SCALE FORMATION IN WELLS DRILLED ON CARBONATE RESERVOIRS DEVELOPED THROUGH WATERFLOOD MECHANISM Gustavo Pereira Projeto de Graduação submetido ao Corpo Docente do Curso de Engenharia de Petróleo da Escola Politécnica da Universidade Federal do Rio de Janeiro como parte integrante dos requisitos necessários à obtenção do título de Engenheiro de Petróleo. Orientadores: Santiago Gabriel Drexler e Paulo Couto. Rio de Janeiro Março de 2020
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SCALE FORMATION IN WELLS DRILLED ON
CARBONATE RESERVOIRS DEVELOPED
THROUGH WATERFLOOD MECHANISM
Gustavo Pereira
Projeto de Graduação submetido ao Corpo
Docente do Curso de Engenharia de Petróleo
da Escola Politécnica da Universidade Federal
do Rio de Janeiro como parte integrante dos
requisitos necessários à obtenção do título de
Engenheiro de Petróleo.
Orientadores: Santiago Gabriel Drexler e Paulo Couto.
Rio de Janeiro
Março de 2020
iii
Pereira, Gustavo Medeiros
Scale Formation in Wells Drilled on Carbonate Reservoirs
Developed Through Waterflood Mechanism / Gustavo
Medeiros Pereira. – Rio de Janeiro: UFRJ/ Escola
Politécnica, 2020.
IX, 42 p.: il.; 29,7 cm.
Orientadores: Santiago Gabriel Drexler e Paulo
Couto.
Projeto de Graduação – UFRJ/ Escola Politécnica/
Curso de Engenharia do Petróleo, 2020.
Referências Bibliográficas: p. 40.
1. Incrustração Salina. 2. Garantia de Escoamento. 3.
Carbonato de Cálcio. 4.Sulfato de Bário. 5. Reservatórios
Carbonáticos. I. Drexler, Santiago Gabriel e Couto,
Paulo. II. Universidade Federal do Rio de Janeiro, Escola
Politécnica, Curso de Engenharia do Petróleo. III. Scale
Formation in Wells Drilled on Carbonate Reservoirs
l d h h fl d h i
iv
“What matters the most is how well you
walk through the fire.”
v
AGRADECIMENTOS
Agradeço aos meus pais, Gisele Matildes Medeiros e João Batista Pereira, por
apoiarem as minhas escolhas e permitirem que eu seguisse meu sonho. Pela
educação e pelo privilégio de ter tido oportunidade de acesso a uma faculdade pública.
Agradeço ao meu parceiro, Felipe Zanetti Comério, por ter me suportado neste
(e em dezenas de outros) desafio acadêmico. Por ter me ensinado muito ao me
mostrar seus pensamentos e compartilhar tantas experiências comigo. Por todo o
amor e por toda a força. Independente do amanhã, vivemos o hoje.
Agradeço aos meus incríveis amigos, que contribuíram para a minha formação
acadêmica, pessoal e profissional, me acompanhando nos anos de Fundão. À família
do 203, meu alicerce ao longo desses anos em terras cariocas: Thayná Gonçalves,
minha maior parceira nos melhores e piores momentos; Willian Velasco, o primeiro
amigo que tive em que me vi, e Vinícius Felipe, que embarcou comigo na primeira
colossal mudança de nossas vidas. Ao amigo com o coração mais dourado que já vi,
Oziel Baiense. Ao super-Grupo 3, Matheus Gonzaga e Marco Tulio Portella, sem o
qual minha trajetória acadêmica teria sido catastroficamente diferente. À Marília
Cizeski e Rafaela de Pieri, pelo amor nutrido, mesmo a distância, pelos desabafos,
conselhos e por compartilharem a dor dessa saudade comigo. E todos os demais que
fizeram parte dessa trajetória.
Agradeço à professora Rosemarie Bröker Bone, que abriu seu laboratório para
receber alunos do país inteiro, nos ensinando não só economia e petróleo, mas
preciosas lições de vida. Por ter sido quase uma mãe sulista em terras cariocas. E por
ter lutado pela excelência do curso de Engenharia de Petróleo da Universidade
Federal do Rio de Janeiro, e por seus alunos, por décadas.
Agradeço ao coorientador Paulo Couto, pelo apoio na monografia, por ser a
referência de uma legião de engenheiros quando se trata de Engenharia de
Reservatórios, e pelos esforços hercúleos em prol do curso de Engenharia de Petróleo
e de seus alunos.
Agradeço ao meu orientador, Santiago Gabriel Drexler, que acreditou neste
trabalho e esteve disponível em todos os momentos para suporte. Pelas ideias de
melhoria, pela paciência e pelo esforço, mesmo em épocas ocupadas. E por suas
aulas ao longo do curso, de preparo, pontualidade e conhecimento exemplares.
Agradeço especialmente aqueles que impactaram de uma maneira inigualável
minha trajetória profissional. À Shell Brasil, especialmente João Baima e Philip
Bogaert, pelos ensinamentos, pela amizade e por acreditarem em meu potencial como
poucos. Vocês me apresentaram ao tema e, sem vocês, esse trabalho não existiria. À
vi
Tatiana Hallak, pela mentoria e pelos conselhos. À rede TrueColors, Luiz Oliveira,
Yasmin Reis e Ruan Melandres, por terem construído um lugar onde as pessoas são
livres para serem quem são e, só assim, florescerem pessoal e profissionalmente.
Por fim, agradeço à Universidade Federal do Rio de Janeiro, a Universidade do
Brasil, por ter se tornado minha segunda casa nesses últimos anos. Por não ter me
ensinado apenas uma engenharia de qualidade inigualável, mas sobre a vida e a
sociedade. Espero um dia poder retribuir a honra de ter me graduado em uma
universidade de tamanha excelência e história.
vii
Resumo do Projeto de Graduação apresentado à Escola Politécnica/ UFRJ como
parte dos requisitos necessários para a obtenção do grau de Engenheiro de
Petróleo.
FORMAÇÃO DE INCRUSTAÇÕES SALINAS EM POÇOS PERFURADOS EM
RESERVATÓRIOS CARBONÁTICOS DESENVOLVIDOS PELO MECANISMO DE
INJEÇÃO DE ÁGUA
Gustavo Medeiros Pereira
Março, 2020
Orientadores: Santiago Gabriel Drexler e Paulo Couto.
Curso: Engenharia de Petróleo
A incrustação de sais inorgânicos no sistema de produção de óleo e gás é um dos
problemas mais comuns de garantia de escoamento, estabilidade e otimização da
produção, principalmente em campos desenvolvidos através da injeção de água
(waterflood). Este estudo visa demonstrar o uso de uma modelagem iônica
realizada no software OLI ScaleChem, somada a uma ferramenta de visualização,
na previsão de deposições no poço e seus arredores. A ferramenta desenvolvida
permite a análise de dezenas de poços simultâneamente, simplificando as
análises técnicas requeridas para a tomada de decisão e tornando mais fácil a
escolha dos poços críticos. Ela também permite a inferência dos tipos de sais
depositados no poço e o melhor plano de tratamento do mesmo, para aumentar a
produção. Colaborando com a análise desenvolvida, este estudo trará uma revisão
bibliográfica do tema e de conceitos químicos a ele relacionados. Por fim, a
ferramenta desenvolvida é utilizada em um estudo de caso de um poço em
reservatório carbonático desenvolvido pelo mecanismo de waterflood. Ela aponta
para a deposição de sulfato de bário e carbonato de cálcio, o que foi corroborado
pelas técnicas usualmente utilizadas na indústria, e considerado para o tratamento
do poço. Tal tratamento permitiu que a produtividade do poço dobrasse, o que
confirma a importância deste estudo, já que permite simplificar o processo de
melhoria na produção de maneira mais rápida e barata.
Palavras-chave: incrustação salina, garantia de escoamento, carbonato de cálcio,
sulfato de bário, reservatórios carbonáticos.
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Abstract of Undergraduate Project presented to POLI/UFRJ as a partial fulfillment
of the requirements for the degree of Engineer.
SCALE FORMATION IN WELLS DRILLED ON CARBONATE RESERVOIRS DEVELOPED THROUGH WATERFLOOD MECHANISM
Gustavo Medeiros Pereira
March, 2020
Advisors: Santiago Gabriel Drexler and Paulo Couto.
Course: Petroleum Engineering.
The deposition of inorganic salts along oil and gas production system is one of the
main issues for flow assurance and production stability and optimization, especially
in fields developed through the waterflood mechanism. This study aims to
demonstrate the use of an ionic model developed in OLI ScaleChem, aligned with
a visualization tool, on predicting the depositions on the well and near-wellbore
area. The developed tool allows for the analysis of dozens of wells simultaneously,
simplifying the required technical analysis that impact directly the decision-making
process by making it easier to define the most critical wells. It also allows the
inference of the types of salts deposited downhole and, therefore, an improved
plan for the treatment and removal of it, which will increase the production.
Supporting the developed analysis, the study carries out a revision of current
literature on the main scale formation mechanisms and most common deposited
salts in the industry, as well as the necessary chemistry concepts. Finally, the
solution presented is utilized on a case study of a well in an uncharacterized
carbonate reservoir developed through waterflood. It points to barium sulphate and
calcium carbonate deposition, which is corroborated by the industry’s usual
diagnostic methods and taken into consideration in the development of a treatment
plan. After the plan was executed, the productivity of the well doubled, which
indicates the importance of this study that can simplify the process of production
improvement in a quicker and cheaper manner.
Keywords: salt deposition, flow assurance, calcium carbonate, barium sulfate,
After all these variables are calculated, every required value for the
charts are available and the analysis can be done.
4.3. Spotfire Plots and Analyses
By plotting the activity values for each cation/anion pair and its related
saturation curve, the assessment of risk of any salt deposition on a chosen part of the
system can be done. As the produced water sample that was chemically analyzed was
taken on the topsides of the producing unit, the ions dissolved on the water should not
reach the saturation curve and if they do that is likely due to the effect of additional
chemical components added to the system (i.e. scale inhibitors) or uncertainties that
this method carries related to the heterogeneities of the different drilled locations in the
reservoir and the modelling itself. Therefore, this analysis provides information about
which salt is more likely to deposit, rather than a quantitative output. This is a very
valuable information, since it can help infer the type of salt depositing on the near
wellbore area and, therefore, what is the most appropriate treatment method for
impairment reduction/production improvement, also pinpointing which wells need an
individual model and analysis with other methods. The following chapters will exemplify
the plots for the main salts deposited on oil and gas operations, stated in Chapter 2,
except for the ones involving Iron, since they are mainly deposited in the production
system and not in the near wellbore area nor inside the well, on “Well A”, the impairing
well presented in Chapter 4.1.
4.3.1. Calcium Sulphate – Anhydrite and Gypsum
For calcium sulphate, by following the procedures stated in the past chapters,
the output will be Figure 4.4 and 4.5. For Gypsum, X axis is Ca activity and Y axis is
SO4 activity, considering the activity of water aH2O (Figure 4.4) and for Anhydrite the
axes are the same but not taking into consideration the water activity (Figure 4.5). The
35
arrows are representing chronology of the sampling and can indicate a change in the
produced water chemistry from reservoir, connate water, to injection water (i.e. less
calcium, more sulphate).
Figure 4.4 Activity plot for Calcite. Source: Prepared by the author.
36
Figure 4.5 Activity plot for Anhydrite. Source: Prepared by the author.
The charts indicate that, due to the distance between the water samples and
the saturation curve for these salts, it is not expected to find Calcium Sulphate
depositions downhole of the well.
4.3.2. Barium Sulphate and Strontium Sulphate
Figure 4.6 displays the chart for Barium Sulphate, with Ba on the X axis and
SO4 on the Y axis. For this salt, the points are mostly inside the curve and there is a
strong indication of this salt’s deposition. Usually, Strontium Sulphate occurs co-
precipitated with Barium Sulphate, and when analyzing the chart in Figure 4.7, the
samples are also close to the saturation curve, corroborating for the case of this salt’s
coprecipitation.
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Figure 4.6 Activity plot for Barium Sulphate. Source: Prepared by the author.
Figure 4.7 Activity plot for Strontium Sulphate. Source: Prepared by the author.
As these salts have a natural occurring radioactivity, gamma ray logging can be
done to ensure the existence of the salt prior to the treatment and scale squeeze
planning. Since there is indication of scale deposition for these specific salts, i.e.
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productivity drop and points near saturation curve, they need to be further investigated.
Possible approaches could be suspended solids analysis and logging. Sulphate-based
scale builds up slowly but is very hard to dismantle, possibly creating unrepairable
damage.
4.3.3. Calcium Carbonate
For Calcium Carbonate, Figure 4.8, most of the chemical analysis are also near
the threshold or above it, indicating that there might be Calcium Carbonate deposition.
Analyzing the suspended solids on the produced water could ensure that the well is
being treated for the right type of salt and in the right manner.
Figure 4.8 Activity plot for Calcium Carbonate. Source: Prepared by the author.
4.4. Treatment, Prevention and Results
A caliper tool was run through the aforementioned well and reported changes in
diameter, particularly below the perforations. This is an indication of scale deposition in
the area, as predicted by the model. Gamma ray also found several radiation points
throughout the wellbore. The well was treated with diesel, solvent, EDTA and HCl,
aiming for the dissolution of sulphate-based scales and calcium carbonate, as
predicted above, plus scale inhibitor to postpone the next deposition. Figure 4.9 shows
that productivity doubled after the treatment, marked as a black line in Figure 4.9,
which would confirm its efficiency, but several of the gamma ray reaction spots did not
disappear and the productivity quickly starts dropping again, creating the possibility that
39
the chosen chemical compound for scale inhibition did not adhere to the rock as
expected, or volumes were not enough.
Figure 4.9 Productivity Index before and after the scale treatment. Source:
Prepared by the author.
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5. CONCLUSIONS
As energy demand increases and the world develops, while petroleum is still
the main energy source worldwide, production protection will need to play a bigger role
in the energy supply. Scaling is still one of the biggest causes of production loss, and
methods to detect the problem before it develops are required. This study introduces a
new methodology to perform surveillance on production wells, avoiding unnecessary
losses and maintaining safe operations.
This study successfully presented a literature review of the issue of inorganic
scaling in oilfield operations, containing its definition, formation mechanisms, usual
salts deposited on oilfield operations, operational problems, associated risks and
preventive and corrective measures. It also introduced he crucial chemistry definitions
to understand the process and the generated model, such as ionic activity, solubility
and saturation ratio. It shall be utilized from here onwards as an important reference for
future works and as introductory material for learning about the issue.
The developed model allows the analysis of hundreds of wells in a second, as
the only requirement is the selection of the desired wells on the Spotfire panel and the
pre-loaded charts will come up. It also permits the comparison between different wells
in the same field, qualitatively knowing which ones are more critical and simplifying a
lot the required analysis to prioritize treatments and, therefore, the decision-making
process. By providing information about which salt is more likely to deposit, it unlocks
the possibility of not only choosing the correct well to prioritize but to assess the correct
treatment method for impairment prevention and remediation.
On the case study, the results brought by the developed model, indicating
barium sulphate and calcium carbonate deposition, were confirmed by physical and
mechanical methods for the presented well. Therefore, the model has proved its
accuracy for qualitative analysis. The cost associated with running it is non-existent
compared to the ones of industry-utilized tools, requiring only man-power and a
software license instead of hundreds of thousand dollars in inspection tools. It does
not, however, replace a more detailed case-by-case analysis on the wells that are
shown to be problematic by the model itself, working as a diagnostic tool and not
necessarily as a treatment-design tool.
Important future work could be done to improve this tool. First, utilizing the
Artificial Intelligence contained in TIBCO Spotfire to generate forecasts of produced
water chemistry and scale deposition based on historical data. Moreover, generating
new data sets for wells surrounding the analyzed produced but that have not had water
breakthrough yet. Finally, additional detailed work on the quantitative side of the model,
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possibly lowering the space taken for a region of the reservoir instead of the entire
reservoir, to allow for a more quantitative analysis that might actually output a
probability of deposition, as the historical data can be manipulated and analyzed in
Spotfire through statistical methods.
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BIBLIOGRAPHY
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