Characteristics of Alkaline Minerals and Logging Evaluation of Trona in Fengcheng Formation of Mahu Sag

Abstract

Abstract: The Fengcheng formation of the Mahu sag in the Junggar basin is primarily composed of alkaline lake sediments. A large number of alkaline minerals are developed near the center of the alkaline lake. As a major type in these alkaline minerals, trona is an important industrial resource worthy of development. Currently, the trona intervals are mainly qualitatively evaluated by using the crossplot method, and a quantitative evaluation method is required. Based on core analysis and thin-section identification on alkaline minerals, together with previous research findings, the alkaline minerals in the Fengcheng formation are classified into four categories: trona, shortite; huntite, and searlesite, and their physical properties and impacts on both reservoir properties and oil-bearing property are identified. The influence of trona content on logging responses is analyzed, and a predictive model for trona content is developed by using the deep-to-shallow resistivity ratio. Core data uninvolved in the modeling are used for verifying the prediction model. It is found that the trona content predicted by the model and the trona content measured from cores are in better agreement, with an average relative error of 5.67%, meeting the requirements for precise mineral content calculations. Finally, based on the logging evaluation results of trona content from eleven wells, the distribution of trona in the Fengcheng formation is clarified. The research results may provide a theoretical and technical support for trona resource evaluation.

Key words: Mahu sag, Fengcheng formation, alkaline mineral, logging response, trona, logging evaluation, physical property, oil-bearing property

MAO Rui, ZHAO Lei, SHEN Ziming, LUO Xingping, CHEN Shanhe, FENG Cheng. Characteristics of Alkaline Minerals and Logging Evaluation of Trona in Fengcheng Formation of Mahu Sag[J]. Xinjiang Petroleum Geology, 2023, 44(zk(English)): 29-35.

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