Literature review of recent best practices for downhole corrosion control in the oil and gas industry- modeling of sweet and sour

systems

Muzammal Arif

Graduate Student, Department of Mechanical Engineering

King Fahd University of Petroleum and Minerals, (KFUPM)Dhahran, Saudi Arabia

Email: m.muzammal.arif@gmail.com

Dr. Yahya T. Al-JanabiR & D Center, Saudi Aramco

Dhahran, Saudi ArabiaE-mail: yahya.janabi@aramco.com

Literature review of recent best practices for downhole corrosion control in the oil and gas industry- modeling of sweet and sour

systems

Introduction to downhole corrosion

Effect of carbon dioxide and hydrogen sulfide

Prevention and treatment method

Co2 corrosion models

Mechanistic model

Empirical model

Semi-empirical model

H2s corrosion models

Physico-chemical model

Mathematical model.

Downhole corrosion monitoring techniques

Introduction to downhole corrosion

Introduction to downhole corrosion

Downhole corrosion is the corrosion in oil and gas well equipment which is under the ground level, like pumps, piping, casing, sucker rods, valves etc

Basic components that cause corrosion are

Oxygen, carbon dioxide, hydrogen sulfide, and dissolved salts, well temperature and Pressure

Effect of carbon dioxide and hydrogen sulfide

CO2 form Carbonic Acid & lowers the PH below 7.

H2S reacts with the metal to form FeS film which protects the metal surface from further corrosion.

Corrosion by the Hydrogen Sulfide is unpredictable.

Corrosion mechanism will be much complex when carbon dioxide and hydrogen sulfide is accompanied by oxygen

Introduction to downhole corrosion

Prevention and Treatment Methods

Design the methodology of corrosion prevention in advance. An effective treatment or false interpretation of the corrosion problem will make the corrosion much move devastating

Proper Piping Design

Material selection of the pipe (on the basis of economical and physical constraints)

The fluid flow conditions (High flow velocities as well as turbulence effect should be minimized)

Coating the Material

Material should be coated internally with some type of paint or plastic

Main problem with coating is to maintain the coating

Introduction to downhole corrosion

Addition of Inhibitors

Most Appropriate method of protecting metal

Removal of Corrosive Gases

Complete removal of gases in impossible however interaction of gases with the metal can be avoided.

Gas blanketing to prevent oxygen to enter the system.

CORROSION MODELS

CO2 CORROSION MODELS

Carbon dioxide corrosion or sweet corrosion is recognized as a major problem in oil and gas industry. Various models are developed to predict the carbon dioxide corrosion rate.

These models are mechanistic, semi-empirical and empirical.

Mechanistic Model

Purely predictive model (do not rely on any measured corrosion rate data).

Solution is obtained as a result of extrapolation and obtained results may be applied to new systems.

Figure 1: Principles of mechanistic CO2 corrosion models.Courtesy: reference [2]

CO2 (g) dissolves in the liquid phase and it reacts with water to form to HCO3

-1 and CO3-2 and

thus it makes the liquid acidic in nature

H2CO3 (aq) diffuses to the pipe surface and reacts at the metal surface to producing HCO3

-1 and H2 gas.

Mechanistic Model The products formed at the metal surface goes away from the metal surface

FeCO3(s) precipitate on the metal surface and forms a protective layer of carbonate.

This protective layer of FeCO3 becomes a diffusion barrier and the overall reaction rate is reduced due to deficiency of H2CO3 (aq).

At the anode

at the Cathode

Figure 1: Principles of mechanistic CO2 corrosion models.Courtesy: reference [2]

Mechanistic Model The electrochemical kinetic reactions at the surface are typically formulated similar to

the Volmer-Butler (VB) equation [2]

In the above equation

i0, k = exchange current density of the kth electrochemical surface reaction. It is a function of concentrations of species at the steel surface.

αk = charge transfer coefficient and

nk = number of electrons transferred by reaction k.

The above equation is solved for the calculating the value of potential, E. After E is calculated the current related to anodic reaction is calculated and then converted to mm/year using faradays law. Basic difficulty faced in this method is the calculation of surface concentration for the estimation of i0,k

Mechanistic Model

One of the first and most widely used mechanistic models is the one proposed by de Waard and Milliams.

Based on the assumption of direct reduction of H2CO3 the authors presented a correlation for the corrosion rate which is a function of the pCO2 and temperature [3]

Drawback or Defects in Mechanistic Model

Mechanistic model may not reproduce exact measured corrosion rate

Much effort is required to apply the given model to entirely new system

Models has to be compared against experimental set of data to check the authenticity and validity of the model

Table 1: Overview of selected Mechanistic [M] CO2 corrosion rate models.Courtesy: reference [2]

 

Empirical Model Empirical models mostly depend linearly or non-linearly on the data obtained

because corrosion rate is measured with data recorded on field.

Corrosion rate is actually calculated from interpolating or extrapolating the experimentally measured corrosion data and Variables and parameters depend directly on measured corrosion data rate

One of the famous empirical model was given by Dugstad

There are also some linear model developed by Adam but CO2 corrosion is highly nonlinear processes so description of CO2 corrosion might not be accurate with this linear model. [3]

Drawback or Defects in Mechanistic Model

These models don’t have solid theoretical background

Model require huge experimentally determined data set to be calibrated and model poorly extrapolate to the conditions different from the measured system

Sometimes extrapolation leads to unwanted and inaccurate results

Introduction of something new in these models is quite difficult and it require the calibration of the whole model

Table 2: Overview of selected empirical (E) CO2 corrosion rate models.Courtesy: reference [2]

 

 

Semi-empirical Model These types of model are quite similar to empirical model but they used some

mathematical equations.

They do not totally depend on measured experimental set of corrosion data nor do they depend completely on mathematical co-relations and equations

These models are very simple to use and they require less effort to find the corrosion rate

If these models are calibrated against sufficient large and reliable experimental database, they can produce good prediction about corrosion but extrapolation sometime can lead into unwanted and unrealistic results

The most common and the most popular model is the De-Waard & Milliams formula. De Waard modified the original model by the introduction of new improved correction factors

Rmax = corrosion rate (millimeter/year)

T= temperature (K)

Pco2=P.mco2

P = total pressure (bar)

mco2=CO2 mole fraction

Semi-empirical Model

Table 3: Overview of selected semi-empirical (S) CO2 corrosion rate models.Courtesy: reference [2]

 

 

H2S CORROSION MODELS

H2S is the biggest contributor of corrosion in pipelines of sour field. Hydrogen sulfide reacts with ferrous to form a H2S film but as this film get dissolved more and more ferrous will be available to get attacked by H2S. The pipeline become thinner and thinner and finally become unsafe for usage

There is nothing you can do to stop the corrosion process completely but you can always make the process occur slowly. H2S is the agent which can trigger the corrosion process to happen as below [6]

H2S CORROSION MODELS

Sour corrosion happens in two steps, heat transfer and mass transfer

Heat transfer will depend upon the temperature, pressure and flow rate of the flowing oil and gas.

Mass Transfer is a function of temperature and concentration of H2S. [8]

Srdjan Nesic and Wei Sun [7] studied the corrosion of mild steel and developed a mechanistic model of H2S corrosion. They conducted glass cell experiment to investigate the corrosion caused by H2S on mild steel and developed Physico-chemical model and mathematical model.

S. Nešić [9] improved the model of carbon dioxide / hydrogen sulfide in multiphase flow. They took original mechanistic model after make modification in it they enable it to estimate the corrosion rate at low temperature (up to 1 C) and at high salt contents (up to 25 % NaCl) in the presence of iron sulfide formation layer over the steel.

DOWNHOLE CORROSION MONITORING TECHNIQUES

Direct

Intrusive (direct contact with corrosive environment)

Direct Intrusive physical

measurement

Metal loss coupon

Visual inspection

Electrical resistance (ER)

Direct Intrusive electrochemical measurement

Linear polarization

resistance (LPR)

Electrochemical noise (ECN)

Coupled multielectrode

array (CMA)

Non-Intrusive (not in direct

contact corrosive environment)

Ultrasonic testing — thickness

measurement

Radiography testing

Electromagnetic-eddy current

testing

Electrical field mapping

Indirect

Offline Techniques(analysis in the

lab)

Online Techniques

(immediate recording of parameters)

References/Bibliography [1] Downhole Corrosion - Prevention and Treatment

Robert F. Weeter,

[2] Improving mechanistic CO2 corrosion models

Philip L. Fosbøl, Kaj Thomsen, and Erling H. Stenby

[3] A Critical Review of CO2 Corrosion Modeling in the Oil and Gas Industry

Srdjan Nesic

[4] Deterministic modeling of corrosion in downhole environments

M. Sundaram, V. Raman, M. S. High, D. A. Tree, J. Wagner

[5] Innovative Approaches to Downhole Corrosion Control

K.A. Esaklul, Amoco Corp.-Amoco Research Center

[6] Monitoring of Downhole Corrosion: An Overview

Yahya T. Al-Janabi, R&D Center, Saudi Aramco, Dhahran, Saudi Arabia

[7] A mechanistic model of H2S corrosion of mild steel

Wei Sun and Srdjan Nesic

[8] A novel approach of H2S Corrosion Modeling in Oil/Gas production Pipeline.

Utjok W R Siagian, H.P Siregar, Ryan K Santoso, Damian D Salam, Shieren Sumarli

[9] A New Updated Model of CO2/H2S Corrosion in Multiphase Flow

S. Nešić, S. Wang*, H. Fang, W. Sun** and J. K-L. Le

[10] CO2 / H2S Corrosion under Scale Forming Conditions

Bruce Brown, Srdjan Nesic

[11] Prediction of Corrosivity of C02/H2SProduction Environments

Sridhar Srinivasan

[12] Mechanistic Modelling of H2S Souring Treatments by Application of Nitrate or Nitrite

D. Coombe, C. Hubert And G. Voordouw

[13] CO2 / H2S Corrosion Prediction – Laboratory Testing and Interpretation of Data

Jan Ivar Skar

[14] Localized Corrosion Resistance of Ni Base Alloy in Sour Environments

Masakatsu Ueda

[15] An Open Source Mechanistic Model for Co2 / H2s Corrosion Of Carbon Steel

Srdjan Nešić, Hui Li, Jing Huang and Dusan Sormaz

[16] Modeling of Water Wetting and the Effect of CO2 Corrosion in Oil-Water Pipe Flows

Jiyong Cai and Srdjan Nesic

[17] Principles and prevention of corrosion (2nd edition)

Denny A.Jones