Cement attack by acid during matrix acidizing operations has created severezonal isolation problems in wells with multiple adjacent permeable zones, operated by PETROBRAS. This effect was observed in several wells treated with conventional HCl-HF acid mixtures, even when cement bond logs prior to the acidjob were excellent. This paper presents a series of lab experiments showing that acetic acid, alone or mixed with HF, dissolves much less cement than HCl and HCl-HF mixtures with the same carbonate dissolving power. The reaction of acetic acid with cement forms a protective skin that inhibits further acid attack. The organic formulations were tested in an acidizing simulator, before being used in the field. The paper also presents field test results which confirmed that the acetic acid mixtures did not break zonal isolation (cement consumption was restrained to the perforated interval) and were able to generate 6- to 40-fold increases in the injectivity and productivity of the wells. Introduction Cement solubility in acids has been shown to be a problem, both in the field and by laboratory testing. Ref. 1 shows that HCl, HCl-HF, and citric acid have a strong detrimental effect on the cement, resulting in weight loss and compressive strength loss. Traditional views held that due to the formation of a protective skin, acid-cement reaction would be limited. However, severe zonal isolation problems have been observed, following HCl-HF treatments. The first approach to solve the problem was the development of acid-resistant cement. These blends use liquid latex that inhibits acid attack by coating cement particles and by reducing the permeability of the cement. Refs. 2 and 3 address the use of acid-resistant cement blends for primary cement and squeeze operations. This solution may be easily applied to new wells, in which the primary cement and squeeze jobs in front of the pay zones are composed of acid-resistant slurries.

fax 01-972-952-9435. AbstractGravel packs completions are widely used today on unconsolidated formations worldwide, as to provide sand control, and, as such, behaves as a filter. A filter is subjected to be plugged by fines, (heavy) hydrocarbons, scale depositions, among others, which may result in a considerable drop of production, or even total lack of. The synergism of coiled tubing rotating, cyclical jetting tools, and adequate acid systems has demonstrated great results in Northeast of Brazil. The cyclical jetting tool acts to disaggregate plugging particles from the gravel, and the acid acts to chemically dissolve acid soluble plugging materials. The acid system utilized is quite unique and simple. The method consists of pressure cyclically jet 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, because the acid system is a high pH one (2 -3), and uses an organophosphonic acid to control the dissolution of carbonates, and, therefore, controls the precipitation of insoluble fluorides. This way, release of calcium ions is less likely to occur. The main acid system is hydrofluoric (HF) based, generating HF on a controlled fashion, using much less hydrochloric acid (HCl) when compared to regular HF acid systems. This paper describes three gravel packed wells treated with this single step acid system. These wells were very similar, and used the same acid recipe However, the first well was treated with a rotating pressure cycle jetting tool, and the remaining two wells used a different pulsation tool. All wells showed production increase, but the first well yielded much better results compared to the last two. Results from these three treatments will be presented and compared as towards the effectiveness of coiled tubing tools deployed.

fax 01-972-952-9435. AbstractGravel packs completions are widely used today on unconsolidated formations worldwide, as to provide sand control, and, as such, behaves as a filter. A filter is subjected to be plugged by fines, (heavy) hydrocarbons, scale depositions, among others, which may result in a considerable drop of production, or even total lack of. The synergism of coiled tubing rotating, cyclical jetting tools, and adequate acid systems has demonstrated great results in Northeast of Brazil. The cyclical jetting tool acts to disaggregate plugging particles from the gravel, and the acid acts to chemically dissolve acid soluble plugging materials. The acid system utilized is quite unique and simple. The method consists of pressure cyclically jet 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, because the acid system is a high pH one (2 -3), and uses an organophosphonic acid to control the dissolution of carbonates, and, therefore, controls the precipitation of insoluble fluorides. This way, release of calcium ions is less likely to occur. The main acid system is hydrofluoric (HF) based, generating HF on a controlled fashion, using much less hydrochloric acid (HCl) when compared to regular HF acid systems. This paper describes three gravel packed wells treated with this single step acid system. These wells were very similar, and used the same acid recipe However, the first well was treated with a rotating pressure cycle jetting tool, and the remaining two wells used a different pulsation tool. All wells showed production increase, but the first well yielded much better results compared to the last two. Results from these three treatments will be presented and compared as towards the effectiveness of coiled tubing tools deployed.