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.
Summary This paper describes a computer package that can be used to calculate the minimum transport velocity (MTV) required to ensure efficient hole cleaning during deviated drilling operations. The package was developed in the Dept. of Petroleum Engineering at Heriot-Watt U. It operates in a Windows environment and allows the user to do the following:Define, from viscometer data, the rheological model (PowerLaw, Bingham Plastic, or Herschel-Bulkley) that best describes a particular drilling fluid.Model the drilling fluid velocity profile in a defined annular geometry.Predict the minimum circulation rate required to ensure efficient cuttings transport for a wide range of operational conditions. The paper describes how the lift and drag forces on the cuttings have been determined and used in the development of the package. Case studies that demonstrate the functionality of the package are also presented. Introduction One of the primary functions of a drilling fluid is to transport drilled cuttings out of the hole. However, because of the wide range of variables involved, it is very difficult to model this process and therefore a great deal of experimental and theoretical research has been focused on this issue.1–12 This work has been largely empirical but has clearly demonstrated that the efficiency of cuttings transport depends on the following factors:Hole angle.Fluid velocity.Fluid properties (rheological properties and density).Cuttings size, shape, and concentration.Annular size.Rate of pipe rotation and pipe eccentricity.Fluid flow regime (laminar or turbulent). The drilled cuttings transport research team in the Dept. of Petroleum Engineering at Heriot-Watt U. have been conducting experimental and theoretical research in the area of drilled cuttings transport since 1986.1–4 The principal objectives of this work have been to develop semiempirical, mathematical models and a computer package that can predict the circulation rate required to ensure efficient hole cleaning. The work has been oriented primarily toward the continuous transport of cuttings. However, the removal of cuttings beds, when formed, has also been investigated. Scope of Work. When drilling ahead, there is a critical annular velocity above which all cuttings will be carried out of the hole, and below which the cuttings will settle vertically, packing off the entire annulus of a vertical well or forming a stationary bed on the low side wall of the annulus, in a deviated well. This critical velocity has been called MTV. For any given situation, the mean annular velocity of the drilling fluid must be greater than or equal to the MTV to ensure that all cuttings are removed from the hole.
The decision to develop a small (t100 million bbl) oil field in the U.K. sector of the central/northern North Sea requires a careful assessment of all aspects of the field-development plan-the reservoir model (reserves and production profile), capital and operating costs, and the current economic climate (oil price, interest rates, and tax regime). This paper describes the development of a knowledgebased software package that allows a "quick-look" assessment of the overall economics and risk profile associated with the development of small oil fields in this region. It is a modular system that uses a cost database, cost-adjustment algorithms, cash-flow analysis engine, and simulation procedures to integrate and analyze the impact of reservoir and production characteristics, costs [capital expenditures (Capex) and operating expenditures (Opex)], and economic factors on the decision to develop such a field. The production-system configurations considered by the system are (1) an unmanned wellhead platform tied back to a third-party platform for fluid processing/export; (2) a floating production, storage, and offloading system (FPSO) with oil export through a shuttle tanker and gas export through a tie-in to the existing North Sea gas pipeline infrastructure; and (3) a straight tieback from a group of subsea wells to a third-party platform for fluid processing/export.
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