High-pressure core flood experiments using gas condensate fluids in long sandstone cores have been conducted. Steady-state relative permeability points were measured over a wide range of condensate-to-gas ratios (CGR; volume of condensate per unit volume of gas, both at test pressure and temperature), and the velocity and interfacial tension (IFT) were varied between tests to observe the effect on relative permeability. The experimental procedures ensured that the fluid distribution in the cores was representative of gas condensate reservoirs. Hysteresis between drainage and imbibition during the steady-state measurements also was investigated, as was the repeatability of the data.A relative permeability rate effect for both gas and condensate phases was observed, with the relative permeability of both phases increasing with an increase in flow rate. The relative-permeabilityrate effect was still evident as the IFT increased by an order of magnitude. The influence of end effects was shown to be negligible under the IFT conditions used in the tests, with the Reynolds number indicating that flow was well within the so-called laminar regime under all test conditions. The observed rate effect was contrary to that of conventional non-Darcy flow, where the effective permeability should decrease with increasing flow rate. A generalized correlation between relative permeability, velocity, and IFT has been proposed.The results highlight the need for appropriate experimental methods and relative permeability relations where the distribution of the phases are representative of those in gas condensate reservoirs.

This paper describes an experimental investigation into drilled cuttings transport in inclined boreholes carried out in the Department of Petroleum Engineering at Heriot-Watt University.

This paper presents the finds to date of a research project initiated to investigate drilled cuttings project initiated to investigate drilled cuttings transport in deviated wellbores. The research programme utilizes a simulated wellbore to study the programme utilizes a simulated wellbore to study the mechanisms of cuttings transport in deviated wells. The cuttings transport column, has been designed to allow easy variation of well geometry m terms of annular size, deviation angle and pipe eccentricity. The column is also equipped with a variable speed motor/gear system for the simulation of drillpipe rotation. This study has investigated the influence of a range of variables such as hole angle, fluid rheology, cuttings size drillpipe eccentricity, circulation rate, annular size, and pipe rotation on cuttings transport efficiency using the concept of Minimum Transport Velocity (MTV). This concept presumes that a hole can be efficiently cleaned by either maintaining cuttings rolling or in suspension, if the annular velocity is equal to or greater than a miniinum transport velocity for that operational condition. Thus, the lower the minimum transport velocity the easier it is to efficiently clean the hole. The results so far have shown that depending on the level of eccentricity and annular size, fluid rheology as well as flow regiine appear to have highest impcct on the MTV. With low viscosity circulating fluid, turbulent flow regime seems to predominate for concentric pipes with suspension and rolling attained at low MTV. The use of high viscosity fluids appears to improve the cuttings transport further especially at highly deviated angles. The transport efficiency is further enhanced by pipe rotation at various levels of eccentricity. Smaller cuttings appeared to be easier to remove than larger ones. There is however a small exception to this when larger cuttings were found to be much easier to remove at low angles with the use of high viscosity fluids. The experimental results have been compared with the predicted MTV from the computer model concurrently predicted MTV from the computer model concurrently being developed and good agreement has been observed. Introduction One of the primary functions of the drilling mud is the efficient transportation of cuttings to the surface, a function that depends largely on the fluid velocity and other parameters such as the fluid rheological properties, cuttings size, etc. properties, cuttings size, etc. However, over the years, it has been found that the well geometry can also have a strong influence on the hole cleaning efficiency and the question arises as to how to adjust the fluid properties and circulation rates to suit the fixed design parameters such as hole angle, pipe eccentricity, etc, in order to ensure optimum pipe eccentricity, etc, in order to ensure optimum hole cleaning efficiency. In the first major study published on cuttings transport, Piggot identified the parameters affecting mud carrying capacity. Williams et al subsequently reported on a series of laboratory and field experiments, and were the first to try and determine the minimum annular velocity necessary to remove cuttings from the hole. They invariably highlighted the various factors that affect the efficiency of cuttings transport which have also been reported by other researchers.

Copynght 1995, Stecting Commttee of the European IOR-Symposiuin. 1hie paper was preented at the Sth. European IOR-Sympoaium in Vienne AustriL May 15-17. 1995 Thie paper was selected for prsentaton by the Steenng Commlttee. foliowing revew ol inforrnallon contalned in an abstract submitted by the author(8). The paper. es preaented has not bean reviewed by the Stearing Committee,

Summary The settling velocities of a variety of shaped particles to simulate drilled cuttings were measured in both Newtonian and non-Newtonian fluids. The results showed that the particle drag coefficient is a function of the particle Reynolds number and, in the case of power-law-model fluids, of the flow behavior index. A new generalized model has been developed for predicting the setting velocities of particles of various shapes in both Newtonian and power-law fluids over a range of flow regimes. Introduction and Previous Investigations Drilling and fracturing fluids are generally classed as power-law-type fluids, and their viscosities vary with shear rate. The problems of drilled cuttings settling out from drilling fluids and of proppants from fracturing fluids are complicated by the shear-dependent characteristics of the fluids. To account for the non-Newtonian effect of drilling fluids on the settling velocity of drilled cuttings, Zeidler1 suggested use of the apparent viscosity at the wall and Moore2 adapted the effective viscosity for annular flow, as defined by Skelland.3 Note that the apparent viscosity or the effective viscosity represents the viscosity at a specific shear rate pertaining to that annular location in an annular flow situation, and does not necessarily represent the viscosity around the settling particles. When the fluid velocity approaches zero and the fluid becomes stagnant, both apparent and effective viscosities will approach infinity. For particles settling in fracturing fluids, several investigators suggested the use of an effective shear rate on a particle to calculate the equivalent Newtonian viscosity around the particle. Novotny4 suggested vp/ds and Daneshy5 suggested 3(vp/ds) to characterize the shear rate for stagnant fluids. When the fluid is in motion, Novotny4 claims that the effective shear rate on a particle is the vector sum of the shear rate caused by particle settling, vp/ds, and the shear rate imposed by fluid motion. On the basis of an apparent viscosity substitution, Shah6 established the correlation of [CD(2-n)NRem'2]½ vs. NRem' and found that this correlation was a function of the flow behavior index. Acharya7 considered the viscoelastic effect of some fracturing fluids and suggested use of a sophisticated drag-coefficient correlation for purely viscous non-Newtonian fluids and another correlation to account for the elastic effect. Other experimental work has been reported on investigations of the settling velocity of particles in drilling fiuids8–13 and fracturing fluids.14,15 In the previous investigations, however, no attempt was made to establish a drag-coefficient correlation for nonspherical particles settling in non-Newtonian fluids, such as disks or rectangular plates. These particles may be used to approximate the shape of drilled cuttings. Theory of Drag-Coefficient Correlation Assuming that the particles are separated sufficiently during settling so that they do not collide or interact with each other, the force causing a particle to settle may be expressed asEquation (1) The resistant force induced by the particle's motion consists of two components. One is the fluid viscous drag, which may be expressed asEquation (2) where Ap is the characteristic area of the particle parallel to the direction of motion. Anther component is the pressure drag, which may be expressed asEquation (3) where AN is the characteristic area of the particle normal to the direction of motion. The total resistant force, usually simply called the "drag force," is the sum of these two components and may be expressed asEquation (4) where CD is the drag coefficient and A is the characteristic area of the particle, which depends on the shape of the particle and its orientation during motion. For particles of different shapes, the distribution of the drag force between viscous drag and pressure drag may vary considerably. For a flat particle settling flatwise, pressure drag will predominate; for settling in an edgewise fashion, viscous drag will be dominant.