CREATE TABLE table_15338 ("Client" TEXT, "Years of Operation" TEXT, "Area of Operation" TEXT, "Country" TEXT, "Services" TEXT)

Where is the area of operation that had drilling during the year 1999?
SELECT "Area of Operation" FROM table_15338 WHERE "Services" = 'drilling' AND "Years of Operation" = '1999'
SELECT "Area of Operation" FROM "table_15338" WHERE "Services" = 'drilling' AND "Years of Operation" = '1999'