The Da’anzhai reservoir in the Gongshanmiao oil field belongs to tight oil type, and its physical properties are extremely tight with porosity less than 2% and permeability below 0.05 mD. The oil reservoir in Da’anzhai extends extensively and has relatively oil enriched places called “sweet spots”. Based on geological information and production data of wells, the authors calculated the recoverable resource using the volumetric method and production decline fitting method, and the result is 3.38 million tons and 1.56 million tons, respectively.