Abstract: In recent years, the Mesozoic clastic oil and gas reservoirs in the southern margin of  Junggar basin have made breakthroughs and become an important exploration field in the basin. Mesozoic strata generally contain gypsum, so the lithology optimization of gypsum-bearing strata is the key to reservoir evaluation. In order to improve the accuracy of lithology identification in this area and correct the reservoir curves of gypsum-bearing strata,  the response characteristics of logging curves of different lithologies based on petrophysical experiments is analyzed, and it is found  that the gypsum-bearing strata will lead to the decrease of compensated neutron value, the decrease of acoustic time difference and the increase of resistivity. The gypsum lithology is identified by logging. The Monte Carlo numerical simulation method is proposed to simulate the compensated neutron logging formation under the conditions of different porosity and different gypsum volume fraction in gypsiferous sandstone. A correction model of the compensated neutron porosity curve is established, and the fine division of lithology is finally realized. The coincidence rate between the interpreted lithology and the thin section analysis reaches 88.2%.

Key words: southern margin of Junggar basin, Mesozoic, gypsum-bearing , stratum, Monte Carlo , numerical simulation, lithology identification, logging