柴达木盆地油泉子储油构造分析

Analysis of the Youquanzi oil-bearing structure in Qaidam basin

通过对野外露头、地震反射剖面和钻井资料的综合分析,查明柴达木盆地油泉子储油构造为共轭膝褶带夹持的不对称半箱状背斜,具有北北东倾的平直转折端,北翼为一宽超过800 m的大型膝褶带,高角度倾向南南西,带内岩层产状直立。带内岩层的旋转指示南侧沿膝褶带向北逆向剪切。南翼发育四条规模较小的膝褶带,向南逆冲剪切,导致该翼呈阶梯状产出,总体南南西倾,倾角约20°。沿南北两翼膝褶带边界仅见小型高角逆断层,膝褶带内裂隙发育,主要为顺层张裂隙,其次为与层理近垂直的张裂隙(主要出现在坚硬的钙质粉砂岩中),偶尔见有小型低角逆冲断层。这些断裂普遍被纤维状石膏充填,并见少量油迹,表明这些断裂为高流体压力下的产物。鉴于膝褶带及相关背斜高点为裂隙发育带,具有油气运移和聚集的双重功能,在缺乏足够理想的岩性储集层的情况下,为寻找裂隙型油气藏提供了新途径。

On the basis of comprehensive analysis data on outcrop, seismic reflection profiles and drilling, the Youquanzi oil-bearing structure is confirmed to be an asymmetric half-box anticline retained by conjugate kink zones with a straight hinge dipping towards NNE. The northern limb is a large scale kink zone of over 800 m wide and dips towards SSW at a high angle with sub-vertical inner-bed in it. The rotation of the inner-beds indicates that the southern side shears reversely towards the north. Four small-scale kink zones are developed on the southern limb and shear reversely southward, carving the limb into the step occurrence dipping SSW at 20° as a whole. Along the boundaries of the kink zones on both limbs, there are merely a few small-scale high-angle reverse faults. Fractures, mainly bedding-separation fractures, followed by separation fractures sub-normal to the bedding （mostly occurring in competent calcareous siltstones）and occasionally small-scale low-angle thrusts, are developed in the kink zones. These fractures are commonly filled with fiber gypsum and show locally some oil traces, indicating that these fractures are the products of high-pressure fluid. Seeing that the kink zones and relevant anticlinal highs are fractured and favorable for both oil-gas migration and accumulation, they can be a new way for finding fissure-type reservoirs with the absence of enough ideal lithologic-reservoirs.