New Cleanup System for Gravel-Pack Completions: A Synergy of a Unique Acid System and Special Rotating Jetting Tool

摘要

Gravel pack completions are widely used today on unconsolidated formations worldwide to provide sand control, and, as such, behave as a filter. A filter is subject to plugging by fines, (heavy) hydrocarbons and scale depositions, among others, which may result in a considerable drop in, or even total loss of, production. The synergism of certain coiled tubing conveyed rotating jetting tools, and process optimized acid systems has demonstrated great results in Northeast of Brazil. The chosen jetting tool acts to disaggregate plugging particles from the gravel without damaging it and the acid acts to chemically dissolve acid soluble plugging materials. The acid system utilized is quite unique but simple. The method uses low intensity cyclic pressure induced flow currents to deliver solvent and a small amount of a specially designed acid system, to clean up the gravel pack. No acidic flushes are used ahead or after the acid system. The main acid system is a phosphonic / hydrofluoric acid (HV/HF) based, generating HF on a controlled fashion, using much less hydrochloric acid (HCl) when compared to regular HF acid systems. Three gravel packed wells were treated combining the single step acid system, and special coiled tubing tools to place it. The wells were very similar, but the tools were different. In the first job a rotating jetting tool was used while in the other two, a tool based on a fluidic oscillator principal was applied. By accurately controlling the rotational speed and pressure through the jetting nozzle the rotating jetting tool introduces differential flow currents behind the screen and in the gravel pack. The other tool causes alternating bursts of fluid, creating pulsating pressure waves within the wellbore and formation fluids. In both cases it is believed that the damage is removed; by a combination of hydraulic and chemical effects. However, the principle behind the delivery of hydraulic energy differs between the two tools.. This paper describes the three gravel packed jobs. Results from these treatments will be presented and the effectiveness of the two coiled tubing tools deployed will be compared.