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Remedial cementing requires as much technical, engineering, and operational experience, as primary cementing but is often done when wellbore conditions are unknown or out of control, and when wasted rig time and escalating costs force poor decisions and high risk. Squeeze cementing is a "correction" process that is usually only necessary to correct a problem in the wellbore. Before using a squeeze application, a series of decisions must be made to determine (1) if a problem exists, (2) the magnitude of the problem, (3) if squeeze cementing will correct it, (4) the risk factors present, and (5) if economics will support it. Most squeeze applications are unnecessary because they result from poor primary-cement-job evaluations or job diagnostics. Squeeze cementing is a dehydration process.
A number of cementitious materials used for cementing wells do not fall into any specific API or ASTM classification.These materials include: Pozzolanic materials include any natural or industrial siliceous or silico-aluminous material, which will combine with lime in the presence of water at ordinary temperatures to produce strength-developing insoluble compounds similar to those formed from hydration of Portland cement. Typically, pozzolanic material is categorized as natural or artificial, and can be either processed or unprocessed. The most common sources of natural pozzolanic materials are volcanic materials and diatomaceous earth (DE). Artificial pozzolanic materials are produced by partially calcining natural materials such as clays, shales, and certain siliceous rocks, or are more usually obtained as an industrial byproduct. Pozzolanic oilwell cements are typically used to produce lightweight slurries.
In many parts of the world, severe lost circulation and weak formations with low fracture gradients are common. These situations require the use of low-density cement systems that reduce the hydrostatic pressure of the fluid column during cement placement. Consequently, lightweight additives (also known as extenders) are used to reduce the weight of the slurry. Neat cement slurries, when prepared from API Class A, C, G, or H cements using the amount of water recommended in API Spec. There are several different types of materials that can be used as extenders.
Abstract The efficiency of the well construction process is highly dependent upon completion of the cementing phase. Drilling ahead is dependent on when the cement will build sufficient strength to support the existing casing. This paper presents a novel lightweight cementing technology through application of advanced chemistry that shows high potential for faster completion of the cementing phase, decreasing the waiting time for the cement to set, thereby allowing continued drilling operations. A unique lightweight density superior performing cement was successfully developed for high early compressive strength development that does not utilize traditional methods and materials for enhancing cement strengths like glass beads, cenospheres, silica fumes, fly ash, modified and/or natural clays.
High Performance Concrete (HPC) is a composite mixture containing cementitious material and aggregate. The cementitious material is blended with Pozzolans such as silica fume particles and fly ash to enhance its binding and durability properties. This paper studies the effect of pozzolanic materials on the compressive strength and modulus of elasticity of HPC. An experimental program is conducted to evaluate the effect of silica fume, fly ash, and combination of the two used as cement supplemental materials on the modulus of elasticity. Results show that adding silica fume to HPC increases both the compressive strength and the modulus of elasticity at early ages. However, the increase subsides at later ages (< 28 days). New equation is proposed to accurately predict the modulus of elasticity of HPC. INTRODUCTION As higher emphasis is made on long-term durability, high-performance concrete (HPC) is becoming a standard for transportation structures in the United States of America (USA) [1-8]. HPC is created to reduce the porosity by adding pozzolanic materials (i.e., silica fume and fly ash) that with the presence of water react with the calcium hydroxide released by Portland cement hydration to form a cementitious compound. As a result, HPC becomes denser with lower capillary pores and prevent chloride ion penetration reducing the corrosion potential of the steel reinforcement. The addition of pozzolanic materials does not only affect the HPC durability but also the mechanical properties, namely the compressive strength and modulus of elasticity. Both the compressive strength and modulus of elasticity are very important properties for structural engineers to design and evaluate the structure, especially for deflection and creep calculations [9, 10]. Thus, the effect of pozzolanic materials on modulus of elasticity needs to be investigated. The objective of this paper is to evaluate the effect of pozzolanic materials, namely silica fume particles and fly ash, on the modulus of elasticity of HPC.
A new pozzolanic composition has been developed for cementing oil wells where moderate to high temperatures prevail. This material is an entirely different concept to other oil well cementing materials, such as portland cements, cements containing additives, or liquid resins. Its characteristics are such that it is not, at present, recommended for use at temperatures less than 140°F. It can be either accelerated or retarded across a wide range of well conditions.
This new cement is composed of a pozzolanic material, hydrated lime, and a chemical activator to give it early initial strength. This material can be used in wells from 6,000 to 18,000 or more feet where temperature conditions are similar to those along the Gulf Coast. This cement, when set, has no soluble portion subject to leaching or any compounds that should be attacked by sulfate waters or brines. For this reason, it should be permanent when placed adjacent to formations carrying any type of fluid.
The compressive strengths in 24 hours are more than adequate for wells where temperatures are 140°F and higher. These values are in excess of many other types of cementing composition presently in use in the field. This pozzolanic composition does not retrogress in strength at high temperatures as do some other types of cementing materials.
The slurry weights of this material will vary slightly according to the specific gravity and water requirements of the pozzolan itself. The materials covered herein will mix from 13.5 to 14.3 lb/gal, and will have a waiting-on-cement time comparable to other materials used under the same conditions.
Economically speaking, this composition is less expensive than either portland cements or retarded cements presently being used under deep well conditions.
Pozzolans are "siliceous material which, though not cementitious in themselves, contain constituents which at ordinary temperatures will combine with lime in the presence of water to form compounds which have a low solubility and possess cementing properties.'' The use of pozzolanic materials dates back many hundreds of years and both the ancient Greeks and Romans were aware that certain volcanic deposits, if finely ground and mixed with lime and sand, yielded a mortar which possessed special properties. Generally, the early strengths of such materials were rather weak and were considered insufficient for modern commercial usages.