New HF-Acid System for a Heavy-Crude Brownfield With Fines Problems

Abstract

This article, written by Technology Editor Dennis Denney, contains highlights of paper SPE 112558, "Increasing Production in a Brownfield With Heavy Crude and Fines Problems by Application of New HF-Acid System: Case Histories," by Folorunso Afolabi, SPE, Austa Opusunju, SPE, and Jaspers Henri, SPE, Shell, and Cletus Onyekwere, SPE, Chris Onyekwere, SPE, and Davalos Juan, SPE, Weafri, prepared for the 2008 SPE International Symposium and Exhibition on Formation Damage Control, Lafayette, Louisiana, 13–15 February. The paper has not been peer reviewed. Minimizing fines migration and improving high-water-cut-well productivities with improved treatment-fluid designs, detailed candidate selection, and enhanced pumping methods yielded positive results in aged-field production enhancement. A slow-release-hydrogen retarded-hydrofluoric-acid (SRH-RHF) system was used on the basis of a detailed candidate selection, case-specific fluid design for high-water-cut wells, and mechanism of fines and clay migration and control methodology to acidize heavy- or medium-crude reservoirs. Introduction Improving productivity in these Niger delta brownfields that produce heavy crude and experience fines migration had been approached with little or no consideration to such challenges as water production. Many wells were treated with a conventional mud-acid system, either with or without a solvent-soak treatment. Clay-control agents are no longer used to stop fines problems because the additive had little effect. Wells with high water cut were treated only with solvent material, realizing minimal effect. Foam diversion often had inconsistent results. Other diverting techniques also proved unpredictable in this environment. A coating of heavy crude on the formation wall inhibited the reaction of the mud-acid system with the formation. An acid system or formulation that would maintain matrix acidizing was needed for well-productivity problems in the Niger delta. In December 1996, an SRH-RHF sys-tem was used. Data indicated a consistent production increase with evidence of deep penetration into the damaged zone. Failures experienced with this sys-tem were traced to a shortage of well information for proper diagnosis and the need for a core-flow test in one field with three treatments resulting in no increase or a reduction in production. In the past, acid stimulation was limited to wells with water cut less than 30%. In late 2001, an improvement was made in candidate selection, treatment design, foam diversion, and pumping method for high-water-cut wells and heavy-crude wells. The high-water-cut limit was increased to 60%. In 2005, a new SRH-RHF system was developed. Its application in nine wells with heavy or medium crude was successful.