Gel Strength Development Research Articles

Kinetic modelling of the mass and heat transfer of a plant-based fishball alternative during deep-fat frying and air frying and the changes in physicochemical properties

The mass and heat transfer of a plant-based fishball alternative (PFB) and the changes in physicochemical attributes within frying were researched. The effective moisture diffusivity Deff and thermal diffusivity α of PFB in deep-fat frying (DF) were larger than in air frying (AF), where the Deff and α of DF-PFB were 2.95 × 10−8 and 7.56 × 10−6 m2/s, respectively, while those of AF-PFB were 2.34 × 10−8 and 6.89 × 10−6 m2/s, respectively, indicating a more effective moisture and heat transfer in DF. The oil uptake of DF-PFB was significantly higher than fishball (FB), with the equilibrium oil content Oeq of 0.120 and 0.039 g/g, respectively; AF would reduce the oil uptake of PFB considerably (0.067 g/g). PFB had a similar trend for texture and gel strength development to FB; the hardness, chewiness, resilience, and springiness during DF developed more rapidly than in AF. Besides, DF induced a larger ΔE (total color difference) than AF, where the surface ΔE of DF-PFB was 32.25, while that of AF-PFB was 26.74. Microstructural observations illustrated that DF-PFB formed a rougher structure than DF-FB, causing more oil absorption in PFB. These results could provide a fundamental understanding of transport phenomena and physicochemical attributes of PFB during frying, demonstrating that the AF could be an alternative way to produce healthier PFB products with less oil absorption while having equal qualities.

Study Compares Methods To Measure Static Gel-Strength Development

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 31348, “Comparing Oilwell Cement Static Gel-Strength Development by Ultrasonic and Intermittent- and Continuous-Rotation Measurement Methods,” by Shameed Ashraf, Rahmad H.M. Husin, and Awang Rizalman, Schlumberger, et al. The paper has not been peer reviewed. Copyright 2022 Offshore Technology Conference. Reproduced by permission. _ Cement-sheath integrity preventing interzonal communication is closely related to static gel strength (SGS). API Standard 65-2 puts importance on the critical gel strength period (CGSP) measurement, which begins when the critical static gel strength (CSGS) is developed and ends when 500 lbf/100 ft2 is attained. The three methods accepted in the industry to measure SGS development are continuous and intermittent rotation, followed by ultrasonic measurement. A laboratory-based study is presented in the complete paper that compares these measurement methods. SGS Measurement Methods Continuous-Rotation Device. The continuous-rotation device used for direct SGS measurement is equipped with a pressure vessel capable of maintaining the set temperature and pressure that simulates actual cementing conditions. The paddle drag created by the continuous movement is converted and measured as SGS by means of correlation. Intermittent-Rotation SGS Device. This device keeps the cement slurry to be evaluated in a static condition inside a pressure vessel at controlled temperature and pressure. The device features a torque-sensing arrangement that obtains the intermittent rotating paddle value. This measured torque value is used to calculate the SGS using correlations related to paddle dimensions. Ultrasonic Method. An ultrasonic device can estimate the SGS of a concrete slurry under high-pressure and high-temperature conditions using an acoustic ultrasonic mechanism based on the attenuation of the acoustic wave communicated through the slurry during the hydration process. The ultrasonic cement-analyzer configuration estimates the acoustic speed, whereas the SGS analyzer measures the signal through the slurry. Thus, the SGS analyzer joins an implanted framework that performs computerized gel analysis. When data collection is complete, investigation of the information calculates the SGS values as a function of time. The authors compared the results obtained by this SGS system with information acquired from the tube rheometer device and shearometer and found them to have similar findings. Testing Methodology The methodology included the cement-slurry formula and the preparations followed by the device settings for each assessment type. Two different paddle configurations are used for the continuous-rotation method. As a result, four types of equipment evaluation are made for each slurry, two for the continuous-rotation type, one for the intermittent-rotation type, and one for the ultrasonic type.

Nonlinear viscoelastic rheological behavior of bentonite and sepiolite drilling fluids under large amplitude oscillatory shear

Common models used to describe rheological behavior of drilling fluids are built on pure viscous flow assumption. Full rheological characterization of drilling fluid under this assumption is not feasible since drilling fluids are viscoelastic materials and exhibit both elastic and viscous features. Gel strength development, yield stress value at near zero shear rates, and sag tendency in drilling fluids are the strong function of viscoelastic responses. Linear and nonlinear viscoelastic responses should be measured to provide complete viscoelastic analysis. Two water-based drilling fluids, sepiolite and bentonite drilling muds, each in four states, were subjected to testing using rheometer. Nonlinear viscoelastic parameters and their indications for both fluid systems were characterized for the first time. Large amplitude oscillation sweep tests were conducted as a function of strain and strain rate at four temperatures and frequencies. Stress response was decomposed through Fourier transform into elastic and viscous stress components. Lissajous-Bowditch loops were assessed as rheological fingerprints to detect the initiation of nonlinear region and the nature of nonlinearity. Results revealed that bentonite fluid systems provided stronger gel strength, a more stable network, and high mechanical stability compared to sepiolite fluid samples up to 50 °C. However, the sepiolite fluid systems outperformed at high temperatures (100 and 150 °C). The elastic nonlinear response was determined to be strain/strain rate softening, and the nonlinear viscous response was shear rate thinning at large strain rates for both fluid systems. Contrary to common knowledge found in literature (shear rate thinning), it was revealed that both fluid systems demonstrated shear rate thickening behavior at low to moderate strain rates. This finding is of importance in understanding gel strength development and evaluating sag tendency in drilling operations. • Nonlinear viscoelastic properties of drilling fluids under LAOS were investigated for the first time. • Thermo-structural stability of drilling fluids was evaluated regarding nonlinear viscoelasticity. • Lissajous-Bowditch curves were established to visualize nonlinear viscoelastic characters of drilling fluids. • LAOS parameters quantified nonlinearity based on LAOS protocols for drilling fluids.

Managed wellhead backpressure during waiting setting of managed pressure cementing

Managed pressure cementing (MPC) has been successfully used to reduce risk lost circulation and improve cementing quality in wells with a narrow safe pressure window. However, during the waiting setting period of MPC, the magnitude of the managed well backpressure is still based on experience, which results in a high risk of leakage or gas channeling especially in formations with a narrow safe density window. Therefore, a backpressure managing method is proposed here based on a model we built for calculating wellhead backpressure. This model was used to analyze the effect of cement slurry, temperature and wellbore pressure on wellhead backpressure. The results show that hydration, filtration shrinkage and gel supporting are essential to reduce wellbore pressure, although hydration is less effective compared with the latter two on pressure reduction. The magnitude and duration of wellhead backpressure depend on the extent of volume shrinkage and the gel strength development of cement slurry. Latex-cement slurry requires minimal wellhead backpressure with the shortest duration. Temperature and wellbore pressure greatly impact wellhead backpressure with temperature playing a more dominant role.

New Lightweight Cement Formulation for Shallow Oil and Gas Wells.

The use of lightweight pozzolanic aggregates as partial replacement of cement results in low-density cement systems. Such systems ensure effective zonal isolation in zones where low equivalent circulating densities are required. However, low pozzolanic materials, such as fly ash and ground granulated blast furnace slag (GGBFS), have poor early-age strength development and long set times, especially when used in high volume, that is, exceeding 50% by weight of cement. The objective of this study is to develop a lightweight oil- and gas-well cement recipe with enhanced properties employing the synergism that exist among fly ash, GGBFS, and silica fume. The experimental work was per laboratory procedure outlined by American Petroleum Institute. Portland class G cement and the aluminosilicate materials were admixed in water to form a 13.5 ppg slurry. Chemical admixtures were used to facilitate the dissolution of reactive components in the pozzolanic materials and the hydration process. The experimental investigations were done at 150 °F and an ambient pressure of 1500 psi. The newly developed lightweight recipe exhibited excellent rheological and mechanical properties, having a wait-on-cement time for about 4 h and a 24 h sonic strength of 3116 psi, at 150 °F and 1500 psi. The thickening time was approximately 4 h (70 Bc). This slurry will be ideal in zones that would require a low hydrostatic slurry column and rapid gel strength development.

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.

Experimental design of a well cement slurry for rapid gel strength development

Hydration of calcium sulfoaluminate cement (CSA) yields mainly ettringite that supports high early-age strength. The hydration characteristics of CSA can help to control gelation of a Portland cement slurry such that fluid migration is mitigated. This paper reports on the performance of well cements incorporated with CSA and gypsum on gel transition time and Right-Angle-Set (RAS) property for utilization in plugging oil wells. Rapid gel strength development is highly dependent on ettringite formation. It is observed that gel transition time shortens with increasing additions of CSA. RAS property is more evident with higher dosage of CSA regardless of retarder content.

Newtonian Fluids in Cementing Operations in Deepwater Wells

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 166456, ’Newtonian Fluid in Cementing Operations in Deepwater Wells: Friend or Foe?,’ by Polina Khalilova, SPE, Schlumberger; Brian Koons, SPE, Chevron; and Don Woody Lawrence and Anouar Elhancha, SPE, Schlumberger, prepared for the 2013 SPE Annual Technical Conference and Exhibition, New Orleans, 30 September-2 October. The paper has not been peer reviewed. This paper discusses the factors to be taken into account when designing cement jobs using fluids in turbulent flow and some of the overlooked benefits of using turbulent-flow design for mud removal. It will be demonstrated that, when designed and executed properly, the use of turbulent-flow mud removal with Newtonian fluids can be beneficial in deepwater (DW) cementing operations. Introduction When one considers the risks associated with poor zonal isolation in DW wells, such as release of well fluids to the environment, gas migration to the surface, underground blowouts, and well-killing operations, the importance of proper cementation and sufficient zonal isolation becomes clear. These issues are often difficult and time-consuming to address, a situation further complicated by the daily cost of DW-well operations. One of the complexities in DW wells is that of drilling with oil-based or synthetic-based muds, commonly referred to as nonaqueous fluids (NAFs). NAFs are compressible fluids that dynamically change density and rheological properties as temperature and pressure increase or decrease. This makes modeling flow regimes for proper mud removal very difficult. These types of drilling fluids also oil-wet the surfaces to be cemented, making cement bonding more troublesome. When cement slurries are contaminated with NAF, it can extend thickening times, cause undesirable gel-strength development, and ruin compressive-strength development. Another complexity in drilling DW wells is the narrow margin between pore pressure (PP) and fracture gradient (FG). A given reservoir that is reached on a land location has a wider PP/FG margin as compared with that of the same reservoir reached from a DW location. The available PP/FG margin would be narrower as the amount of overburden available on land is reduced relative to the depth of water. This hinders cementing because it reduces the equivalent circulating density (ECD) under which the cement slurries can be placed. An additional challenge with DW wells is that increasing water depth brings an increasing length for the fluids to travel to reach their placement depth. Unless mechanical separation (wiper balls or darts) is used, the spacers and cement slurries will have an increased mixing interface and will be exposed to additional contamination from mud film remaining on the pipe inner surface while being pumped through the drillpipe or casing before reaching their final placement position in the annulus. Currently, there are two primary flow regimes used when planning a mud-removal design for cementing: turbulent flow and effective laminar flow. Turbulent flow is generally considered the preferred method for efficiently removing drilling fluids, but there are requirements for turbulent flow to be effective that may not always be achievable. Effective laminar flow is the most widely used placement method because of the ease of maintaining hydrostatic control of the well, the ability to achieve effective mud removal at the low velocities typically required during cementing in DW wells, and the ability to maintain ECD below the FG. Drilling fluids, weighted spacers, and cement slurries are all placed by use of the effective-laminar- flow method. Brines, water, and chemical washes are all placed by use of turbulent flow. There are many examples in historical publications and operational case histories in which turbulent flow is used for effective mud removal, but no defined guidelines or discussions were found by the authors of the original paper for the use of Newtonian fluids specifically in DW-cementing operations (although case studies in which that method was used in DW do exist; several are provided in the complete paper).

Transglutaminase and high pressure effects on heat-induced gelation of Alaska pollock (Theragra chalcogramma) surimi

A prior high pressure processing (HPP) treatment has previously been shown to enhance subsequent (at atmospheric pressure) low temperature ‘setting’ (glutamyl-lysine, non-disulfide protein crosslinking) induced by transglutaminase (TGase; endogenous or added microbial enzyme). This enhanced setting induces greater gel strength and deformability of subsequently cooked surimi gels. We sought to determine if 25°C incubation carried out simultaneous with, rather than following, HPP might similarly induce a setting effect on subsequently cooked gels. Pollock surimi pastes (± added microbial TGase) were subjected to HPP 200, 300, or 400MPa; at 5°C (little or no setting effect expected during HPP at this temperature) for 30min or at 25°C (optimal setting temperature for pollock pastes) for 30, 60, or 120min. Pastes were then directly cooked (90°C for 20min) (pressureP°C/time>C), or first allowed to undergo setting at atmospheric pressure (25°C for 30, 60, or 120min), followed by cooking (90°C 20min) (pressureP°C/time>Stime>C). With no microbial TGase added to the raw paste (e.g., endogenous TGase only), 300MPaP5°C/30min>S25°C/120min>C induced highest gel fracture stress and strain. The same treatment but with HPP at 200 or 400MPa gave only slightly lower fracture stress (gel strength). Increasing the temperature of the HPP treatment to 25°C (300MPaP25°C/30min>S25°C/120min>C), even with longer HPP time (300MPaP25°C/60 or 120min>C), gave weaker gels, similar to those obtained by setting and cooking without a prior HPP treatment (S25°C/60min>C). Thus, attempting to induce TGase crosslinking by setting at 25°C during HPP treatment actually seemed detrimental to gel strength development. However, when HPP was carried out at 25°C and microbial TGase was added, gel strength and deformability (fracture stress, strain) were enhanced above that of all other treatments tested. All treatments containing microbial TGase evidenced enhanced protein polymerization. Scanning electron microscopy revealed a more dense and fibrous structure in such gels, and reduction of free thiol (SH) groups was noted as a result of microbial TGase addition.

Effects of potassium alum addition on physicochemical, pasting, thermal and gel texture properties of potato starch

SummaryThe study investigated the effects of the addition of different concentrations of potassium alum (PA, 0, 0.1, 0.3, 0.5, and 0.7 g 100 g−1; w/w, on a starch weight basis) on the pasting, thermal, gel texture and other physicochemical properties of potato starch. The addition of PA resulted in a significant increase in solubility and a decrease in swelling power and light transmittance of stored pastes. Differential scanning calorimeter analysis demonstrated an increase in gelatinisation temperatures and gelatinisation enthalpy and a decrease in phase transition temperature range (ΔTr) with increasing PA concentration. Results of rapid visco‐analysis indicated that addition of PA decreased the peak, trough, breakdown, final and setback viscosities, but increased in peak time. Textural tests showed that the addition of PA retarded gel strength development during refrigerated storage. The high ionic strength and water‐binding capacities of Al3+, K+ and SO42− point to being the key factors for these observed changes.

Cement-Shrinkage Measurement in Oilwell Cementing—A Comparative Study of Laboratory Methods and Procedures

Summary Cement-sheath shrinkage after placing the cement slurry in the annulus has been of concern in oilwell cementing because of the potential detrimental effects that shrinkage can have on long-term zonal isolation. This paper compares several methods for measuring cement shrinkage under a variety of conditions including those downhole. Using the various methods, cement shrinkage in environments where the cement slurry is either closed to or open to external water sources was measured, and the values were compared. The methods used for measurement under atmospheric conditions were based on American Petroleum Institute (API) test apparatus (balloon and ring mold) and flask methods currently used in laboratories. Measurements under pressure were performed using the balloon and ring-mold methods, in-house designed equipment, and commercial equipment. The values obtained by the different methods are discussed. Procedure modifications are proposed for measuring volume changes to cement slurries on the basis of placement time, shear history, and gel-strength development. The results presented in this work can be used to test shrinkage characteristics of cement slurries in the laboratory under downhole conditions and to select a cement system that is fit for purpose.

Use of Finite Element Analysis to Engineer the Cement Sheath for Production Operations

Abstract Many successfully cemented wells begin to show annulus pressure buildup, which is often caused by damage to cement sheath integrity due to post-cementing operations. This problem may be temporarily dealt with by releasing the annulus pressure. However, this method of annular gas production is not a long-term solution to the problem. A finite element analysis (FEA) method has been developed to analyze the effects of various well events and operations such as cement hydration, casing pressure testing, completions and production on the integrity of the cement sheath during the life of the well. The three-dimensional FEA modeling considers the sheath's mechanical properties, such as Young's modulus, Poisson's ratio and tensile strength, in addition to confined compressive strength, and helps provide the user with a cement design that can maintain an annular seal over the life of the well. This paper discusses how a cementing design specialist can model the events upon and after cement placement to help provide a long-term seal of the annulus. The required input data is discussed and the output information is shown for example wells. Life of the Well The main purpose of the annular cement is to provide effective zonal isolation for the life of the well so that oil and gas can be produced safely and economically(1). To achieve this objective, the drilling fluid should be removed from both the wide and narrow annulus and the entire annulus should be filled with competent cement. The cement should meet both the short-term and long-term requirements imposed by the operational regime of the well. Traditionally, the industry has concentrated on the short-term properties that are applicable when the cement is still in slurry form. This effort is necessary and important for effective cement slurry mixing and placement. However, the long-term integrity of cement depends on the material/mechanical properties of the cement sheath, such as the Young's modulus, the tensile strength and the resistance to downhole chemical attack. Considering properties of the cement sheath for long-term integrity is critical if the well is subjected to common changes in the pressure and temperature of the cased well. After cement is placed in the annulus, if no fluid immediately migrates to the surface, short-term properties such as density, rate of static gel strength development and fluid loss of the cement may have been designed satisfactorily. However, recent experience has shown that after well operations such as cement hydration, casing pressure testing, completions and production, the cement sheath could lose its zonal isolation capabilities to provide zonal isolation(1). This failure can create a path for formation fluids to enter the annulus, which pressurizes the well's annulus, and could render the well unsafe to operate. The failure can also result in premature water production that can limit the economic life of the well. Failure of the cement sheath is most often caused by pressure or temperature-induced stresses inherent in well operations. Loss of isolation can shorten or destroy the life of the well because of corrosive fluid attack on the casing and cement sheath and/or sustained gas pressure on the casing annulus.

Transition Time of Cement Slurries

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 90829, "Transition Time of Cement Slurries, Definitions and Misconceptions, Related to Annular Fluid Migration," by M.J. Rogers, SPE, R.L. Dillenbeck, SPE, and R.N. Eid, SPE, BJ Services Co., prepared for the 2004 SPE Annual Technical Conference and Exhibition, Houston, 26-29 September. Cement-slurry transition time is a term that has been used in the oil industry for many years. During this time, the term has been defined, redefined, and misused to cover a wide range of cementing topics. This has led to numerous misconceptions and confusion as to what “transition time” really means. For many years, this term has been tied to the term right-angle-set, which relates to the speed at which slurries undergoing continuous shear go from a pumpable to a non-pumpable state. The full-length paper establishes a definition for cement transition time and discusses the misconception of using only gel-strength development to control gas migration. Introduction Annular gas-migration control after cementing has been the subject of many studies and papers. The two things that all these studies have in common are that they all present valid conclusions and, although beneficial, they all have failed in field applications at one time or another. These failures illustrate that although we have learned a great deal about the causes and prevention of gas migration, there is still a lot to learn. The term transition time has been used to refer to the dynamic-set profile of cement slurries as exhibited on a pressurized consistometer. Slurries that had a short transition time were those that had a “right-angle-set” on a thickening-time chart. A right-angle-set is one where the viscosity of a slurry remains relatively low through most of the test and then increases rapidly in 20 to 45 minutes to more than 70 Beardon units of consistency (Bc). Once cement movement is stopped, static gel-strength (SGS) development may occur within several minutes to more than an hour, depending on well conditions and slurry design. Wellbore temperature and pressure as well as slurry density and additives are the main factors determining how SGS develops. The term right-angle-set (a dynamic analysis) should not be used when referring to slurries with short transition times (static-state test). Another misconception about transition time is the use of the initial compressive-strength determination derived from an ultrasonic cement analyzer. In some cases, the time from 50 to 500 psi has been used as a determining factor for how fast a slurry will transition into a solid. The time to 500 psi is important in reducing waiting-on-cement time, but it may have little to do with SGS development of cement slurries. Transition time also has been described as the period during which the slurry changes from a true hydraulic fluid to a highly viscous mass showing some solid characteristics under static-state conditions. It is generally accepted that at SGS development greater than 100 lbf/100 ft2, gas or fluid intrusion into the gelled cement can occur. This is considered the start of the transition time and is the point where full hydrostatic-pressure transmission is restricted. The transition time ends when the SGS increases to 500 lbf/100 ft2. At this point, the slurry has developed sufficient gel strength to prevent fluid or gas migration into the cement column. It has been proposed that the transition time between 100 and 500 lbf/100 ft2 be reduced to less than 40 minutes to minimize the time for fluid or gas intrusion into the cement.

An Improved Cementing Method for Solid Expandable Tubulars

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 90923, "Improved Method of Cementing Solid Expandable Tubulars," by Charles Fanguy, SPE, Dan T. Mueller, and Dale R. Doherty, SPE, BJ Services Co., prepared for the 2004 SPE Annual Technical Conference and Exhibition, Houston, 26-29 September. Failure of cement slurry to remain fluid and stable after placement can prevent successful expansion of solid expandable tubulars (SETs). The property of being both stable and fluid is difficult to achieve with conventional cement technology because conventional slurries tend to settle under downhole conditions after an extended period. The full-length paper describes the premixed-slurry properties and quality-assurance/quality-control (QA/QC) procedures that are required for successful expansion of SETs. The paper also provides test methods and procedures used for fluidity-time testing as well as case histories of successful SET cementation. Introduction There are several challenges when cementing SETs. The primary challenge is to obtain “fluidity” time at static wellbore conditions. Fluidity time is defined as the time the cement slurry exhibits a static gel strength of less than 100 lbf per 100 ft2. True fluidity time is required to ensure that gellation does not occur during the expansion phase that follows cement-slurry placement in the annulus. Gelation can result in “voids” or bypassed mud above the pre-expansion top of cement. Severe gelation also can cause formation breakdown and lack of zonal isolation. In addition to gelation, density segregation and settling can occur during extended static periods at bottomhole conditions. This also can lead to bypassed drilling fluids and potential formation breakdown. These challenges, along with low displacement rates and lack of available centralization, complicate the primary cementing process. Because of these challenges, many expandable liners have been squeezed after expansion as opposed to being cemented before expansion. The technologies and methods described in the full-length paper have led to an increase in the success rate associated with cementing SETs. As this technology becomes more accepted and mainstream, increased focus will be placed on cementing techniques and technologies that can enable complete zonal isolation in the entire annulus. Premixed Cement System A storable, premixed cement system is used for cementing expandable liners. These pre-mixed slurries are blended at a bulk plant before arrival at the wellsite. After the slurry is mixed, liquid samples of slurry are sent to a laboratory so that physical properties can be verified. Properties that are tested include free fluid, fluid-loss control, thickening time, fluidity time, gel-strength development, and compressive-strength development. These properties can be modified with liquid additives if necessary. Premixed slurries also exhibit several characteristics that are beneficial for use with expandable liners. These slurries contain specialized additives that ensure slurry stability under extended storage conditions, so fluidity time at wellbore conditions is easily achieved. These slurries also have improved rheological properties and improved tolerance to mud contamination, as exhibited by contamination tests conducted with both destructive and non-destructive compressive-strength testing. The improved rheologies and resistance to contamination have helped to obtain zonal isolation even with low displacement rates and no centralization.

SMALL AMPLITUDE OSCILLATORY TESTING (SAOT). APPLICATION TO PECTIN GELATION

The setting characteristics of pectin gels during cooling from 105°C to 25°C and reheating to above 100°C have been determined using a versatile food rheometer capable of small amplitude oscillatory testing. Gel strength development during cooling was linearly correlated to temperature and on reheating the gel softened initially then hardened again as the temperature exceeded about 70°C. The linear parameters (slope, intercept) describing the gel development on cooling were related to pectin concentration up to 0.85% but 1% pectin could not be distinguished from 0.85%. On cooling, 75–85% of the gel strength attainable on standing overnight was developed within 30 min. The quick set up on cooling provides the possibility of developing a rapid test method for determining pectin gel properties.

Drilling fluid shear stress overshoot behavior

Shear stress overshoot behavior was studied in four drilling fluid systems and ten bentonite dispersions. These overshoot properties, also described by the American Petroleum Institute as gel strengths, were measured after gelation times of 10 s to 24 h at temperatures of 20–80 °C. Two different rheometers were used to measure overshoot behavior. Gel strength development with time followed a first-order model. Gel development rates at 20 °C varied from 0.005 to 0.01 min−1 for drilling fluid systems and from 0.0004 to 0.02 min−1 for bentonite dispersions. Increasing the gelation temperature for each drilling fluid system caused an increase in the gelling rate constant. Comparison of gel strengths in bentonite dispersions were made using a Fann 35 A viscometer and a Weissenberg Rheogoniometer. Higher gel strength values observed using the Rheogoniometer were believed to be due to differences in instrument spring stiffness and fixture inertia.

The Relationship of Thickening Time. Gel Strength, and Compressive Strength of Oilwell Cements

Summary A previous investigation1 of the effect of thickening times on early compressive-strength and gel-strength development has been expanded to include a wider range of well conditions, a greater variety of slurry types, and a more thorough evaluation of static gel strength. No positive relationship between thickening time and the onset or the rate of static-gel-strength development could be found. With few exceptions, all slurries tested developed values greater than 48 Pa [100 lbf/100 sq ft] gel strength in less than 20 minutes. Data presented show that times needed to develop a specific static gel strength are more closely related to the type of slurry than to thickening time. A calculation method is given for estimating shutdown factor from static-gel-strength data. New data confirm that 12- and 24-hour compressive strengths are not significantly reduced by reasonable increases in thickening time. The maximum single-stage cement interval without an unreasonable waiting-on-cement (WOC) time for specified compressive strength has been redefined in terms of interval temperature differences.

Effect of Heating Rate on Thermally Formed Myosin, Fibrinogen and Albumin Gels

ABSTRACTMyosin, fibrinogen and albumin gels were formed by heating in pH 6.0 phosphate buffer at three heating rates. Turbidity (A660nm) and solubility were monitored along with gel strength, as measured with an annular pump. Myosin and fibrinogen suspensions became turbid and solubility decreased as temperatures preceding the development of gel strength. Linearly increasing heating rates of 12°C/hr and 50°C/hr produced the strongest myosin and fibrinogen gels at 70°C, whereas albumin gels formed at 95°C by heating at 12°C/hr or constant heating for 20 min did not differ in strength.

KINETICS OF HEAT COAGULATION OF EGG ALBUMIN DETERMINED BY WATER BINDING AND RHEOLOGICAL MEASUREMENTS

Dynamic testing of heat coagulated egg albumin revealed that phase angle, a measure of the fluidity of a viscoelastic material, exhibits a first order change during heating in a similar manner as the changes in the spin-lattice relaxation time (T1) of water protons measured by a pulsed nuclear magnetic resonance instrument. The absolute modulus, on the other hand, which is an index of the elastic properties exhibited a zero order change in a similar manner as the development of gel strength measured by constant rate penetrometry using an Instron universal testing instrument. Arrhenius activation energy of 29 kcal/mole for the phase angle and 38.9 kcal/mole for the absolute modulus indicate that the process of protein-water interaction to immobilize water within the gel and that of protein-protein interaction to form the solid gel network occur simultaneously during heating, but they proceed by different mechanisms with the latter process showing greater heat sensitivity.

Gel Strength Development During Heating of Surimi in Combination with Egg White or Whey Protein Concentrate

ABSTRACTGel strengths (work of penetration) of surimi (refined minced fish, MF) alone and in combination with egg white or whey protein concentrate were periodically measured by an annular pump during constant rate heating. Combination gels containing low percentages of MF were of a lesser strength than an additive relationship would have predicted. However, the strength of gels containing greater percentages of MF did relate to the gel strengths of the uncombined proteins.