Nondamaging Viscoelastic Surfactant-Based Fluids Used for Acid FracturingTreatments in Veracruz Basin, Mexico

摘要

For the last eight years acid fracturing stimulation has beenperformed in the Veracruz basin to increase gas production innaturally fractured carbonate formations. Several techniqueshave been proved to enhance the results of these jobs,including the diverting technique and the application ofnondamaging viscoelastic fluids technology specifically a selfdivertingviscoelastic based acid system and a polymer-freeviscoelastic surfactant gel for fracture initiationand propagation.This paper presents the results of successful acid fracturingtreatments recently performed using nondamaging viscoelasticsurfactant-based fluids to increase gas production fromnaturally fractured carbonate formations.Most of the wells drilled and completed in the carbonateformations of cretaceous age in Veracruz basin do not flownaturally because of low matrix permeability anddrilling/completion fluids damage. Therefore, acid fracturingtreatments are necessary to produce these wells ateconomical rates.The objective of these treatments is to increase gasproduction by creating a deeply etched fracture that willbypass the damaged zone and connect to the network ofnatural fractures and/or fissures. The etched fracture lengthaffects well performance in low-permeability reservoirs;increased fracture length should result in greater productionresponse. The use of nondamaging viscoelastic fluids isnecessary to obtain longer effective etched fractures.Combining this with the properties of a viscoelastic divertingacid will significantly increase fracture conductivity as well asthe effective stimulation of all perforated intervals.The fluids were combined by using a pumping techniquethat consists of alternating stages of nonreactive fluids,reactive fluids and diverter fluid to reduce wormhole creationat the nearwellbore area and increase etched fracture length. Four field cases are presented in this paper. In three,multiple intervals were treated, resulting in longer etchedfractures as deduced from after-treatment production responseand radioactive tracer logs. In the fourth case, not all theintervals were effectively stimulated because diversion wasnot used.