Opportunities and Pitfalls When Locating Horizontal Wells in a Geologically Uncertain Environment

Abstract

Horizontal wells are often much more efficient for oil production than vertical wells. However, the reservoir engineer is faced with several challenges specific for this technology both with regard to location of the horizontal section and reservoir management. The Troll field offshore Norway will be developed by 18 horizontal wells. on average at least 800m long. The performance of the horizontal wells is very sensitive to the local geological setting. Due to large permeability contrasts, numerous calcite cemented layers and a limited database for this huge reservoir. the geological control still remains uncertain prior to development. This paper discusses new challenges that appear when locating horizontal wells in this ge~logical environment. The challenges of optimizing well locations and predicting well performance in an uncertain environment are discussed. The uncertainties of several parameters are considered, including: depth to reservoir sands, thickness of sands, the areal extension and pOlition of the oil leg in high permeability sand, degree of calcite cementation within the sands, effective well length and drilling accuracy. Reservoir modeling aspects are also considered. Some important geological features have been incorporated in a stochastic model which simulates the well location management and the overall production success.References and illustrations at end of paper.