A Comparative Study of Mechanical Properties of Density-Reduced Cement Compositions

Abstract

This paper discusses the tests conducted to determine the mechanical properties and the integrity of the cement sheath when subjected to cyclic loads. In addition, lower-density cement systems are discussed in this paper, along with how the density was lowered by incorporating conventional additives such as:Pozzolanic beads (cenosphere)Hollow glass beadsGas bubblesWater-binding additivesSilica fumeFly ash Primary cementing compositions for oil-well applications are becoming increasingly complex and challenging because of the extremes encountered in well-operating conditions. The stresses exerted on the cement sheath during well operations could be severe enough to damage the cement sheath and negatively affect the safety and the economics of the well. The results discussed in this paper should help operators design a cement sheath that can withstand the stresses from well operations and thus help improve the safety and economics of the wells. Introduction The oil and gas industry is exploring and producing oil and gas from extreme environments, such as high-pressure and high-temperature (HPHT), deepwater, shallow gas, and accelerated production rates. The stresses exerted on the cement sheath from these extreme operating conditions could be severe and could damage the cement sheath. Examples of well operations that could exert stress on the cement sheath are:Cement hydrationChangeover from displacement fluid to completion fluidHydraulic stimulationHydrocarbon productionFluid injectionGas lift These types of operations could change the pressure and temperature of the cement sheath after the slurry is placed in the annulus. The cement sheath could be damaged if the magnitude of pressure or temperature change is large and the stresses in the cement sheath exceed key values of the cement sheath. The key values are measured values and vary depending on cement slurry formulation. Some major consequences of damage to the cement sheath, such as sustained pressure on the annulus side or damage to the casing, could force well shutdown or result in high remedial costs. Other consequences of damage to the cement sheath, such as loss of hydrocarbon production, production of unwanted fluids (e.g. water), and growth of wellhead, could negatively affect the safety and economics of oil and gas assets because the remedial jobs are expensive to impossible in some cases. Hence, the integrity of the cement sheath should be considered during the early stages of well construction and designed for uninterrupted, safe, and economic production of hydrocarbons. A detailed engineering analysis should be conducted to evaluate how the different well operations affect the integrity of the cement sheath. In other industries, for example, bridge construction, applying engineering analysis is a common way to optimize material properties. The oilfield is slowly adopting these techniques. This adoption has occurred because of a combination of increased risk to cement-sheath integrity in expensive wells operating in extreme operating environments, and increased safety standards.1–7 A three-step approach, outlined in Fig. 1, should help operators construct a well that can produce hydrocarbons safely and economically. Step 1 is the engineering analysis. The outcome of the engineering analysis is to help provide the optimum cement sheath properties needed to withstand the well operations. Step 1 is discussed and presented by Bosma et al., Ravi et al., and other authors.8–12

Aplication of Local Cement for Cementing Oil Wells in the South Eastern Region of the Pannonian Basin

“…Since the temperature at the bottom of wells does not exceed 50 ° C using a local cement without additives, Table 6. In some oil fields [6] in the south-eastern part of the Pannonian Basin, where the temperature at the bottom of the wells does not exceed 120 º C and pressure gradient layer fracturing of 0148 -0.18 bar / m adaptation of local cements successfully performed cementing annulus between the production casing OD 139.7 mm and hole size 215.9 mm use of lead [7] and tail cement slurries, Tables 7 and 8. Rheological properties of these cement mixtures, Table 9 does not allow the achievement of a turbulent regime of displacement (displacement capacity greater than 1800 l / min) [8], but the displacement of slurry occurs in a highly laminar regime -Re = 2000.…”

Stress Changes in Cemented Borehole Annulus

“…It is necessary to set one of three materials fracture criterion (Mohr-Coulomb, Hoek-Brown, Drucker-Prager) and define the material, depending on available sizes, elastic or plastic. Table 1 gives an overview of material [4] properties, the Mohr-Coulomb's criterion, which were used for these models. All materials are considered as elastic.…”

Analyzing Cement Rheological Properties Using Different Additive Schemes at High Pressure and High Temperature Conditions

“…Mostly models are described for above relationship based on the Newtonian, Bingham Plastic and Power Law models. All most fluids and cement slurries for drilling cementing are Non-Newtonian fluids and have been treated using a Bingham Plastic or Power Law Type Model [11,12].…”

“…The yield value of the cement slurry decreases with an increasing concentration of the dispersant. Glycerine acts as a slurry viscosifier and it has been found that the associated increase in viscosity at the lower shear rates is significantly lower than that at higher shear rates [11,18,19].…”