A Novel Technique to Acidize Multilateral Open Hole ER Horizontal Wells Drilled in Carbonate Formations

摘要

A new development strategy used by Saudi Aramco for carbonate reservoirs is to drill multilateral, extended reach, horizontal and fishbone wells. This strategy has a significant impact on reducing the development cost per bbl of oil produced, by drilling less wells and requiring less offshore platforms. This is also applied for the development of carbonate reservoirs in highly populated areas. Drilling multilateral wells is intended to maximize reservoir drainage and minimize water production due to water coning. However, inherent problems with these wells are poor accessibility and uneven acid distribution during matrix acidizing, especially in reservoirs with high permeability streaks. This paper discusses an innovative approach to treat multilateral wells. This technique comprises mechanical diversion in the wellbore and chemical diversion in the formation. In the past, reentry access to sidetracks from an open hole main wellbore was not possible. This prevented remedial operations on individual laterals and precluded effective reservoir management. To selectively enter and stimulate the desired lateral, a coiled tubing conveyed orienting tool was used. This ensured better acid distribution over the wellbore. To enhance acid diversion in the formation, a viscoelastic surfactant-based acid system was employed. Well "A" is an offshore dual open hole multilateral horizontal well with a motherbore length of 2,256 ft and a lateral section of 3,558 ft. The lateral was rotary jetted with acidic brine during the completion phase, but the well did not sustain flow after a nitrogen gas lift. A special CT conveyed multilateral tool was successfully used to enter the lateral. A viscoelastic surfactant-based acid was utilized to remove formation damage induced by drilling fluids, and to enhance the permeability of the formation in the critical wellbore area. The well responded to the acid treatment and its production exceeded expectations. Challenges, design criteria, field treatment and evaluation, lessons learned, and recommendations are discussed in this paper.