Log response characteristics and lithological evaluation of volcanic rocks in Yingcheng Formation from the second scientific drilling borehole (SK-2 east borehole) in Songliao basin of Northeast China

In order to conduct long-term deep observation, fluid experiments and investigate volcanic events in Songliao basin, the authors carried out lithological evaluation of volcanic rocks in Yingcheng Formation by using abundant and complete geophysical logs from SK-2 east borehole. The log response analysis of volcanic rocks shows that the radioactivity and electric conductivity of tuffs are the strongest. Agglomeratic lavas have low density because of high porosity. The density of rhyolites is the highest and the electric conductivity is the weakest. Volcanic rocks of Yingcheng Formation along SK-2 east borehole consist of rhyolites, transitional tuffl lavas, agglomeratic lavas and a little tuffs by using cross plots and imaging models. A volcanic eruptive gap may exist, as evidenced by tuff with high GR, low RD and low DEN. Rhyolites are characterized by high alkali, high Si, low Fe and low clay mineral. T₂ analysis suggests that the rhyolites are favorable for carrying out long-term observations and fluid experiments. The results provide a reference of interpretation for subsequent volcanic rock in Huoshilin Formation and research of volcanic rocks in the whole basin.