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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.
Abstract The goal was to search for a replacement of CaCl2 which presents the most widely used accelerator for oil well cement used in cold and arctic environments and sometimes in deepwater drilling. For this purpose, novel calcium silicate hydrate (C-S-H) nanoparticles were synthesized and tested. The C-S-H was synthesized by the precipitation method in an aqueous solution of polycarboxylate (PCE) comb polymer which is widely used as concrete superplasticizer. The resulting C-S-H-PCE suspension was tested in the UCA instrument as seeding material to initiate the crystallization of cement and thus accelerate cement hydration as well as shorten the thickening time at low temperature. It was found that in PCE solution, C-S-H precipitates first as nano-sized droplets (Ø ~20 - 50 nm) exhibiting a PCE shell. Following a rare, non-classical nucleation mechanism, the globules convert slowly to nanofoils (HR TEM images: l ~ 50 nm, d ~ 5 nm) which present excellent seeding materials for the formation of C-S-H from the silicate phases C3S/C2S present in cement. Thickening time tests performed at + 4 °C in an atmospheric consistometer revealed stronger acceleration than from CaCl2 while very low slurry viscosity was maintained, as was evidenced from rheological measurements. Accelerated strength development was checked on UCA cured at + 4 °C and under pressure, especially the wait on cement time was significantly reduced. Furthermore, combinations of C-S-H-PCE and HEC as well as an ATBS-based sulfonated fluid loss polymer were tested. It was found that this C-S-H- based nanocomposite is fully compatible with these additives. The novel accelerator based on a C-S-H-PCE nanocomposite solves the problems generally associated with CaCl2, namely undesired viscosity increase, poor compatibility with other additives and corrosiveness against steel pipes and casing.
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.
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.
This paper describes the properties and uses of cementitious mixtures containing 10 to 20 per cent bentonite and 2 per cent or more sodium chloride. Salt additions improve bentonite cement by increasing early strength and stabilizing viscosity without changing thickening time. The volume yield of cement is increased 20 per cent or more without lowered early strength. The unique properties of salt in this type of system make savings of more than 10 per cent possible where light-weight, low-strength cementitious material is adequate to fill behind pipe. The density range of these mixtures is 12 to 13 lb/gal and the filtration rates are medium-low, aiding the placement of long columns in primary cementing. Where available, sea water is an ideal salt source in preparing these slurries.
Accelerators increase the rate of cement hydration. In speeding reaction with water, they can affect cement performance by reducing thickening time and increasing early strength after set. Accelerators that cause both effects can be considered "total", and those which produce only one effect can be called "partial". Materials that act conversely to accelerators are retarders, and they also can be total or partial. Partial retarders make high-temperature cementing possible by prolonging thickening time while impairing early strength only slightly. Most known accelerators are total. A useful partial accelerator would increase strength without altering thickening time. This report concerns material combinations in which a normally total accelerator exerts unique partial properties. Utilizing these limited effects improves bentonite cement.
SEPARATE EFFECTS OF SODIUM CHLORIDE AND BENTONITE ON CEMENT
Sodium chloride and calcium chloride are commonly used in cement, and at low concentrations their effects are similar. Ludwig studied sodium chloride in API Class A and Class E cements. Figs. 1 and 2 summarize his data taken at 140F on slurry pumpability and early strength. Normal water-to-cement ratios are 0.46 and 0.40, respectively, for Class A and Class E cements. At saturation the salt content is 12 to 14 per cent of the weight of cement solids. The illustrations, therefore, cover the range of salt solubility in the mixing water. The data show that sodium chloride is a total accelerator of the Class E cement studied over the range of solubility. It is total in Class A cement to 6 per cent. Above this concentration salt becomes a retarderpartial from 6 to 10 per cent and total above. These results a re general for different brands of Class A cement, although the shift from acceleration to retardation may occur at different salt concentrations for different temperatures. The results are specific for the Class E brand studied. In discussing his data, the investigator emphasized that different Class E cements might respond erratically to salt, depending on the brand chosen. Morgan and Dumbauld describe the properties of bentonite cement in a paper that is a standard reference in using these systems. Bentonite functions in cement as an enabling agent; each bentonite addition equal to 1 per cent of the weight of dry cement makes possible the further addition of 4.5 per cent water. Thus, 10 per cent bentonite in Class A cement, normally slurried neat with 46 per cent water, enables the slurry to contain another 45 per cent before settling. Water is one of the lightest and cheapest cement extenders; it reduces density and cost. Bentonite cements produce uniform slurries having low susceptibility to solids separation. After set, they offer low resistance to perforation.