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.
This paper focus on factors attributing to casing failure, their failure mechanism and the resulting failure mode. The casing is a critical component in a well and the main mechanical structural barrier element that provide conduits and avenue for oil and gas production over the well lifecycle and beyond. The casings are normally subjected to material degradation, varying local loads, induced stresses during stimulation, natural fractures, slip and shear during their installation and operation leading to different kinds of casing failure modes. The review paper also covers recent developments in casing integrity assessment techniques and their respective limitations.The taxonomy of the major causes and cases of casing failure in different well types is covered. In addition, an overview of casing trend utilisation and failure mix by grades is provided. The trend of casing utilisation in different wells examined show deep-water and shale gas horizontal wells employing higher tensile grades (P110 & Q125) due to their characteristics. Additionally, this review presents casing failure mixed by grades, with P110 recording the highest failure cases owing to its stiffness, high application in injection wells, shale gas, deep-water and high temperature and high temperature (HPHT) wells with high failure probability. A summary of existing tools used for the assessment of well integrity issues and their respective limitations is provided and conclusions drawn.
In recent times, the oil industry has shown increasing awareness towards the maintenance of optimum well productivity through better drilling/completion practices. Attempts are being made to control the invasion of high permeability sands by mud solids through the use of sized Loss Control Materials (LCM) which can be difficult to clean up. Recent developments involve the use of sized carbonate and sized salt systems with mixed results. Whilst these special systems have been known to provide efficient fluid loss control, the cleanup efficiency especially in horizontal wells has been known to be poor in certain instances. Likewise, the completion of long horizontal sections through highly permeable, unconsolidated reservoirs has witnessed increasing use of prepacked screens many of which are reported to be plugged/damaged by filter cake debris and completion fluid solids as well as formation fines. Gravelpacks are also known to have been damaged not only by formation fines but also by solids in completion fluids injected from the wellbore especially during cleanup operations. The migration of sized particles in the drilling and completion fluids through high permeability reservoir sands, prepacks or gravelpacks is characterised by flow capacity decline which may be instantaneous or gradual depending on the migration process and the pore bridging phenomena. Therefore, accurate prediction of the prevailing pore blocking mechanism for a given pore throat-particle size relationship can provide a good basis for the estimation of the maximum allowable size of particles in various completion fluid systems and also provide a good guide to the design for optimum prepack and gravelpack performance through the use of properly sized gravels. In this paper, attempts have been made to analyse the impact of a number of key parameters on productivity impairment. The analysis has been based on the results of in-depth research into particle-pore bridging phenomena. Based on rigorous experimental studies to define the phenomena, a number of deterministic models have been developed to mathematically define the unconsolidated pay sand/pack sand systems permeability decline profile as a function of invasion pattern, migration/pore blocking mechanism, production/injection rate, production time and fines concentration and fines textural properties. Application of the results to the optimisation of drilling/completion fluids design as well as prepack/gravelpack design and analysis are illustrated with specific case studies. Introduction The oil industry has continued to use sized particulates in many facets of its well completion programmes either as dispersed solids in drilling/completion fluids or as pack sands to control the migration of fines from unconsolidated reservoirs. In all of these cases, particulate size distribution appears to be the only current criterion adopted as a basis for the design of the following: P. 355
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