CNL-DEN response and pore types of sandstones：a case study on sandstones in Lower Cretaceous of Wunan depression in Hailar basin

Abstract：The Logging Calibration geological methods were used in this article in order to im- prove the accuracy of logging interpretation of sandstone in the areas containing volcanic deb- ris. XD-N（value difference between density logging （DEN） and compensated neutron logging （CNL）） was used to express the relationship of the two response curves. There are three rela-tionships between the two response curves, namely; intersection XD-N ;3）, approach（-3〈XD-N〈3） and separation（XD-N〈-3）. Combining lithology, pore types and log response in each case, the characteristics of pore types and response CNL-DEN of the sandstones with different interstitial materials are discussed. The relationship among lithology, pore types and the two response curves were also established. The results show that the relationships between the two response curves are intersectional, approach and separation when the sandstones are of sandy interstitial material, approach and separation when the sandstones are of tuffaceous and calcareous interstitial materials, and separation when the sandstones are of argillaceous interstitial material. The main type of pore space in sandstones is intergranular pore when the sandstones are of sandy and calcareous interstitial materials. The contents of intergranular and intragranu- lar pores are nearly equal when the sandstones are of tuffaceous and argillaceous interstitial ma- terials. The porosity is highest when sandstones are mainly of argillaceous interstitial material and the characteristics of CNL and DEN curves are similar.