CERTIFICATION OF ORIGINALITY

Geopolymer cement successfully reduced CO2 emissions to five to ten times less than OPC, but still resulted in the same permeability trend as OPC. This project introduced microsilica into geopolymer cement to study its effect on the permeability problem in OPC and geopolymer cement. The test results show that the permeability of cement increases when the percentage of microsilica and curing time are increased.

At standard room conditions, the viscosity of the cement slurry increased and the density of the samples decreased as microsilica increased. In general, samples A, B and C can replace OPC up to 4000 psi and 120℃, while all samples outperform OPC in liquid loss up to 500 psi and 70℃, ambient rheology and density, and standard room conditions. The molds are inserted into the pressure vessel 16 Figure 15: The cylinder plug is screwed into the pressure vessel 17 Figure 16.

INTRODUCTION

Problem Statement

Ordinary Portland cement (OPC) and geopolymer-based cement create high permeability when exposed to high temperature in the hole condition. High permeability cement allows gas migration between cement particles (Figure 2) which can reduce the integrity of the cement and can lead to swelling.

Objectives

Scope of Study

LITERATURE REVIEW

Geopolymer Cement

The difference between geopolymer cement and OPC lies in the different energy applications for the activation process. Fly ash contributes to increase the mechanical activation due to increase in surface area [7]. Using fly ash as a raw material in cement manufacturing can reduce CO2 emission and high energy required for the calcination process [7].

The difference between grade C and grade F is based on the amount of calcium, silica, aluminum and iron content in the ash. Micro silica is categorized as a very effective pozzolanic material due to its extreme purity and high silica content with 85% to 95% of amorphous SiO2 [40]. Acting as an expander, microsilica allows 0.532 gallons of water to be added to the cement slurry per kilogram of microsilica [38].

Plastic viscosity and yield strength of cement will increase when microsilica is mixed with Portland cement. Strong network between microsilica and cement is created due to increase of slurry gels as microsilica tends to absorb more water in the solution [40]. With the average size of 0.1 µm, microsilica particles can fill the pores between cement particles and block the narrow passages of liquid, thus lowering the permeability of the cement.

In addition, microsilica can reduce fluid loss in the permeable formation by bridging and blocking between the cement particles. Cement permeability and fluid loss can also be improved by uniform distribution between cement particles and microsilica [41]. High reactivity of microsilica will increase the strength of cement due to increased rate of dehydration.

Adding 35% micro silica to the cement slurry produces a strong and impermeable crystalline phase called tobermerite.

Figure 3. Geopolymerisation process

Experimental Program

Previous research shows a 64% strength gain in 8 hours and a 43% strength gain when 2% By Weight of Cement (BWOC) microsilica is added to the cement class H [38]. Portland cement will convert crystalline phases to alpha silica hydrate, a weak and porous compound when the cement is exposed to temperatures above 230℉. This can be achieved by having the same mass or volume of cementitious materials as OPC in WCR [29].

Reducing these ratios can improve the workability of cement, but will reduce its early strength. In the WGS ratio, the water component is the total mass of water used in making an alkaline solution plus any additional water added to the mixture. Geopolymer solid is the sum of the mass of sodium silica solid, sodium hydroxide solid and fly ash.

For alkaline solution to fly ash ratio, alkali is mass of alkali used in the mixture, for example the total mass of sodium silicate solution and sodium hydroxide solution.

METHODOLOGY

Key Milestones

Project Timelines

RESULTS

Static Fluid Loss Test

The static fluid loss test is performed to observe the performance of the developmentinClass G cement in retaining the aqueous phase or losing it as filtrate in the formation when subjected to differential pressure in a permeable medium. Once the cement reaches its destination, a cement filter cake can form against the formation wall. The high permeability of the cement filter cake causes a large loss of fluid from the cement into the formation.

In this project, all samples were tested under low pressure, low temperature conditions at 500psi and 70℃ for 30 minutes using static liquid loss tester in accordance with API standard. From the result, grade G cement shows the highest fluid loss while sample D which contains 40% fly ash and 60% microsilica has the lowest fluid loss. However, samples A, B, C and D show the ideal API Standard for fluid loss with filtrate volume below 50 ml in 30 minutes.

The small size of micro silica, which is less than 0.5 micrometer, acts as a micro-filler between the cement and fly ash particles, blocking the flow of liquid between these particles and into the cement filter cake, thus reducing the volume of fluid loss. Based on previous research, the small particle of fly ash and microsilica will react with excess calcium oxide and calcium hydroxide during early hydration to form additional tricalcium silicate cementitious material and fill the void space between the cement particles [ 28]. Furthermore, the higher percentage of micro silica is expected to increase the water demand of cement and reduce the possibility of fluid loss and [53].

Increasing the percentage of micro silica will prevent the bleeding within the cement due to the large surface area of ​​micro silica compared to fly ash and Class G cement. Most of the free water is used to wet the large surface area of ​​the microsilica and thus reduces the free water remaining in the mixture that can bleed [54]. Bleeding is the settling of solid particles within the cement and water phases that tend to push to the top of the cement.

All of these concepts explain why sample D, which contains a higher percentage of microsilica, has the lowest filtrate, and grade G cement, with the largest particle size, has the highest filtrate (beyond the ideal fluid loss zone) [51].

Rheology Test

According to Figure 48 and Figure 49, all samples are categorized into two rheological models; Bingham's Plastic Model and Power Law Model and all samples show non-Newtonian fluid behavior. Grade G cement, sample A and sample B have demonstrated the Power Law Model while the Bingham Plastic Model is shown by Sample C and Sample D (Figure 48). A log graph of shear stress versus shear rate is prepared (Figure 49) to support the results from the linear plots.

Based on API Recommended Practice 10B-2 Section 12, the Power Law Model resulted in a straight line in the log-log graph as represented by Sample C and Sample D, while Bingham Plastic Model produced a curve as represented by Cement G, Sample A, and Monster B. Consistency index, k measures the viscosity of the fluid, while n measures the degree of deviation of cement slurry from Newtonian behavior [43]. Lower apparent viscosity is preferred during grade G cementing to prevent loss of circulation during cement placement.

Increasing the percentage of microsilica in the cement sample resulted in a high apparent viscosity due to the high surface area of ​​microsilica compared to Cement G and fly ash. A high surface area also enhances the attractive forces between cement particles, resulting in strong networks for the samples high in microsilica [44]. As mentioned, the viscosity of cement slurry increases when there is an increase in microsilica and this trend can be observed in Figures 51 and 52.

Plastic viscosity is defined as an indicator of the number, size and shape of solids in a liquid, while pour point measures the attraction that occurs between solids in the liquid itself [48]. Micro silica has the smallest size and least weight compared to fly ash and grade G cement [46]. As defined, plastic viscosity is a function of solids, so increasing micro silica will increase solids content and cause high plastic viscosity.

High yield stress in sample D compared to sample C is caused by microsilica binding of large amounts of water, preventing the water from lubricating the flow of larger grains and requiring additional stress to initiate the flow [45].

Figure 49. Logarithmic plot of shear rate vs. shear stress for all samples

Density Test

For the same weight, particles with smaller size and lower weight will have high solids content. Cement G has the highest density while Samples D consisting of 40% fly ash and 60% microsilica show the lowest density with a 10.13% density difference compared to Class G Cement. The density differences for each sample are affected by the difference in the specific gravity of each material in the mixture formulations.

CONCLUSIONS & RECOMMENDATIONS

Recommendations

Vary the curing temperature from 20 ͦ C to 200 ͦ C to observe the effect of temperature on cement performance. Increase the curing duration to one month to observe the permeability of the cement in the downhole state in relation to time. Comparison of mechanical behavior of geopolymer and class G cement as well as cement at different curing temperatures for geological sequestration of carbon dioxide.

Mechanical properties of geopolymer cement in brine: its suitability as well as cement for geological storage of carbon dioxide. Emerging technologies for energy efficiency and CO2 emission reduction for cement and concrete production: a technical overview. Mechanical, rheological and microstructural properties of Saudi Type Class G silica flour cement slurry used in Saudi oil field under HPHT conditions.

THE EFFECT OF THE RATIO OF THE ALKALI SOLUTION AND THE CURE TEMPERATURE ON THE PROPERTIES OF FLY GAS-BASED POLYMERS. Potential Studies of Using Local Cement in Oil and Gas Well Cementing Operations in Malaysia. Retrieved from VINCI TECHNOLOGIES Laboratory and Field Instruments for the Petroleum Industry: http://www.vinci-technologies.com/products-.

Experimental investigation of microsilica as a cement extender for line cementing in Iranian oil/gas wells.