Overcoming Excessive Fluid Loss in Tip-Screen-Out Stimulations of Depleted,High-Permeability Reservoirs Using a New-Generation Viscoelastic Fluid:Successful Case Histories in West Venezuela

摘要

Tip-Screen-Out (TSO) stimulations of high permeability reservoirs have been performed in North and South America (i.e.,USA,Venezuela,Trinidad,Colombia),in Africa (i.e.,Nigeria,Gabon,Congo,Ivory Coast,Cameroon),in Europe (i.e.,North Sea,Italy),in the Middle East (i.e.,Saudi Arabia) and in Asia (i.e.,Indonesia).As reservoirs in these regions mature,fluid loss control and fluid-inflicted formation damage become increasingly important and conflicting issues.On one hand,the use of classic fluid loss additives and/or fluids with good fluid loss control characteristics (i.e.,polymer-based fluids) is typically associated with well production impairment because of residues left in the formation.On the other hand,fluids that are considered nondamaging,such as viscoelastic surfactant (VES) fluid systems,typically exhibit limited fluid loss control capabilities,making fluid efficiencies low and proppant placement inadequate.Nondamaging fluids are needed that can deliver adequate fluid loss control under severe reservoir conditions (i.e.,upon concomitant occurrence of high permeabilities and low reservoir pressures).Bachaquero field located in Lake Maracaibo,Venezuela,and managed by Petróleos de Venezuela (PDVSA) is a critical example of these depleted,high-permeability reservoirs.Permeabilities in this field range from 100 mD to 1 D.The average pressure gradient is 0.2 psi/ft.VES fluids typically have been used to hydraulically fracture reservoirs in this field.However,fluid efficiencies observed in recent jobs were as low as 2% and proper proppant placement under these conditions was no longer possible.In our study,we consider relevant technical aspects and case histories in a systematic study that is aimed at assessing the usefulness of a new-generation VES fluid tailored for high-permeability reservoirs to address low fluid efficiencies in the Bachaquero field.The study encompassed adjustments in fluid formulation to ensure compatibility with local production water and crude oils,specific engineering and quality assurance/quality control guidelines,and field trials in 10 wells,followed by quantification of the enhancements achieved in fluid efficiency and well production.Field tests showed that fluid efficiencies increased by up to 325%,as compared to conventional VES fluids previously used in this field.Production expectations were exceeded in all tested wells by an average of 65%.The study concluded that the new-generation VES fluid is suitable for use in the Lake Maracaibo area and it has been adopted as the fluid of choice for Bachaquero field.What we learned from this successful campaign is valuable when assessing stimulation strategies for mature high-permeability reservoirs worldwide.^