Stimulation Applications for Carbonate Reservoirs: An Overview ofAcidizing Technologies and Methods Used in Pre and Post Salt Reservoirsin Brazil

摘要

Pre and post salt carbonate reservoirs are becoming the main source of hydrocarbon production in Brazil.One of the reasons behind this success is the development of many fields located on pre salt areas alongthe Brazilian shore.Production optimization is vital for sustainability,which requires efficient methods andtechnology to stimulate these reservoirs.The main cost-effective approach used in Brazil to improve the production in carbonate reservoir areasis matrix acidizing.Stimulation fluids are pumped into the formation below the fracture pressure to createwormholes that can bypass near wellbore damage and increase the drainage radius along the wellbore.This study offers an insight of the most common methods and technology used to perform matrix acidizingon offshore carbonate reservoirs in Brazil.The main aspects of the study are fluids selection,pumpingstrategies,completion design and pressure behavior analysis.Before 2012,most of the offshore stimulation operations in Brazil were performed on sandstonereservoirs.With the advent of pre salt development this scenario changes drastically leading to a high volumeof matrix acidizing on carbonate reservoirs in both post and pre salt zones.The main challenges to designingand executing matrix acidizing on carbonate reservoirs in Brazil are the long reservoir intervals combinedwith high permeability contrasts,high formation temperature and the need of large fluid capacity toaccommodate the required treatment designs.Additionally,super duplex stainless steel metallurgies must beconsidered for corrosion inhibition protection.To overcome these challenges: first,a proper fluid diversiontechnique must be employed to distribute the treatment fluid across all targeted zones; next,a proper fluidselection must be made to avoid carbonate face dissolution; and finally,corrosion protection is required forthe well bore completion components from the corrosion rates increased by the high temperatures downhole.The lessons learned and best practices captured over the past decade on more than 250 offshore carbonatematrix acidizing operations has led to much success in the post and pre salt zones of Brazil.