Oil Production from the Troll Field: A Comparison of Horizontal and Vertical Wells

Abstract

ABSTRACT Oil production from thin oil columns in deep water environments, such as one finds in the Troll Field in the North Sea, presents difficult coning problems at economical production rates. A pattern of oil production wells must effectively drain a designated area at a high oil production rate. If too few vertical wells are drilled, the wells will be shut in due to high gas-oil ratio before the oil recovery is satisfactory. If two many wells are drilled they interfere with each other and may cone gas even earlier. The drilling of horizontal wells has been proposed as a possible solution to this problem. This paper investigates numerically the performance of various patterns of vertical wells and compares the results with the performance of a pattern of horizontal wells. The effect of the length of the horizontal wells, their location relative to the fluid contacts, the change in performance with production rate, and the effect of an oil saturation in the rock below the water-oil contact are all investigated. The most significant results found were that a 1500 foot horizontal well would produce the same amount of oil as two vertical wells in a typical sector pattern when the sector is produced at a constant oil production rate, and a 2000 foot horizontal well would perform much better than three vertical wells. Also, specially designed production schedules were determined that would increase the life of the horizontal wells significantly, and yield oil recoveries of up to 30%.