柴达木盆地西部黑北凹地—大浪滩深层卤水钾盐储卤层地震响应特征研究

柴达木盆地西部深层卤水型钾盐是近期新发现的一种以砂砾层为储存介质的氯化钠亚型钾盐资源,其中,以黑北凹地—大浪滩次级盐湖凹地工作程度较高,研究也相对深入。该区已经求取该类型KCl资源量(333)约3.5亿吨。对该类型成矿地质体的解剖可对该区钾盐找矿在面上和纵深拓展提供借鉴。鉴于此,笔者根据实际生产需要,系统收集了该区的钻井、测录井及地震探测资料,通过地震资料解释和属性分析,对比钻孔揭露储卤层岩性特征,获得研究区域内中深部孔隙储卤层地震响应特征:储卤层底部同相轴振幅较强、局部连续性较好,顶部同相轴为中-强振幅,内部多为弱反射振幅,成团块状;瞬时频率属性表现为中-低频反射特征;甜点属性表现为顶、底为甜点高值而内部为甜点低值的特征;包络属性表现为顶、底为异常高值而储层内部为低值分布。通过对地震剖面及钻孔资料分析,建立了砂砾储卤层的地球物理识别标志,为预测中深部储卤层分布范围及优选水文-地质钻孔提供依据。

Seismic response characteristics of the Heibei Concave-Dalangtan potassium-rich deep brine reservoir in western Qaidam Basin

The deep brine type potash in western Qaidam Basin is a newly discovered sodium chloride subtype potash deposit with gravel layers as the storage media. In particular, a great deal of in-depth research has been done in the Heibei Concave (or Heibei'aodi)-Dalangtan secondary salt lake depression, where ~350 million tons of KCl resource of this subtype has been obtained. By dissecting this type of ore-forming system one can provide reference for the exploration of potash deposits in the area. The Heibei'aodi-Dalangtan area is the main distribution area of brine reservoir, a piedmont proluvial fan type pore brine reservoir in northeastern Qaidam Basin. In this study, we collected drill, logging and seismic-prospecting data according to the actual production needs. Through seismic reflection profile interpretation and attribute analysis, as well as drill data comparison revealing the reservoir lithology characteristics and distribution, we obtained the seismic response characteristics of the medium-deep pore brine reservoir in the study area. High amplitude in-phase reflections appeared at the bottom of the reservoir, with good local continuity; medium to high amplitude in-phase reflections were observed at top of the reservoir; at the lumpy middle part low amplitude reflections were recorded. The instantaneous frequencies were mainly medium to low frequencies. Larger “sweet spots” were observed at the bottom and top of the reservoir compared to the middle part with a low sweetness value. The envelope attribute was characterized by abnormal high peak values at the top and bottom and low peak values at the middle part of the reservoir. Through seismic profile and borehole data analyses, geophysical indicators for potash deposits were established, which provided a basis for predicting the distribution range of medium-deep reservoir and optimizing hydrogeological survey for borehole drilling.