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Two forms of derivatized cellulose have been found useful in well-cementing applications. The usefulness of the two materials depends on their retardational character and thermal stability limits. This is commonly used at temperatures up to approximately 82 C (180 F) for fluid-loss control, and may be used at temperatures up to approximately 110 C (230 F) BHCT, depending on the co-additives used and slurry viscosity limitations. Above 110 C (230 F), HEC is not thermally stable. HEC is typically used at a concentration of 0.4 to 3.0% by weight of cement (BWOC), densities ranging from 16.0 to 11.0 lbm/gal, and temperatures ranging from 27 to 66 C (80 to 150 F) BHCT to achieve a fluid loss of less than 100 cm3 /30 min.
Abstract Cement must be designed in a way to ensure acceptable properties such as mix ability, stability, rheology, fluid loss, and adequate thickening time. Different chemicals are used when designing cement slurries. These chemicals are used as retarders, fluid loss additives, dispersants, gas migration additives and expansion additives. Typical examples of compounds used as retarders include: calcium lignosulfonate, sodium lignosulfonate, sodium tetra borate decahydrate (borax), starch derivatives, hydroxyethyl cellulose and weak organic acids. Examples of dispersants are ferrous lignosulfonate, acetone, and polyxythylene sulfonate. Many additives for fluid loss are water soluble polymers such as Vinyl sulfonate based on the 2-acrylamido-2-methyl-propane sulfonic acid. To the best of the author's knowledge, there is no study that compares the performance of different chemicals in cement designs. The objective of this paper is to detail some of the cement chemistry and to go over the chemicals used in cementing oil and gas wells and their mechanisms of actions.
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.
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.
This paper presents a review of experience for successful cementing in oil and gas wells. Recommendations and considerations for use of various cements, flushes, control additives and placement techniques are given for best results in placement techniques are given for best results in zone isolation and support of pipe in wells. Recommendations for control of difficulties with gas migration, mud contamination, high temperature retrogression, small annular clearances, and displacement of drilling fluids are described.
The purpose of this paper is to describe the latest advancements in oil and gas well cementing.
As drilling operations become deeper and more costly, the significance of zonal isolation in cemented wells cannot be overemphasized. High temperature strength retrogression of cements and inefficient displacement of contaminants from small annular clearances has become more critical for economical exploration. Use of specially formulate cements, special control additives, and well planned programs for cementing have largely alleviated the programs for cementing have largely alleviated the basic problem of cementing failures, i. e., channeling.
With basic cements, additives are used that control filtrate loss, control retardation of hardening, provide desired hydrostatic column weight, and assist placement of permanent bonding materials to help prevent fluid migration and communication. Other additives stabilize hardened cement strength and maintain low permeability in cement even under extreme conditions of temperature and pressure associated with deep drilling. The problems of cementing in complex geometries and narrow annuli have been combated by perfecting techniques of slurry placement through rheological design, use of effective washes and flushes, and improving the mechanical aspects by using pipe movement with centralizers and scratchers. The delayed set technique for cementing has also been introduced to overcome some of these complications.
This paper describes these cements, additives and techniques as they are currently being used for successful cementing.
All factors responsible for fluid migration after cementing are not yet clearly understood.