Cementing Of Oil Wells Research Articles

Kinematic instabilities in two-layer eccentric annular flows, part 2: shear-thinning and yield-stress effects

This paper investigates the possibility of kinematic interfacial instabilities occurring during the industrial process of primary cementing of oil and gas wells. This process involves flows in narrow eccentric annuli that are modelled via a Hele-Shaw approach. The fluids present in primary cementing are strongly non-Newtonian, usually exhibiting shear-thinning behaviour and often with a yield stress. The study is a sequel to Moyers-Gonzalez and Frigaard (J Eng Math, DOI 10.1007/s10665-007-9178-y , 2007), in which the base analysis has been developed for the case of two Newtonian fluids. The occurrence of static mud channels in primary cementing has been known of since the 1960s, (see McLean et al. 1966; SPE 1488), and is a major cause of process failure. This phenomenon is quantified, which provides a simple semi-analytic expression for the maximal volume of residual fluid left behind in the annulus, f static, and illustrate the dependency of f static on its five dimensionless parameters. It is shown that three of the four different types of static channel flows are linearly stable. Via dimensional analysis, it is shown that the base flows depend on a minimal set of eight dimensionless parameters and the stability problem depends on an additional two dimensionless parameters. This large dimensional parameter space precludes use of the full numerical solution to the stability problem as a predictive tool or for studying the various stability regimes. Instead a semi-analytical approach has been developed based on solution of the long-wavelength limit. This prediction of instability can be evaluated via simple quadrature from the base flow and is suitable for use in process optimisation.

Mud removal and cement placement during primary cementing of an oil well – Laminar non-Newtonian displacements in an eccentric annular Hele-Shaw cell

A two-dimensional model is derived of the displacement flows that occur during primary cementing of oil and gas wells. The displacement geometry is a long narrow eccentric annulus, between the casing and the rock formation. The model consists of a series of first-order convection equations for the fluid concentrations and a quasi-linear Poisson-type equation for the stream function. Coupling is through the velocity field and the concentration-dependent fluid properties.

The Use of Salt Cement Blends as an Aid to Better Cementing in Formations Containing Fresh Water Sensitive Clays

Abstract The application of salt for primary cementing in Western Canada has been restricted largely to salt cavern storage wells and to the development of potash reserves in south-central Saskatchewan. The value of salt cement blendsin cementing through fresh water sensitive formations has recently broughtabout wide usage of this technique in certain areas of the United States, andthere is good reason to believe that there are several areas in Canada wherethe success of primary cementing could be improved by the use of saltcements. There has been considerable work done on the applicability of salt cement, with emphasis on improved cement-formation bonding and the minimization offormation deterioration by water contact. Field results have shown that saltcements have improved the success of primary and squeeze cementing jobs. Laboratory work has been done to evaluate the change in slurry properties with the addition of varying concentrations of salt to commonly used cementing blends. Introduction The use of salt cements in Canada has been quite limited and, as a result, the primary purpose of the information presented here is to illustrate theadvantage of salt for primary cementing of oil and gas wells where the formations encountered contain fresh water sensitive clays and shales. The first known use of salt cements in Western Canada occurred within thepast ten years. Initially, salt cements came into use because of the failure toset fresh water cement abandonment plugs in the salt and potash zonesencountered in potash test holes. Earlier experience in the U.S.A. proved that a good cement-formation bond through a salt section could only be achieved byusing a salt cement. Figure 1 illustrates the bonding of cement to rocksalt. The illustration shows how a fresh water slurry will dissolve a portionof the salt, with the result that there is no bond between the salt and cement, while the saturated salt slurry does not dissolve any portion of the salt, resulting in good contact and bonding between the salt and the cement. Operators in Saskatchewan found that casing could be cemented successfully in salt cavern gas storage wells with a sodium chloride slurry; more recentwork has employed a sodium chloride and potassium chloride (potash) saturated slurry (1). Later, casing was set into the potash for a solution mining project, and again salt cements were used to obtain a good primary cement job.