Well Heifudi-1 is a small diameter geological survey well for oil and gas, and in the context of drilling of the well, the basic principle and operation steps of the gas logging is introduced in this paper. The problems encountered and relevant solutions in gas logging are described. The evaluation principle for abnormality detected by gas logging in the well is explained and used for evaluation of gas formation encountered in the well. With reference to the results and experiences of gas logging, this paper analyzes the influence of major factors on gas logging data accuracy and logging curve continuity, explores the operating procedure of gas logging in small diameter geological survey wells for oil and gas, and describes the effect of small diameter drilling characteristics on the evaluation of oil and gas reserves.