Fault characteristics and its significances on hydrocarbon accumulation in northeastern Baiyun Sag, Pearl River Mouth Basin
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摘要:
珠江口盆地白云凹陷东北部具有“内气外油”的分布特点,断裂在油气运聚成藏过程中起到了重要作用。本文主要依据地震资料解释成果,分析断裂发育特征,定量评价断裂输导性能,并结合钻探结果探讨断裂对油气运聚成藏的影响。白云凹陷东北部主要发育NWW向和近EW向正断层,在剖面上表现为铲式和板式形态。根据断裂对油气运聚成藏的影响,划分出油源断裂和控圈断裂。油源断裂在成藏期的活动速率达到20~40 m/Ma,在珠江组下段的断层泥比率多大于50%,而且断面正压力超过了泥岩的极限抗压强度,有利于油气沿断裂发生运移。控圈断裂的活动速率一般都小于20 m/Ma,在珠江组下段的断层泥比率都大于95%,而且断面正压力都小于泥岩的极限抗压强度,侧封性能良好。白云凹陷东北部表现出油气差异聚集成藏的特点,远源反向控圈断裂下盘高效封堵聚集原油,而天然气则主要发生近源聚集。
Abstract:The distribution of oil and gas fields in the northeastern Baiyun Sag of the Pearl River Mouth Basin is characterized by the “inner gas, outer oil” pattern, and faults play important roles on hydrocarbon migration and accumulation. Based on seismic interpretation and borehole data, fault characteristics and its significances on hydrocarbon accumulation in the northeastern part of the Baiyun Sag are analyzed in this paper. NWW- and EW-trending faults are predominant in the study area, which are listric and planar shapes in cross section. According to their significances on hydrocarbon accumulation, the faults in the northeastern Baiyun Sag can be divided into oil-source faults and trap-controlled faults. The oil-source faults dipping into source kitchen have an activity rate of 20~40 m/Ma in the key accumulation stage, and a value of shale gouge ratio more than 50% in the lower Zhujiang Formation. Also, the normal stress on oil-source fault surface is larger than the ultimate compressive strength of mudstone. These are helpful for hydrocarbon migration along the oil-source faults. In contrast, the trap-controlled faults have perfect lateral sealing ability, because of activity rate less than 20 m/Ma and value of shale gouge ratio more than 95% in the lower Zhujiang Formation, as well as normal stress on fault surface less than the ultimate compressive strength of mudstone. The feature of differential accumulation of hydrocarbon in the northeastern Baiyun Sag is obvious. Oil is accumulated in the footwall of the far-source antithetic trap- controlled faults, and gas is in the near-source traps.
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图 2 珠江口盆地白云凹陷地层综合柱状图[20]
Figure 2.
表 1 白云凹陷东北部主要断裂珠江组下段SGR和断面正压力计算结果
Table 1. Shale gouge ratio and positive pressure of major faults in the lower Zhujiang Formation in the northeastern Baiyun sag
断裂类型 断裂编号 泥岩厚度/m 断距/m SGR/% 断面正压力/MPa 油源断裂 F1 774 948 82 48.77 F2 627 790 79 66.58 F3 1051 1217 86 48.79 F4 331 483 69 47.93 F5 1967 2152 91 24.58 控圈断裂 F6 233 238 98 23.09 F7 165 175 94 22.68 F8 308 321 96 21.69 F9 116 136 85 19.03 -
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