Application of high-resolution reflection seismic in deep brine exploration in Heibei Concave of the Qaidam Basin

This paper is the result of geological survey engineering.

Objective Dalangtan-Heibei Concave area of western Qaidam Basin is rich in deep-buried sandstone and gravel-type potassium-rich brine deposits, which are expected to become China's next large-scale potassium salt resource base. The seismic data acquired for oil and gas exploration in this area have a low resolution in the brine accumulation layer, which hinders the detailed exploration and resource assessment of brine resources.

Methods This paper conducts high-resolution 2D reflection seismic survey for potassium-rich brine resources in this area firstly, conducting in-depth research to improve the resolution of seismic exploration from aspects such as geometry designing, acquisition parameter tests, and fine data processing. High-resolution reflection seismic profiles have been obtained, and detailed structural interpretations have been made on the profiles. We delineated the deep brine layer on the seismic profiles and divided the area into three favorable potassium-rich brine zones.

Results The sandstone and gravel brine layer shows characteristics of low frequency, low continuity, and weak reflection amplitude on the seismic profile, vertically distributed below the unconformity, which is the Quaternary base, mainly hosted in the Upper Ganchaigou Formation, Youshashan Formation, and Shizigou Formation. Laterally, it is divided into three zones: the Dalangtan zone, the northern Heibei Concave zone, and the southern Heibei Concave zone. The northern Heibei Concave zone between Hongsanhan to Jianbei Latent is distributed in a shape of shallow in the north and deep in the south, divided into two sections of east and west by a low amplitude antinode located at the L2 line. The deepest part of the western zone is about 1800 m thick, mainly located to the west of the L1 line, while the eastern zone is located between the L2 and L3 lines, with the thickest part reaching about 1200 m.

Conclusions The high-resolution seismic profiles indicate that the northern Heibei Concave zone has favorable metallogenic conditions and is the most important sandstone and gravel brine deposit area in the region. This study provides an effective basis for the investigation and evaluation of potassium salt resources in the region.