Arild Saasen

Mechanistic model for cuttings removal from solid bed in inclined channels

This paper presents the results and analysis of a set of erosion rate experiments, designed to investigate the removal rate of stationary sand bed particles in an inclined channel. The erosion rate tests of three beds with different bed particle-size ranges show that beds with intermediate average particle size have the maximum erosion rate. The theoretical analysis using a mechanistic model supports this observation. The instantaneous acceleration of bed particles at the beginning of transportation is correlated with particle removal rate. It is shown that the mechanistic model can predict optimum operating parameters to improve the efficiency of hole cleaning.

Effects of time and shear energy on the rheological behaviour of oilwell cement slurries

In the present study, it has been evaluated if the configuration of the high-speed mixer propeller blades used in cement slurry preparation done in accordance with API specifications [Specification for Materials and Testing for Well Cements, API Spec. 10, 5th edn., 1990.] does influence the input of mixing energy applied to the cement slurry. It has been shown that the term specific mixing energy (SME) is not valid for all types of slurries. It has also been shown through a comparison between a Vicat apparatus series of experiments and a consistometer study that there is no direct link between the consistometer data and the initial set of a cement slurry. Furthermore, the Vicat test was found not to give the initial set either. Finally, the study investigated the effect of mixing energy input on viscous properties and gel formation properties of the slurries. A drop in viscosity as a function of mixing energy has previously been considered to be a result of a structural breakdown. In the present study, it is suggested that this drop is a result of change in cement morphology.

Selecting Drilling Fluid Properties and Flow Rates For Effective Hole Cleaning in High-Angle and Horizontal Wells

This paper presents a method to determine optimum drilling fluid properties and flow rates to minimize cuttings bed height and circulation time in high angle and horizontal wells. The method uses empirical models relating the cuttings bed height and the bed erosion time to drilling fluid properties and flow rates. Bed erosion tests have been conducted using a cuttings transport facility available at the University of Tulsa. Cuttings bed height as a function of time has been investigated by using variable flow rates (200 - 400 gpm) and four different drilling fluid compositions. Experimental results were used together with a non-linear regression analysis program to establish a functional relationship among drilling fluid properties, flow rate, cuttings bed height and the time required to circulate the borehole clean. A numerical example is provided to explain the field application of the method. The sequential calculations involved in determining optimum combination of the Power Law viscosity parameters n and K, and the flow rate to minimize the cuttings bed height and circulation time are also given. Field implementation of the proposed empirical correlations and the new method can aid optimization of circulation practices before tripping, and so reduce the associated risk of non-productive time.

Critical Fluid Velocities for Removing Cuttings Bed Inside Horizontal and Deviated Wells

Abstract This study aims to estimate the critical fluid flow velocity for preventing the development of a stationary bed using empirical correlations valid for horizontal and highly inclined wellbores that can be easily used at the field. For this purpose, experiments have been conducted at METU-PETE Cuttings Transport Flow Loop for various conditions. Observations showed that a stationary bed is developed when the fuid velocity is less than 6.0 ft/s, and a critical fluid velocity of 8.0 ft/s is required to establish a no-bed condition. Results showed that the critical velocity and the thickness of the stationary bed, if developed, could be estimated with a reasonable accuracy.

The effect of the cement zeta potential and slurry conductivity on the consistency of oil-well cement slurries

Abstract The effect of time and input of different amounts of mixing energy on the zeta potential and particle size of an oil-well cement slurry have been studied using an AcoustoSizer. It has been shown that the zeta potential development seems to control the consistency of cement slurries in the early time of hydration. Furthermore, conductivity measurements along with pH and a special particle size distribution measurement has indicated the precipitation of solid fine grain material within the liquid phase at the time the consistency starts to increase. This is at the time the cement slowly starts to thicken and long before the cement sets and starts to solidify.

The Effect of Drilling Fluid Rheological Properties on Hole Cleaning

This paper was selected for presentation by an IADC/SPE Program Committee following review of information contained in an abstract submitted by the author(s). Contents of the paper, as presented, have not been reviewed by the International Association of Drilling Contractors or the Society of Petroleum Engineers and are subject to correction by the author(s). The material, as presented, does not necessarily reflect any position of the IADC or SPE, their officers, or members. Papers presented at the IADC/SPE meetings are subject to publication review by Editorial Committees of the IADC and SPE. Electronic reproduction, distribution, or storage of any part of this paper for commercial purposes without the written consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The

Annular Frictional Pressure Losses During Drilling—Predicting the Effect of Drillstring Rotation

Controlling the annular frictional pressure losses is important in order to drill safely with overpressure without fracturing the formation. To predict these pressure losses, however, is not straightforward. First of all, the pressure losses depend on the annulus eccentricity. Moving the drillstring to the wall generates a wider flow channel in part of the annulus which reduces the frictional pressure losses significantly. The drillstring motion itself also affects the pressure loss significantly. The drillstring rotation, even for fairly small rotation rates, creates unstable flow and sometimes turbulence in the annulus even without axial flow. Transversal motion of the drillstring creates vortices that destabilize the flow. Consequently, the annular frictional pressure loss is increased even though the drilling fluid becomes thinner because of added shear rate. Naturally, the rheological properties of the drilling fluid play an important role. These rheological properties include more properties than the viscosity as measured by API procedures. It is impossible to use the same frictional pressure loss model for water based and oil based drilling fluids even if their viscosity profile is equal because of the different ways these fluids build viscosity. Water based drilling fluids are normally constructed as a polymer solution while the oil based are combinations of emulsions and dispersions. Furthermore, within both water based and oil based drilling fluids there are functional differences. These differences may be sufficiently large to require different models for two water based drilling fluids built with different types of polymers. In addition to these phenomena washouts and tool joints will create localised pressure losses. These localised pressure losses will again be coupled with the rheological properties of the drilling fluids. In this paper, all the above mentioned phenomena and their consequences for annular pressure losses will be discussed in detail. North Sea field data is used as an example. It is not straightforward to build general annular pressure loss models. This argument is based on flow stability analysis and the consequences of using drilling fluids with different rheological properties. These different rheological properties include shear dependent viscosity, elongational viscosity and other viscoelastic properties.

Gravity waves and Rayleigh Taylor instability on a Jeffrey-fluid

A theory for linear surface gravity waves on a semi-infinite layer of viscoelastic fluid described by a Jeffrey model is presented. Results are given for the decay rate and the phase velocity as a function of the parameters of the fluid: a nondimensional time constant, and a ratio of the retardation time to the relaxation time. At small wave numbers the behavior is Newtonian. In other cases depending on the nondimensional parameters, a number of possible other behaviors exist. The influence of the non-dimensional parameters on the growth rate of Rayleigh-Taylor instability is also discussed.

Automatic Measurement of Drilling Fluid and Drill-Cuttings Properties

Abstract In order to remotely control the drilling process it is necessary to measure several drilling fluid parameters automatically. This will increase objectivity of the measurements as well as make it possible to immediately react to changes. The current paper describes in detail the design for an integrated tool combination and the results of a full size yard test of such a combined s et of tools for measuring drilling fluid parameters and formation properties automatically. Some of the automated tools have been tested on rig site operations. Results from these individual tests are also presented. The automatic drilling fluid analysis includes viscosity, fluid loss, electric stability measurements and chemical properties like pH. Full viscosity curves for the drilling fluid are measured using configurations and shear rates similar to those suggested by API procedures. Since gel formation curves and fluid loss properties require some sort of controlled static periods, these measurements are made semi-continuous. However, they are automatic and are measured as frequently as possible. An automatic system is included to measure the particle size distribution, concentration and morphology. Knowledge of these parameters is necessary, especially when drilling in depleted reservoirs where particles are added for increasing the wellbore strength. The produced cuttings volume is measured. An automatic system is adapted that determines, with accuracy comparable to that of visual analysis, whether the particles separated at the shaker screens are drill cuttings or cavings produced by an unstable formation. The mineralogy of the cuttings is analysed automatically using Raman spectroscopy, making it possible to evaluate continuously the different formations being drilled.

Viscous Flow with Large Fluid-Fluid Interface Displacement

The arbitrary Lagrange-Euler (ALE) kinematic description has been implemented in a 3D transient finite element program to simulate multiple fluid flows with fluid-fluid interface or surface displacements. The description of fluid interfaces includes variable interfacial tension, and the formulation is useful in the simulation of low and intermediate Reynolds number viscous flow. The displacement of two immiscible Newtonian fluids in a vertical (concentric and eccentric) annulus and a (vertical and inclined) tube is simulated