Influence of Nanoclay Content on Cement Matrix for Oil Wells Subjected to Cyclic Steam Injection

Mixed Micromax and hematite-based fly ash geopolymer for heavy-weight well cementing

Ordinary Portland cement (OPC) has introduced different environmental and technical issues. Researchers tried either adding new materials to cement or developing alternatives for both technical and environmental challenges. Hematite as a weighting agent is used to increase cement slurry density. Heavy particles sedimentation in cement and geopolymer slurries is a serious issue which creates heterogenous properties along the cemented section. This work presents a new class of geopolymers using both hematite and Micromax as weighting materials for high density well cementing applications. The first system used only hematite while the other system used both hematite and Micromax. The main goal behind using Micromax with hematite is to check the possibility of eliminating the sedimentation issue associated with hematite in geopolymers. Moreover, the effects of adding Micromax on different FFA geopolymer properties were also evaluated. Different mixtures of retarder, retarder intensifier and superplasticizer were introduced to increase the thickening times of the developed geopolymer systems. The results showed that adding Micromax to hematite decreased the average density variation from 12.5% to almost 3.9%. Micromax addition reduced plastic viscosity by 44.5% and fluid loss by 10.5%. Both systems had a close performance in terms of strength, elastic properties, and permeability. The thickening time was 390 min for the hematite system and 300 min for the mixed system using the proposed additives mixtures.

Development of Heavy-Weight Hematite-Based Geopolymers for Oil and Gas Well Cementing

In the petroleum industry, ordinary Portland cement (OPC) is utilized for different cementing applications. Yet, there are some technical and environmental issues for the usage of OPC in well cementing. The technical problems include gas invasion while setting, instability at corrosive environments, cement failure while perforation and fracturing due to high stiffness and brittleness, and strength reduction and thermal instability at elevated temperatures. Moreover, OPC production consumes massive energy and generates high greenhouse gas emissions. This study introduced the first hematite-based class F fly ash geopolymer formulation that can be used in oil and gas well cementing. Different properties of the designed slurry and hardened samples such as rheology, thickening time, strength, and elastic and petrophysical properties were evaluated. Moreover, mixability and pumpability challenges of heavy-weight geopolymer slurries were investigated. Unlike most of the studies in the literature, this work used 4 M NaOH solution only as an activator that can reduce the overall cost. The results showed that increasing the hematite percentage significantly decreased the thickening time. The developed formulation fell within the recommended fluid loss ranges for some cementing applications without using a fluid loss control additive. A proposed mixture of retarder and superplasticizer was introduced to enhance the thickening time by almost 5 times. The compressive strength increased by 49% and the tensile strength was enhanced by 27.4% by increasing the curing time from 1 to 7 days. The improvement in both compressive and tensile strength with curing time indicated that the geopolymerization reaction continued for extended time but with a smaller rate. The developed slurry acted more like a power law fluid at low temperatures and more like a Bingham plastic fluid at high temperatures. The elastic properties of the developed geopolymer samples proved that they are more flexible than some cement systems.

The Use of Graphite to Improve the Stability of Saudi Class G Oil-Well Cement against the Carbonation Process

Oil-well cement physical characteristics considerably change after being carbonated by a CO₂-rich solution. In this study, the influence of graphite particles in the characteristics of oil-well cement reacted with a CO₂-rich solution at 130 °C and 10 MPa for 10 days was studied. After 10 days of carbonation, incorporating 0.2% by weight of cement (BWOC) of graphite into the cement slurry decreased the carbonation depth by 29.8% as confirmed by the direct measurement and the micro-computerized tomography scan technique. The addition of 0.2% BWOC of graphite also reduced the cement matrix permeability by 31.4% and increased its compressive strength by 16.4% and tensile strength by 23.8% compared to the sample without graphite. The decrease in the cement matrix portlandite concentration and permeability of the samples prepared with graphite contributed to promote the cement matrix carbonation resistance. The microscopic images also proved that the incorporation of graphite delayed the leaching of calcium carbonate, and this is also attributed to decreasing the cement strength deterioration.

Reduction of Fractionation of Lightweight Slurry to Geothermal Boreholes

When designing the cement slurry for casing string cementing in geothermal boreholes, the appropriate thermal conductivity is selected. In the zone of geothermal water, where thermal energy is collected, cement slurry is used, from which the cement sheath has high thermal conductivity. On the other hand, the remaining part of the opening is sealed with slurry, from which the cement sheath will reduce thermal energy losses through appropriate thermal insulation. Cement slurry with appropriate thermal insulation includes light insulating materials. However, the use of such additives is very problematic as they are fractionated due to their low density. Therefore, measures should be taken to prevent fractionation of the cement slurry for sealing geothermal boreholes. This article presents the results of research on fractionation of cement slurries for sealing geothermal boreholes. 12 slurries were used for the tests. Six of them are based on class A cement, and six based on class G cement. This action shows the differences in fractionation depending on the binder used. However, the main area of research is determining the effectiveness of counteracting fractionation by the means used for this purpose. As a result of the conducted works, a very good improvement of the cement slurry stability is obtained after the introduction of xanthan gum, as well as filtration perlite. These measures prevent fractionation, so that the cement slurry has a homogeneous structure, and the cement sheath provides the required thermal insulation in the geothermal well.

The Use of the Granite Waste Material as an Alternative for Silica Flour in Oil-Well Cementing

Silica flour is one of the most commonly used material in cementing oil wells at high-temperature conditions of above 230 °F to prevent the deterioration in the strength of the cement. In this study, replacement of the silica flour with the granite waste material at which an inexpensive and readily available material in cementing oil-wells is evaluated. Four cement samples with various amounts of silica flour and granite powder were prepared in this work. The effect of including the granite waste instead of silica flour in the cement elastic, failure, and petrophysical properties after curing the samples at 292 °F and 3000 psi was examined. The results revealed that replacement of the silica flour with 40% by weight of cement (BWOC) optimized the cement performance and confirmed that this concentration of granite could be used as an alternative to the silica flour in oil-well cementing. This concertation of granite slightly improved the elastic properties of the cement. It also improved the cement compressive and tensile strengths by 5.7 and 39.3%, respectively, compared to when silica flour is used. Replacement of the silica flour with 40% BWOC of granite waste also reduced the cement permeability by 64.7% and porosity by 17.9%.

Improving Saudi Class G Oil-Well Cement Properties Using the Tire Waste Material

After oil and gas well drilling, they should be cased and cemented to ensure the stability of the wellbore and to isolate the trouble zones. To achieve these jobs, several additives are incorporated into the cement slurry to improve the cement matrix durability, especially at temperatures above 230 F. The tire waste material is an industrial waste that comes from automobile tires. The purpose of this work is to investigate the prospect of utilizing tire waste in oil-well cement under high-temperature and high-pressure conditions of 292 F and 3000 psi. Three cement samples with different concentrations of the tire waste material were prepared. The effects of tire waste on the cement rheological properties, elastic and failure parameters, and permeability were examined. The results showed that adding 0.3% by weight of cement (BWOC) of the tire waste material considerably improved the cement to the cement slurry and cement matrix properties, and it decreased the cement plastic viscosity by 53.1% and increased its yield point by 142.4% compared to the base cement. The cement samples with 0.3% BWOC of tire waste have Young's modulus which is 10.8% less than that of the base cement and Poisson's ratio of 14.3% greater than that of the base cement. By incorporating 0.3% of the tire waste, both compressive and tensile strengths of the cement increased by 48.3 and 11.7%, respectively, compared with those of the base cement. The cement permeability was decreased by 66.0% after adding 0.3% of the tire waste. Besides the improvement in the properties of cement, the use of the tire waste material has other economical and environmental advantages because these are very cheap materials dominant in our life.

Influence of Weighting Materials on the Properties of Oil-Well Cement

The integrity of oil and gas wells is largely dependent on the cement job. Maintaining the properties of the cement layer throughout the life of a well is a difficult task, particularly in high-temperature and -pressure conditions such as those in deep wells. Cementing deep wells require slurries with high densities. Heavyweight cement systems are those designed with weighting materials. These materials have a higher specific gravity in comparison to cement. The purpose of this work is to investigate the influence of weighting materials on the properties of Class G oil-well cement and to make necessary recommendations for their use. The rheology, fluid loss, gas migration, and dynamic elastic properties of three cement slurries containing different weighting materials, namely, hematite, barite, and ilmenite, were studied. The results indicate that cement slurry designed with barite exhibits the best rheological behavior that would provide a perfect solution for deep wells where cement placement is a concern. The barite slurry had the lowest plastic viscosity. The plastic viscosity of the hematite and ilmenite-weighted systems was higher by 11.5 and 12.4%, respectively. The barite-based slurry also had the highest yield point of 84.3 lb_f/100 ft², whereas the yield points of hematite and barite cement were 37.9 and 29.5 lb_f/100 ft², respectively. Furthermore, the gel strengths of barite cement were the highest, with 10 s and 10 min gel strengths of 11.5 and 39.5 lb_f/100 ft², respectively. Ilmenite had the most positive impact on fluid loss control, which would be appropriate in high permeable formations. It had a fluid loss of 66 mL/30 min, lower than those of the hematite (80 mL/30 min) and barite (82 mL/30 min) systems. Furthermore, the best dynamic elastic properties were exhibited by the ilmenite system, with the smallest Young's modulus (27.3 GPa) and the highest Poisson ratio (0.252). This would make the ilmenite to be very useful in developing heavyweight cement composites that could withstand severe external loads imposed on the casing and cement. The hematite cement was the most impermeable to gas migration, with a gas volume of 127.8 cm³, whereas the volume measured in the barite and ilmenite systems were 20.9 and 78% higher, respectively. This makes the hematite to be very useful in deep gas wells where gas migration control is important.

Influence of Graphene Oxide on Rheological Parameters of Cement Slurries

In recent years, graphene-based nanomaterials have been increasingly and widely used in numerous industrial sectors. In the drilling industry, graphene oxide in cement slurry has significantly improved the mechanical parameters of cement composites and is a future-proof solution. However, prior to placing it in a borehole ring space, cement slurry must feature appropriate fluidity. Graphene oxide has a significant influence on rheological parameters. Therefore, it is necessary to study graphene oxide’s influence on the rheological parameters of cement slurries. Thus, this paper presents rheological models and the results of studies on rheological parameters. A basic cement slurry and a slurry with a latex addition were used. The latex admixture was applied at concentrations of 0.1%, 0.03%, and 0.06%. In total, studies were carried out for six slurries with graphene oxide and two basic slurries. The obtained results of studies on the slurries with graphene oxide were compared with the control slurry. It was found that the smallest graphene oxide concentration increased slurry value, some rheological parameter values, plastic viscosity, and the flow limit. Surprisingly, a concentration up to 0.03% was an acceptable value, since the increase in plastic viscosity was not excessively high, which allowed the use of cement slurry to seal the hole. Once this value was exceeded, the slurry caused problems at its injection to the borehole.

Effects of Nanoclay and Silica Flour on the Mechanical Properties of Class G Cement

The mechanical properties of oil well cement slurry are usually measured to evaluate the durability, sustainability, and long-lasting behavior of a cement sheath under wellbore conditions. High-pressure and high-temperature (HPHT) conditions affect the mechanical properties of cement slurry such as its strength, elasticity, and curing time. In this study, an organically modified montmorillonite nanoclay (NC) and silica flour (SF) materials are used to enhance the strength of the class G cement. Four different cement slurries with the addition of different concentrations of NC (1% and 2%) and SF (20%) in a class G cement were tested under temperatures ranging between 70 and 100 °C and pressure ranging between 1000 and 3000 psia. The slurries were prepared by maintaining a water to cement ratio of 0.44. All the slurries were cured for 24 h before any test was conducted. Extensive laboratory experiments were carried out to measure the compressive and tensile strength of cement slurries cured at HPHT conditions. Compressive strength was measured using unconfined compressive strength (UCS) tests, scratch tests, and ultrasonic cement analyzer (UCA). Tensile strength was measured using breakdown pressure tests and Brazilian disc test analysis. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and petrophysical analysis were also carried out to evaluate the performance of new cement additives at HPHT conditions. Results showed that the addition of organically modified NC and SF significantly increased the compressive and tensile strength of the class G cement slurry cured at HPHT conditions.

The Effect of Weighting Materials on Oil-Well Cement Properties While Drilling Deep Wells

In deep hydrocarbon development wells, cement slurry with high density is required to effectively balance the high-pressure formations. The increase in the slurry density could be achieved by adding different heavy materials. In this study, the effect of the weighting materials (barite, hematite, and ilmenite) on the properties of Saudi Class G cement matrix of vertical homogeneity, compressive strength, porosity, and permeability was evaluated. Three cement slurries were weighted with barite, hematite, and ilmenite, and cured at 294 °F and 3000 psi for 24 h. All slurries have the same concentration of the different additives except the weighting material. The amount of weighting material used in every slurry was determined based on the targeted density of 18 lbm/gal. The results of this study revealed that the most vertically homogenous cement matrix was the ilmenite-weighted sample with a vertical variation of 17.6% compared to 20.2 and 24.8% for hematite- and barite-weighted cement, respectively. This is attributed to the small particle size of the ilmenite. The medical computerized tomography (CT) scan confirmed that the ilmenite-weighted sample is the most homogeneous, with a narrow range of density variation vertically along the sample. Hematite-weighted cement showed the highest compressive strength of 55.3 MPa, and the barite- and ilmenite-weighted cement compressive strengths are each 18.4 and 36.7% less than the compressive strength of the hematite-weighted cement, respectively. Barite-weighted cement has the lowest porosity and permeability of 6.1% and 18.9 mD, respectively. The maximum particle size of ilmenite used in this study is less than 42 μm to ensure no abrasion effect on the drilling system, and it minimized the solids segregation while maintaining a compressive strength that is higher than the minimum acceptable strength, which is the recommended weighting material for Saudi Class G cement.