塔北地区寒武纪深层白云岩构造-岩相古地理特征及勘探方向

Tectonic-lithofacies palaeogeography characteristics of Cambrian deep dolomite and exploration prospects in northern Tarim Basin

由于塔北地区寒武系深层白云岩资料点少,有效恢复岩相古地理成为制约寒武系深层白云岩勘探领域优选的关键地质要素之一。利用有限的14口钻井和4个野外露头地质资料点以及地震资料,探讨了塔北地区寒武纪深层白云岩岩相古地理特征,精细刻画了台地类型及台缘特征,并尝试刻画台内沉积分异。塔北地区寒武纪总体发育轮南断控陡坡型台缘和北部沉积缓坡型台缘2种类型的台缘,台内滩、膏云坪、膏盐湖及台内洼地等沉积单元分异明显。台缘特征及台内沉积分异控制了储盖组合的配置,由此得出长期继承性隆起上的寒武系台缘礁滩、礁后滩白云岩与蒸发盐湖相膏盐岩和蒸发潮坪相膏泥质白云岩形成的优质储盖组合为有利的勘探方向。塔北地区寒武系具有2个现实的有利勘探区带:轮南陡坡型台缘带和北部缓坡型台缘带,其中,轮南台缘带后侧、泻湖靠海一侧的礁后滩储层上覆致密碳酸盐岩盖层;北部台缘带藻丘及滩体复合型白云岩储层上覆中、下寒武统泥晶白云岩、膏质白云岩及含泥白云岩等致密盖层。北部缓坡型台缘带储盖组合要优于轮南陡坡型台缘带,勘探前景更为乐观。

Limited by lacking data points, effective reconstruction of lithofacies palaeogeography becomes one of the critical factors for exploration zone optimization of Cambrian deep dolomite in northern Tarim Basin. The data from 14 drilling wells and 4 outcrops as well as seismic data were applied to discuss the lithofacies palaeogeography characteristics of Cambrian deep dolomite, describe platform margin characteristics and try to clarify facies differentiation inside the platform. The results show that the Cambrian platform margin in the northern Tarim Basin could be divided into Lunnan fault-controlled steep slope type and northern sedimentary type with gentle slope, the sedimentary differentiation is obvious inside the platform, and main sedimentary units such as intraplatform shoal, gypsum-bearing dolomitite flat, gypsum-salt lake and depression can be well recognized. Reservoir-seal assemblage in the Cambrian dolomite is controlled by the characteristics of platform margin and sedimentary differentiation inside the platform, so it is considered that the favorable reservoir-seal assemblages are platform margin reef-shoal, back-reef shoal dolomite and gypsum-salt rock and argillaceous dolomite developed under long-term inherited palaeohigh. The reef-shoal located behind the platform margin belt and near the sea side of the lagoon are favorable reservoirs with caprock of tight carbonate, which can form good reservoir-seal assemblages. Platform margin belt in gentle slope in northern Tarim Basin is a set of dolomite reservoir for algal mound and reef-bank complex with caprock of Middle-Lower Cambrian dolomicrite, gypsum dolomite and mud dolomite and such dense layers, of which the reservoir-seal assemblage is superior to that in Lunnan area and has better exploration prospects.