Papers by Keyword: Oil Well Cement

Abstract: A superplasticizer or dispersant acts as a friction reducer to enhance the rheological properties of cement slurry, thereby eliminating the need for high pump pressure to pump the viscous slurry behind the casing. Polynaphthalene sulfonate (PNS) is a common dispersant for well cement; however, with the emergence of geopolymer technology for oil wells, the application of PNS in the industry has yet to be investigated. The focus of the research is to examine the influences of PNS on the early, medium, and final compressive strength of geopolymer cement cured at 3000 psi and 100 °C with PNS concentration ranging from 0.0 to 2.0 by weight of fly ash (bwof %). The findings show that PNS can increase the 8-hour compressive strength of geopolymer cement, but it can decrease the 24-hour compressive strength. However, only the sample with the highest concentration of PNS exhibits better compressive strength than the control sample at 48 hours. Additionally, the results demonstrate that the compressive strength of geopolymer cement with PNS increases with a longer curing duration. It is advisable to run a prediction plot to determine the optimum concentration that can result in high compressive strength for 8, 24 and 48 hours.

Abstract: In order to study the effect of brine environment on the performance of oil well cement fluid loss additive (FLA) sodium p-styrene sulfonate/N-methylol acrylamide/itaconic acid (SSS/HAM/IA), the water loss of three different cement slurry systems added with different FLA additions (fresh water cement slurry, semi-saturated brine cement slurry and saturated brine cement slurry) were tested at 90°C and 150°C. The results show that SSS/HAM/IA has good salt tolerance. The water loss of three cement slurry systems was controlled within 100mL with FLA addition adjusted in the range of 1%~3% below 150 °C. The salt tolerance mechanism of SSS/HAM/IA was analyzed based on the microstructure of the three system terpolymer solutions characterized under environmental scanning electron microscopy (ESEM).

Abstract: With 2-acrylamido-2-methylpropanesulfonic acid (AMPS) units on polymeric additive, additive showed high effectiveness used for oilwell cement. However, due to chemical absorption and chelation mechanism of AMPS units to Ca²⁺ hydrating cement particles, adding of AMPS type additives caused delay of cement hydration process. In this research, AMPS type fluid loss additive, named as FLA A additive, was studied for its hydration delay side effect to class G Portland cement. Furthermore, polyvinyl alcohol (PVA) polymer, modified by glyoxal and boric acid, called as PVAGB was used as a synergistic functional additive to AMPS type polymer fluid loss additive to research on hydration delay problem of AMPS type additive to cement and the improvement for the effectiveness of AMPS type fluid loss additive. When AMPS type additive showed functional drawbacks, with more disordered chemical absorption and chelation behaviors to Ca²⁺ hydrated cement particles rather than constituting a completed and superior fluid loss control system, and this kind of modified PVA polymer was utilized for making up its failure. New compound additive formula, PVAGB/FLA A fluid loss additive formula, was investigated, which showed superior and more stable fluid loss control ability, i.e. about 50 mL at 30°C and 108 mL at 80 °C with just 0.2 % BWOC (weight percentage by weight of cement) PVAGB and 0.5 %BWOC (weight percentage by weight of cement) FLA A addition. In addition, within 28-day curing period, cement samples showed a healthy compressive-strength development with no less than 28MPa after 7-day curing period rather than failure due to cement strength retrogression. With scanning electron microscope (SEM) analysis, PVAGB showed accelerating effect to cement hydration process, in which hexagonal plate Ca(OH)₂ crystal and aggregated product of C-S-H gel were formed when compared with pure cement and cement with FLA A additive added.

Abstract: The conventional oil-well cement dispersant has the characteristics of poor dispersion at high temperature, poor compatibility with other additives, and environmental pollution during the production process. In this article, with ultra-early strong polyether monomer, acrylic acid, 2-acrylamine-2-methylpropyl sulfonic acid, sodium methacrylate as copolymer monomers, an environmentally friendly polycarboxylic acid dispersant, DRPC-1L, was prepared by the aqueous solution free-radical polymerization. The chemical composition and thermal stability of the synthetic copolymer were characterized by FTIR and TGA techniques. The evaluation results show that DRPC-1L has a wide temperature range (30~210 °C), good salt-resistance and dispersing effect. It can significantly improve the rheological performance of cement slurry, and it is well matched with oil-well cement additives such as fluid loss agent, retarder and so on. Moreover, it is beneficial to the mechanical strength development of set cement, especially the early compressive strength. It can also inhibit the abnormal gelation phenomenon of cement slurry, flash set, that occurs during high temperature thickening experiments, which plays an important role in enhancing the comprehensive performance of cement slurry. Consequently, the novel polycarboxylic acid dispersant has good application prospects in deep and ultra-deep wells cementing.

Abstract: This paper presents an experimental study to investigate the effects of compressive stress during the CO₂ attack on wellbore cement under carbon capture and storage (CCS) conditions. Oil well cement samples were designed to be exposed to humid supercritical CO₂ gas and CO₂-saturated brine and simultaneously subjected to external compressive stresses with load levels of 0, 25%, 50%, and 75% of the ultimate compressive strength. Morphology changes were determined using phenolphthalein dye testing and scanning electron microscopy. Mineral changes were detected by X-ray diffraction. Relative compressive strength and gas permeability of exposed cement were analyzed. It is shown that the 25% stress level has little effect on degradation of cement while the applied compression load up to 50% increased the compactness of cement and finally slowed down the degradation rate. In contrast, a much higher compressive stress level up to 75% facilitated the generation and propagation of micro-cracks. The stress induced micro-crack finally caused a surge in CO₂-rich fluids and then significantly accelerated the degradation rate of oil well cement. Findings from this study expanded the understanding of the integrity of oil well cement for CCS wells.

Abstract: The improvement of strength and ductility is a challenging task for application of oil well cement. As a 2D nanomaterial with high strength and toughness, graphene oxide (GO) was used as a reinforcing additive in oil well cement. The mechanical properties and micro-structure of oil well cement enhanced by GO were investigated. The compressive strength and flexrual strenghth of cement stone both showed a good enhancement effect when the content of GO was 0.02% -0.05%. The compressive strength and flexrual strength could increase by 15.8% and 33.5%, respectively. The results of SEM and MIP revealed that GO played a template role in promoting the formation of hydration products and further filled in the pores between the hydration products, which refined the micro-structure and improved mechanical properties of the cement consequently.

Abstract: In this research, the influencing factors of oil well cement on the rheological property were experimentally studied. Based on the experiments and surveys of other class G oil well cement plants, the main influencing factors in the routine inspection were sample storage and processing condition and inspection equipment accuracy. The experimental results illustrate that sample storage and processing condition had a highly effect on the rheological property of drilling cement slurry. In addition, temperature positive deviation increased the rate of cement hydration by causing more rapid nucleation of hydration products, leading to earlier thickening time; conversely, minus deviation delayed cement nucleation, causing later thickening time. Compared with temperature deviation, the effect of pressure deviation was not obvious.

Abstract: For many years, Ordinary Portland Cement (OPC) is used in oil well cementing operation. But the OPC gets degraded in the acidic environment because of having poor mechanical characteristics. A new technology called geopolymeric cement system is developed from the secondary byproducts of the industry to replace the conventional cement slurry in oil well cementing operation. This study focus on the preparation of cement slurry with new formulation using fly ash and alkali binders at two sodium hydroxide treatment methods with various concentrations of NaOH solution and analyzing the prepared cement slurry for compressive strength, defiance to acid and fluid loss amount. Different cement slurry compositions made of 70:30 fly ash to alkaline activator ratios with 10, 12, 14 Molar NaOH solution with two sodium hydroxide treatment methods of direct addition and mixing after one day soaking of NaOH were prepared and cured for 24 hours at a temperature of 80°C and pressure 3000 psi. The obtained cement specimens were tested for compressive strength, resistance towards acid and density. Then based on the results, geopolymer can be considered as alternative for Class G cement in oil well cementing operation due to its high compressive strength and high acid resistance.

Abstract: Carbon dioxide CO₂ could corrode the oil well cement paste matrix under agreeable moisture and pressure condition in deep oil wells, which could decrease the compressive strength and damage the annular seal reliability of cement paste matrix. The problem of oil well cement paste matrix corrosion by CO₂ was researched in the paper for obtain the feasible corrosion prevention technical measures. The microstructure and compressive strength of corroded cement paste matrix were examined by scanning electron microscope SEM and strength test instrument etc. under different corrosion conditions. The mechanism and effect law of corrosion on oil well cement paste matrix by CO₂ were analyzed. And the suitable method to protect CO₂ corrosion in deep oil wells was explored. The results show that the corrosion mechanism of cement paste matrix by CO₂ was that the wetting phase CO₂ could generate chemical reaction with original hydration products produced from cement hydration, which CaCO₃ were developed and the original composition and microstructure of cement paste matrix were destroyed. The compressive strength of corrosion cement paste matrix always was lower than that of un-corrosion cement paste matrix. The compressive strength of corrosion cement paste matrix decreased with increase of curing temperature and differential pressure. The corroded degree of cement paste matrix was intimately related with the compositions of cement slurry. Developing and design anti-corrosive cement slurry should base on effectively improving the compact degree and original strength of cement paste matrix. The compounding additive R designed in the paper could effectively improve the anti-corrosive ability of cement slurry.

Abstract: On the basis of analyzing the oil well cement corrosion mechanism by SO₄^2- and HCO₃-, the corrosion products, microstructure and compressive strength of cement stone were measured and the changing regularity and influence factors of compressive strength were analyzed under different experimental conditions. The following conclusions can be drawn. Under the interactive corrosion effect of SO₄^2- and HCO₃-, Ca(OH)₂ in cement stone was dissolved out and consumed, the calcium silicate hydrate was decomposed, ettringite, gypsum, calcite and thaumasite were produced which destroyed the structure and components of cement stone primary products and led the compressive strength of corrosion cement stone decline. With the increases of ion concentration of corrosive solution, temperature and corrosive time, the compressive strength was decreased gradually, even collapsed completely.