SPE-190079-MS Lightweight and Ultra-Lightweight Cements for Well Cementing - A Review A. Anya, Texas Tech University Copyright 2018, Society of Petroleum Engineers This paper was prepared for presentation at the SPE Western Regional Meeting held in Garden Grove, California, USA, 22-27 April 2018. This paper was selected for presentation by an SPE program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of SPE copyright. Abstract Lost circulation is a very common and expensive problem during drilling and cementing operations in the oil and gas industry. The lost circulation problems encountered during drilling or cementing are a result of one of two factors. These factors are the presence of zones of weak fracture gradients and the presence of high permeability or thief zones downhole. Light weight cements are an effective solution for curbing lost circulation caused by the breakdown of weak zones by conventional cement slurries. This paper presents a discussion of the different methods, additives and technologies that have been and are currently employed in the formulation of lightweight and ultra-lightweight cement slurries for cementing oil wells as well as recent developments based on an extensive literature review. This paper also discusses the mechanical performance, cost effectiveness and field logistical considerations of lightweight slurries formulated using different methods as these are important factors that impact decision making on what slurry extension method to choose for any given scenario. The information presented in this paper is derived from an extensive review of information contained in papers, journals and books spanning the last 50 years of well cementing and is summarized in such a way that the paper serves as a quick guide to cement slurry extension technology and techniques. An extensive review of the literature regarding lightweight cements showed that there are three general methods of obtaining lightweight cement slurries. These methods include increasing cement slurry water content (water extension) with the aid of viscocifying agents such as bentonite and sodium metasilicate, adding lightweight materials like glass microspheres and incorporating foam into slurries. Reported test data shows that apart from cement slurries containing glass microspheres and foamed cements, lightweight slurries exhibit lower compressive strength and slower compressive strength development than heavy slurries. Foamed cements pose the greatest design and field logistics challenge while cement slurries with glass microspheres have gained more popularity due to the excellent compressive strength values achievable at ultra-low densities despite their higher cost compared to water-extended slurries and lightweight slurries containing other lightweight additives like fly ash. The literature review presented also indicates a need for more research into improving lab mixing and testing methods that replicate field applications of foam cement. There is also a need for research into more cost-effective slurry extension additives and technology that exhibit acceptable mechanical performance for well integrity assurance and rheological properties favorable to proper cement placement in the annulus. 2 SPE-190079-MS Introduction Lost circulation in drilling and cementing operations is a common problem encountered in the oil and gas industry. Two main causes of lost circulation are zones of weak fracture gradient that are easily broken down by drilling fluids and cement slurries and thief zones or high permeability zones that permit the flow of fluid from the wellbore into vugs and natural fractures in the adjacent formation. Lost circulation leads to cost increases in the form of increased rig time, fluid replacements, loss circulation treatments, remedial cementing and in a worst-case scenario, well abandonment. Economics, driven by low oil prices, are causing operators to look for cost saving measures in drilling and completion operations. Lost circulation not only increases these costs, but typically causes the implementation of more casing strings or multi-stage cementing which both contribute to higher costs. There are generally two methods for combatting lost circulation problems depending on the cause of the losses. The first method involves the use of bridging agents and gelling agents in drilling fluids. Bridging agents may be fibrous, flaky, granular or blended to bridge over thief zones. Gelling agents flocculate and form a spongy mass on contact with water. These spongy masses plug vugs and fractures that may serve as flow paths for drilling fluid into the formation. The second method used to curb lost circulation problems is the use of advanced fluid formulations. These include lightweight drilling fluids and cement slurries, cement slurries with short wait-on-cement times and thixotropic cements. Lightweight drilling fluids and cement slurries reduce both the amount of overburden on adjacent formations and bottomhole ECD to prevent breakdown of weak zones in the wellbore. Cements slurries with short wait-on-cement times develop gel strength quickly enough to prevent significant fluid loss into high permeability zones. Thixotropic cements gel up as soon as they enter large cavities due to the absence of shear stress acting on the fluid in such cavities, preventing further inflow from the wellbore. The use of conventional and unconventional lightweight cement to combat wellbore losses due to a weak formation fracture gradient is a field of research that has seen numerous innovations over the last four decades. Lightweight cements can be generally classified into water-extended cements, cements with lightweight particles and foamed cements. Water-extended cements exhibit lightweight by means of an increased water-cement ratio and typically contain viscosifying agents to prevent excessive free water and provide slurry stability. Lightweight-particle cements contain solid particles that have specific gravities lower than that of Portland cement. The idea is that the addition of enough lightweight particles in the slurry composition will lead to reduced densities. Foamed cements are cements with gas, usually nitrogen injected to produce a lightweight gas-liquid dispersion with ultralow to low specific gravity and acceptable mechanical performance. Certain challenges arise in the design of lightweight slurries for oil and gas applications. The main concern in cement slurry design is the resulting set cement mechanical properties. The mechanical properties of set cement determine its ability to support casing, withstand cracking due to thermal and mechanical stress and maintain zonal isolation through the life of the well. Typically, set cement compressive strength and compressive strength development have been the main mechanical properties of interest in the petroleum industry. Lightweight cements compromise strength to achieve a lower density due to the reduced amount of cementitious material. However, it is important to note that recent studies have shown other mechanical properties such as hydraulic bond strength, Young's modulus and tensile strength to be more important to the long-term integrity of a cement sheath (Thiercelin et al., 1998; Bosma et al., 1999). Second, increased water-cement ratios and improperly dispersed lightweight additives increase the chance for slurry instability and excessive free water. Third, there is also an increased chance of long wait-on-cement times due to compromised strength development. Finally, there is a likelihood of ending up with a cement column that is permeable to formation fluids or susceptible to attack from reactive downhole fluids if the lightweight system is poorly designed. Lightweight cements can improve the economics of a well by preventing the need for multiple cementing stages or reducing the amount of stages needed. This paper briefly discusses SPE-190079-MS 3 the current technology and methods available for formulating low and ultra-low density cement slurries. The application, advantages and disadvantages of each method will be discussed. Water-Extended Cements Water-extended cements are cements that exhibit lower than conventional densities by means of increased water-cement ratios. API Specification 10A (an outline of standards for the manufacture and testing of oil well cements published by the American Petroleum Institute) lists the water requirements for neat cements made from each class of cement. Table 1—Mix water requirements for neat cements of every class (American Petroleum Institute, Specification 10A). Cement Class Mix Water (%BWOC) Slurry Density (ppg) A 46 15.6 B 46 15.6 C 56 14.8 D 38 16.45 E 38 16.45 F 38 16.45 G 44 15.8 H 38 16.45 The mix water percentages employed in any slurry design will vary from the values shown in table 1 depending on the properties desired. The mix water percentage is a major factor that affects the slurry density, free water level, solids settling, rheology, fluid loss control, slurry permeability and compressive strength development of a cement slurry. With the addition of more water to a slurry, the risk of excessive free water, solids settling and segregation, set cement permeability to formation fluids, slow compressive strength development, long wait-on-cement time and diminished set cement compressive strength become much higher. In addition to reduced density, water-extended cement slurries also lead to higher slurry yield and volume. To prevent the formation of excessive free water and maintain slurry homogeneity, viscosifying agents are added to the slurry. The function of these viscosifying agents is to improve the solids suspension capabilities of the slurry and prevent excessive free water formation through slurry viscosity increase and gelation. The two most common viscofying agents used in cement slurry formulations are clays and sodium silicates. The most common clay extender is bentonite and the most common sodium silicate extender is sodium metasilicate. Bentonite is a very common additive for water-extended cement slurries. Bentonite is a water absorbent which expands when in contact with water, absorbing about 5.3% water for every 1% BWOC (by weight of cement) added causing an increase in viscosity and gel strength. The addition of bentonite to cement slurries leads to increased slurry viscosity and solids suspension capacity. Hence, slurry stability and water retention can be maintained in slurries with higher water-cement ratios. Above bentonite concentrations of 6% BWOC, a dispersant is required to reduce the viscosity and gel strength of the slurry mixture (Nelson and Guillot, 2008). Bentonite is a more effective extender when it is prehydrated with the mix water as demonstrated below. 4 SPE-190079-MS Table 2—Comparison between slurry with prehydrated bentonite and slurry with dry-blended bentonite (Nelson and Guillot, 2008). Prehydrated Bentonite (%BWOC) Dry-Blended Bentonite (%BWOC) Fresh Water (gal/sk) Prehydrated Slurry Density (ppg) Dry-Blended Slurry Density (ppg) 0.5 2 6.4 14.8 14.8 1 4 7.6 14.1 14.2 1.5 6 8.8 13.5 13.7 2 8 10 13.1 13.3 2.5 10 11.2 12.7 12.9 3 12 12.4 12.4 12.6 4 16 14.8 11.9 12.2 5 20 17.2 11.5 11.8 However, there is no significant difference in the compressive strength obtained from both methods for preparing the bentonite. Competent cement slurries with density as low as 11.5 ppg can be obtained with bentonite as an extender (Nelson and Guillot, 2008). However, this density reduction comes with a price in the form of reduced compressive strength. Figure 1 illustrates the effect of bentonite addition on set cement compressive strength. Figure 1—Effect of bentonite on compressive strength of set cement (Nelson and Guillot, 2008). Bentonite is a relatively cheap clay and offers a cost-effective solution for designing lightweight cement slurries. High concentrations of bentonite also offer the added benefit of improved fluid loss control. The salinity of the mix water is a very important factor to be considered with regards to bentonite hydration. High salinity will inhibit bentonite hydration and consequently reduce slurry extension and cement yield. For high salinity slurries, the use of attapulgite is suggested as an alternative to bentonite (Nelson and Guillot, 2008). Another common viscosifier used in the design of cement slurries is sodium metasilicate. Sodium metasilicate is a white soluble powder manufactured by fusing silica with sodium carbonate at a temperature of 2552 degree Fahrenheit (Heinold et al., 2002) and is available as a solid or liquid. Sodium metasilicate viscosifies the slurry by reacting with lime (calcium hydroxide) or calcium chloride in the cement to form calcium silicate gel. This process permits the addition of more water to increase the water-cement ratio SPE-190079-MS 5 without risking the formation of excessive free water. Slurry densities as low as 11.1 ppg (Nelson and Guillot, 2008) can be obtained with sodium metasilicate at concentrations that vary from 0.1 percent to 4.0 percent (Heinold et al., 2002). Sodium metasilicate can be used as an additive up to a temperature of 200 degrees Fahrenheit. It is important to note that sodium metasilicate can act as an accelerator. This tendency to accelerate the cement hydration reduces the effectiveness of other additives that may be present in the slurry. When the solid form of sodium metasilicate is used, it is recommended to dry-blend it with the cement or else, the addition of calcium chloride may be necessary to cause gel formation (Nelson and Guillot, 2008). When the liquid form of sodium metasilicate is used, it is added to the mix water before mixing in the slurry. Typical performance for class G cements with sodium metasilicate is illustrated in Table 3. Table 3—Performance of class G cement with added sodium metasilicate (Nelson and Guillot, 2008). Sodium Metasilicate (%BWOC) Slurry Density (ppg) Mix Water (%BWOC) 24 hr Compressive Strength at 120°F (psi) 0 15.8 44 4770 0.15 14.5 60 1746 1 14.5 60 1896 0.25 14 68 1420 1 14 68 1640 0.5 13.5 78 946 2 13.5 78 1327 0.5 13 90 750 2 13 90 120 0.75 12.5 > 100 382 2 12.5 > 100 633 1 12 > 100 265 2 12 > 100 420 1.5 11.5 > 100 147 3 11.5 > 100 271 2 11 > 100 102 3 11 > 100 145 Water-extended cements have the advantage of being relatively easier to design because the standard API testing methods can be used without any modification. This means that the prediction of slurry behavior and properties downhole is straight forward and adjustments on the well site are easy to implement if required. Cements with Lightweight Particles Various lightweight substances have been applied to the design of lightweight cement slurries. These include pozzolans, gilsonite, ceramic microspheres and hollow glass microspheres. These materials have a specific gravity less than that of Portland cement. Mixing a calculated amount of these substances with cement can yield low density slurries suitable for weak fracture gradient zones. Pozzolans Pozzolans are one of the most common cement slurry extenders in use today. They exist naturally as volcanic ashes and diatomaceous earth for example, and artificially as fly ash. Fly ash is the most common form of pozzolan and is obtained as a by-product of coal combustion in power plants. It has a particle size that is 6 SPE-190079-MS close to that of Portland cement and is mainly composed of silica and alumina. The specific gravity of fly ash varies from 2 to 2.7 (Hewlett, 2001) and slurries with density as low as 13.1 ppg (Nelson and Guillot, 2008) can be designed with acceptable properties. An interesting property of pozzolans is that when used in cement slurries, they react with calcium hydroxide produced as a by-product of the cement hydration process. This reaction produces a cementitious material that contributes positively to the compressive strength development of the slurry. This means that pozzolan slurries not only provide weight reduction but also provide better set cement strength than slurries extended with bentonite alone. The reaction with calcium hydroxide prevents degradation of the cement due to free calcium hydroxide in the cement that can be attacked by exterior chemical agents. The permeability of set pozzolan cements is very low which is desirable with regards to the zonal isolation objectives of cementing (Nelson and Guillot, 2008). A major challenge with using pozzolan cements is the inconsistency in particle size and specific gravity that exists from one batch to another. It is important to measure every batch of pozzolan used in the field and adjust the cement mixing operations to ensure that laboratory design parameters are adhered to. Another challenge regarding the use of pozzolans in cement is the decreasing number of coal-fired plants because of the move towards more environmentally friendly power generation methods. Because of this trend, a shortage in the future supply of fly ash for cement extension is anticipated. Cement slurries can be extended with a combination of pozzolans and bentonite to obtain more density reduction than that which would be obtained with pozzolan alone as well as incorporate some of the benefits of bentonite such as fluid loss reduction. For higher temperature applications above 200 °F, an appropriate amount of silica can be added to maintain the effectiveness of the pozzolan additive. If the cost of shipping is minimized or the supply source is nearby, pozzolans offer an economical solution for lightweight slurries with good strength performance. Table 4 shows typical properties for different blends of cement and pozzolan. Table 4—Performance of Cement Slurries with Class H and Fly Ash (Jangid and Marjason, 2013). Slurry Density (ppg) Poz:ClassH (% by volume of blend) Compressive Strength (psi) 12.0 75:25 392 12.0 50:50 555 13.0 75:25 1050 13.0 50:50 1378 13.5 75:25 1294 13.5 50:50 1452 13.5 75:25 1349 14.5 75:25 1796 14.5 50:50 2270 14.5 25:75 1611 Expanded Perlite Expanded perlite is made by heating crushed volcanic glass to its melting point. It has a very low bulk density of about 1.03 ppg and can be used to formulate slurries with densities as low as 12 ppg (Nelson and Guillot, 2008). Bentonite is usually added to the slurry mix to prevent segregation of the perlite. It is important to note that perlite becomes significantly denser under pressure, hence its applications are limited to shallow wells where the variation between the downhole slurry density and the surface mixing density is kept to a minimum. Cements formulated with expanded perlite exhibit decent performance. For example, a 10.60 ppg slurry with cement-perlite ratio of 1:2 (by volume), 15.5 gal/sk of mix water and 4% bentonite SPE-190079-MS 7 will yield a compressive strength of 520 psi after 24 hours under a curing pressure of 3000 psi (Nelson and Guillot, 2008). In addition to density reduction and slurry yield increase, the inert nature of perlite helps to render the set cement more durable due to increased resistance to external chemical attack from corrosive environments. Gilsonite Gilsonite is a naturally occurring mineral with a specific gravity of 1.05. It has a low water requirement and hence will result in lightweight cements with relatively good set cement compressive strength. While the primary use of gilsonite is as a bridging agent for lost circulation control, it can be used to obtain slurry densities as low as 12 ppg. When high concentrations of gilsonite are used in cement slurries, it is necessary to add an appropriate amount of bentonite or another viscosifier to minimize or eliminate particle segregation. Finally, it is recommended that gilsonite not be used in wellbores with bottomhole temperature greater than 300 degrees Fahrenheit. Gilsonite will start to melt at 385 degrees Fahrenheit and above 240 degrees Fahrenheit, the gilsonite particles begin to fuse and the downhole slurry density becomes significantly heavier than the surface slurry density (Nelson and Guillot, 2008). Powdered Coal Powdered coal has a specific gravity of 1.3 and a wide particle size distribution. It can be used to obtain slurry densities as low as 11.9 ppg. It is also very well suited for thermal wells due to its high melting point of 1000 degrees Fahrenheit. Use appropriate amounts of bentonite with powdered coal extended cements to prevent particle segregation (Nelson and Guillot, 2008). Ceramic Microspheres Ceramic microspheres also known as cenospheres are hollow spheres filled with nitrogen or carbon dioxide, consisting mainly of silica and alumina and produced as a by-product of coal combustion in coal-firing power plants. Ceramic microspheres have a wide range of specific gravity and particle size depending on the source. The crush rating for ceramic microspheres are generally close to 3000 psi (Sarmah et al., 2015). The variation in specific gravity and particle size poses a challenge to field mixing because each batch must be tested to ensure consistency with the properties of the slurry as designed in the lab. Competent slurries with density as low as 9 ppg are obtainable with ceramic hollow spheres (Dajani and Curtis, 2009). In field applications, a certain percentage of the cenospheres in the slurry will break under downhole pressures. When this happens, the slurry density downhole becomes higher than the slurry density on the surface and in wellbores with a narrow pressure window, the lost circulation prevention function of the slurry may be lost. Proper testing is necessary to simulate downhole conditions in the lab and determine the crush resistance of the cenospheres to be used so that the density variation can be accounted for. A class G slurry with ceramic microspheres and 1% calcium chloride with a density of 8.5 ppg yielded a 24-hour compressive strength of 215 psi under a curing pressure of 3000 psi (Nelson and Guillot, 2008). 8 SPE-190079-MS Figure 2—Sample of ceramic microspheres showing imperfections and size variation between spheres (Dajani and Curtis., 2009). Glass Microspheres Glass microspheres are gas filled hollow spheres manufactured from borosilicate glass with an appearance of fine white powder. They have an average specific gravity of 0.32 (Olutimehin et al., 2015) but specific gravity can vary between 0.2 and 0.4. Glass microspheres have a particle size that is generally larger than that of Portland cement but smaller than that of silica flour ranging from 0.5 to 2 microns (Smith et al., 1980), and they can be used to obtain slurries with densities as low as 7.5 ppg (Nelson et al., 2008). Glass microspheres are more crush resistant than ceramic microspheres and are manufactured at fixed crush resistance ratings up to 18000 psi (Dajani and Curtis, 2009). Because glass microspheres are manufactured in a precise fashion, the batch to batch variations that exist with ceramic cenospheres are minimized or absent with glass microspheres. The uniformity in the particle size and consistency in specific gravity from one batch to another result in more predictable slurry mixtures. Glass microsphere cements are especially suited for situations that require low to ultra-low density but high set cement strength as well. A glass microsphere-based slurry with a density of 9.65 ppg yielded a compressive strength of 1755 psi after 24 hours and 2069 psi after 48 hours (Sarmah et al., 2015). Cement slurries extended with glass microspheres also exhibit fast compressive strength development due to the low water requirement for achieving a pumpable slurry. Glass microsphere cements also retain their strength at high temperatures and exhibit insignificant permeability to water. These characteristics have made them one of the most popular means of extending cement slurries for combatting lost circulation problems today. Glass microspheres like every other extender are not without their drawbacks. Very much like ceramic microspheres, a certain percentage of the spheres will break under pressure. This breakage will lead to higher slurry densities downhole. Thus, as in the case of cenospheres, sphere breakage should be accounted for in the design of the slurry. Slurry instability is another challenge that arises in the use of glass microspheres. This is caused by segregation of the microspheres in the cement due to their low density. Slurry design with glass microspheres must minimize segregation to prevent excessive free water and subsequent loss of zonal isolation in the borehole. SPE-190079-MS 9 Figure 3—Sample of glass microspheres showing more homogeneity compared to ceramic microspheres (Dajani and Curtis, 2009). Foamed Cements Foamed cement can best be described as a gas-liquid dispersion of nitrogen stabilized as microscopic bubbles in a base cement slurry (Kutchko et al., 2016). Nitrogen is injected into a base slurry containing a foaming agent and foam stabilizer along with other required additives under pressure during mixing on the surface and is then pumped into the wellbore. Foamed cements can be designed with densities as low as 6.0 −7.0 ppg (Nelson and Guillot, 2008). They offer good fluid loss control, cement columns with low hydrostatic pressure, better strength than water-extended slurries, high tensile strength and ductility, efficient mud displacement and hole cleaning performance (Mariott et al., 2005). Even though foamed cements can yield ultra-low density slurries, a maximum of 33 percent – 35 percent foam quality is recommended for the slurry to be competent (Bybee K., 2006; Mariott et al., 2005). The resulting permeability and porosity of a typical foamed cement slurry is higher than that of conventional lightweight cement and is determined by the foam quality (gas volume divided by slurry volume) (Kutchko et al., 2016). According to Dusterhoft (2003), the cement permeability rapidly increases below a slurry density of 8 ppg. The surface treating pressure and prevailing wellbore pressure are also important factors that determine the set cement permeability and porosity (Kutchko et al., 2015). The compressive strength of the set cement is determined by the bubble size and bubble distribution through the cement, the compressive strength of the base slurry and the nitrogen content or foam quality. Minimum contact between the bubbles in the slurry is desirable for ensuring structural integrity in the set cement. Lab tests should be used to determine the appropriate design parameters to optimize the bubble distribution in the slurry (Mariott et al., 2005). Table 5 on the next page shows the compressive strength and cement permeability for foamed cements of different densities and bubble size distributions for a base slurry comprised of class G cement cured for 72 hours at 80 degrees Fahrenheit. Table 5—Performance of Foamed Cements (de Rozières and Ferrière, 1991). Broad Bubble Size Distribution Density (ppg) Compressive Strength (psi) Permeability (md) 14.8 3016.78 0.05 12.2 2030.52 0.0076 Narrow Bubble Size Distribution Compressive Strength (psi) Permeability (md) 1189.31 1.25 10 SPE-190079-MS Broad Bubble Size Distribution Narrow Bubble Size Distribution Density (ppg) Compressive Strength (psi) Permeability (md) Compressive Strength (psi) Permeability (md) 10.2 1363.35 0.017 986.26 5.7 9.0 1305.34 0.054 826.72 25.7 7.5 1087.78 89 464.12 1.99 5.1 739.69 58890 232.06 6800 Density variation of the pumped slurry from surface to bottomhole is also a challenge in foamed cement application. As the wellbore pressure increases, the slurry density increases due to the compression of the nitrogen gas. Proper design and testing of the slurry at simulated wellbore conditions is necessary to account for this problem. Software simulation can be used to model the hydrostatic pressure profile to be expected for any job. Such models can then be factored into the operational parameters of the cement job to ensure that the cement placed in the borehole maintains the properties it was designed for. Cementing a wellbore with foamed cement is a technically challenging process because of the special equipment required for the injection of nitrogen gas into the base cement slurry as it is pumped downhole. Field results for foamed cementing may be vastly different from results obtained in the lab. Part of the problem is due to the difficulty in characterizing foamed slurry behavior in the lab under downhole conditions in a way that yields accurate and reliable results. Foamed slurries consisting of the same components in the same composition can have different properties based on the mode of preparation. This is because the preparation parameters such as mixing speed (shear rate), and mixing pressure greatly affect the bubble size distribution and as mentioned earlier, bubble size distribution affects the compressive strength and permeability. For example, Davies et al. (1981) showed that foamed cement prepared in the field under high shear rate and high pressure conditions are more stable than their laboratory-prepared counterparts. Conclusions Various methods are used for the extension of cement slurries for combatting lost circulation in wellbores where the formation pressure gradient is too weak to support the hydrostatic pressure imposed by conventional slurry mixes. The method chosen should be decided based on the prevailing conditions and challenges in the well of interest, additive availability, logistical considerations and cost of implementation. Table 6 is a comparison of the average cost range of each lightweight additive discussed in this paper obtained from publicly available vendor information on the internet. Table 6—Average Price Range of different Additives. Material Average Cost Range (US$ / Metric Ton) Bentonite 60 – 150 Sodium Silicate 150 – 300 Fly Ash 40 – 60 Ceramic Microsphere 600 – 1350 Glass Microsphere 5000 – 5500 Expanded Perlite 98 – 205 Gilsonite 1000 – 1300 SPE-190079-MS 11 Interest in the use of glass microspheres and foamed cement have especially garnered a lot of renewed interest due to improved technology, their effectiveness in highly critical situations across the globe and a better technical understanding of the processes that govern the behavior of such slurries. It is of great research interest in well cementing to understand and quantify the relationship between the various mechanical properties of cement and zonal isolation performance and wellbore integrity. Compressive strength has been the main mechanical property used to evaluate the capacity of oilwell cements to provide adequate zonal isolation. However, as mentioned previously, other factors like tensile strength and Young's Modulus have been shown to be at least just as important for maintaining wellbore integrity under stresses induced by completion, stimulation and production activities. A better understanding of the significance of the above mentioned mechanical properties with regards to wellbore integrity will be critical to formulating more reliable advanced lightweight slurries that will be specifically optimized for the prevalent scenario expected in any given well. Nomenclature °F API BWOC ECD gal/sk hr md ppg psi = Degrees Fahrenheit = American Petroleum Institute = By Weight of Cement = Equivalent Circulating Density = Gallons per Sack = Hour = Millidarcy = Pounds per Gallon = Pounds per Square Inch SI Metric Conversion Factors (°F – 32) * (5 / 9) = °C psi * 6.894757 E+02 = bar ppg * 1.1982639 E+02 = kg/m3 References Bosma, M., Ravi, K., van Driel, W., & Schreppers, G. J. (1999, January 1). Design Approach to Sealant Selection for the Life of the Well. Society of Petroleum Engineers. doi:10.2118/56536-MS Bybee, K. (2006, February 1). New Ultralightweight-Cementing Technology Combines Benefits of Current Leading Methods. Society of Petroleum Engineers. doi:10.2118/0206-0065-JPT Curtis, J. A., & Dajani, M. R. (2009, January 1). Guidelines for Appropriate Application of Non-Foamed Ultralightweight Cement Slurries. Society of Petroleum Engineers. 10.2118/119535-MS Davies, D. R., Hartog, J. J., & Cobbett, J. S. (1981, January 1). 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