Cement Slurry Design Research Articles

A cement hydration kinetics model and its application in designing cement formulation for natural gas hydrate well

To guide the research and development of cement slurries with low hydration heat release for natural gas hydrates (NGHs), the effects of fly ash (FA) and phase-change material (PCM) on the early performance of cement at low temperatures were investigated using isothermal calorimetry (IC), semi-adiabatic temperature (ST), and mechanical strength tests. A specialized in-house device was designed to simulate NGHs well conditions and examine the impact of cement slurries on the formation temperature field. A novel model for cementing temperature prediction based on hydration kinetics was developed, and a new methodology for NGHs well cement slurry design was proposed. The experimental and modeling results indicated that the prediction error of the temperature model was within 6.5 %. By adding approximately 14 wt% of PCM the temperature rise could be controlled below the hydrate decomposition temperature, while achieving a 72 h compressive strength of greater than 2.5 MPa.

New Approach to Encapsulation for Controlled Release of Chemical Additives

Summary A new approach for the synthesis of bio-inspired polymer microcapsules used to encapsulate chemical additives and designed for small molecule release and delivery is shown here. The flexibility to design different microcapsules using an emulsion template results in various encapsulated additives for a new polymer technology platform. The base materials for encapsulation are polyaramids that are highly crosslinked membrane shells around an empty core. These empty capsules provide a carefully designed space to site-isolate chemical additives, various encapsulants for encapsulation, and delivery where needed. These microcapsules have demonstrated that after being formed from a simple one-pot synthesis between two immiscible solutions, a new method for encapsulation for applications in ordinary Portland cement is possible. The final product is a free-flowing solid that can be easily added to any fluid application. Experimental results show that when added to a basic cement slurry design, cement responds to the release of a salt accelerant as measured using standard oilfield equipment, like the pressurized consistometer, which measures changes in viscosity and thickening times. In one of many applications, the consistency of cement remains favorable at 20 Bc after adding encapsulated calcium chloride for up to 5 hours, for example. Over time, various capsules caused cement slurries to set at right angles at various thickening times with the controlled release of encapsulated calcium chloride. This new approach for encapsulation is promising for the chemical and energy field.

ANALYSIS OF CEMENTING WELLS X-1 and Y-1 USING MULTIFUNCTION ULTRASONIC IMAGING LOGGING TOOL

By analyzing the measurement principle of the ultrasonic pulse method, a multifunctional ultrasonic image recording device and the application of the measurement technique were designed. It can perform surface imaging well in high-resolution imaging mode in open holes. Can also perform casing inspection and cement bond evaluation in full wave mode at casing holes. The proposed tool was tested in practice. This shows that this tool can evaluate geological feature information such as fractures and layered structures in open holes. Imaging casing thickness, inner and outer diameters and cement impedance can also be measured at casing holes. Cement analysis in wells Logging Tool (MUIL), cement slurry design and operations during cementing. The logging results above can be analyzed quantitatively including amplitude readings which can then determine compressive strength prices and bond index prices. Meanwhile, qualitative analysis was carried out comprehensively from VDL recordings and using the Enhanced Logging Imaging System. For analysis from a design perspective, it looks at the cement slurry planning, while from an operational perspective it looks at the suitability between planning and implementation in the field.

Experimental Investigation to Enhance Oil Well Cement Compressive Strength by Using Nano Silica and Synthetic Fiber

The cementing process is one of the main and vital elements in the drilling and completion of oil and gas wells. Cement slurry design plays an essential role in cementing operations. Compressive strength, which represents a material's ability to sustain forceful conditions over time, is an essential property of oil well cement. This study provides an experimental investigation on the impact of coupled synthetic fiber and Nano Silica (nano-SiO2) on improving the compressive strength of Iraqi oil well cement class G. In addition, the results were compared to those of a previous study that utilized Nano Silica alone in conjunction with Iraqi oil well cement. The results indicated that the Iraqi oil well cement class G, after special additions, conforms to the specifications of the American Petroleum Institute (API). Results showed that adding synthetic fiber and Nano-Silica together significantly increased the compressive strength of Iraqi class G cement slurry cured at different conditions. Samples curing was done at 38°C and 60°C for 8 hours. The results indicated that the cement system with 1.5% by weight of cement (BWOC) of Nano-Silica and 1.5 gm of Synthetic Fiber increased the compressive strength by 50.38 and 39.92% at 38°C and 60°C, respectively. Through comparison with previous studies, it was found that the amounts of Nano Silica added to cement can be reduced by a large percentage when synthetic fibers are added with it, thus reducing the cost of using nanomaterials.

Rheological and mechanical properties of oil-well cement reinforced by hybrid inorganic fibers

The mechanical integrity of cement sheath during reservoir stimulation is critical for oil and gas wells. It is essential to optimize and design a cement slurry system that not only meets the primary cementing requirements but also has a good mechanical performance. In this study, effects of hybrid inorganic short-cut carbon fiber and basalt fiber on the rheological and mechanical performances of shale gas well cement were investigated. The rheological performance of prepared cement reinforced with hybrid inorganic fibers was researched by the viscometer, filtration loss meter, and consistometer. And the cement stone samples were tested by pressure testing machines. According to rheological behavior experimental results, the Power-law model was most suitable for describing the rheological behavior of slurries among the three models used in this study, and the rheological parameters, including consistency coefficient, yield point, and plastic viscosity of the studies cement slurries with fibers slightly increased in a suitable engineered addition. Combination of carbon fiber and basalt fiber can compromise the effect of the addition of a single fiber on the rheological properties of slurry and does not affect the workability and pumpability of slurry in terms of the fibers' additive amount of this study. Moreover, the fibers can also improve the sedimentation stability of cement slurry without significantly affecting its filtration loss and thickening time. In terms of mechanical properties of cement stone, no markedly difference in compressive strength was found between reference slurry and slurries with fibers, while the addition of carbon fiber and basalt fiber significantly improved the tensile strength and flexural strength, and also mitigated the brittleness of cement stone. The findings of this study can offer a key reference for the cement slurry design of oil and gas wells requiring reservoir stimulation.

Fatty Alcohol Polyoxyethylene Ether Sodium Sulfate–Modified Cement to Improve the Bonding and Sealing of Cement to Oil-Wet Casing or Formation Surface in Shale Gas Wells

Summary In shale gas wells, oil-based mud (OBM) changes the casing and rock surface wettability during drilling. It negatively affects the bonding and sealing of cement sheaths with casing or formation rock. Although the spacer is widely used in primary cementing, the casing and formation rock surface are wetted by OBM or oil phase due to poor displacement. For this work, a novel oleophilic cement slurry modified by fatty alcohol polyoxyethylene ether sodium sulfate (AES) was investigated to decrease the negative effect of OBM- or oil-wetted surface. The contact angle of nonpolar solvent 1-bromonaphthalene on the cement surface decreased from 35° to 8°, showing an ideal oleophilic property. The hydraulic isolation capacity; microstructure of the cement-casing or cement-rock interface; and the pore structure, hydration, and mechanical property of AES-modified cement were investigated by interfacial hydraulic isolation test device, computed tomography (CT), mercury intrusion porosimetry (MIP), X-ray diffraction (XRD), thermogravimetric analyses (TGAs), and mechanical test. The results showed that the oleophilic cement could directly bond with an oil- or OBM-wetted surface and significantly eliminate the microchannel and connected pores caused by the oil phase or OBM on the interface. The fluid channeling on the OBM-wetted cement-rock and casing interface was prevented, and the sealing pressure of the interface was increased from approximately 3 to 7 MPa/m (fluid channeling occurred) to higher than 275 MPa/s (fluid channeling did not occur), respectively. Besides, the hydration degree, porosity, and mechanical property of the oleophilic cement remained at the same level as the conventional cement, indicating that the AES has no adverse effect on cement hydration and properties. The findings of this study can contribute to the cement slurry design in shale gas well cementing to improve the interface bonding and sealing when poor displacement happens.

Cement Slurry Design for High-Pressure, High-Temperature Wellbores Using Polymer Nanocomposite: A Laboratory Scale Study Based on the Compressive Strength and Fluid Loss

For the successful cementing operation of petroleum wells, the design of cement slurry plays a crucial role. Cement slurry must address the requirements of higher compressive strength; lower fluid loss; durability; and high-pressure, high-temperature (HPHT) challenges. A large number of chemical additives in cement slurry affects the required rheological properties; therefore, the development of multifunctional additives is desirable. In the present study, this problem has been addressed with the use of a single polymeric nanocomposite additive to address multiple requirements. A novel tetrapolymer nanocomposite (TPN) was synthesized in the laboratory by in situ polymerization in the presence of zinc oxide nanoparticles. Four monomers, namely acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, vinyl phosphonic acid, and N-[3-(dimethylamino)propyl] methacrylamide, were selected for the in situ polymerization reaction. The synthesized product was characterized using 1H NMR, FTIR, and TGA techniques. Laboratory-synthesized TPN was mixed in varying concentrations in the cement slurry as an additive. The performance of the enhanced cement slurry was then evaluated by performing compressive strength analysis and a filtration test using an ultrasonic cement analyzer and an HPHT filter press, respectively. These experimental analyses show that the addition of the TPN improved the compressive strength of the cement slurry and, at the same time, abbreviated the fluid loss, which is desired for efficient cementing operation. With the addition of 1.0% by weight of cement (BWOC) of TPN, the compressive strength increased by ∼136% compared with base cement. Additionally, this small dosage also reduced HPHT fluid loss by ∼67%. This experimental investigation shows that the novel TPN additive is capable of improving the efficacy of oil-well cement slurry at high-temperature conditions without compromising on thickening time because the additive also improved the waiting-on-cement time for HPHT conditions.

Evaluation of the Suitability of Carboxylmethyl Cellulose (CMC) from Rice Husks/Saw Dust as Replacement for Conventional Hydroxy Ethyl Cellulose (HEC) as Additive for Cement Slurry Design

This study will evaluate the suitability and effectiveness of using Cellulose derived from Rice husk and Saw dust as cement slurry additive to replace the conventional cellulose in order to minimize cost and optimize drilling. Rice husks and Saw dusts were processed and Carboxylmethyl Cellulose (CMC) extracted with Sodium Hydroxide, Ethanol and Sodium Monochloroacetate. Three cement slurry samples from the produced CMC (Rice husks and Saw dust) and the conventional HEC were formulated. Different mass percent concentration of 0.2, 0.4, 0.6,0.8 and 1 of the CMC from Rice husks, Saw dust and Conventional HEC were added and subjected to different temperature conditions of 200°F, 300°F, 400°F, 500°F, 600°F. Rheological Properties of the formulated cement slurry such as Yield point and Plastic viscosity were tested at those temperature conditions. Results show that the yield point for all the temperature conditions and the additive concentration for the CMC from Rice husks and Saw dust have the same trend with the conventional HEC. Also, the plastic viscosity of the CMC from the Rice husks and Saw dust were in agreement and same trend with the conventional HEC. The results reveals that cellulose prepared from Rice husks and Saw dust gave almost the same rheological properties with that of the convention HEC and can be used in place of conventional HEC to reduce cost and also achieve the same results.

The Influence of Glass Fiber and Milled Glass Fiber on the Performance of Iraqi Oil Well Cement

The reinforced fiberglass in cement slurry reflects the effect on its properties compared to usual additives. Fiberglass is typically used in cement slurry design for one or another of the following goals: (Earth earthquake, bearing storage, and with differential stresses, to enhance cement durability and increase its compressive strength). The main goal is to use glass fiber and ground fiberglass to improve the tensile strength and moderate compressive strength significantly. On the other hand, the use of glass fibers led to a slight increase in the value of thickening time, which is a desirable effect. Eleven glass fiber samples and milled glass fiber were used to show these materials' effect on Iraqi cement with (0.125, 0.25, 0.5, 0.75, 1, and 2) % of cement weight. Those tests used to study cement slurry‟s following properties were compressive strength, thickening time, rheology properties of free water, filtering, and density. These evaluations showed that slurries with less than 1% fiber content gave a higher compressive strength than a sample containing more than 1% glass fiber. However, the slurry mixed with equal or less than 1% milled glass fiber is higher compressive than the sample mixed with more than 1% milled glass fiber. So the optimal concentration for glass fiber is less than 1% by weight of cement (BWOC); either for milled glass fiber, it is less or equal to 1% BWOC. Both materials contributed to increasing the compressive strength of the cement. However, attention must be paid to the idealThis work is licensed under a Creative Commons Attribution 4.0 International License.
 concentration that should be added during the cement slurry preparation because if we use these two materials carelessly for the ideal concentration, this leads to the collapse and bombardment of the resistance of the cement rock. In other words, the collapse of cement resistance and causing problems during the cementing process.

A Brief Review of Gas Migration in Oilwell Cement Slurries

Gas migration in oil and gas wells is defined as gases and/or fluids from adjacent formations invading a freshly cemented annulus. During well completions, gas and/or fluids can migrate to zones with lower pressure or even to the surface. Static gel strength (SGS), related to the yield stress of the cement, is a widely accepted measurement used to predict and minimize gas migration. In this review article, we look at the mechanisms and some possible solutions to gas migration during oil and gas well cementing. The use of static gel strength (SGS) and experimental measurements for SGS and wellbore pressure reduction are discussed. Rheological properties, including the yield stress and the viscosity of cement slurries, are also briefly discussed. Understanding the rheological properties of cement is complex since its material properties depend on cement type, as well as the shape and size distribution of cement particles. From this brief review, it is evident that in order to reduce free water and settling of the cement particles, to lower fluid loss, and to develop compressive strength in the early stages of cementing, an optimal cement slurry design is needed. The SGS test is a standard method used in estimating the free water in the well and could be a reference for gas migration reduction for oilwell cement slurries.

West Africa Salt-Zone Cementing Best Practices: Laboratory Evaluation and 5-Year Field Application Review

Summary To determine which salt-based cement system (potassium chloride or sodium chloride) was suitable for cementing across halite and anhydrite salt sections in West Africa, eight slurry recipes were tested to assess how formation salt contamination would affect slurry properties. The formation salt used for testing was sampled from a deepwater, presalt well in Angola. The recommendations developed from the laboratory study were implemented in 10 projects across West Africa over 5 years with 100% operational and well integrity success. A candidate deepwater well was selected in which the surface and intermediate strings penetrated salt formations. Four slurry designs (a lead and tail slurry used on each casing string) were programmed. Each slurry was designed and tested as two distinct systems using potassium chloride and sodium chloride salt, respectively, yielding a total of eight slurry designs. Using the methodology and data presented by Martins et al. (2002), the mass of dissolved formation salt that each slurry may receive during placement was estimated and duly incorporated into each slurry design. Subsequently, the salt-contaminated slurries were tested and compared with the properties of the initial uncontaminated slurries. On the basis of these results, conclusions were then made on which salt slurry system (potassium chloride or sodium chloride) exhibited better liquid and set properties after contamination with formation salt. Subsequently, this knowledge was applied to 10 projects across three countries in West Africa. This study showed that when the contact time of liquid cement slurry to salt formation was low—typically when the salt-formation interval across which the cement slurry flowed was less than 100 m thick—the level of formation salt dissolution entering the slurry during placement was limited. In this case, a potassium chloride salt-based slurry delivered improved liquid and set properties as compared with a sodium chloride salt-based slurry. In the field, this knowledge was applied in all oilfield projects cemented by an oilfield service company between 2015 and 2020. This included deepwater, shallow offshore, and onshore wells. All related salt-zone cement jobs, including sidetrack plugs, placed across the salt formations were successful on the first attempt. In an absence of industry consensus around salt-formation cement slurry design, this paper validates a guideline for West Africa, based on results from laboratory testing and 5 years of field application. In contrast to current literature that recommends only sodium chloride salt-based slurry designs across halite or anhydrite salt intervals, this work demonstrates that potassium chloride salt-based slurry systems can effectively be used to achieve well integrity where a halite or anhydrite salt interval is less than 100 m (328.1 ft) thick.

An Experimental Assessment of Iraqi Local Cement and Cement Slurry Design for Iraqi Oil Wells Using Cemcade

This effort is related to describe and assess the performance of the Iraqi cement sample planned for oil well-cementing jobs in Iraq. In this paper, major cementing properties which are thickening time, compressive strength, and free water in addition to the rheological properties and filtration of cement slurry underneath definite circumstances are experimentally tested. The consequences point to that the Iraqi cement after special additives encounter the requests of the API standards and can consequently is used in cementing jobs for oil wells. At this research, there is a comparative investigation established on experimental work on the effectiveness of some additives that considered as waste materials which are silica fume, bauxite, and glass powder, and other conventional additives which are: (SCR -100 Retarder, HR-5, FWCA, Hollow Glass Spheres (HGS) and Halad-9) that currently used in our fields on local Iraqi cement and putting foreign cement results as a governor. Chemical analysis for Iraqi cement, imported cement, and waste materials samples was determined using the X-ray fluorescence (XRF) technique and found minor differences in composition between those samples and depending on the results of X-ray, we selecting the appropriate additives to prepare cement slurry samples. The X-ray fluorescence (XRF) results show that Iraqi Cement has a low value of silica which is about 18.63% while Omani cement about 37.58%. This research examined the potential of micro silica, bauxite, and waste glass powder to produce sustainable cement slurry. The results showed that adding micro silica and bauxite enhances the performance of Iraqi cement but also leads to a slight decrease in thickening time. To avoid this problem, Superplasticizer is used to make the process of cement pumping more easily, in other words, increase thickening time and increase compressive strength. Furthermore, adding glass powder increase the value of compressive strength. Both additives (waste and conventional) are used for the slurry design for achieving better slurry properties, but waste additives increase and enhance Iraqi cement performance than conventional additives, in other words, making it more effective than commercial cement. Depending on the results of the compressive strength test, the optimal concentration of the waste materials used in this research was found, and then the optimal concentration was used to prepare cement samples. The results showed that the use of waste materials to prepare cement slurry is a promising way to improve the efficiency of cement work and to reduce the negative environmental impact resulting from the industry. The results of the program CemCADE proved to be the sample A and C showed good performance through high cement bonding and ideal distribution of fluids designed to accomplish the cementing process.

Designing of Cement Slurry to Enhance Compressive Strength and Rheology: An Experimental Study

The most essential function of oil and gas well cement is to provide isolation of zones in a production well. Cement isolates the wellbore in completion of oil and gas wells, prevents failure of casing, and it also prevents wellbore fluids so that they cannot be contaminated from fresh water aquifers. In slurry state cement is distinguished by rheological properties like plastic viscosity and yield stress. Proper selection of cement slurries plays a vital role in well commenting and that could be possible with the utilization of efficient materials that may results the superior rheological properties of cement slurry i.e. plastic viscosity, gel and yield strength. The selection of cement has been done on account of higher values of compressive strengths for which quality of cement sheath will be enhanced. Cement Slurry design can be optimized by operators for which it is mandatory for operators that they have knowledge about actual temperature that cement will encounter inside wellbore. Down hole temperatures of cementing have impact on thickening time, rheology, and compressive strength development. In this research work Rice Husk Ash (RHA) and Egg Shell Powder (ESP) are used in cement slurry so that compressive strength of cement specimen can be increased. The cement slurry has been made from locally manufactured cement, water, RHA and ESP. Cement slurry of 600ml by volume has been prepared. Specimens with size of 2×2×2 inch cubic molds are made for compressive strength testing at different curing conditions. Three variants of the specimen with varying concentrations of RHA and ESP are made. In present work during slurry state the rheological properties are determined while in solid state compressive strength of cement specimen at three curing ages of 08 hours, 24 hours and 72 hours is determined.

Drilling Fluid and Cement Slurry Design for Naturally Fractured Reservoirs

For years, drilling engineers have been faced with the challenge of drilling wells through naturally fractured reservoirs that are present around the world. During drilling, the pressure at the bottomhole of a well is frequently intentionally higher than formation pressure, which can result in the loss of mud in surrounding rocks. During well cementing, the bottomhole pressure is even higher than it is during drilling, because the cement slurry density is higher than the density of the mud. Therefore, if natural or induced fractures in the surrounding rocks are not plugged during drilling, the cement slurry can be lost to them, reducing their permeability which is undesirable in the case of a pay zone. To prevent the loss of circulation and the related consequences, it is necessary to apply good drilling and cementing practices and to use adequate methods and carefully selected materials for plugging the loss zones. The aim of this article is to give an overview of the preventive and corrective methods that can be applied in drilling and cementing through fractured zones as well as improvements in drilling and cementing technology to avoid lost circulation issues (e.g., aerated drilling fluid, casing while drilling, managed pressure drilling, expandable tubulars, lightweight cement slurries, etc.).

Polyelectrolyte-Complex Nanoparticles for Fluid-Loss Control in Oilwell Cementing

Summary This paper focuses on the application of polyelectrolyte-complex (PEC) nanoparticles to fluid-loss control of oilwell cements. Cement-slurry design involves considerable complexities, including the interplay of viscosity, yield point (YP), fluid-loss control, setting time, sedimentation, gel-strength development, and density. Polymers such as hydroxyethyl cellulose (HEC), carboxymethyl HEC (CMHEC), and polyvinyl alcohol have been used extensively for fluid-loss control in oilwell cementing. However, the resulting increase in slurry viscosity often led to unwanted side effects, such as increased pumping requirements. PECs were originally developed as drug carriers for pharmaceutical applications. Our previous work (Cordova et al. 2008; Lin et al. 2014; Johnson et al. 2016) showed that they can also be effective in improved-oil-recovery applications. In this study, we explore the potential of using PEC nanoparticles to achieve effective fluid-loss control while maintaining good fluid properties of the cement slurry. Results from this proof-of-concept study demonstrated that a PEC system comprising common oilfield polymers can be used to achieve effective fluid-loss control. Simultaneously, the system shows improved rheological properties over control samples while maintaining other desirable slurry characteristics.

Portland cement solutions for ultra-high temperature wellbore applications

Designing highly stable and low permeability high-strength oil well cement above 500 °F (>260 °C) is extremely difficult because the Portland cement undergoes strength retrogression starting at 230 °F (110 °C). Thus, fine crystalline silica stabilizer is required in the cement slurry design when cured until 400 °F (204.4 °C) to prevent this problem. However, the optimum particle size and the right practical dosage of silica in the cement slurry have not been clearly determined and studied for cement that will be subjected at such extremely high temperature (>500 °F), condition applicable for many ultra-deep geothermal and steam injection wells. Due to extreme heating conditions and tedious experimentation, there are only few published studies to date toward understanding the behavior of Portland cement used at that exceedingly high temperature; and thus, making the initial cement design highly challenging. Based on thorough experimental study, this paper presents new understanding and provides proper guidance to designing highly stable non-retrogressing and low steady permeability oil well cement for ultra-high temperature use. Moreover, this research carefully investigates the effect of the particle size of crystalline silica to the compressive strength, porosity and permeability of the cured cement. Finally, the substitution of crystalline silica with amorphous silica material in the ultra-high temperature cement is also exploited. Supplementary powder X-ray diffraction measurement identifies high temperature stable crystal phase Xonotlite (Ca6Si6O17(OH)2) in the silica-stabilized Portland cement. However, based from these current experimental results, it is observed that formation of Xonotlite crystal phase does not completely guarantee the longer term mechanical integrity of the cement sheath at ultra-high temperature, especially when the mixture contains amorphous-type silica in the blend.

Oil Well Cement Additives: A Review of the Common Types

Abstract Additives play significant role in oil and gas well cementing operations. There are varieties of cement additives that have been developed to allow the use of Portland cement in many different oil and gas well operations. In an attempt to formulate the appropriate cement slurry for any cementing job, the right additive must selected and the right quantity must be added. Additives have different functions and are broadly classified as accelerator, retarders, extenders, fluid loss agents, dispersants and many more. Each of the broad classification has different categories of additives that have been developed to perform almost the same function during cement slurry design. However, there some additives under each major type that are commonly used in cement slurry design for oil and gas well cementing operations. This paper reviews the broad classification of oil well additives giving emphasis to the commonly used additives during oil and gas well cementing operations.

Fe2O3 nanoparticles improve the physical properties of heavy-weight wellbore cements: A laboratory study

The application of nanomaterials to solve problems in wellbore cementing has been investigated in recent years by several research groups in the petroleum industry. This study includes the laboratory examination of the effect of Fe2O3 nanoparticles as a weighting agent on the physical properties of a heavy-weight wellbore cement. In the research process a candidate well is selected and the properties of the used cement slurry in a problematic section of the well are tested in the laboratory. Then Fe2O3 nanoparticles are added as a weighting agent to partially replace the Hidense and the improvements in the cement slurry and stone properties are studied. This article discusses the problems associated with the conventional heavy-weight wellbore cement used in the candidate well and gives the detail of the improvements in cement properties obtained by adding Fe2O3 nanoparticles to cement slurry formulation as a weighting agent. These properties include cement slurry rheological properties, free water, fluid loss, thickening time, cement stone elastic properties and compressive strength. The nano additive increases the yield point and plastic viscosity and decreases the free water and fluid loss of a cement slurry. In addition, cement stone compressive strength increases, however, there is an optimum concentration of nano additive at which the maximum compressive strength is reached. Moreover, elastic properties of the cement stone are improved and higher values for the Young's modulus and Poisson's ratio are achieved. The results of this study can be used to optimize the cement slurry design in any given set of conditions. The modified cement using this approach, is applicable in high pressure fluid bearing zones.

Cement slurry optimization and assessment of additives according to a proposed plan

Wellbore cementing is an essential part of every completion plan. The primary target of a cement job is zonal isolation and avoiding formation fluids to invade the well. Failure of cements in this important task result in disasters, significant financial damages and many more consequences. Good Cement slurry design is the key factor of having a gas resistant cement column. The aim of the study was to optimize slurry formulations following a determined checklist of criteria. The performance of two anti-gas migration and thixotropic agents were also assessed. As the final stage of the slurry optimization plan the results were verified using fluid migration analysis (FMA) test. According to the results, total gas migration flow rate of cement slurry optimized using the presented checklist was recorded as 0.23 ml/min. It was also observed that thixotropic agents improved gel strength profile, filtration control, waiting on cement time (WOC), critical hydration time and cement transition time significantly.

PETROPHYSICAL AND MICROSTRUCTURAL EVALUATION OF THE THERMAL CYCLE LOADING EFFECT ON GEOTHERMAL WELLBORE CEMENTS

Five wellbore cement designs with a range of additives and fibers were subjected to 100 thermal cycles of ΔT ~50°C at 100% relative humidity in salt brine. The experimental results show leaching of portlandite will occur from the cement irrespective of wellbore cement slurry design, which causes the porosity and hydraulic conductivity to increase and the mechanical strength to decrease. Furthermore, the study shows the presence of steel fibers can improve the mechanical properties of the cement sheath under thermal cycle loading conditions; although it would not prevent it from completely degrading as the well ages.