Oilwell Cement Research Articles

Dilatometric behavior and crystallographic characterization of Portland-polyurethane composites for oilwell high-temperature cementing applications

In order to improve the behavior of Portland-based oilwell sheath to high-temperature applications and the corresponding thermal gradients, polymeric admixtures can be added. Steam injection, for instance, raises the cement sheath-steel casing interface temperature to ∼300 °C which can be deleterious to the mechanical stability and zonal isolation provided by the cement sheath as a result of cracking of the cement. Polyurethane can be added to the cement to improve its plastic behavior and reduce the thermal expansion mismatch between casing and sheath. However, the use polymeric admixtures, especially as aqueous dispersion, can affect the kinetics of the hydration reactions and, as a consequence, the crystallographic composition and coefficient of thermal expansion of the material. Therefore, the present study aimed at evaluating the effects of the addition of different concentrations of polyurethane on the thermomechanical properties of Portland cement pastes cured at 300 °C from 14 to 90 days. Formulations containing 1 gpc (0.052 kg), 2 gpc (0.102 kg) and 3 gpc (0.153 kg) of polyurethane, respectively named PU1, PU2 and PU3 were prepared according to the American Petroleum Institute guidelines. A standard PU-free slurry was also prepared. X-ray diffraction and dry dilatometric tests were carried out. The results revealed that the curing time does affect the kinetics of hydration of Portland-polyurethane composites, retarding the formation of high-temperature stable phases, i.e., tobermorite and xonotlite. Moreover, longer curing times were necessary to reveal the improved expansion of the composites with respect to the standard sample. The addition of polyurethane can be pointed as an approach to high-temperature oilwell cement applications, since it reduces the thermal mismatch between cement sheath and steel casing for and retards but do not prevent the formation of xonotlite.

Relationship Between the Microstructure/Pore Structure of Oil-Well Cement and Hydrostatic Pressure

In cementing operations, hydrostatic pressure reduction in cement slurries is a serious threat to operation safety and cementing quality. This study combines X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, low-field nuclear magnetic resonance, and nano-computed tomography to investigate the mechanism of hydrostatic pressure reduction in cement slurries. The experimental results reveal that hydrostatic pressure transmission in a fresh cement slurry follows Pascal’s law. However, in the slurry, some cement particles undergo sedimentation with an increase in the hydration time, which reduces a part of the hydrostatic pressure. Further, another part of the hydrostatic pressure, which is maintained by the free water in the slurry pores, is reduced during the hardening stage. When the hydration reaction of the slurry is accelerated, the pore water in the slurry is supersaturated and hydration products start to rapidly nucleate and grow between the cement particles. These hydration products are porous gel structures and can change the pore structure of the cement slurry; a macro-pore is divided into many micropores, such as capillary pores and gel pores. Because these pores are filled by water in the slurry, during this process, free water in the macro-pores is changed to capillary water and gel water. However, gel water and capillary water cannot transmit hydrostatic pressure in the cement slurry. Meanwhile, in the fresh cement slurry, many pores containing free water are connected and some hydration products rapidly grow in the macro-pores and fill them, which may reduce the column height of the free water in the pores and lead to hydrostatic pressure reduction in the slurry.

A Newly Developed Wellbore-Simulation Apparatus To Study Performance of Oilwell Cements

Summary Research has been dedicated to the development of laboratory-scale simulation devices for studying mechanisms of gas migration. Cement-hydration analyzers (CHAs) are commercially available to assist industry in the design of gas-tight slurries. Although cement slurries under controlled conditions in the laboratory can be gas-tight, the in-situ performance of cement slurries is highly variable and difficult to predict. Therefore, a new approach has been designed to evaluate gas-migration potential under a range of representative borehole conditions. A laboratory-scale wellbore-simulation chamber (WSC) has been developed to replicate hydrostatic-pressure reduction in the cemented annulus and evaluate the potential for gas invasion under a range of borehole conditions. A discussion is presented on the development of the WSC that includes the details of the design and monitoring systems as well as the performance characteristics. Calibration-test results are examined to evaluate the performance of the WSC and the ability of the WSC to simulate in-situ wellbore conditions. Analysis of the results verifies the capability of the WSC in successfully recording the necessary parameters.

Benefits of using mineral additives, as components of the modern oil-well cement

In this study the Influence of fine mineral additives such as zeolite tuff, metakaolin, microspheres and fly ash on the properties of light-weight oil-well cement was investigated. Strength, physical and performance requirements of light-weight oil-well cements were determined. The results have shown that the most effective facilitating additive which gives the lowest density is the microsphere. However, at raised pressures, it has been revealed that walls of the grains of the microspheres do not withstand a pressure of more than 20 MPa, and thus they will be destroyed leading to an increase in the density of the slurry and significantly limits the permissible depth for using this composition. On the other hand, it was found that using zeolite in combination with metakaolin improves the physico-mechanical properties of the oil-well cement stone.

Investigations on Oilwell Cement Strength Response to Ultrasonic Measurements in the Presence of Additives1

Well cements are an important aspect of wellbore integrity and recent investigations focus on describing the cement lifetime using, when possible, nondestructive tests like ultrasonic measurements. However, the original API and ASTM testing standards were based on destructive mechanical testing of cements, leading to the decision to investigate the backward and forward compatibility between ultrasonic measurements and mechanical testing, which makes the subject of this work. Ultrasonic cement measurement became a very popular method to assess the mechanical properties of the cement in a nondestructive manner. Since various measurement systems exist on the market, the development of an accurate reference data base that can be used to calibrate such measurements becomes very important. Two major systems have therefore been compared: the ultrasonic compressive strength, using the ultrasonic pulse velocity (UPV) principle, and the unconfined compressive strength (UCS), using the standard testing frame according to API and ASTM standards. The tests have been performed at different curing times, using both devices, on API Class G cements with bentonite and other additives. This paper presents the results of over 200 experiments that have displayed a different UPV response as a function of the additive content. Cement specific UPV versus UCS correlations were established. Thereby, a new level of accuracy was reached. Moreover, it was observed that after a given curing time, depending on the additive and its concentration, the UPV response is not as sensitive as the results yielded by the UCS method. The outcomes are an important step forward to improve and understand the wellbore integrity.

Activation of cement hydration with carbon dioxide

Additions of carbon dioxide to hydrating concrete have been observed to result in performance benefits. In this study, oil-well cement (selected for its very low initial carbonate content) was hydrated in the presence and absence of pure CO2 gas. The evolution of the products and reactants was assessed through isothermal calorimetry, Quantitative X-ray Diffraction (QXRD), Loss on Ignition, and Total Inorganic Carbon. A one minute exposure to carbon dioxide gas during mixing improved the heat of hydration though 24 h by 8%. The amount of C-S-H formed increased by 20%, and the estimated degree of hydration increased by 23%. The carbon dioxide promoted the formation of calcium carbonate that was observed in the sample immediately after treatment with carbon dioxide. The carbonate was initially amorphous calcium carbonate not detectable with QXRD, but it changed over 24 h to crystalline calcite (CaCO3) detectable by QXRD.

Improving the Performance of Oilwell Cement by Graft-modified PB Latex

Graft-modified polybutadiene (PB) latex was synthesized and used as an admixture to improve the performance of oilwell cement. Results showed that the addition of latex to pure cement slurry can significantly reduce the fluid loss of the cement slurry. When the dosage was 8%, the fluid loss was only 38 mL, and the fluidity of the cement slurry was improved. With an increasing amount of latex, the fluidity of the cement slurry increased continuously. The toughness of cement was significantly enhanced, whose average elastic modulus was 4.2 GPa. Scanning electron microscopy revealed that the filter cake of the cement slurry with latex was thin and dense, and the surface was coated with a layer of latex film. The microstructure of the cement stone showed a high density, and an interweaving mesh network formed in the cement. The results of cement hydration heat analysis and X-ray diffraction showed that latex inhibited the hydration of cement; the effect was stronger under a larger amount of latex. It is indicated that the graft-modified PB latex has great potential to replace the conventional styrene-butadiene rubber (SBR) latex for cementing in the future.

Evaluation of Guinea Corn Husk Ash as Oil-Well Cement Slurry Extender

Evaluation of Guinea Corn Husk Ash as Oil-Well Cement Slurry Extender

Оценка влияния термобарических условий на реологические свойства магнезиальных тампонажных растворов

Оценка влияния термобарических условий на реологические свойства магнезиальных тампонажных растворов

Modelling acid attack of oilwell cement exposed to carbonated brine

A diffusion-reaction model for the carbonation process of oilwell cement exposed to carbonated brine under CO2 geological storage conditions is presented. The formulation consists of two main diffusion/reaction field equations for the concentrations of aqueous calcium and carbon species in the pore solution of the hardened cement paste, complemented by two diffusion-only field equations for chloride and alkalis concentrations, and by a number of chemical kinetics and chemical equilibrium equations. The volume fraction distribution of the solid constituents of the hardened cement paste and the reaction products evolve with the progress of the reaction, determining the diffusivity properties of the material. The model is used to simulate experimental tests performed by Duguid and Scherer (2010), leading to promising results indicating that the fundamental aspects of the phenomenon are captured.

Studying The Effect of Nano-Metakaolin Admixture Material On Mechanical Properties of Oil Well Cement (OWC)

This work aimed to study the effects of incorporate Nano-metakaolin (NMK) as pozzolonic material on some mechanical properties (compressive strength) of Oil Well Cement (OWC). Nano-metakaolin (NMK) was prepared from Kaolin rock brought by thermal activation of kaolin clay at different temperatures (700–800 oC) for 2 h then crushing and ball milled for (40-60) hours. The cement used in this study comprise of Oil Well Cement class G and NMK were incorporate as a partial replacement additive by NMK of (3%, 6% & 10%) by weight of cement with two different average particle sizes (75nm,100nm) and a w/c of 0.44. Several techniques were used to prepare and characterize NMK Particle Size Analyzers (PSA), X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM) and the Brunauer-Emmett-Teller (BET). The results showed and approved that the NMK was not only work as filler, but also as an activator to consolidate hydration process, through NMK particles react and consumes calcium hydroxide CH crystals to produce more C–S–H, fills pores to increase the strengths, decrease the size of the crystals at the interface zone and transmutes the calcium hydroxide feeble crystals to the C–S–H crystals, and upgrade the interface zone and cement paste domain.

Effect of Carbon Dioxide Curing on Strength Development of Cement Mortar

This study was conducted to assess the acceleration of strength development by CO2 curing and to evaluate the strength and microstructure of two cement mortars. Three curing pressures (1, 5, 8 bars), three curing time (20, 120, 180 minutes) and four CO2 concentration (0%, 25%, 50% and 100%) were used in this investigation. Two mortar specimens are made with Type Ι Portland cement and oil-well cement. After the CO2 curing duration and demolding, the mortar samples were assessed through the mass gain, the compressive strength, the pressure drop, the temperature rise in the curing chamber, and the microstructure characteristics. The performance of the CO2 cured mortars was found through the measurement of pressure drop, temperature rise, strength development, mass gain and carbonation. In general, higher CO2 concentration, longer carbonation time, higher CO2 pressure could increase the compressive strength of the mortar and promote more CO2 absorption. The better results obtained from this study are the Type 1 cement mortars curing three hours under 5-bar pressure with 100% CO2 concentration using one-time supply method. The three-hour mortar samples had a high percent strength development. The increasing of CO2 concentration results in higher carbonation degree of mortar, more mass gain, and a stiffer and denser material.

Lessons Learned from the Development of Cementitious Grouts for Deep Borehole Disposal Applications

The performance of grouts made using oilwell cement is markedly different above 90°C than at lower temperatures, and the rapidity with which grouts thicken can cause failures in well cementing. One grouting application in which such temperatures are encountered is deep borehole disposal (DBD). DBD is a concept for disposing of high-level radioactive wastes where the temperature and pressure will be 90–140°C and 30–50 MPa, respectively. In developing DBD grouts, a number of issues have been identified that will be of interest to well-cementing organizations. (1) The type of retarder used to delay grout thickening above 90°C is of extreme importance, and should be selected based on local temperature, pressure, and geochemical environment. Addition level might vary considerably depending on the retarder used. (2) Temperature and pressure will shorten the time for grouts to thicken, particularly the former. Water content will also affect grout properties such as consistency, viscosity, and flow. (3) The retarder may not influence hardened grout composition, which suggests that only the time at which the cement hydration reactions occur is influenced.

Synthesis of microcrystalline brownmillerite Ca2(Al,Fe)2O5 and its influence of mechanical properties to the class G oil-well cement

This study investigated the use of calcium oxide (CaO), aluminum oxide (Al2O3) and ferric oxide (Fe2O3) as raw materials for the production of brownmillerite Ca2(Al,Fe)2O5, after firing at 1330, 1350 and 1370 °C. Lithofacies analysis, SEM/EDS and XRD were used to analyze the phase transition and microstructure of the clinkers during the firing process, and the contents of free calcium oxide (f-CaO) in the clinkers were determined by chemical titration. The results showed that the optimum temperature for the preparation of brownmillerite was 1370 °C (within the selected temperature range). By firing and quenching, microcrystalline brownmillerite (MB) was obtained (crystallinity index was 0.7). Compared with the compressive strength of class G oil-well cement matrix (M0) without MB, the compressive strength of specimens (M4) with 4 wt% MB addition increased by 67, 12, 20 and 33% (after curing for 1, 3, 7 and 14 d, respectively). meanwhile, the elastic modulus of M4 (after curing for 7 d) was reduced by 24% relative to that of M0, indicating that the mechanical properties of M4 were better than that of M0. To investigate the effect of microcrystalline brownmillerite on the strength and toughness of the class G oil-well cement matrix, triaxial testing was used in this study, and the toughening mechanisms were established.

Investigation on Mixed Oil-Cement for Wellbore Integrity Using Acoustic Velocity

Oilwell cementing is part of completing a well prior to production. As a casing is installed after a section of the well is drilled, cement is pumped downhole. Reservoir fluid such as oil which may encroach into the wellbore due to naturally fractured or unconsolidated formation would mix with the cement pumped downhole. Recent studies have shown that the presence of oil affect cement quality to an extent where the cement compressive strength is greatly reduced. Early detection of possible oil contamination into cement may prevent well integrity problem. With intense application of acoustic principle into wellbore, however, not many references available to detect the presence of oil in cement system using this principle. This study investigates whether acoustic waves can detect oil in cement. Class G cement is mixed with both water and brine where crude oil is then added to the mixture. The resulting slurry were cured using High Pressure High Temperature (HPHT) curing chamber at 120°C and 4,000 psi for 24 hours and is then cored into 1-inch cylinder. SonicViewer-SX is used to propagate acoustic waves through the core sample where the transit time is recorded and analyzed. It is found that oil can be detected in cement using acoustic waves since oil-filled samples have slower P-waves and S-waves velocities than cement-filled samples. The case is also proven when water is replaced by brine as the mixing fluid which oil-filled samples have lower P-waves and S-waves velocities to that of cement-filled samples.

Real-Time Monitoring of Piezoresistive Smart Cement To Verify Operations

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper OTC 27060, “Field Test for Real-Time Monitoring of Piezoresistive Smart Cement To Verify Cementing Operations,” by C. Vipulanandan, M. Ali, B. Basirat, A. Reddy, N. Amin, and A. Mohammed, University of Houston; S. Dighe, SPE, Baker Hughes; and H. Farzam, Cemex, prepared for the 2016 Offshore Technology Conference, Houston, 2–5 May. The paper has not been peer reviewed. Copyright 2016 Offshore Technology Conference. Reproduced by permission. A field well was designed, built, and used to demonstrate the concept of real-time monitoring of the flow of drilling mud and smart cement and the hardening of the cement in place. A new method has been developed to measure the electrical resistivity of the materials with the two-probe method. Using the new concept, it has been proved that resistivity dominated the behavior of drilling fluid and smart cement. Introduction With reported failures and growing interest in environmental and economic concerns in the oil and gas industry, integrity of the cement sheath is of major importance. Oilwell cement serves many purposes in cemented oil and gas wells. Foremost among these is to form a sealing layer between the well casing and the geological formation. In order to characterize the cement and cement concrete in various applications, electrical-resistivity measurement has been used by many researchers. Studies have also examined the piezo-resistive behavior of modified cement-based and polymer composites. One conclusion is that the change in resistivity has the potential to be used to determine the integrity of the materials. Smart Oilwell Cement Cement-slurry flow and stability are the major requirements in well cementing. Oil- and gas-well cements are usually made from Portland cement clinker or from blended hydraulic cements. When admixtures are used with cement, tensile and flexural properties are modified. Also, admixtures will have an effect on the rheology, corrosion resistance, shrinkage, thermal conductivity, specific heat, electrical conductivity, and absorption (heat and energy) properties of cement. A smart cement has been developed that can sense any changes going on inside the borehole during cementing and during curing after the cementing job. The smart cement can sense the changes in the water/cement ratio, different additives, and any pressure applied to the cement sheath in terms of piezo resistivity. The failure compressive strain for the smart cement was 0.2% at peak compressive stress, and the resistivity change is on the order of several hundreds, making it more than 500 times more sensitive. Theory and Concept Impedance Model. Equivalent Circuit. It is important to identify the most appropriate equivalent circuit to represent the electrical properties of a material to characterize its performance with time. In this study, different possible equivalent circuits were analyzed to find an appropriate equivalent circuit to represent smart cement and drilling fluid.

Influence of carbon nanotubes, nanosilica and nanometakaolin on some morphological-mechanical properties of oil well cement pastes subjected to elevated water curing temperature and regular room air curing temperature

Nanotechnology has shown great potential in different applications and presents solutions to some of the upstream and downstream challenges in the oil and gas industry. This research work aimed to improve the mechanical properties of oil well cement (OWC) pastes using multiwall carbon nanotubes (CNTs), nano-silica (NS) and nano-metakaolin (NMK). The effect of different curing temperatures, namely; room temperature and elevated temperature (90°C) on the hydration reaction of OWC pastes admixed with different nano materials was investigated. XRD, TG/DTG, and SEM techniques were used to investigate the phase composition and the microstructure of some selected hardened specimens. The obtained results indicated that all of the nano materials used in this study cause a notable improvement in the mechanical properties of hardened OWC pastes at both curing temperatures. In addition, NMK – OWC hardened pastes present the highest improvement in the mechanical properties among all of other tested mixes.

Effect of the hydration temperature on the microstructure of Class G cement: C-S-H composition and density

Curing temperature has a significant influence on cement paste microstructure and the properties of its principal hydrate C-S-H. In this paper, the effect of the hydration temperature in the range of 7°C to 90°C on the microstructure of a class G oil-well cement is studied. This is done by combining various experimental methods, including X-ray diffraction associated with the Rietveld analysis, thermo-gravimetric analysis, mercury intrusion porosimetry and porosity evaluation by drying. The experimental results show an increase of the capillary porosity and a decrease of the gel porosity by increasing the hydration temperature. This is attributed to a decrease of the C-S-H intrinsic porosity and a corresponding increase of the C-S-H density for higher curing temperatures. The experimental results are used in a simple analysis method to evaluate the density of C-S-H, as well as its C/S ratio and H/S ratio in dry and saturated conditions. The evaluated C-S-H density varies from 1.88g/cm3 at 7°C to 2.10g/cm3 at 90°C. The results also show a decrease of molar C/S ratio with increasing hydration temperature from 1.93 at 7°C to 1.71 at 90°C and of the H/S ratio from 5.1 at 7°C to 2.66 at 90°C.

Formation of System of Indicators for the Choice of Grouting Solutions by Expert Assessment Method

В условиях современного рынка успех развития и роста компании во многом зависит от работы маркетолога, от правильно выбранной маркетинговой стратегии. Для решения основной проблемы повышения эффективности управления проектно-изыскательской организацией нужно прорабатывать каждую составляющую будущего проекта. Анализ маркетинговой среды и оценка рыночных возможностей организации осуществляются в ходе комплексных маркетинговых исследований рынка, цель которых состоит в сборе информации о рынке и ее изучении для совершенствования процесса разработки и сбыта товаров. Маркетинговые исследования рынка являются обязательным условием успеха товаров, предлагаемых на рынке. Они эффективны в том случае, когда рассматриваются не только как процесс получения труднодоступной коммерческой информации, но и как средство, обеспечивающее руководство организации аналитическими выводами об изменениях маркетинговой среды с целью улучшения возможностей системы управления. Маркетинговое исследование строительного рынка напрямую связано с управлением ресурсами проекта. Грамотно построенная стратегия маркетинга является обязательным условием успешного управления ресурсами строительства. В проектно-изыскательской организации, занимающейся строительством на просадочных грунтах, одним из самых важных и значимых разделов любого проекта нового строительства или реконструкции является проектирование фундаментов, усиление грунтов. В статье описана процедура формирования системы показателей для оценки и выбора тампонажных цементных составов при строительстве на просадочных грунтах с использованием метода экспертного опроса. Этот метод позволяет выявить мнение специалистов по исследуемой проблеме, проранжировать какие-либо признаки и определить степень важности. Для каждого показателя рассчитан коэффициент весомости. С помощью рассчитанного коэффициента весомости определим степень значимости конкретного показателя для оценки качества.

Crumb waste tire rubber surface modification by plasma polymerization of ethanol and its application on oil-well cement

Crumb waste tire rubber (WTR) was pretreated by oxygen low temperature plasma (LTP) and modified by LTP polymerization process of ethanol monomer to improve the adhesion property with oil-well cement matrix and the mechanical properties of cement. The surface properties of modified crumb WTR and the mechanical properties and structures of modified oil-well cement were investigated by means of contact angle measurement, dispersion test, attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), mechanics performance tests, permeability test and scanning electron microscopy (SEM). It was demonstrated that LTP treatment changed both the surface composition and roughness. The contact angle of pretreated crumb WTR dramatically fell from 122° to 34°, and sample with ethanol LPT polymer film decreased even further to 11°. The ATR-FTIR and XPS analysis results demonstrated that hydrophilic groups, such as –COOH, C–OH, and –CHO, were introduced on the WTR surface. The oxygen atomic percent increased from 8.11% to 14.50% and 24.83%. The mechanical properties, porosity and permeability of raw cement were compared to samples modified by untreated crumb WTR, pretreated crumb WTR and ethanol LTP polymerization treated crumb WTR. It was found that after 28 days, the compressive strength of the samples with the untreated crumb WTR decreased to 80% with respect to raw cement. The tensile strength and flexural strength also had a slight reduction compared with the raw cement. On the contrary, after 28 days, the tensile strength of cement modified by LTP polymerization treated WTR increased 11.03% and 13.36%, and the flexural strength increased 9.65% and 7.31%, respectively. A decrease in the compressive strength also occurred but was inconspicuous. A tight interface bonding for ethanol LTP polymerization treated WTR with cement matrix was observed via an SEM image.