柴达木盆地应用叠前偏移技术消除“气烟囱”效应

经过前期勘探，巳证实柴达木盆地中部存在浅层生物成因天然气，并发现了6个浅层天然气田，即涩北一号、涩北二号、台南、台吉乃尔、驼峰山和盐湖。在过气田的时间地震剖面上存在典型的“气烟囱”效应，即由于天然气藏的气体向上运移及逸出，由于地震波能量被吸收而在时间地震剖面上出现的下拉、低频、深层成像差等现象。叠前深度偏移(PSDM)是石油勘探家行之有效的一种解释性方法，它能够改善成像质量，提高信噪比，使深度剖面具更高的解释可信度。成像质量的提高是通过建立精确的速度模型而实现的。建立了精确的速度模型，就能够准确地归位目标层反射能量，提高信噪比，从而达到消除“气烟囱”效应的目的。在涩北区块(柴达木盆地)，应用以上方法得到的深度地震剖面消除了时间剖面伴有的速度效应，使得解释人员能更好地解释区块的构造背景，并应用Geosee2D软件对涩北一号和盐湖构造进行构造形成期分析。图8参7

To Remove Gas Cloud Effects by Using PSDM in Qaidam Basin,Northwest China

In the central part of Qaidam Basin, Quaternary bio genetic gas system has been proved for the shallow layers, which consist of six gas fields, i.e., Sebei 1, Sebei 2, Tainan, Taijinaier, Yanhu, Tuofengshan. Apparently, due to gas cloud effects, typical phenomena, such as pull down, low frequency, and poor deep imaging, occur in time sections across the gas fields. Pre stack depth migration (PSDM) is an effective interpretation tool for the explorationist, as image enhancement and depth sections provide new reliable insights. Image improvement is achieved by building an accurate velocity model, enabling reflective energy to be correctly positioned and thereby increasing signal to noise ratio. In Sebei Block (Qaidam Basin), the resulting depth sections removed velocity effects associated with time sections and allowed the interpreter to better understand the structural setting and timing.