Behavior of oil well cement slurry systems aged in CO 2 -saturated water under high pressure and temperature
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Behavior of oil well cement slurry systems aged in CO2‑saturated water under high pressure and temperature Jonathan Dias Nascimento1,3 · Camila Aparecida Abelha Rocha2 · Cristina Aiex Simão3 · Romildo Dias Toledo Filho1 Received: 14 February 2020 / Accepted: 15 September 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract This paper aims at studying the effect of the exposure of hardened cement slurries, intended for oil wells, to carbon dioxide (CO2) in the state of water saturation. Four different systems of cement slurry with water/solid (w/s) ratio of 0.33 ± 0.01 and density of 1.98 ± 0.06 g cm−3 were design. The first cementitious system was a reference cement slurry (PR) commonly used for the cementation of wells. The other systems were obtained modifying the reference slurry with the addition of styrene-butadiene rubber (PRSBR), silica fume (PRSF) or crystalline silica (PRCS). The slurries were optimized in order to fulfill the rheological, physical and mechanical requirements to the cementation of oil fields. Cement slurries samples were aged in CO2-saturated water at 65 °C and 21 MPa pressure, for 30, 60 and 90 days. The degradation of the slurries was studied by thermogravimetric analysis. The carbonation rate with time and the carbonation profile along the diameter of the cylindrical samples were evaluated. Gas permeability and total porosity tests were carried out before and after aging also were determined to complement the analysis. From the results obtained, it was observed that the PR and PRSF mixtures presented the smallest amounts of calcium carbonate, especially in the internal layers of the sample. This happens due to the low permeability and total porosity of these mixtures that presented a high content of hydration products, including C–S–H. The PRSBR and PRCS mixtures presented high porosity and permeability and consequently higher carbonation than the PR mixture for all ages of CO2 exposition evaluated. Keywords Silica fume · Styrene-butadiene rubber · Crystalline silica · Cement slurry · Carbonation · Thermal analysis
Introduction The pre-salt petroleum discovery has provided the Brazilian industry with a great increase in oil and gas reserves. Nevertheless, these stocks might present high rates of carbon dioxide (CO2), and their reaction to cement slurries components, during the productive life of oil fields, may lead to carbonation occurrences, degradation and loss of integrity of petroleum well’s hardened cement slurry.
* Romildo Dias Toledo Filho [email protected] 1
Programa de Engenharia Civil (PEC), Universidade Federal do Rio de Janeiro (UFRJ), Rio De Janeiro, RJ, Brazil
2
Departamento de Engenharia Civil (TEC), Universidade Federal Fluminense (UFF), Niterói, RJ, Brazil
3
Petróleo Brasileiro S.A. (PETROBRAS), Rio De Janeiro, RJ, Brazil
According to Savija and Lukovic [1], the carbonation progress rate is proportional to the content of materials susceptible to carbonation, such as calcium hydroxide (CH)1 , calcium silicate hydrate (C–S–H), and others com
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