走滑断裂带及内部结构模式控制,且分布非均质性极强,表明构造成岩作用是主要控制因素。综合多种资料,开展了断裂带构造成岩成储分析,为致密砂岩油藏高效开发提供了依据。研究表明:受构造应力应变差异控制,走滑断裂带与走滑断裂带之间区域的构造成岩作用及控储特征存在差异,主要表现在:(1)走滑断裂带的构造应力应变具有簇状分布特点。走滑断裂带为高应力应变区(HSSZ),走滑断裂带之间的区域为低应力应变区(LSSZ)。走滑断裂带沿走向可划分为张扭段、压扭段和走滑段;垂直于断层走向可概括出三大类八小类侧向分带结构模式。(2)走滑断裂带的构造成岩作用包括:变形条带、胶结作用、溶蚀及交代作用、微裂缝、碎裂作用、构造涂抹。(3)构造应力应变差异控制了构造成岩差异,进而控制了储层物性:① HSSZ区域和LSSZ区域的压实减孔作用均强于胶结作用。但是HSSZ区域的构造成岩减孔作用强于LSSZ区域,而LSSZ区域的胶结减孔作用强于HSSZ区域。②分段控储作用由好到差依次为:张扭段、断层端部、弱张扭段、走滑段、压扭段。
Abstract:Objective The distribution of tight sandstone sweet spots in the Chang 8 to Chang 6 members of the Jinghe Oilfield is primarily influenced by strike-slip fault zones and their internal structural patterns, which demonstrate significant heterogeneity. This finding indicates that tectonic diagenesis is the main controlling factor of reservoir heterogeneity.
Methods This paper integrates various datasets to analyze structural diagenesis and reservoir formation within fault zones, thereby providing a foundation for the efficient development of tight sandstone reservoirs.
Results and Conclusions Variations in structural stress and strain lead to differing structural diagenesis and reservoir characteristics between and within strike-slip fault zones. The key findings include the following: (1) The structural stress and strain in strike-slip fault zones show clustered distribution characteristics. The zones are categorized into high-stress–strain zones (HSSZs) and low-stress–strain zones (LSSZs). Additionally, within strike-slip faults, transtensional, transpressional, and strike-slip segments can be distinguished along the fault strike, while three major categories and eight secondary categories of lateral zoning structural patterns are summarized along the fault dip. (2) Structural diagenesis within strike-slip fault zones includes deformation bands, cementation, dissolution and replacement, microfracturing, cataclasis, and smearing. (3) The differences in structural stress and strain govern the variations in structural diagenesis and, consequently, reservoir physical properties: (a) Both the HSSZ and LSSZ experienced more significant compaction and porosity reduction compared to cementation. However, the porosity reduction caused by structural diagenesis in the HSSZ was more intense than that in the LSSZ, whereas cementation in the HSSZ was greater than that in the LSSZ. (b) Under the influence of structural diagenesis, the physical properties of different segments decrease in the following sequence: transtensional segments, fault tips, weak transtensional segments, strike-slip segments, and transpressional segments.
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表 1 泾河油田长6-长8段不同构造期的最大主应力值(声发射AE测试)
Table 1. Maximum principal stress values of the Chang 6- Chang 8 Members across different tectonic stages of the Jinghe Oilfield (AE test)
井号 岩性 声波时差/
(μs·m−1)深度/m 最大主应力σ1/MPa 燕山期 喜马拉雅期 现今 JH29 细砂岩 256 1312.07 72.5 62.7 35.8 JH30 细砂岩 214 1588.50 100.8 58.9 30.7 Z2 细砂岩 211 1406.56 134.8 57.6 42.8 平均 / / 102.7 59.7 36.4 表 2 泾河油田长6-长8段走滑断层侧向分带结构模式特征
Table 2. Characteristics of the lateral zonal structure of strike-slip faults in the Chang 6-Chang 8 Members of the Jinghe Oilfield
侧向分带结构模式 特 征 类型 亚类 Ⅰ型 Ⅰa 位于走滑断层张扭性端部,主要发育张开型微裂缝和膨胀型变形条带,溶蚀作用较发育 Ⅰb 主要发育走滑断层压扭性端部,多发育闭合型微裂缝及压实型变形条带,胶结作用较发育 Ⅱ型 Ⅱa 断核常见断层角砾及空腔,溶蚀作用发育,破碎带多由剪切解聚和膨胀碎裂变形条带及张开缝等组成 Ⅱb 断核多由胶结角砾岩及闭合缝组成,胶结作用发育,破碎带多由压性闭合缝及压实碎裂变形带等组成 Ⅱc 断核多由剪切碎裂岩及高角度剪切缝密集带组成,破碎带以剪切缝及胶结剪切变形带为主 Ⅲ型 Ⅲa 断核多为断层角砾+断层泥,破碎带为张裂缝密集带及膨胀碎裂带 Ⅲb 断核见胶结碎裂角砾、断层泥,具有页理化组构糜棱岩。破碎带见密集闭合微裂缝及压溶变形条带 Ⅲc 断核见剪切碎裂岩、断层泥及涂抹层,偶见糜棱岩。破碎带见密集剪切微裂缝带及剪切碎裂变形条带 表 3 成岩早-中期阶段解聚变形条带的成因及识别特征
Table 3. Genesis and identification characteristics of disaggregation bands during the early-middle diagenetic stages
变形构造 识别特征 实例 解
聚
变
形
条
带压实
解聚成岩早-中期,碎屑颗粒间存在孔隙空间(后期钙质胶结),颗粒旋转与颗粒间错动发生重组,形成颗粒顺层排列。变形条带中颗粒呈线接触;变形条带之间颗粒呈点接触。后期铁方解石胶结,图像处理面孔率估算变形带面孔率为2%,变形条带之间面孔率为17%,两者孔隙度相差15%(红色为硒素红染色,代表后期钙质胶结,统计时不考虑胶结物面积),反映了局部变形导致储层硬化 JH2井,长812小层,细砂岩,早胜断裂带,压扭段(单偏光) 剪切
解聚剪切应力作用下,颗粒平移-旋转-滑动发生重组,形成颗粒长轴顺层排列。变形条带之间,发育线状微裂缝。颗粒线接触。由于剪切解聚作用,粒间孔明显发育(蓝色面积),变形带有储层“软化”现象。变形条带面孔率为17.2%;变形条带之间面孔率为1.6%,两者相差15.6%(蓝色为铸体孔隙),正交,铸体薄片 JH25井,长823小层,细砂岩,宫河断裂带,端部张扭马尾段 表 4 成岩中-晚期阶段碎裂变形条带的成因及识别特征
Table 4. Genesis and identification characteristics of the cataclasite band in the middle-late diagenetic stages
变形构造 识别特征 实例 碎
裂
变
形
条
带膨胀
碎裂颗粒碎裂,大小不一,角砾状,构造角砾岩,颗粒呈点接触;中-细晶方解石斑状充填于砾间,裂缝发育,空腔发育,方解石、沥青充填,缝洞型储层。物性好,岩心实测孔隙度为9.42%,渗透率为16.7×10−3 μm2 JH9井, 1047 m,长811小层,正交光。宫河断裂带,张扭段压实
碎裂颗粒碎裂,分选差,棱角-次棱角状,颗粒定向明显,呈紧密连接状(interlocking)的压实条带,偶见微裂缝,颗粒以线接触为主,微显位移,钙质胶结,物性较差,孔隙度为4.4%,渗透率为0.05×10−3 μm2 JH41井, 1126 m,长81亚段,细砂岩,正交光。芋圆走滑断裂带压扭段剪切
碎裂见剪切缝,微裂缝一侧为角砾岩,另外一侧为断层泥,反映较强的剪切碎裂作用,由于微裂缝发育,因此,孔隙度较低,为4.9%,渗透率较好,可达0.26×10−3 μm2 JH13井, 1422 m,长81亚段,灰色细砂岩;宫河走滑断裂带东北走滑段表 5 泾河油田长6-长8段走滑断裂带不同分段砂岩的钙质胶结物
Table 5. Calcareous cement of sandstone in different segments of the strike-slip fault zone of the Chang 6-Chang 8 Members, Jinghe Oilfield
分段 钙质胶结物体积分数/% 样品数 代表井号 最大 最小 平均 张扭段 49.0 1 8.87 78 JH8、JH17、JH18、JH25、JH9 压扭段 48.0 1 11.94 58 JH11、JH22、JH23、JH13、JH26 走滑段 20.5 4 12.15 11 JH16、JH33 表 6 泾河油田长6-长8段不同应力应变带视压实率与视胶结率计算结果统计
Table 6. Statistical data of the calculated compaction and cementation rates of the Chang 6, Chang 7 and Chang 8 Members in high and low stress, strain zones in the Jinghe Oilfield
层位 走滑断裂带间低应力应变带(LSSZ) 走滑断裂带内高应力应变带(HSSZ) 视压实率CR/% 视胶结率CE/% 视压实率CR/% 视胶结率CE/% 范围 均值 范围 均值 范围 均值 范围 均值 长6段 29~49 39.0 18~63 33.00 26~81 49.6 2.6~53 25.80 长7段 25~63 47.0 18~54 28.00 28~65 56.2 2.59~78 27.00 长8段 10~70 51.1 9~75 33.36 31~88 65.0 1~72 18.64 -
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