What type of visa I should apply. What are the documents I should supply with the visa application?

I am Sri Lankan ex Saudi Aramco employee, I was invited to work in Beijing with Saudi Aramco project name Jazan power plant, detail designing work for period of 18 months. I will be working for Saudi Aramco. The Aramco contract won by china company. I may get every three months one week leave. I may have to travel Colombo and Beijing every three months.