Drilling is one of the major means for oil and gas exploration and development. Extended reach wells (ERWs) are defined as directional wells or horizontal wells with horizontal displacement (HD) to vertical depth (VD) ratio greater than or equal to 2. Extended reach drilling (ERD) confronted many technical difficulties. Risk analysis of ERD before drilling is of great significance for preventing complex accidents during drilling operations, improving the drilling rate and efficiency. Based on gray matter-element theory, this paper established a comprehensive risk assessment model for ERD operations and applied this model to evaluate the drilling risk of Well B6ERW07(HD to VD ratio 5.94, horizontal displacement 7,419.42 m, vertical depth 1,248.50 m, measured depth 8,144.31 m)in the Liuhua oil field, South China Sea. The assessment results show that the predicted success rate of drilling this ERW is 49.9%. This result can be important criteria and thus contributes greatly to decision making.