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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.
Abstract To mitigate strength retrogression at temperatures, higher than 230°F, well cement designs typically include strength retrogression control additives (SRCAs). Solid siliceous materials (e.g., silica flour, fume, and sized-sands) are commonly used SRCAs that are incorporated into cements using dry-blending techniques. This study highlights liquid silica compositions as alternative SRCAs to dry-blended silica for high-temperature cementing. Liquid additives can be managed easily, delivered accurately, and offer a reduced on-site footprint, thus making them particularly advantageous for operations offshore and in remote locations. This paper presents a study on the use of liquid silica compositions as SRCAs and their effect on cement slurry properties, such as thickening time, mixability, fluid loss, rheology, and free water. The cement slurry used during the current study was prepared and tested according to API RP 10B-2 (2005). The performance of the liquid silica composition was tested at temperatures up to 400°F. Set cement samples were prepared using the liquid silica composition and silica flour, cured for up to 14 days at different temperatures. In addition, permeability testing was also performed on the samples. This paper presents the findings of this research, including strength and permeability test results on cement blends cured at temperatures of 300, 330, 350, and 400°F. The liquid silica composition, which provided silica to the cement formulation equivalent to 35% BWOC dry silica (48% BWOC liquid SRCA), functioned effectively as an SRCA at temperatures up to 330°F. Signs of strength retrogression were observed at 350°F and were more pronounced at 400°F. A greater concentration of the liquid silica composition may be necessary to prevent strength retrogression at temperatures higher than 330°F. The liquid silica composition also demonstrated mild retardation and a dispersing effect on the slurry. However, it helped enable improved slurry stability and suspension, thus providing improved control over free water without adverse effects on fluid loss and sedimentation. The study results demonstrate that a liquid SRCA can help improve the performance of annular cement designs to provide dependable barriers and effective zonal isolation during high-temperature cementing applications. The improved performance enabled by this liquid silica composition verifies its potential use as an alternative SRCA for high-temperature oil well cementing operations.
Murtaza, Mobeen (King Fahd University of Petroleum & Minerals) | Rahman, Mohammad Kalimur (King Fahd University of Petroleum & Minerals) | Al Majed, Abdulaziz Abdulla (King Fahd University of Petroleum & Minerals) | Tariq, Zeeshan (King Fahd University of Petroleum & Minerals) | Mahmoud, Mohamed (King Fahd University of Petroleum & Minerals)
Abstract The mechanical properties are determined to measure the sustainability and long-lasting behavior of cement slurry under wellbore conditions. Different measurement methods were adopted in the past to study the mechanical behavior of a cement slurry. The most commonly used methods applied in oil and gas sector are cement crushing and acoustic velocities measurements. Both techniques have some limitations and additional techniques are warranted. Scratch test technique is commonly used for characterization of mechanical properties of metals, coatings and other materials. Advances in scratch testing of materials has resulted in its application to cohesive material such as rocks and cement. Recently, scratch test has been successfully applied for the strength evaluation of oil well cement. In this paper, we present the results of scratch tests carried out on oil well cement using type G cement and the specimens modified using nanoclay as an additive. The compressive strength test results from scratch test was compared to the macro level testing of cement cores loaded in compression up to failure. The dynamic elastic parameters of cement mix, elastic modulus and Poisson's ratio, were also determined using the scratch test. The scratch test based strength measurement technique will serve as a very handy tool for drilling and geomechanics engineers to study the mechanical properties of the cement slurry aged under different wellbore conditions with high level of certainty.
ABSTRACT: Cement strength retrogression under high-temperature restricts the use of the oil well cement. Previous studies evaluated the effect of the silica (SiO2) particles on mitigating the effect of temperature on the mechanical properties of the cement at specific time periods. In this work, the changes in the mechanical properties of the SiO2 based cement will be evaluated continuously with time from a slurry to set. Two samples were prepared, one without SiO2 while the other one containing 35% BWOC of SiO2 particles. The changes in the mechanical properties of the samples when exposed to 140°C were then studied. The results of this study confirmed that incorporating 35% BWOC of SiO2 particles accelerated the hydration process, and thus, improved the cement strength retrogression resistance. The final stabilized compressive strength of the base sample (i.e. sample without SiO2 particles) was 743 psi compared to 6200 psi for the sample incorporating SiO2 particles. Poisson's ratio of the sample incorporating SiO2 stabilized at 0.19 which is equivalent to 52.8% of the Poisons ratio for the base cement. The final stabilized bulk, Young's, shear, and uniaxial compaction moduli of the sample including 35% BWOC of SiO2 are 1.87, 3.86, 2.71, and 2.46 of those for the base sample, respectively.
Oil well cement is used to provide oil and gas wells with the desired mechanical stability needed to prevent formation of micro-cracks which will present conduits for the formation fluids to flow between different drilled formations and enable the corrosive formation fluids to contact the well casing. To meet the requirement of the needed isolation efficiency throughout the life of the well, the cement sheath filling the gap between the casing and the formations must be hard enough and durable (Rabia, 2001; Mitchell and Miska, 2011).
The downhole operating temperature or the reservoir temperature to which the cement will be subjected is one of the main parameters to be considered while designing the cement slurry and cementing operations, this is because the temperature change affects both the liquid slurry and solid cement sheath (Luke, 2004; Vu et al., 2012; Shahab et al., 2015; Maharidge et al., 2016; Costa et al., 2017; Wang, 2017).
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.
Mahmoud, Ahmed Abdulhamid (King Fahd University of Petroleum & Minerals) | Elkatatny, Salaheldin (King Fahd University of Petroleum & Minerals) | Ahmed S., Abdulmalek (King Fahd University of Petroleum & Minerals) | Mahmoud, Mohamed (King Fahd University of Petroleum & Minerals)
Abstract The hydrated products of Portland cement drastically change after exposure to high-temperatures, compromising the cement physical properties, especially, its compressive and tensile strengths, this phenomenon is known as strength retrogression. Previous studies showed that the use of silica flour (SF) enhances Class G oil wells cement (OWC) resistance to the strength retrogression due to the formation of long silica chains. In this work, the influence of adding modified montmorillonite nanoclay (NC) particles, which are nanoparticles of layered mineral silicates, on Class G cement strength retrogression resistance under the high-temperature condition of 300°C was evaluated. Six cement slurries were considered in this study, the base sample which has no silica or nanoclay particles, one sample contains 35% BWOC of SF particles only, and 4 samples incorporating 1.0, 2.0, 3.0, and 4.0% BWOC of NC and 35% BWOC of SF were prepared and tested under conditions of low (38°C) and high (300°C) temperature after 7 days of curing. The 300°C was selected to represent one thermal cycle condition when steam is injected into the oil well to increase the oil production for the purpose of enhanced oil recovery (EOR). After preparation, the samples were poured into different molds with specific dimensions based on the targeted test, then cured at the low-temperature condition of 38°C using a water bath, the samples were cured for 7 days. Some of the samples cured at the low temperature for the whole period while others removed in the last three days and cured at a high temperature of 300°C to mimic one steam injection cycle condition. In order to evaluate the effect of the NC particles on mitigating the cement strength loss at high-temperature, the unconfined compressive strength (UCS) and tensile strength tests were performed. The change in the permeability of the samples as a function of NC content and temperature were evaluated. The percentage loss in the water absorbed by NC particles after exposing the cement samples to the high-temperature condition (300°C) was measured. The results revealed that the use of NC (up to 3.0% BWOC) can prevent the cement deterioration under extremely high-temperature conditions of 300°C. This is attributed to two facts, first of all, the NC particles reduced the initial permeability of the samples by filling the nanoscale porous these expected to dominate the control samples (i.e. sample with 0% nanoclay), secondly acceleration of the hydration reaction which results in formation of more stable forms of calcium silicate hydrates (CSH) which leads to enhancement in the cement matrix resistance to the expected forces. At high-temperature environment, the original permeability of the NC-based cement matrix increased mainly due to evaporation of the water absorbed by NC particles when their concentration is maintained below 3.0% BWOC, the use of NC content beyond that concentration (i.e. >3.0%) severely damaged the cement matric microstructure due to agglomeration of nanoparticles.
Abstract Oil and gas operators are facing more challenges than ever before to sustain production and to effectively minimize workover cost associated with remedial cementing. Previously, achieving the initial hydraulic seal with a good cement bond log was considered the only indicator of complete and durable zonal isolation throughout the lifetime of the well. However, in a well drilled in a stressful environment, the initial zonal isolation can be jeopardized because of the changes in downhole conditions, primarily temperatures and pressures. Such cyclic changes in downhole pressures and temperatures generate radial cracks in cement and can cause the development of microannulus at casing/cement and cement/formation interfaces. Extensive studies have been conducted in the past to understand the technical challenges to designing cement slurries with enhanced mechanical properties regulating the flexibility of set cement to withstand the stressful environment at downhole conditions. However, limited work has been done to evaluate the structural changes and impact on the set cement durability due to the requirement of expansion in set cement to eliminate the risk of microannulus. A new methodology called industrial computed tomography is introduced to investigate the structural changes or cracks in set cement cured with various concentration of expansive additives. The novelty of this new methodology is that it represents a step change in defining the linear expansion requirement for given well conditions without jeopardizing the wellbore integrity.
Abstract Synthetic polymers have long been used as fluid-loss additives (FLAs) in hydraulic cement slurries for cementing subterranean zones. Typically used synthetic polymeric materials include N,N-dimethylacrylamide and sulfonated acrylamide monomers, which are preferred for high temperature applications. However, as these materials are less environmentally acceptable, the search for more environmentally acceptable chemical increases. Although preferred materials are biopolymers, they sometimes impart high slurry viscosity at ambient temperature, and cause thinning and settling of the cement slurries at elevated temperatures. Thus, there is a need for an additive composition that is environmentally acceptable and performs better over a wide temperature range. This paper presents a novel idea of using a combination of two biopolymers, a hydrophobically modified (HM) biopolymer and a hydroxypropyl derivative of cyclodextrin (DCY) for controlling fluid loss, while imparting better cement slurry properties, stability, and viscosity. HM biopolymer as an FLA by itself causes excessive surface slurry viscosification at ambient temperature. However, when DCY was added into the cement slurry, optimum slurry viscosities were observed at ambient temperature, thus avoiding pumping issues. Laboratory experiments showed that the fluid-loss control was excellent, but the viscosity of cement slurry was high at ambient temperature when the HM biopolymer was used as a FLA by itself. The addition of DCY reduced the surface viscosity without compromising fluid-loss control and without affecting other properties. Studies conducted at elevated temperatures revealed that the HM biopolymer was left intact to maintain the cement slurry viscosity at that temperature, thereby helping prevent settling issues. Also, no significant effect on compressive strength development and thickening time of the cement slurry was observed with the addition of DCY molecules. The results of laboratory experimentation at ambient and elevated temperatures support the formation of in-situ inclusion complex formation of DCY molecules with the HM biopolymer.
Cadix, A.. (SOLVAY Novecare) | Wilson, J.. (SOLVAY Novecare) | Bzducha, W.. (SOLVAY Novecare) | Gomez, J.-R.. -R. (SOLVAY Novecare) | Feuillette, A.. (SOLVAY Novecare) | Guichon, H.. (SOLVAY Novecare) | Thant, K.. (SOLVAY Novecare) | Nelson, T.. (SOLVAY Novecare)
Abstract Oil well cementing is a technically critical job and requires a well controlled placement along the wellbore and an even fill of the annular volume. As a consequence fluid loss control additives, preventing water from filtering into the formation are key ingredients of cement designs. These additives are often based on synthetic high molecular weight sulfonated copolymers. The mechanism of action of these polymers has been studied recently and it was demonstrated that adsorption onto the cement surface is key to the achieve product performance. Unfortunately this adsorption yield is generally limited and typically performance decreases significantly as temperature increases. In order to overcome that loss, formulators typically increase loading to regain acceptable performance. Due to the high molecular weight nature of these AMPS copolymers, the subsequent drawback of increased loading is also an increase in cement slurry viscosity. In addition, as higher density slurries are typically used when downhole temperature increases, the problem is exacerbated and these limitations highlight the need for alternative technologies. In this study we investigated the use of block copolymers comprising first a strong adsorbing block, then a long second hydrophilic block providing filtration control. This technology has already demonstrated to be very effective in preventing performance losses in presence of competitive formulation additives such as dispersant or retarders (see SPE173758). In this work, the behavior of such fluid loss additive is investigated in several cement grades and at elevated temperature. Thanks to systematic methodology combining adsorption quantification with a standard HP/HT filtration, it is possible to quantify fluid loss polymer adsorption. This methodology using steric exclusion chromatography applies even in the case of complex formulations comprising retarders. This work focuses on the analysis of the adsorption of fluid loss polymers on several cement grades and at elevated temperature. Comparison of conventional copolymers and diblock copolymers show that conventional systems are very sensitive to cement grades even at moderate temperatures and gets very difficult to use above 100°C. On the other hand diblock copolymers are consistently performing at moderate temperature. Some potential performance limitation of this additive may occur at very high temperature if sulfate/aluminate balance of cement is such that ettringite thermal degradation can take place.