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Accelerators speed up or shorten the reaction time required for a cement slurry to become a hardened mass. In the case of oilfield cement slurries, this indicates a reduction in thickening time and/or an increase in the rate of compressive-strength development of the slurry. Acceleration is particularly beneficial in cases where a low-density (e.g., high-water-content) cement slurry is required or where low-temperature formations are encountered. Of the chloride salts, CaCl2 is the most widely used, and in most applications, it is also the most economical. The exception is when water-soluble polymers such as fluid-loss-control agents are used.
Summary Experiments on oil well cement (OWC) slurries were performed using the newly developed laboratory-scale wellbore simulation chamber (WSC). The WSC can simulate hydrostatic pressure reduction in the cemented annulus and possible gas migration under representative conditions. Forensic analysis shows that pressurized fluids can result in porous cement and gas channeling during cement slurry gelation. By analyzing the temperature history of hydrating cement using degree of hydration, the evolution of cement hydration was characterized for slurry designs cured at different hydration rates. This provides the opportunity to parameterize the slurry designs and other important factors associated with wellbore conditions. Introduction Gas migration into hydrating cement slurries, which requires costly remedial well treatments, is a major reason for well completion failures (Bonett and Pafitis 1996). The first documented research attempting to explain the gas communication by means other than leakage along interfaces was performed by Carter and Slagle (1972). It was found that gases and other fluids can invade the annular cement slurry as a result of hydrostatic pressure reduction during the early stage of cement hydration (short-term gas migration) (Nelson and Guillot 2006). Available theories regarding gas migration during this early hydration stage attribute the occurrence of gas migration to an ineffective initial hydrostatic head, an unstable cement slurry design, fluid loss after cement placement, and weak bonding at interfaces as cement hydrates. Gases do not invade the cement slurry if the slurry pore pressure remains above the formation gas pressure (Cheung and Beirute 1985). It was found that hydrostatic pressure in the cement column declines shortly after cement placement (Brufatto et al. 2003). Once the hydrostatic pressure decreases to a point below the formation gas pressure, gas migration may occur if the cement matrix has not yet developed enough strength to withstand gas invasion. In the Minerals Management Service reporting system, nearly all post-cementing gas flows occurred 3 to 8 hours after cementing jobs (Kellingray 2007). Cement hydration involves changes in both the chemical and physical properties of the cement slurry. Due to the difficulties in modeling time-dependent properties of hydrating cement slurry, the petroleum industry uses empirical approaches when designing cement slurries able to reduce the risk of gas migration (Kremieniewski and Rzepka 2018).
Sugar is widely recognized as a cement retarder by the drilling industry and has been used in cementing operations where cement returns are expected on surface. Experts disagree about the effect that sugar has on cement slurries, a few believe that it acts as both an accelerator and a retarder depending on the concentration, but the majority believe that the sugar acts as a retarder only. Preliminary lab tests performed at Louisiana State University showed that sugar could be both, a retarder or accelerator, depending on the concentration of sugar used. The effect appeared to be quite controversial and the issue deserved further study. The objectives of this research project were to verify these unexpected results, perform more testing, and try to find an ambient concentration of sugar that has no effect on the thickening time of the slurry.
Abstract The goal was to search for a replacement of CaCl2 which presents the most widely used accelerator for oil well cement used in cold and arctic environments and sometimes in deepwater drilling. For this purpose, novel calcium silicate hydrate (C-S-H) nanoparticles were synthesized and tested. The C-S-H was synthesized by the precipitation method in an aqueous solution of polycarboxylate (PCE) comb polymer which is widely used as concrete superplasticizer. The resulting C-S-H-PCE suspension was tested in the UCA instrument as seeding material to initiate the crystallization of cement and thus accelerate cement hydration as well as shorten the thickening time at low temperature. It was found that in PCE solution, C-S-H precipitates first as nano-sized droplets (Ø ~20 - 50 nm) exhibiting a PCE shell. Following a rare, non-classical nucleation mechanism, the globules convert slowly to nanofoils (HR TEM images: l ~ 50 nm, d ~ 5 nm) which present excellent seeding materials for the formation of C-S-H from the silicate phases C3S/C2S present in cement. Thickening time tests performed at + 4 °C in an atmospheric consistometer revealed stronger acceleration than from CaCl2 while very low slurry viscosity was maintained, as was evidenced from rheological measurements. Accelerated strength development was checked on UCA cured at + 4 °C and under pressure, especially the wait on cement time was significantly reduced. Furthermore, combinations of C-S-H-PCE and HEC as well as an ATBS-based sulfonated fluid loss polymer were tested. It was found that this C-S-H- based nanocomposite is fully compatible with these additives. The novel accelerator based on a C-S-H-PCE nanocomposite solves the problems generally associated with CaCl2, namely undesired viscosity increase, poor compatibility with other additives and corrosiveness against steel pipes and casing.
Atlasov, R. A. (M.K. Ammosov North-Eastern Federal University, RF, Yakutsk) | Nikolaeva, M. V. (M.K. Ammosov North-Eastern Federal University, RF, Yakutsk) | Popov, B. I. (M.K. Ammosov North-Eastern Federal University, RF, Yakutsk)
The PDF file of this paper is in Russian.
The authors analyzed exploration wells of Mastahskoye gas-condensate field and Nedzhelinskaya area of Yakutgazprom JSC. Possible reasons of low cement up to the surface at high permeability of sandstones of Lower and Middle Jurassic are considered. The practical application of cementing intermediate columns in two stages was studied and taken apart as well as direct and reverse cementing of columns with OD 324mm in abnormal geological conditions. When cementing surface casings in permafrost zones it is necessary to consider low cement up to the surface due to the presence interpermafrost aquifers with low formation pressure and high permeability and tight contact between rock and casing. When cementing the long conductor and surface casings it is absolutely necessary to add cement setting accelerators. To prevent freezing cement slurry must be entered when mixing with special additives reducing setting time. Based on the price to quality ratio the most effective and wide spread cement setting accelerator is calcium chloride. The amount of accelerator is received within 5-10% depending on the cement period of storing. The most rational way to deal with low cement up to the surface is the usage of lightweight cement. Surface casing cementing in permafrost zone without additives of cement setting accelerators does not provide a reliable contact between the casing and the walls of the well. Surface casing cementing in permafrost zone is recommended to do with the addition of calcium chloride and 10% of dry cement weight. In order to lift the cement slurry for the technical and operational columns to the wellhead in the presence of cementing, absorption should be carried out in two or more stages. To run in hole of intermediate columns must be divided into sections. While cementing production casings cementing collars must be used. During the run in hole production casing with OD 146mm cementing collars must be installed above the intermediate shoe string. It is recommended to use the cement slurry with a specific weight of 1.25-1.30 kg/m3.
Выполнен анализ материалов геолого-разведочных скважин Мастахского газоконденсатного месторождения и Неджелинской площади ПО «Якутгазпром». Рассмотрены возможные причины недоподъема цементного раствора до устья скважины при высокой проницаемости песчаников нижней и средней юры. Исследованы и подробно разобраны практики применения цементирования технических колонн в две ступени, а также прямого и обратного цементирования 324-мм колонны в осложненных горно-геологических условиях. При цементировании кондукторов в зонах многолетнемерзлых пород необходимо учитывать такие осложнения, как недоподъем цементного раствора до устья в связи с наличием межмерзлотных водоносных пластов с низкими пластовыми давлениями и высокой проницаемостью и ненапряженный контакт цемента с породой и обсадной колонной. При цементировании удлиненных направлений и кондукторов обязательно добавление ускорителей сроков схватывания цементного раствора. Для предотвращения замерзаний цементного раствора необходимо при его затворении вводить специальные добавки для сокращения сроков схватывания. Самым эффективным и распространенным ускорителем сроков схватывания цемента является хлористый кальций. Количество вводимого ускорителя принято в пределах 5-10 % в зависимости от срока хранения цемента. Наиболее рациональным способом борьбы с недоподъемом цементного раствора является применение облегченных цементов. С целью подъема цементного раствора за техническими и эксплуатационными колоннами до устья при наличии зон поглощения цементирование рекомендовано проводить в две и более ступени. Для этого необходимо спуск технических колонн проводить секционно; при цементировании эксплуатационных колонн применять заливочные муфты. При спуске 146 мм эксплуатационных колонн заливочные муфты необходимо устанавливать выше башмака технической колонны. Рекомендовано применение цементных растворов с плотностью 1,25-1,30 кг/м3.
Abstract The primary objective of oilwell cementing is zonal isolation (i.e., restricting fluid movement across various zones within formations). Another equally important function is to support casing from various operationally induced mechanical and thermal stresses. To achieve successful zonal isolation, the cement sheath should possess important properties, including low permeability, high early compressive strength, good tensile strength, etc. This article presents a detailed experimental investigation of the effects of various nanomaterials on cement slurry properties. Nanomaterials are used in several fields, including catalysis, polymers, electronics, and biomedical applications. Because of their small particle size, these materials have high surface energy and hence higher reactivity. For this reason, nanomaterials are often necessary in small quantities for enhancing specific properties of the base material. The development of high-performance fluid systems for oil and gas applications is possible through nanotechnology. In recent years, many studies have shown the usefulness of nanomaterials in enhanced oil recovery (EOR) and drilling fluid applications. Investigations have also shown the use of nanomaterials in oilwell cementing. The experimental investigation of the effects of various nanomaterials on cement slurry properties shows that the addition of a mere 1.5% of halloysite increased tensile strength by approximately 141%. Similarly, the addition of nano-alumina resulted in achieving early compressive strength at temperatures as low as 40°F. Hence, these nanomaterials can act as nonchloride-based accelerators for low-temperature applications. Additionally, it was observed that, to obtain the greatest benefit of using nanomaterials, it is necessary to disperse them in desired media before use. The results of this study on the applications of nanotechnology in oilwell cementing provide an opportunity to use nanomaterials for enhanced cement slurry properties with minimal cost.
Zeng, Jianguo (Tianjin Bo-Xing Engineering Science & Technology Limited Company of CNPC) | Yu, Gang (Tarim Oilfield Branch Company of PetroChina) | Liu, Aiping (Tianjin Bo-Xing Engineering Science & Technology Limited Company of CNPC) | Sun, Fuquan (Tianjin Bo-Xing Engineering Science & Technology Limited Company of CNPC) | Xia, Yuanbo (Tianjin Bo-Xing Engineering Science & Technology Limited Company of CNPC) | Li, Pengxiao (Tianjin Bo-Xing Engineering Science & Technology Limited Company of CNPC) | Yuan, Zhongtao (Tarim Oilfield Branch Company of PetroChina)
The main challenging cement shiny problems, such as weak formation with the pressure gradient of about 1.60g/cm3, non-retrogressive compressive strength at 240 °C in steam stimulation and fast compressive strength development at about 18°C in the wellhead, have been encountered in thermal production wells. To answer these challenges, the high-temperature resistant lightweight cement slurries with the densities of 1.40g/cm3 and 1.50g/cm3 were designed by choosing density reducer cenosphere and applying the high packing theory. These additives, such as retarder, fluid loss additive and accelerator, were also developed. The rheology, API fluid loss, compressive strength, free water and compressive strength stability in 240°C were researched as well. The result showed that the properties of the cement slurries meet the need of the cementing job at 50°C. The compressive strength on the top of the lightweight cement slurry column was more than 3.5MPa after curing for 36h at 18 °C. The compressive strength was more than 30M4Pa and did not regress after curing for 28d at 240 °C. The properties of the high-performance lightweight cement slurries could meet the requirements of the thermal production wells at 240°C.
Both the China's increasing demand for energy and the decline of traditional oil and gas reserves have forced operators to go after unconventional resources. As an abundant and important unconventional resource, heavy oil could be an answer to the demand for energy. Thermal recovery technology, the most effective heavy oil exploitation way, is currently the largest and most mature applied FOR techniques of the world. The technology predominantly via steam huff and puff also with continuously applied steam flooding, electric heating and SAGD technology could benefit 1500 ×104 tons of oil every year in China (Wang, 2010).
The main challenging cement slurry problems, such as weak formation with the pressure gradient of about 1.60g/cm³, non-retrogressive compressive strength at 230° C. in steam stimulation and fast compressive strength development at about 18°C in the wellhead, have been encountered in thermal production wells. The conventional lightweight cement slurries, however, usually developed low and retrogressive compressive strength, which limits their applications in cementing for heavy-oil reservoirs. In order to cope with these challenges, the high-tolerant lightweight cement slurries for 232°C steam huff and puff of the thermal production wells, based on concept of high packing density, were invented by Schlumberger Oilfield Services in the late 20th century [Biosnault, 1999 and Al-Suwaidi, 2001]. In this paper, high-performance lightweight cement slurries for thermal production wells with the densities of 1.40g/cm³ and 1.50g/cm³ have been developed based on high-packing theory. The long-term compressive strength of set cements at 240°C was also investigated.
ABSTRACT: As the operation time of tunnels grows, the potential damages due to earthquake have become an issue that cannot be neglected. This research implemented accelerators in a highway tunnel passing through a slope in southeast Taiwan. After a seismic event with 5.0 Richter magnitude from 12.7 km beneath, 12.8 km to the case tunnel, the coseismic acceleration at five different locations in the tunnel returns satisfactory outcome. The Fourier spectra after Discrete Fast Fourier Transform reveal a 4–6 Hz predominant frequency of the tunnel lining. The maximum coseismic acceleration is 37.38 gal. All five accelerators on vault and two sidewalls show similar predominant frequencies in three dimension, proving that the predominant frequency of a site governs the predominant frequency of a tunnel. However, the secondary frequencies of accelerators on hill side sidewall of 11.4 and 11.7 Hz in vertical direction are apparently higher than the other two accelerators on creek-side sidewall of 8.6 and 6.4 Hz. The results describe the influences of both site characteristics and topography on the seismic response of a tunnel. The rare in-situ monitored data sets a starting post to quantify and verify contemporary methodologies on seismic-related problems of tunnels.
Riyanto, Latief (PETRONAS Carigali Sdn. Bhd. (PCSB)) | Saleh, Malaz (PETRONAS Carigali Sdn. Bhd. (PCSB)) | Goh, Kellen (PETRONAS Carigali Sdn. Bhd. (PCSB)) | Ambrose, Jonathan (Halliburton) | Kristanto, Tutus (Halliburton) | Hong, Chua Yek (Halliburton)
Abstract The integrity of sand control method is often compromised as wells get older and the field becomes more mature. An operator in East Malaysia pursued a cost-effective alternative remedial sand-control solution to restore the functionality of its sand control completion and provide unhindered oil production in a well. The well, located offshore Sarawak Malaysia, was a single string oil producer completed in 1987 with gravel pack and screens. It was a producing well for several years until the gravel pack completion failed and the well started to produce excessive sand. The well was beaned down (BD) to achieve an acceptable sand production limit by the operator of below 15 pound per thousand barrels (pptb). The initial remedial sand control measure was to install a thru-tubing screen, hung inside the production tubing. The thru-tubing screen failed to control the formation sand and a second 200 micron thru tubing screen was installed. That screen managed to control the sand production at acceptable levels but induced significant pressure drop, which reduced the oil production from the optimum level of production. Workover (WO) operations would involve pulling the existing completion, and re-gravel packing the zone would be costly. In addition to cost, induced mechanical skin in a gravel pack might not be lower than thru-tubing screen application. Chemical consolidation treatments using solvent-based resins historically have been used successfully as alternatives to remedial sand control, although their application, has typically been limited to short intervals. An aqueous based consolidation resin was developed that provides some advantages compared to conventional solvent based resin systems. The aqueous based resin system uses an internally cured water-based epoxy resin. Unlike the solvent based resin systems, which have a low flash point, the aqueous base consolidation resin system is not flammable. It is safer and less complex operationally. The consolidation-fluid mix can also be foamed for diversion purposes to treat wells with relatively large variations in permeability over longer zones compared to the solvent based resins. This paper describes the treatment background, engineering approach, laboratory testing, fluid design stages, quality assurance/quality control (QA/QC) procedures, and the treatment execution for the chosen well. The field trial showed no sand was produced after treatment. In fact, the production rate was twice that of the production rate with the thru tubing screen in place. The promising result from this well creates new opportunities for simple, environmentally acceptable, and cost-effective remedial sand-control solutions for the operator.