Research and Application of Micro-Expansion and Anti-Channeling Cement Slurry System in Agadem Oilfield

The overall liner cementing qualification rate is only 40% in Agadem block of Niger, The cement slurry system used in the field has a UCA transition time of 43min, and an expansion rate of -0.03% in 24h, which result in a poor anti-gas channeling performance. The expansive agent and the anti-gas channeling toughening agent of anti-channeling agent were optimized through experiment study. A novel micro-expansion anti-gas channel cement slurry system which is suitable for Agadem block was obtained through experiment optimization study: 100% G +2 ∼ 4% fluid loss agent +3 ∼ 4.5% anti-channeling agent +1 ∼ 2% expansion agent-100S +0.15 ∼ 0.4% retarder +0 ∼ 0.3% dispersant +0 ∼ 0.25% defoamer + water. This new cement system has a good anti-gas channeling performance, the cement strength is 24.5-35.0MPa after 24hrs, the UCA transition time is 16-18min, and the expansion rate is 1.5-1.7%. At the same time, a cementing prepad fluid suitable for the block and the micro-expansion cement slurry system is selected to ensure the performance of the cement slurry's anti-channeling performance. The field test results proofs the good performance of the new cement system. The cementing qualification rate of Koulele W-5 well is 96%, and the second interface cementation is Good. The cementing qualification rate of Trakes CN-1 well is 100% which second interface cementation is Excellent. This paper has positive guidance and reference for cementing in Agadem block.

Numerical Simulation of Shale Reservoir Fluid-Driven Fracture Network Morphology Based on Global CZM

There are a large number of natural fractures in shale reservoirs, which create great challenges to hydraulic fracturing. Activating the natural fractures in reservoirs can form a complex fracture network, enhance fracturing effects, and increase shale gas production. Reservoir geological conditions (low in situ stress, natural fracture distribution, and cement strength) and operation parameters (fracturing fluid viscosity and injection rate) have an important influence on fracture network propagation. In this article, a two-dimensional hydraulic fracturing fluid-mechanic coupling numerical model for shale reservoirs with natural fractures was established. Based on the global cohesive zone model, the influence of geological conditions and operation parameters on the propagation of the hydraulic fracture network and fracturing process is investigated. The numerical simulation results show that when the horizontal in situ stress difference, approach angle, and cement strength are low, it is easier to form a complex fracture network. Research on the construction parameters indicated that when the viscosity of the fracturing fluid is low, it is easier to form a complex network of fractures, but the length of the fractures is shorter; in contrast, the fractures are straight and long. In addition, increasing the injection rate is beneficial for increasing the complexity of the fracture network while increasing the initiation pressure and width of the principal fracture reduces the risk of sand plugging. This article also proposes an optimization solution for hydraulic fracturing operations based on numerical simulation results.

Mathematical modelling of crushed rock dust concrete: Performance using compressive strength

The paper gives out a mathematical model developed using linear regression statistical method to envisage the 28-day strength of CRD concrete, considering M20, M30 and M40 grades concrete and CRD replacement percentages of 0%, 10%, 20%, 30% and 40% by weight of cement. Strength results of M40, M30 and M20 grades concrete are used to develop the relationship between CRD content and compressive strength. The ratios of compressive strengths between CRD and control concrete (CC) have been related to CRD replacement percentage. The expression, derived is with strength ratios and not with experimental strength values. The mathematical equation developed is independent of the specimen parameters and may be applicable to all types of specimens. The model is considered as it involves non-dimensional variables and is independent of the specimen size, water to binder ratio (w/b) and grade of concrete.

A statistical DEM approach for modelling heterogeneous brittle materials

By utilizing numerical models and simulation, insights about the fracture process of brittle heterogeneous materials can be gained without the need for expensive, difficult, or even impossible, experiments. Brittle and heterogeneous materials like rocks usually exhibit a large spread of experimental data and there is a need for a stochastic model that can mimic this behaviour. In this work, a new numerical approach, based on the Bonded Discrete Element Method, for modelling of heterogeneous brittle materials is proposed and evaluated. The material properties are introduced into the model via two main inputs. Firstly, the grains are constructed as ellipsoidal subsets of spherical discrete elements. The sizes and shapes of these ellipsoidal subsets are randomized, which introduces a grain shape heterogeneity Secondly, the micromechanical parameters of the constituent particles of the grains are given by the Weibull distribution. The model was applied to the Brazilian Disc Test, where the crack initiation, propagation, coalescence and branching could be investigated for different sets of grain cement strengths and sample heterogeneities. The crack initiation and propagation was found to be highly dependent on the level of heterogeneity and cement strength. Specifically, the amount of cracks initiating from the loading contact was found to be more prevalent for cases with higher cement strength and lower heterogeneity, while a more severe zigzag shaped crack pattern was found for the cases with lower cement strength and higher heterogeneity. Generally, the proposed model was found to be able to capture typical phenomena associated with brittle heterogeneous materials, e.g. the unpredictability of the strength in tension and crack properties.

Influence of Porosity on Fracture Toughness and Fracture Behavior of Antibiotic-Loaded PMMA Bone Cement

Aseptic loosening is the most common reason for long-term revision of total joint replacement (TJR). Infection is the main reason for short-term revision of TJR. In our previous studies, experimental results showed that acrylic bone cement-loaded with antibiotics had a detrimental effect on cement strength such as bending strength, compressive strength, and fracture toughness. This result implied that the mechanical failure of antibiotic loaded bone cement was potentially related to porosity volume fraction. Hence, the objective of this study was to investigate the effect of pore size and distribution on bone cement fracture toughness. The effect of pores was analyzed using the extended Finite Element Method (X-FEM) method to model crack propagation and its modulation by pore sizes and locations. Numerically obtained load-displacement responses were compared to experimental results. We observed that crack propagation is affected by several pore parameters; as expected these include pore size and pore locations (pore-pore interactions) and are related to implicit pore-crack interactions. The experimental and numerical investigations presented in the current study contribute to a better understanding of the effect of pores on bone cement fracture toughness; key insights include the identification of a critical pore size for reduced fracture toughness, and relative insensitivity of crack propagation to stochastically distributed pore locations.

The Impact of Contaminating Poly (Methyl Methacrylate) (PMMA) Bone Cements on Their Compressive Strength

This study presents an analysis of the impact of doping bone cement with saline. The two-ingredient cement, made right before the surgery, is subject to various kinds of organic contaminants and liquids used in the operating area, such as saline used to cleanse or cool it, during the process of mounting the prosthesis or bone-filling procedures. The processes of experimental destructive testing and statistical analysis have shown that, depending on the degree of saline doping, the static compressive strength parameters may greatly improve (with a low degree of contamination) or significantly worsen (when the contamination degree is higher). The limit value of the degree of salt admixture was estimated (2%), with which no statistically significant differences were observed in the cement strength in relation to the strength of non-contaminated cement.

Hardening Cement Conglomerates by Mining Industries Waste

About 3.5 billion tons of mining waste is generated annually in Russia. The task of their utilization is urgent in connection with the accumulation of large-tonnage waste of simultaneously mined rocks, enrichment waste and crushing screenings. The problem can be solved by using these wastes as mineral additives to artificial cement-based conglomerates. According to the study results it was found, that the compressive strength of hardened cement paste increased during all hardening periods, when finely dispersed mining wastes were introduced. In the early stages of hardening, limestone had a predominant effect. Introduction of diopside led to the greatest hardening together with the hardening period increase. Linear and nonlinear mathematical models, describing the dependence of cement strength on the type and amount of mineral additives, were constructed. The highest strength values of hardened cement paste, both after hardening under normal conditions for 28 days, and after heat and moisture treatment could be achieved with 7% dispersed diopside. At the same time, the hardening effect (increase in the strength of cement by 35–40%) was retained when 1/3 of the diopside in the complex additive was replaced by dispersed limestone. An increase in the content of limestone in the complex additive composition over 1/3 was impractical.

Effect of Addition of Alccofine on the Compressive Strength of Cement Mortar Cubes

In the modern era, many research works are going on throughout the world for finding suitable cementitious material for the replacement of cement since it causes environmental pollution. In this order Fly ash, Silica fume, GGBS, Metakaolin, Micro materials, Quartz powder, etc. are tried out for replacing partially or fully the cement in concrete. A new ultrafine material called Alccofine (AF) which is manufactured from glass wastes is tried out for replacing partially in this research. Compressive strength is one of the important properties of cement. Strength tests are not made on neat cement paste because of difficulties of excessive shrinkage and subsequent cracking of neat cement. Cement mortar of 1:3 mix proportion is used to cast the cubes having an area of 50 cm2 are used for the determination of compressive strength of cement as per IS: 4031-1988 (Part-6). The graded Indian Standard sand (Ennore Sand -ES) confirming to IS: 650-1991 is used for preparing the cubes. In the same mix proportion, the same size cubes are cast with the River Sand (RS) to study the difference of the compressive strength between the Indian standard sand and river sand. Ordinary Portland cement (OPC) and Portland Pozzolana Cements (PPC) are used. The present study is the influence of Alccofine on cement mortar cubes by replacing the cement by Alccofine with various proportions like 5%, 10%, 15%, 20% were cast and tested in the laboratory as per Indian Standard 4301-1988 (Part-6) and the results were analysed and presented in the form of charts and graphs. It is observed that the early age strength is obtained for all the combinations but 10 percent of Alccofine yields more strength than other dosages. Doi: 10.28991/esj-2021-01265 Full Text: PDF