相干技术及其在西沙周缘深水区油气勘探中的应用

Seismic coherence technology and its application in petroleum exploration in deepwater area offshore off Xisha Island

近年来珠江口盆地南部深水区油气勘探不断取得重大突破,证实了该区油气地质条件优越。西沙周缘深水区与其同处于一个构造带上,具有相似的构造沉积演化史,类比推测西沙周缘深水区可能具有良好的油气勘探前景。文章在介绍相干技术的基础上,采用近年来西沙海域新采集的高分辨率地震资料对比各代相干算法的计算效果,并将相干技术应用于该区深水油气勘探工作中。1)相干技术对地震数据的不连续性十分敏感,可有效精确地识别断层。在相干切片上,断层走向清晰,相互切割关系明确。2)相干技术强调振幅加强和边缘检测,可用于深水水道的识别刻画。在相干切片上,水道的整体形态、曲流特征和侧向侵蚀特征清晰,水道边缘为不连续性条带。3)由于生物礁核部岩性较均一,地震响应特征相似,而礁体边缘部位的地震反射杂乱,因此可以利用相干技术突出不连续性的特点识别生物礁。4)火山岩内部与围岩地震响应特征差别明显,因此可利用相干技术识别火山岩体。在相干切片上火山岩发育区为明显的弱相干,且会出现以火山岩为中心向四周发散的放射状断层。

In recent years, significant breakthroughs of hydrocarbon exploration have been achieved in deepwater area off the southern Pearl River Mouth Basin. They helped to verify this area has a favorable geology condition for hydrocarbon. Deepwater area offshore off Xisha Island lies in the same structural belt as the deepwater area off the southern Pearl River Mouth Basin, and they have similar structure and sedimentary evolution history. Through analogy and geological research, the authors conclude that there is a good prospect for hydrocarbon exploration in deepwater area offshore off Xisha. Based on the coherence technology, results of different generations of the technology were compared with the high resolution seismic data acquired in recent years. The coherence technology was applied in hydrocarbon exploration in this deepwater area. First, the coherence technology is very sensitive to discontinuity in seismic data, and the faults can be effectively identified. On a coherence slice, the fault trend and the interaction cutting relation are very clear. Secondly, the coherence technology emphasizes amplitude strengthening and marginal detection and can be used in deepwater channel identification and description. On a coherence slice, the whole size of a channel, meandering characteristic, lateral erosion are distinct, and the edge of the channel appears as a discontinuity belt. Moreover, the core of the reef appears uniform （with similar seismic reflection characteristics）; and seismic reflection clutter occurs at the edge of the reef. So, a reef can be identified by the coherence technology. Finally, there is an obvious difference between inner and outer layers of a volcanic rock. The coherence technology was applied to identify a volcanic rock. On a coherence slice, the volcanic rock developing area shows obvious weak coherence and there were radial-type faults in the core center of the volcanic rock.