user: Question: Where is the area of operation that had Drilling during the year 1999?
Columns: ['Client', 'Years of Operation', 'Area of Operation', 'Country', 'Services']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['Agoco', '1991-current', 'Sarir field', 'Libya', 'Drilling, workover']
SQL:

assistant: SELECT "Area of Operation" FROM "Table" WHERE "Services" = 'Drilling' AND "Years of Operation" = '1999';