The key objective is to design a set of casing strings, capable of withstanding a variety of external and internal loads(pressure, thermal, self-weight etc.) to ensure technical integrity for the life of the well.


      Procedures for leak-off and limit tests (LOT, LT, FIT)

      Procedures for leak-off and limit tests (LOT, LT, FIT)

      Procedures for leak-off and limit tests. Leak-off and Limit tests are carried out during the drilling phase of the well. The BOP is closed around the drillpipe, and the well is slowly pressured up,…

      Production string

      Production string

      The Production string is a string which is installed to separate productive zones from other reservoir formations or for testing purposes.

      • The string through which the well will be completed,…

      Casing design factors

      This article describes the uniaxial collapse, burst, axial and compression design factors, and the triaxial design factor, recommended for use, together with a brief overview of the considerations…

      Connection types

      Connection types

      Casing connections should satisfy several functional and operational requirements which are presented in this article.

      Functional aspects

      • to provide a leak resistance to internal or external fluid…

      Connection Thread compounds

      Thread compounds are used for three distinct purposes:
      - to prevent corrosion of the connection parts during storage;
      - to facilitate the running of connections during make-up/break-out;
      - to seal the…

      Conductor string

      Conductor string is a string which is installed to cover unconsolidated formations, to seal off shallow water sands and to provide protection against shallow gas flows. The string is cemented to the…

      Casing Storage, Handling and Transport

      This article describes the recommended guidelines for casing storage, handling and transport that need to be taken account in the design phase of the casing.

      1 Storage

      The design of pipe racks is…

      Influence of corrosion on casing strength

      Corrosion can pose a major threat to the installations whether above or below ground. With particular respect to casing, corrosion can impair the ability of the casing to perform its functions in two…

      Pressure loads (burst and collapse)

      The burst and collapse loads are calculated by taking the difference (Pi-Pe) between the internal and external pressure profiles for each load case.

      If the resulting load line is mainly positive, it…

      Stove pipe, marine conductor or foundation pile

      The purpose of Stove pipe, marine conductor or foundation pile is to:

      - protect the incompetent surface soils from erosion by the drilling fluid.

      - reduce the wave and current loads imposed on the…

      Running and Testing Casing

      Running and Testing Casing

      To ensure that the casing is run efficiently to the correct depth and in the desired condition, specific equipment and techniques should be considered in the design phase.

      1 Rig hoisting capacity

      The…

      Burst loads

      1. Burst during drilling

      Burst loads can occur during the drilling phase due to displacement of the borehole to hydrocarbons. There are, however, a number of special cases to be considered. The base…

      Preparation for Running Casing

      Preparation of casing before running serves two purposes. 1. ensure that the pipe body and threads are adequately protected from possible damage when being moved to the drill floor. 2. ensure that…

      Basic aspects of rock mechanics

      Borehole pressure required to reach tensile failure depends on:

      • tensile strength of the rock;
      • state of stress in the formation;
      • orientation of the wellbore with respect to the state of stress;
      • shape…

      Reliability and structural integrity of connections

      This article addresses the possible loads on a connection and its sealing and structural capacity. It should be highlighted that these capacities do not always produce the same value.

      1 Imposed loads…

      Influence of wear on casing strength

      The burst, collapse and axial strengths of casing are directly related to wall thickness, and hence are reduced by wear. The casing must be designed so that wear will not reduce the strength of the…

      Casing scheme selection

      The output of this process is a preliminary well configuration specifying the minimum casing diameter and the minimum casing-shoe setting depth for all strings. This serves as input for the detailed…

      Connections Surface treatments

      In order to ensure the functional efficiency of a connection, even after multiple make-up operations, surface treatments are applied to the box, the pin or to both. The surface treatments are applied…

      Resistance to buckling

      The buckling theory showed that for buckling to occur, the reduced axial force, Fa*, must be negative. However, it is not necessarily the case that buckling will occur if the reduced axial force is…

      Ordering casing

      Ordering casing

      Casing is one of the most critical well consumables with respect to timing. Total elapsed time for procurement of Oil Country Tubular Goods (OCTGs) varies from 6-18 months. This includes tendering…

      Casing Design parameters

      Early collection of all the relevant data is essential and it should be done by a multidisciplinary team. Considerable effort is required from the Petroleum Engineering and Operations departments when…

      Collapse loads

      1 Evacuation during drilling

      Collapse loads occurring during drilling are usually the result of borehole evacuation due to natural or induced losses. There are however other cases to be considered.

      1.1.…

      Casing design considerations

      Casing design considerations

      The objective of the casing design is to define a set of casing strings (casing scheme), capable of withstanding a variety of external and internal pressures, thermal loads and loads related to the…

      Casing Design Loads

      Introduction to Casing Design Loads (Collapse, Burst and tension Load)

      1  Collapse Load

      The design load case for collapse is based on a partial evacuation of the casing string.

      For partial…

      HPHT well

      In High Presure High Temperature (HPHT) environments, high differential pressures often lead to the use of high strength, thick-walled, and occasionally non-standard, casing.

      High temperatures…

      Installation loads

      After the casing string has been designed to withstand the anticipated collapse and burst loads, it should be checked against the loads that will be experienced during the installation, and against…

      Installation loads

      This articel describes the various installation loads and how they are calculated.

      • self-weight (in air) loads
      • pressure (buoyancy) loads
      • bending loads
      • dynamic drag loads
      • shock loads
      • point loads
      • static…

      Steam well

      The design of steam wells is complicated by the fact that the axial stress exceeds the yield strength in compression during heating and exceeds the yield strength in tension during subsequent cooling.…

      Monitoring Casing Condition

      Once a casing string has been successfully cemented in place and tested, subsequent operations must be planned to ensure that the casing remains fit for purpose. Condition monitoring systems should be…

      Liner

      A liner (other than slotted liners) is a string of casing which does not extend all the way to the surface. Liners are installed to permit deeper drilling, to separate the productive zones from the…

      Influence of fatigue on casing strength

      Casing failure can have various causes. Casing may fail after exceeding, even once, the ultimate tensile or compressive strength, but also after repeated load cycles below the ultimate tensile or…

      Detailed Design and Analysis

      In the detailed design phase, the casing designer determines the material grade and casing wall thickness for each section of the casing scheme selected, which will allow it to withstand all…

      Liner hanger selection - Design criteria

      • Expanding latch hanger mechanisms should recock when the string is picked up (if accidentally engaged in the BOP's etc.). All liner tools should have OD profiles that do not catch or snag on the…

      Service loads

      The previous article presented the methods to quantify the installation and as-landed loads. The purpose of this article is to present methods to quantify the changes in stress in the cemented casing…

      Stove pipe, foundation pile, marine conductor and conductor string

      The load determination for a stove pipe, foundation pile or marine conductor is a complex issue. This determination is usually followed by specialised stress analysis resulting in the involvement of a…

      Connections Selection and ordering

      When selecting a casing connection the actual load on the connection should be compared to the connection's capacity. This is applicable for all types of wells: exploration, appraisal and development…

      Reservoir compaction environment

      Production of hydrocarbons will, in time, lead to a reduction in reservoir pore pressure if pressure is not maintained by a drive mechanism. The resulting increase in effective stress leads to…

      Squeezing salt well

      When a hole is drilled through a salt formation, and subsequently casing is set, the salt will gradually move and make contact with the casing. The following paragraphs describe the loading on the…

      Permafrost well

      The consequences of permafrost thaw resulting from increased surface temperatures during drilling and production, affect casing design in a number of ways.

      Permafrost is a permanently frozen soil.…

      Casing Thread protectors

      Before casing joints are installed in a well, they are exposed to a variety of harsh conditions during transport, handling and storage. The threaded pipe ends frequently have to withstand accidental…

      Intermediate string

      Intermediate string

      The intermediate string is a string which is used to isolate weak formations, to case off loss zones, sloughing, caving and reservoir formations. Such strings are also set in transition zones to…

      Connections Testing and qualification

      The general accepted method for the qualification of casing connection designs is, at the moment, the conducting of tests on a number of full scale specimens. The aim of such an investigation is to…

      Gravity structure

      With time, a concrete gravity platform structure will induce considerable deformation within the supporting soil. The casing, particularly the marine conductor, will have, at least in part, to follow…

      Load bearing capacity

      It should be noted that the strengths require down rating to account for the effects of wear, corrosion and fatigue and for the effect of temperature on yield strength.

      The appearance of commercial…

      Gas-lift well

      Casing designs for wells in which gas-lift completions are to be installed are based upon different design load cases from standard wells. They have to be treated differently from standard wells in…

      Post-buckling analyses

      The onset of buckling does not necessarily mean pipe failure. The acceptability of buckled casing must be assessed in two ways, i.e. the resulting stresses in the casing wall, and the access through…

      Horizontal well

      There are a number of areas in horizontal well casing design that may differ from a standard well. These mostly relate to the casing loading, although there can be instances where the capacity of the…

      Deep-water well

      Deep-water wells present two problems for the casing designer, casing setting depth, and environmental loading above the seabed.

      Firstly, these environments have lower fracture gradients than…

      Pressure (Collapse and Burst) loads on casing

      This article describes the methods to quantify the different casing loads are presented. Internal and external pressure profiles are generally independent and therefore separate design loads will be…

      Surface string

      The purpose of the surface string is to provides blowout protection during drilling. Setting depth is often chosen to isolate troublesome formations, loss zones, shallow hydrocarbons, water sands, or…

      Service loads

      The initial casing design, is not an exact reflection of the service loads, as it assumes that the casing string is not fixed at either end. It must be ensured that the incremental stresses resulting…

      Slim hole well

      For a slim hole casing design all the design loads, inclusive burst, collapse, and tensile load requirements, should be determined as for all other wells. For a fixed influx volume and assuming a…

      Fundamental equation for reduced axial force

      By examining the reduced axial force, Fa*, in a casing string, the operating conditions under which the uncemented portion of the casing will buckle are defined. This leads directly to methods of…

      Connection sealing

      Threaded casing connections utilise three basic mechanisms to establish a leak tight joint. These mechanisms are:

      • tapered interference fit thread seal;
      • metal-to-metal seal;
      • resilient seal.

      1 Tapered…