Seminar report on

„Detailed casing design‟

Submitted to

University of Pune

In partial fulfilment of ME-II curriculum

Submitted by:

Nikhil G Barshettiwar

ME-II (Third semester)

Maharashtra Institute of Technology, Pune

Certificate

This is to certify that, seminar report entitled “Casing Grade Selection” submitted by Mr.

Nikhil Barshettiwar, Exam Seat number:5086, ME-II Petroleum Engineering, is a record of

bonafide work carried out by him /her under my supervision, in partial fulfilment for ME

Second Year Course requirement of University of Pune, Pune

Prof Dr. P. B. Jadhav, Prof. Sanjay Joshi

Head, Date: Jan 02, 2015

Department of Petroleum Engineering, Seminar Supervisor

MAEER‟s Maharashtra Institute of Technology,

124, Paud Road, Pune -411038

Acknowledgement

First and foremost would like to first thank Prof. Sanjay Joshi for guiding me through my

Masters. It is through his patience and teaching that I could reach here to present a seminar on

“Casing Grade Selection”.

I am extremely grateful to entire Petroleum Engineering faculty for their excellence in

guidance. I firmly believe that they have battered me as petroleum engineer and I will carry

with me the skills that they have given in future work.

Last but not least I would like to thank my parents for encouragement at important junctures

of studies.

Submitted By:

Nikhil G. Barshettiwar

ME-II (Semester III)

Maharashtra Institute of Technology, Pune

Contents

Contents Summary ................................................................................................................................................. 5

Chapter1. Introduction ............................................................................................................................ 6

Chapter2. Load Cases in Grade selection ............................................................................................... 7

Collapse loads during drilling ............................................................................................................. 8

Quality of cement ............................................................................................................................ 8

Annulus fluid column ..................................................................................................................... 8

Collapse loads during production phase ............................................................................................. 9

Burst load cases during drilling phase .............................................................................................. 10

Burst load cases during production phase ......................................................................................... 11

Axial loads ........................................................................................................................................ 12

Chapter3: Casing grade selection for Sour service ............................................................................... 13

Calculation of partial pressure: ......................................................................................................... 13

API Grades for sour service: ............................................................................................................. 13

Chapter4. Case Study ............................................................................................................................ 14

Summary This study is mainly focused on detailed casing design. Detailed casing design includes

selection of appropriate weight and grade of the casing. Loads during drilling and production

operations are broadly classified into collapse and burst loads. All the discussed load

conditions in report are taken into account for solving case study. Report contains brief

paragraph on grade selection for sour service.

Chapter1. Introduction

Well engineer or casing designer is responsible for selection of most appropriate grades for a

well in order to;

Ensure mechanical integrity of well for anticipated loads

Minimum cost

Clear documentation of the design basis to operational personnel at wellsite.

With above given objectives one needs to design string without negotiating with safety.

Minimum cost concept ensures the lowest cost that can be achieved without using any

shortcuts in design.

Grade selection directly impacts the feasibility of project. Though lowest cost design is

obtained, well integrity can hamper the project. Hence selection of most suitable grades is

necessary.

Casing design method is widely divided into two phases i.e. preliminary design and detailed

design. Preliminary design includes data gathering from offset wells and its interpretation,

determination of casing shoe depths, selection of combination of hole and casing sizes, mud

weight and directional design.

Detailed design includes selection of pipe weights and grades for each section. The pipe

selection involves determination of maximum anticipated loads. Then these pipes with

specific grades with its rating compared with the calculated loads. If it achieves the design

factor according to company policy then pipe is selected. Otherwise whole procedure needs

to be carried out till pipe rating satisfies maximum allowable loads.

Chapter2. Load Cases in Grade selection

In order to select proper optimised grades, designer needs to obtain the burst and collapse

load in given situation. Initially one needs to calculate the internal pressure profile and

external pressure profile for a given load case. Burst pressure is defined as the difference

between internal pressure and external pressure at a specified depth. Similarly collapse

pressure is the difference between external pressure and internal pressure at specified depth.

Assuming best load cases during well planning key parameter in successful casing design.

When considering internal pressure profile (Bust or collapse), in drilling phase on mud losses

is taken into account. In production phase, a distinction must be made between internal

profile below and above the packer. When considering external pressure profile, quality of

cement behind casing and quality of fluid in the annulus above top of the cement are the

critical factors should be considered.

Various load cases are discussed below. Being a good designer, suitable case or worst case

needs to take into account for design purpose.

Decision Tree for Collapse Load cases during drilling phase

Drilling ecacuation

External Pressure profile

Cement

Good cement column ?

Good cement column

Poor cement column

Annulus Fluid

Type of well

Development well

Original Annulus fluid

Exploration well

Original Annulus fluid

Internal Pressure profile

Mud loasses to Pore

Pressure

SPECIAL CASES

Full evacuation after blowout,

Full evacuation for air and foam drilling

SPECIAL CASES salt loading and formation

compaction

Collapse loads during drilling Collapse load occurring during drilling are mainly because of borehole evacuation. Internal

pressure during drilling corresponds to loss situation. In loss situation, mud column in

borehole is balanced by the pore pressure at target depth. Height of mud column should be

always found using lowest possible pore pressure. This gives lowest evacuation level.

External pressure profile should be constructed on the basis on quality of cement column and

annulus fluid in the wellbore.

Quality of cement

Assuming that set cement behaves like porous matrix having least permeability with pore

fluid inside at a certain pressure. If cement column set across the high permeability

formation, the pressure in the cement will be equal to the pore pressure in the formation. If

cement column set across the low permeability formation, then pressure in the column will

depend upon the quality of it.

In good quality cement column, it acts as a effective seal between high permeability

formation and top of cement (TOC). Thus pore pressure across low permeability formation is

nothing but the gradient of line joining top of the high permeability formation to top of the

cement. It can be called as semi-static pressure profile.

In poor quality cement column, it does not act as effective seal between high permeability

formation and TOC. The cement pressure across the low permeability formation interval will

then be equal to the cement mixwater gradient.

Annulus fluid column

In case of a high quality cement column over a high-permeability formation, annulus fluid

pressure line extends downwards upto the TOC with its original gradient (generally its mud

in which casing is set). For low quality cement column across the high permeability

formation, the annulus fluid line extends upwards with same gradient from the pressure at the

TOC towards the wellhead.

If the cement column does not pass through any high-permeability, then quality of cement

doesn‟t matter. Annulus fluid pressure line should extend downward assuming zero wellhead

pressure upto the TOC.

For special cases;

Type of load (Activity) Internal Pressure Profile External Pressure Profile

Air, foam or aerated drilling Full evacuation Cement column and annulus

fluid

Salt loading Partial evacuation Cement column, annulus

fluid and additional step

change due to external

pressure at the top and

bottom of the salt formation.

Formation compaction Partial evacuation Formation compaction

Blowout Full evacuation Cement column and annulus

fluid

Decision tree for Collapse Load cases during production phase

Collapse loads during production phase

Collapse loads during production arise due to production evacuation from natural or induced

losses. Internal pressure profile is divided into two categories i.e. Below production packer

and above production packer. Casing below packer must be always designed to withstand full

internal evacuation. Generally during normal production operations casing doesn‟t subject to

critical collapse load. But during completion and workover, losses may lead to evacuation of

upper section of production casing. External profile should be considered same as for drilling.

Special cases during production phase;

Type of load Internal profile External Profile

Artificial lift wells Full evacuation Cement column and annulus

fluid

Salt loading Partial evacuation Cement column and annulus

fluid with effect of salt

loading

Blowout Full evacuation Cement column and annulus

fluid

Production evacuation

External Pressure profile

Cement

Good cement column ?

Good cement column

Poor cement column

Annulus Fluid

Type of well

Development well

Deteriotion of unstable

annulus fluid

Exploration well

Original Annulus fluid

Internal Pressure profile

Below packer

Full evacution

Above packer

Losses to Pore pressure

SPECIAL CASES

Full evacuation after blowout,

Full evacuation for air and foam drilling

SPECIAL CASES salt loading and formation

compaction

Decision tree for burst load cases, drilling phase

Burst load cases during drilling phase Generally in order to design to withstand with maximum loads, kick during drilling of next

section is assumed. In worst scenario, complete loss of primary control need to taken into

account. It means mud has been completely displaced by the gas kick, wellbore full of gas

and well is closed-in at surface. The difference between pore pressure and gas column will

give maximum anticipated surface pressure (MASP). This MASP is completely different

from MAASP which is margin at the shoe. The external pressure profile is assumed to be

same as in drilling phase.

Special cases;

Type of load Internal Pressure Profile External Pressure Profile

Over-pressured aquifer in

borehole below casing

Full displacement of

wellbore to water with well

closed at surface.

Cement column and annulus

fluid.

Salt loading Displacement of casing to

HC or water.

Cement column and annulus

fluid. Salt loading assume to

be absent when calculating

external pressure profile.

Drilling Burst

Internal Pressure Profile

Displacement to Gas/Oil

External Pressure Profile

Cement

Good cement column?

Good cement column

Poor cement column

Annulus fluid

Type of well

Development well

Original Annulus fluid

Exploration well

Original Annulus fluid

SPECIAL CASES

Over Pressured acquifier

SPECIAL CASES salt loading assumed absent in salt

formation

Decision tree for burst load cases, production phase

Burst load cases during production phase Again load during production is divided as above and below packer. Burst load above

production packer is due to tubing failure. Maximum burst load can be expected when leak

occurred at surface in production/injection tubing or test string. This additional surface

pressure will act on column on packer fluid.

In case of production wells, assume casing full of gas column, the difference between pore

pressure at TD and gas column pressure gives maximum closed in tubing-head pressure.

Below packer, worst case scenario is full displacement of this section of casing to HC.

External pressure profile assumed to be same as drilling phase in collapse loads.

Special cases;

Type of load Internal Pressure Profile External Pressure Profile

Gas-Lift wells Kick-off pressure plus

column of packer fluid

Cement column and annulus

fluid

Salt loading Leak- pressure at the surface

plus column of packer fluid

Cement column and annulus

fluid. Salt loading assume to

be absent when calculating

external pressure profile.

Drilling Burst

Internal Pressure Profile

Above Packer

Type of well

Production well

CITHP on packer fluid

Injection well

ITHP on packer fluid

Below Packer

Type of well

Production well

Displacement to Gas/ Oil

Injection well

Injection BHP

External Pressure Profile

Cement

Good cement column?

Good cement column

Poor cement column

Annulus fluid

Type of well

Development well

Original Annulus fluid

Exploration well

Original Annulus fluid

SPECIAL CASES

Kick of process for gas lift wells

SPECIAL CASES

Salt loading assumed absent in salt formation

Axial loads Following loads are considered in axial load calculations;

1. Self-weight

Self-load is due to gravitational effect. The casing weight per feet decides the weight of

string.

2. Buoyant load

This is compressive load acting on the casing bottom when string is submerged in borehole.

Buoyant forces are function of mud weights.

3. Bending load

Bending loads are induced due to curved portion in the wellbore. These are mixed stresses.

Inner curved portion is subjected to compression forces while external curved portion is

subjected to the tensile forces.

4. Dynamic drag load

Dynamic drag loads are encountered when object is in motion. During casing running in hole,

friction induces due to contact between casing and wellbore. Drag load also depends on

quality of borehole. In-gauge hole gives less drag.

5. Shock load

Sudden obstruction during motion causes shock loads. Two shock waves are generated at the

point of contact i.e. upward travelling compression wave and downward travelling tension

wave.

6. Point load

Point loads are arises during operational activities such as pressure testing.

Chapter3: Casing grade selection for Sour service Sour service indicates presence of high H2S content in reservoir fluid. Sour service is defined

as a threshold on partial pressure of H2S above 0.05 psi. Common casing grades cannot

sustain in sour service. Grades should have special chemical properties in order combat with

sour service.

Hydrogen sulphide is made up of combined atoms of sulphur and hydrogen. It forms due to

bacterial decomposition of organic matter in oxygen-poor environments. Generally it‟s

associated with hydrocarbons. It has special attraction towards the metal like steel. Generally

well tubular are made up of steel hence it needs critical attention while selecting appropriate

grades.

According to ISO 8044, corrosion is a physiochemical interaction between a metal and its

environment that results in changes in properties of metal and which may lead to significant

impairment of the function of the metal, the environment, of which these form part.

ISO 15166/NACE MR0175-2009: partial pressure of H2S and pH are major

parameters (Vallourec oil and gas magazine)

Calculation of partial pressure: PH2S = ppm/10

6 * BHP (psi)

Or

PH2S = mole %/ 100 * BHP (psi)

API Grades for sour service:

L80, C90, T95 and C110 is dedicated API grades suitable for sour service

environments. They comply with following requirements:

Chemical composition

Grain size finer tha ASTM 5

Hardness Limitation

MACE test methods A, B or D

Chapter4. Case Study

Data Input-

Step-1:

Step-2: Obtaining mud window.

Step-3: Once mud window is obtained, then seats need to be selected. Seat

selection includes criteria like kick tolerance, MAASP, Differential sticking etc.

Step-4: specifying production data

Step-5: specifying temperature data

Step-6: Parameters according to design safety

Similar procedure need to be carried for all remaining sections. Final results obtained are

given below for other casings.