Cement Seal Research Articles

Exploring epoxy resin sealants for sustained casing pressure mitigation in the wellbore

A significant challenge is sustained casing pressure(SCP) during oil and gas production. This study investigated a solid-free epoxy resin sealant to replace Portland cement. Properties such as sealant viscosity, curing time, compressive strength, and tensile strength were investigated. The sealing and fatigue resistance of cement and epoxy resin were compared. The results indicated that the curing time of epoxy resin was controlled at 3.1 ∼ 10.4 h. Adding a 25% viscosity reducer reduced the epoxy resin's viscosity by 97.63%. Remarkably, the epoxy resin surpassed cement in compressive strength, tensile strength, and elongation at break. The breakthrough pressure of the epoxy resin was higher than that of cement, and this advantage was more evident as the length increased. The convergence time of 10 mm epoxy was prolonged by 189.01% over that of cement. The epoxy resin effectively suppressed the rate of pressure increase after gas breakthrough. Under cyclic loading of 20% to 80% breakthrough pressure, the cement seal failed after 12 cycles, while the epoxy maintained seal integrity for 17 processes. The fatigue resistance of epoxy resin was superior to that of cement, ensuring long-term annulus sealing under alternating load perturbations. Epoxy resin sealant can potentially provide a new solution to the SCP problem.

An investigation of fatigue response of well cement under cyclic loading and impact on zonal isolation performance

Cyclic bottomhole pressure fluctuation is very prevalent in modern well construction and enhanced petroleum recovery applications and poses a great challenge to annular seal integrity and successful zonal isolation, even in cases where the cement seal exhibits excellent initial quality. Thus, annular sealants must be designed to mitigate or minimize the deleterious effects of cyclic pressure fluctuations on the annular seal. Optimal cement designs for this purpose require a proper understanding of damage modes and mechanisms associated with a cyclic pressure regime, as well as the impact of the cement mechanical integrity evolution on the leakage of the cemented annulus. Using four cement formulations with distinct mechanical and microstructural properties, we investigated the mechanical integrity evolution and leakage characteristics of cemented pipe specimens subjected to confinement pressure fluctuations. Via microscopic inspection of the cement/pipe interface after pressure cycling and permeability measurements during pressure cycling, we attempted to correlate cement properties with leakage and suggest a recommendation for optimal cement design and successful zonal isolation in wellbores subjected to cyclic pressure. Test data indicate that under high enough pressure variation, interfacial cracking at the cement pipe interface is unavoidable and the cement seal's ability to maintain zonal isolation will be dependent on the microstructural morphology and microscale mechanical resilience of the cement formulation. Stiffer conventional cements also appear to have a higher chance of leakage through non-interfacial fractures than their more flexible counterparts. Latex cements show great promise for effective zonal isolation under cyclic bottomhole pressure conditions and should be studied in more detail.

On hydrogen-cement reaction: Investigation on well integrity during underground hydrogen storage

Underground hydrogen storage (UHS) is becoming a promising technology to help achieve full hydrogen economy and support the energy transition to carbon net-zero. One of the important parameters for securing UHS for example in depleted gas reservoirs is related to the wellbore integrity and cement seal, which is rarely addressed. When hydrogen is injected, it can react with the cement around the wellbore, and cause various alterations in cement petro-physical properties. Therefore, it is crucial to understand the associated reactions between hydrogen and cement and their implications for cement degradation. In this study, hydrogen injection experiments were performed on two cement core plugs (class G) under 1400 psi and 75 °C for 125 days, and the impact on cement integrity was evaluated. The results show low reactivity of hydrogen with cement and minor alteration in the petro-physical properties of the cement samples. The XRD results show a minor increase in Alite contents after hydrogen injection, while the observed calcite growth was attributed to the cement hydration process. Despite the presence of high mobility elements such as Ca, Mg, K and Al in the cement plugs, the minor redox reactions between cement minerals and hydrogen inhibit the precipitation of high-density minerals. However, we indeed observed for the first time an increase in cement weight and density with hydrogen injection, which suggest that hydrogen/brine injection may promote the precipitation of high density products. This caused a reduction in the CT porosity by 8.86% and 8.43% in samples C#1 and C#2 respectively. However, the total reduction in porosity is considered minor, suggesting a limited impact on cement integrity -which is favorable for UHS-. Furthermore, the alteration in the statistical distributions of P- and S-waves caused a minor increase in Poisson's ratio and dynamic elastic modulus (E), suggesting a low risk of wellbore cement degradation during UHS. The obtained results provide clear analyses of the reactivity of cement to hydrogen injection, and suggest that no significant impact on wellbore integrity or cement seal would be expected during UHS.

Study on the whole life cycle integrity of cement interface in heavy oil thermal recovery well under circulating high temperature condition

Cement seal failure is common in heavy oil thermal recovery wells, but the effects of steam stimulation on wellbore interface seal performance is unclear. The finite element model of plastic zone formation of cement sheath during high temperature circulating is established. The damage variable of the cement sheath is proposed to define the elastic-plastic transformation process of cementing interface, the interfacial debonding and micro-annulus size caused by thermal stress cycling are quantified, and the effects of key parameters such as steam injection temperature, cycle times, mechanical properties of cement sheath on the change of interface integrity are clarified. The results show that the tensile failure of cement sheath and the micro-annulus always formed on the inner wall of cement sheath, and outer wall remains intact. Excessive steam injection temperature (360 °C–420 °C) will cause an 8–45 μm micro-annual, excessive elastic modulus of cement sheath (>10 GPa) will cause a 20–62 μm micro-annular, the cement sheath with heat shrinkage property will form a 47–54 μm micro-annulus. Based on the sensitivity analysis, the matching relationship between the thermal cycle construction parameters and the performance index of cement sheath is established. The results can provide a reference for the design of cement parameters and engineering parameters under the thermal stress cycles.

Composition and Origin of Surface Casing Fluids in a Major US Oil- and Gas-Producing Region.

Fluids leaked from oil and gas wells often originate from their surface casing─a steel pipe installed beneath the deepest underlying source of potable groundwater that serves as the final barrier around the well system. In this study, we analyze a regulatory dataset of surface casing geochemical samples collected from 2573 wells in northeastern Colorado─the only known publicly available dataset of its kind. Thermogenic gas was present in the surface casings of 96.2% of wells with gas samples. Regulatory records indicate that 73.3% of these wells were constructed to isolate the formation from which the gas originated with cement. This suggests that gas migration into the surface casing annulus predominantly occurs through compromised barriers (e.g., steel casings or cement seals), indicative of extensive integrity issues in the region. Water was collected from 22.6% of sampled surface casings. Benzene, toluene, ethylbenzene, and xylenes were detected in 99.7% of surface casing water samples tested for these compounds, which may be due to the presence of leaked oil, natural gas condensate, or oil-based drilling mud. Our findings demonstrate the value of incorporating surface casing geochemical analysis in well integrity monitoring programs to identify integrity issues and focus leak mitigation efforts.

A Study on the Integrity Evaluation of Cement Sheaths for Deep Wells in Deep Water

The complex temperature and pressure conditions of deepwater wells have a serious impact on cementing quality. Therefore, the integrity of the cement seal becomes a critical factor that can restrict the safety of the wellbore, especially for wells ranging from the conventional deep water to deep water with more prominent deep stratum problems. The operating conditions of deep wells in deep water (referred as the dual-deep well) are complex and harsh. For the conventional evaluation device, it is difficult to accurately simulate the alternating HTHP conditions and to clarify the location and situation of the cement sheath leakage, which directly leads to the deviation of the evaluation results from the engineering reality. To solve this defect, based on the condition and structure characteristics of dual-deep wells, a device and method for casing/cement sheath/formation seal integrity evaluation for dual-deep wells at HTHP has been developed and established. Combined with the analysis of microstructure and micromorphology, the sealing ability and integrity of different cement slurry systems were evaluated. Through this study, a set of cement slurry systems suitable for dual-deep wells is selected that can satisfy the requirements of dual-deep wells with excellent isolation ability and seal integrity under temperature and stress changes. The research results provide a reference for deepwater wells’ wellbore integrity evaluation and research.

Features of morpho functional changes in periodontal structures in rats with the presence of a photo of a polymer or cement seal

High prevalence of caries is a great public health burden. To choose the optimal filling material for the restoration of hard tissues of teeth in caries patients is quite relevant. When choosing materials for dental restoration the doctor is guided by aesthetics quality, long-term guarantee of therapy, comfort at work and cost/quality ratio. The objective: under the conditions of an experiment to establish the relationship between the morphorfunctional state of periodontal components in the presence of either photopolymeric or cement filling and compare the data obtained with the results of intact animals. Materials and methods. The jaws of 41 white laboratory rats were used. 3 groups were formed: group 1 - intact; group 2 included animals with a photopolymer filling; group 3 consisted of rats with a cement filling. Histobacteriological, immunohistochemical, histochemical and statistical methods were used. Results: the animals with photopolymer filling material, in contrast to animals of the intact group, and those with cement filling, had a greater number of microbial cells in the biofilm during the whole experiment. The microbial cells exhibited enzymatic activity, against which there was a reduced number of glycosaminoglycans in the intercellular substance of the epidermis. Conclusions: Against the background of microorganisms increase in the biofilm of the epithelium, changes in carbohydrate-containing biopolymers of the biofilm, reducing the total number of glycosaminoglycans in animals with photopolymer filling material, the number of lymphocytes and functional activity of antigen-presenting cells in the lamina propria of the gums took place. This indicates the activation of humoral nonspecific and specific links of immunity.

Geochemical narrowing of cement fracture aperture during multiphase flow of supercritical CO2 and brine

For carbon capture and storage operations, wells are used as a necessary conduit for injecting CO2 at depth, but they can also act as leakage conduits if the cement seals are compromised. The specific objective of this research was to experimentally investigate the nature of self-healing of a fracture within cement under multiphase flow of CO2 and brine, and to compare the findings with the predictions of a recently developed model. This was accomplished by flowing a multiphase mixture of supercritical CO2 and brine through a cement fracture. The influent end of the fracture was degraded as evidenced by the formation of cracks across the surface. At the effluent end of the fracture, the initial aperture of 137 μm was reduced to 50 μm. This reduction by 87 μm compared well with an aperture reduction of 80 μm predicted by a recently developed model tested in this study. Self-healing of the fracture contributes to permeability reduction through the potential leakage pathway.

Tissue Engineering of Necrotic Dental Pulp of Immature Teeth with Apical Periodontitis in Dogs: Radiographic and Histological Evaluation.

To evaluate tissue engineering technology to regenerate pulp-dentin like tissues in pulp canals of immature necrotic permanent teeth with apical periodontitis in dogs. The study was performed on 36 teeth in 12 dogs. The experiment was carried out using split mouth design. In each dog 3 teeth were selected for implementing the study procedure. Apical periodontitis was induced in Group A and B teeth. Group (A): immature upper left 2nd permanent incisors that were transplanted with a construct of autologous dental pulp stem cells with growth factors seeded in a chitosn hydrogel scaffold. Group (B): immature upper right 2nd permanent incisor that received only growth factors with scaffold. A third tooth in each dog was selected randomly for isolation of dental pulp stem cells (DPSCs). Both groups were closed with a double coronal seal of white MTA (Mineral trioxide aggregate) and glass ionomer cement. Both groups were monitored radiographically for 4 months and histologically after sacrificing the animals. There was no statistically significant difference in radiographic findings between group (A) and group (B) for healing of radiolucencies, while there was statistically significant difference between group (A) and group (B) regarding radicular thickening, root lengthening and apical closure. Histologically, group (A) teeth showed regeneration of pulp- dentin like tissue while group (B) teeth did not show any tissue regeneration. Dental pulp stem cells and growth factors incorporated in chitosan hydrogel are able to regenerate pulp- dentine like tissue and help in complete root maturation of non-vital immature permanent teeth with apical periodontitis in dogs.

Geochemical modeling of carbonation of hydrated oil well cement exposed to CO2-saturated brine solution

Storage of CO2 into geological formations, such as deep saline aquifers and depleted oil/gas reservoirs, is being investigated to help reduce releases to the atmosphere. A critical issue is the long-term efficacy of engineered (man-made) hydrated cement seals that surround or plug boreholes. In order to investigate the impact of CO2 interactions with hydrated cement, the present study focuses on the alteration processes that were observed in a hydrated cement core (based on Type-G Portland cement) after laboratory experimental reaction with a CO2-saturated brine for 6 months. The carbonated cement block consisted of an orange outer zone, an alteration rim, and the intact cement core. The PHREEQC geochemical code was used to simulate the experimental conditions and data using 1D reactive transport modeling. The first phases to dissolve were portlandite, CS and ettringite providing calcium to solution. Three CaCO3 polymorphs were predicted to precipitate, but the less stable of these (aragonite, vaterite) were transformed to calcite over time. According to simulations the final product after 1000 years of reaction will be 68% calcite, 18% Friedel's salt and 14% Al-Fe-Si hydro/oxides. As the reaction front moved within the sample, porosity decreased due to the formation of amorphous phases and carbonates. The proposed model is a useful tool in describing longer-term hydrated cement alteration behavior during CO2 geological storage and to compare their results with in situ observations from field experiments.

Effect of Different Ferrule Length on Fracture Resistance of Endodontically Treated Teeth: An In vitro Study.

A ferrule has been described as a key element of tooth preparation when using a post and a core. It is a vertical band of tooth structure at the gingival aspect of crown preparation. It lessens the stress transmission to the root which is due to forces from posts or bending during seating of the post. The incorporation of a ferrule can help to withstand the forces of occlusion, preserve the hermetic seal of the luting cement, and minimize the concentration of stresses at the junction of post and core. To evaluate and compare the effect of ferrule length on fracture resistance of endodontically treated mandibular premolar teeth, restored with prefabricated glass fiber post luted with resin cement, composite core and a full coverage metal crown. Forty freshly extracted mandibular premolars were treated endodontically. They were randomly divided into four groups according to their ferrule height: 3 mm, 2 mm, 1 mm and 0 mm (no ferrule). All specimens were restored with prefabricated glass fibre posts (Reforpost, Angelus) and composite resin (Filtek™ Z250XT). Standardized preparation was done on each specimen to receive a cast metal crown. The specimens were thermocycled and compressive static load at a crosshead speed of 1 mm/min was applied at an angle of 30° on lingual incline of buccal cusp of the crown until failure occurred. The load (N) at failure and mode of failure were recorded. Statistical analysis was performed with Kruskal Wallis test. Fracture resistance values among the groups was found to be statistically significant (p<0.001). The 3 mm ferrule group had significantly higher failure load (971.99±133.07) compared to 2 mm (848.84±109.60), 1 mm (714.64±133.89) and 0 mm ferrule groups (529.36±119.95). More favourable failure modes were observed in almost all groups. The results of this study showed that fracture resistance of endodontically treated teeth increases as ferrule length increases.

The relationship between methane migration and shale-gas well operations near Dimock, Pennsylvania, USA

Migration of stray methane gas near the town of Dimock, Pennsylvania, has been at the center of the debate on the safety of shale gas drilling and hydraulic fracturing in the United States. The presented study relates temporal variations in molecular concentrations and stable isotope compositions of methane and ethane to shale-gas well activity (i.e., vertical/horizontal drilling, hydraulic fracturing and remedial actions). This was accomplished by analyzing data collected, between 2008 and 2012, by state and federal agencies and the gas well operator. In some cases, methane migration started prior to hydraulic fracturing. Methane levels of contaminated water wells sampled were one to several orders of magnitude greater than the concentrations due to natural variation in water wells of the local area. Isotope analyses indicate that all samples had a thermogenic origin at varying maturity levels, but from formations above the hydraulically fractured Marcellus Shale. The results from the initial water well samples were similar to annular gas values, but not those of production gases. This indicates that leakage by casing cement seals most likely caused the impacts, not breaks in the production casing walls. Remediation by squeeze cementing was partially effective in mitigating impacts of gas migration. In several cases where remediation caused a substantial reduction in methane levels, there were also substantial changes in the isotope values, providing evidence of two sources, one natural and the other man-induced. Sampling water wells while venting gas wells appears to be a cost-effective method for determining if methane migration has occurred.

Offset Bow Centralizers Meet Underreamed Well Challenges

Technology Update Underreamed wells are among the toughest challenges to using a centralizer, a device that keeps the casing or liner in the center of a wellbore. Underreaming, the technique of enlarging of a wellbore beyond its originally drilled size, is a drilling method widely used to increase the openhole size, which may be required for various reasons. Some well planners believe it is safest to drill unknown shallow formations with a small diameter bit and enlarge the pilot hole if no gas is encountered. Underreaming may also be performed if a small additional amount of annular space is desired, for example, if a liner must be run to protect against surge pressures. A fundamental problem with under-reamed wells is achieving effective casing centralization in the underreamed section. The job of the centralizer is to center the casing to improve run in hole (RIH), allow easier pipe rotation, and to enable the cement column to circulate freely around the tubular and produce a robust cement seal to ensure zonal isolation. Mud displacement is vital to achieving a good cement bond. The more central the pipe, the more efficient the mud displacement will be. In deviated and horizontal wells, if the tubular is not centralized, it will lie along the low side of the borehole and make cement circulation and the achievement of a uniform cement sheath difficult. Poor centralization can also impair the cement bond by causing channeling, which can lead to various live annulus problems. Like any fluid, cement will take the easiest route in the annulus, and this can result in an inadequate seal if the casing or liner is not centralized. In addition, if the annular clearance is restricted in some sections, backpressure may result that requires a much reduced flow rate during cementation to avoid fracturing the formation and thereby losing fluid. Offset Bow Centralizer The Uros offset bow centralizer developed by Centek is designed for use in underreamed or washed-out well sections. The device significantly reduces initial insertion forces and drag when running through previously set casing. Once through this compressed stage, the offset bow centralizer will revert to its designed outer diameter in the open hole and thus maximize standoff without additional drag. The device achieves a reduction in drag compared with other centralizers because of its patented bow design, in which the high points of the bows are offset alternately without reducing the strength of the unit or its capacity to centralize the casing in the open hole.

The Long-term Corrosion Behavior of Abandoned Wells Under CO2 Geological Storage Conditions: (3) Assessment of Long-term (1,000-year) Performance of Abandoned Wells for Geological CO2 Storage

A hypothetical CO2 storage site that has some abandoned wells located near the injection well is considered. Generally, cement plugs are set to cover or isolate porous or productive formations and to isolate usable groundwater from hydrocarbons. When CO2 is injected into a reservoir, supercritical CO2 or dissolved CO2 spreads out in the reservoir. This dissolved CO2 can react chemically with cement seals (plugs and casing cement) in abandoned wells. As a result, minerals in the cement seals (plugs and casing cement) may alter to form other minerals or mineral phases.The first simulations concerning migration of supercritical CO2 and dissolved CO2 in a saline aquifer and a depleted gas field reservoir, were carried out using TOUGH2. The following temperatures and depths of reservoir were selected: 50°C at E.L.-1,000 m, 60°C at E.L.-1,500 m and 70°C at E.L.-2,000 m.Secondly, geochemical reactions of cement seals (plugs and casing cement) were simulated. The results of reservoir simulations were used as boundary conditions for the geochemical calculation of cement seals. Geochemical simulation of the reactions yielded the extent (length) of alteration of cement seals (plugs and casing cement) after long time periods; for example, the alteration length of cement seals after 1,000 years was about one meter. This length is short enough so that the usable cement seals (plugs and casing cement) of abandoned well are able to continue to isolate CO2 in the reservoir from the upper aquifer.

Geochemistry of Wellbore Integrity in CO2 Sequestration: Portland Cement-Steel-Brine-CO2 Interactions

### Geochemistry and wellbore integrity in CO2 sequestration Effective geologic sequestration of CO2 requires long-term storage with very low leak rates. Injection wells are an obvious leakage pathway for CO2 because they perforate the confining caprock. In addition, sequestration sites are likely to use monitoring wells to assess performance and, in the case of depleted oil and gas fields, may contain 10s to 1000s of older operating and abandoned wells. All wells may have leakage pathways due to faulty construction or other defects. However, it is the subject of this chapter to consider whether geochemical reactions induced by CO2 could result in damage to wells and the development of leaks. This concern is based on the thermodynamic incompatibility of CO2-saturated fluids with the Portland cement and steel used to prevent fluid migration to the surface. Portland cement is an alkaline substance with pH > 12.5 and is not in equilibrium with CO2-bearing fluids (pH < 6). Low-carbon steel used as well casing is subject to aggressive corrosion by carbonic acid. As a result, well integrity has been a central issue in risk analysis of sequestration sites (Gasda et al. 2004; IPCC 2005; Viswanathan et al. 2008; Nordbotten et al. 2009). At the outset, it is important to bear in mind that geochemical reactions alone do not yield insight into wellbore integrity, which is governed primarily by the effective permeability of the Portland cement seal and the mechanical integrity of the system. Thus the significance of chemical reactions must be considered with respect to their impact to changes in permeability or in strength. There is an unfortunate tendency in the literature to not distinguish between reaction and impact. Often CO2 reactions are described as “degradation of cement” or “corrosion of cement” without adequately defining what these terms …

Immediate Load Fiber Reinforced Hybrid Implant Prosthetics

Immediate loading of implants placed at time of implantplacement requires both adequate insertion torque and rigidityof the provisional prosthesis to allow placement of a restorationduring the healing phase. Screw-retained provisional prosthesisallows better stability during the healing phase than cementedprosthetics and prevents cement seal breakage that couldtransfer greater loads to individual fixtures during this criticalphase. Various methods of increasing the rigidity of theprovisional material have been utilized and reported in theliterature. A case describing the use of a woven fiberreinforcement ribbon will illustrate how to use this material andthe benefits over either metal wire reinforcement or utilizationof a cast frame.

Effect of cavity varnish and intermediate restorative material on coronal microleakage in endodontically treated tooth

Evaluation of microleakage in endodontically treated teeth that have been coronally sealed with eugenol and noneugenol containing zinc oxide cement, with and without the use of cavity varnish. The crowns of single rooted teeth were removed at the cementoenamel junction (CEJ) and the root canals were prepared and obturated with gutta-percha points and zinc oxide eugenol (ZOE) sealer using lateral condensation technique. The samples were randomly divided into four groups-group 1, coronal seal was obtained with ZOE cement; in group 2, three coats of cavity varnish followed with coronal seal of ZOE cement; in group 3, Litark a (noneugenol cement) was placed in the prepared cavity as in group 1; and in group 4, cavity varnish and Litark were placed instead of ZOE as in group 2. The specimens were immersed in 2% methylene blue dye and examined under traveling microscope for evidence of dye penetration of the material. In this study, Kruskal-Wallis test, Mann-Whitney U, and Wilcoxon W tests were used. Kruskal-Wallis test with P=0.000 indicated that a significant difference exists between the four groups. Mann-Whitney U test and Wilcoxon W test showed a significant difference at 0.05 levels as follows: group 1 with group 3 and 4, group 2 with group 3 and 4, and group 3 with group 4. There was no significant difference at 0.05 levels between group 1 and group 2. Group 4 showed significant less amount of dye penetration as compared with other groups.

Avoiding the Blowout

This article elaborates the steps that a driller can take to keep oil and gas secure in a deep seawell. The first step is to use drilling fluid to create hydrostatic pressure in the wellbore to prevent oil and gas from surging up the well. Later, when the well is completed, the wellbore is usually filled with a completion fluid also designed to have a density sufficient to prevent escape of oil and gas from the rock formation. Drilling and completion fluids must be designed in such a way that they do not create excessive hydrostatic pressure. Too much pressure will incur waste because large volumes of the fluids will leak into the rock formations penetrated by the wellbore, where they cannot be retrieved. The next step of preparation is to pump a cement slurry containing various additives through the casing. Once hardened, the cement seals off the oil- and gas-bearing rock from the wellbore until the oil company is ready to produce the well.

Fasciola gigantica : Eggshell solubility and permeability properties

The cross-linkages contained within the proteinaceous opercular cement seal holding the egg operculum of Fasciola gigantica solubilised in 0.1N saturated NaOH, concentrated HCl, H2SO4 and H3PO4, whereas the quinone tanned eggshell solubilised only in concentrated HNO3 and NaOCl. In TCA, H3BO3 and CH3COOH, the cross linkages of proteinaceous opercular cement and the quinone tanned eggshell remained unaffected. This study has shown that the cross linkages of the opercular cement, the operculum and the quinone-tanned eggshell differ in their permeability and solubility properties. Keywords: Fasciola gigantica, eggshell, permeability and solubility in acids, alkali and chemicals

Fasciola gigantica : Eggshell solubility and permeability properties

The cross-linkages contained within the proteinaceous opercular cement seal holding the egg operculum of Fasciola gigantica solubilised in 0.1N saturated NaOH, concentrated HCl, H 2 SO 4 and H 3 PO 4 , whereas the quinone tanned eggshell solubilised only in concentrated HNO 3 and NaOCl. In TCA, H 3 BO 3 and CH 3 COOH, the cross linkages of proteinaceous opercular cement and the quinone tanned eggshell remained unaffected. This study has shown that the cross linkages of the opercular cement, the operculum and the quinone-tanned eggshell differ in their permeability and solubility properties.