Well Design PE 413 Introduction and API Standards of Casing

Casing Design Introduction Choosing the correct size, type, and amount of casing that is used in well construction is of utmost importance to the success of the well. The casing must be of sufficient size and strength to allow the target formations to be reached and produced. Casing has become one of the most expensive parts of a drilling program; the average cost of tubulars is about 18% of the average cost of a completed well. Thus, an important responsibility of the drilling engineer is to design the least expensive casing program that will allow the well to be drilled and operated safely throughout its life

Casing Design Introduction The main functions of the casing in any well are: Maintain hole integrity Isolate abnormally pressured zones Protect shallow weak formations from heavier mud weights required in the deeper portions of the hole Prevent contamination of freshwater-bearing strata Support unconsolidated sediments

Component Parts of A Casing String Casing Components Component Parts of A Casing String

Casing Components Conductor Casing Sea off unconsolidated formations at shallow depths Stop washouts under the drilling rig. Protect fresh water sands. To give a base and support for the next string of casing The conductor pipe is the first casing to be put in place, and is generally installed before the rig arrives on location. Such casing can be driven to 250 feet. Conductor casing measuring between 16 to 24" outside diameter is used onshore, and between 24 to 48" for offshore.

Casing Components Surface Casing Protect, water sands Support the wellhead and BOP equipments Case unconsolidated formations Support other casings Case off lost circulation zones Surface casing is the first string of casing used after the conductor pipe. It is required in some instances by law (to protect ground water) and is normally cemented full length. Surface casing supports the BOP stack and subsequent casing and tubing strings, and is normally the only string designed to carry compression loads.

Casing Components Intermediate Casing Intermediate casing is any string between the surface and production string. Intermediate casing may or may not be cemented full length. Intermediate casing may be used to: Seal off weaker zones Protect previous casing strings from higher Pburst Provide support for liner casing.

Casing Components Production Casing The fourth but not necessarily the final string of pipe run in the hole is the production casing. The production casing is used to control the hydrocarbon bearing zones that will be produced. This string of pipe adds structural integrity to the wellbore in the producing zones. Production casing should be set before completing the well for production. It should be cemented in a manner necessary to cover or isolate all zones which contain hydrocarbons.

Casing Components Running Casing

Casing Components Running Casing Mississippi: Not encounter abnormal formation pressure, lost circulation zones, salt sections. Required only conductor casing, surface casing and production casing Offshore Louisiana and Texas Delaware Basin: Encounter abnormal pore pressure, lost circulation zones, salt sections, unstable shale sections. Required intermediate casing to protect formation below the surface casing from the pressures created by the required high drilling fluid density. Liner is used to lower the cost of drilling. It serves similarly to intermediate casing in that it isolates troublesome zones that tend to cause well problems during drilling operations.

Casing Design Bit – Hole - Casing

API Standard API Standard The size of the casing refers to the outside diameter (O.D.) of the main body of the tubular (not the connector). Casing sizes vary from 4.5" to 36" diameter. Tubulars with an O.D. of less than 4.5” are called Tubing.

API Standard Casing Length The API standards recognize three length ranges for casing: Range 1 (R-1): 16 – 25 ft Range 2 (R-2): 25 – 34 ft Range 3 (R-3): > 34 ft Casing is run most often in R-3 lengths to reduce the number of connections in the string. Since casing is made up in single joints, R-3 lengths can be handled easily by most rigs.

API Standard Casing Weight For each casing size there are a range of casing weights available. The weight of the casing is in fact the weight per foot of the casing and is a representation of the wall thickness of the pipe. There are for instance four different weights of 9 5/8" casing. (Drift diameter refers to the guaranteed minimum ID of the casing.)

API Standard Casing Grade In addition to the API grades, certain manufacturers produce their own grades of material. Both seamless and welded tubulars are used as casing although seamless casing is the most common type of casing and only H and J grades are welded.

Definition of Yield Strength API Standard Definition of Yield Strength Proportionality limit: Up to this amount of stress, stress is proportional to strain (Hooke’s law), so the stress-strain graph is a straight line, and the gradient will be equal to the elastic modulus of the material. Elastic limit (yield strength): Beyond the elastic limit, permanent deformation will occur. The lowest stress at which permanent deformation can be measured is defined as yield strength. Typical yield behavior for non-ferrous alloys. 1: True elastic limit 2: Proportionality limit 3: Elastic limit 4: Offset yield strength

API Standard Casing Grade The chemical composition of casing varies widely, and a variety of compositions and treatment processes are used during the manufacturing process This means that the physical properties of the steel varies widely. The materials which result from the manufacturing process have been classified by the API into a series of “grades”. Each grade is designated by a letter, and a number. The letter refers to the chemical composition of the material and the number refers to the minimum yield strength of the material e.g. N-80 casing has a minimum yield strength of 80000 psi and K-55 has a minimum yield strength of 55000 psi. Hence the grade of the casing provides an indication of the strength of the casing. The higher the grade, the higher the strength of the casing.

API Standard Connections Individual joints of casing are connected together by a threaded connection. These connections are variously classified as: API; premium; gastight; and metal-tometal seal. In the case of API connections, the casing joints are threaded externally at either end and each joint is connected to the next joint by a coupling which is threaded internally. The standard types of API threaded and coupled connection are: • Short thread connection (STC) • Long thread connection (LTC) • Buttress thread connection (BTC)

API Standard Connections

API Specifications, Standard and Bulletins API Standard API Specifications, Standard and Bulletins API SPEC 5CT, “Specification for casing a tubing”: Covers seamless and welded casing and tubing, couplings, pup joints and connectors in all grades. Processes of manufacture, chemical and mechanical property requirements, methods of test and dimensions are included. API STD 5B, “Specification for threading, gauging, and thread inspection for casing, tubing, and line pipe threads”: Covers dimensional requirements on threads and thread gauges, stipulations on gauging practice, gauge specifications and certifications, as well as instruments and methods for the inspection of threads of round-thread casing and tubing, buttress thread casing, and extreme-line casing and drill pipe. API RP 5A5, “Recommended practice for filed inspection of new casing, tubing and plain-end drill pipe”: Provides a uniform method of inspecting tubular goods.

API Specifications, Standard and Bulletins API Standard API Specifications, Standard and Bulletins API RP 5B1, “Recommended practice for thread inspection on casing, tubing and line pipe”: The purpose of this recommended practice is to provide guidance and instructions on the correct use of thread inspection techniques and equipment. API RP 5C1, “Recommended practice for care and use of casing and tubing”: covers use, transportation, storage, handling, and reconditioning of casing and tubing. API RP5C5, “Recommended practice for evaluation procedures for casing and tubing connections”: Describes tests to be performed to determine the galling tendency, sealing performance and structural integrity of tubular connections. API BULL 5A2, “Bulletin on thread compounds”: Provides material requirements and performance tests for two grades of thread compound for use on oil-field tubular goods.

API Specifications, Standard and Bulletins API Standard API Specifications, Standard and Bulletins API BULL 5C2, “Bulletin on performance properties of casing and tubing”: Covers collapsing pressures, internal yield pressures and joint strengths of casing and tubing and minimum yield load for drill pipe. API BULL 5C3, “Bulletin on formulas and calculations for casing, tubing, drillpipe and line pipe properties”: Provides formulas used in the calculations of various pipe properties, also background information regarding their development and use. API BULL 5C4, “Bulletin on round thread casing joint strength with combined internal pressure and bending.”: Provides joint strength of round thread casing when subject to combined bending and internal pressure.

Casing Running Procedures Rig-Site Operation Casing Running Procedures Casing leaks are often caused by damaging the threads while handling and running the casing on the rig. It has also been known for a joint of the wrong weight or grade of casing to be run in the wrong place, thus creating a weak spot in the string. Such mistakes are usually very expensive to repair, both in terms of rig time and materials. It is important, therefore, to use the correct procedures when running the casing.

Casing Running Procedures Rig-Site Operation Casing Running Procedures

Casing Running Procedures Rig-Site Operation Casing Running Procedures As more joints are added to the string the increased weight may require the use of heavy duty slips (spider) and elevators If the casing is run too quickly into the hole, surge pressures may be generated below the casing in the open hole, increasing the risk of formation fracture. A running speed of 1000 ft per hour is often used in open hole sections. If the casing is run with a float shoe the casing should be filled up regularly as it is run, or the casing will become buoyant and may even collapse, under the pressure from the mud in the hole. The casing shoe is usually set 10-30 ft off bottom.

Casing Running Procedures Rig-Site Operation Casing Running Procedures Regular Slip Heavy duty slip

Liner Running Procedures Rig-Site Operation Liner Running Procedures Liners are run on drillpipe with special tools which allow the liner to be run, set and cemented all in one trip. The liner hanger is installed at the top of the liner. The hanger has wedge slips which can be set against the inside of the previous string. The slips can be set mechanically (rotating the drillpipe) or hydraulically (differential pressure). A liner packer may be used at the top of the liner to seal off the annulus after the liner has been cemented.

Liner Running Procedures Rig-Site Operation Liner Running Procedures The basic liner running procedure is as follows: (a) Run the liner on drillpipe to the required depth; (b) Set the liner hanger; (c) Circulate drilling fluid to clean out the liner; (d) Back off (disconnect) the liner hanger setting tool; (e) Pump down and displace the cement; (f) Set the liner packer; (g) Pick up the setting tool, reverse circulate to clean out cement and pull out of hole.

Liner Running Procedures Rig-Site Operation Liner Running Procedures