Group KMSc. Petroleum Engineering

LONDON SOUTH BANK UNIVERSITY,UK.

Group K -members Ilya Pushkarev 2936077 Mike Arhin 2935901Musa Muhammed 2933794 Samuel G. Emenogu 2933966 Uzochukwu A. Morah 2922166

Contents Introduction Effects of Formation Damage Causes of Formation Damage Control and Remediation The Concept of Acid Stimulation

Introduction Formation Damage can be described as the

reduction in permeability in the reservoir rock due to the infiltration of drilling or treating fluids into the area adjacent to the well bore.

It occurs in the near bore region of the formation (reservoir) where radial flow is dominant.

It results from a combined reduction in porosity and permeability in the near well bore region of the formation.

Understanding and preventing Formation

Damage should be the responsibility of every Oilfield professional because it is the main reason many Oil and Gas wells produce at rates that fall far-short of their theoretical capabilities. (Sub-optimal Oil production)

This phenomenon also impairs injection and disposal wells, thereby limiting the efficiency of pressure maintenance schemes and increasing operating costs.

Effects of Formation DamageSwelling of clays The swelling of clays reduces

permeability

Mud filtrates and formation fluids

Formation of emulsions which reduces permeability

Invasion Drill solids invade into the formation matrix thereby causing skin effect and reducing porosity.

Well performance Reduction in flow efficiency in the near well bore formation during the various phase of oil and gas production

Table 1

Fig 1, Source: B. Bennion, 1999

The are four primary mechanisms of formation damage:

1. Mechanical 2. Chemical 3. Biological

4. Thermal

Mechanical Formation Damage• Caused by a direct, non-chemical, interaction between the equipment or fluid used and the formation.

• This result in a reduction in the permeability of the formation.

• Changes in the properties of the reservoir fluids during production operations.

1. Fines Migration

2. External Solids Entrainment

4. Glazing/Mashing

5. Geomechanics

Mechanical Impairment Mechanism

e.g. migration of potentially transportable materials (Clays).

e.g. Invasion of particulate matter suspended in drilling fluid.

e.g. Capillary pressure and relative permeability effects.3. Phase Trapping and Blocking

e.g. Damaged caused by bit/heat into the formation face.

6. Perforation Damage

Chemical Formation Damage

Interactions between the introduced fluids and the rock formation.

• Clay swelling - Hydration of hydrophilic clays (e.g. smectite).

• Clay deflocculation - Kaolinite is a non-water sensitive clay.  

• Chemical adsorption - Polymers and high molecular weight materials present in fluids can bound to surfaces.

• Paraffins & Waxes - Low cloud point temperatures result in crystallization of alkanes and waxes

 

• Emulsions - Water in oil emulsions exhibit high viscosity.

Biological (Microbial) Formation Damage

• Plugging - Secretion of viscous polysaccharide polymers as a by-product

• Corrosion- Electro kinetic hydrogen reduction reaction can result in pitting and H2 stress cracking on metallic surfaces downhole

• Toxicity- SRB reduce elemental sulphate which may be present in formation/injection water and create H2S

 

Thermal Formation DamageDamage mechanisms which are associated with the high temperatures

• Mineral transformation - Above 180oC non reactive clay species may be catalyzed and form hydratable reactive products

 

• Dissolution – Mineral solubility increases with temperature .  

• Wettability alterations– Formations become more water wet as temperature increases

Control and remediation of formation damage.

Ensure adequate formation evaluation;

Use of specially design drill- in- fluids or work over and completion fluids thereby minimizing formation damage;

Use of formation heat treatment in the near wellbore region;

Sand control mechanism;

Use of improved perforation techniques (underbalanced perforation, removal of crushed zones and other perforating debris);

Hydraulic Fracturing.

Control and remediation of formation damage

Fig 2. Formation damage impairs productivity.

Mueche, W. T. (1982) Principles of acid simulation

ACID STIMULATION

• Acid stimulation is the process by which mineral impairment in the near wellbore region of the formation is removed or reduced by the action of acid on the mineral deposit. It helps increase production by improving flow into the wellbore.

• Impairment is caused by pore throat filling by drilling chemicals, completion fluids and debris jetting into perforation channels by perforation.

ACIDISATION MECHANISMMechanism is made effective by spotting the

chemical or debris down hole with the use of the coiled tube. The chemical is pumped through the pipe and jetted directly onto the damaged area.

The chemicals dissolve the materials restoring permeability in the process and the reservoir fluids will flow into the wellbore cleaning out what is left of the damaging material.

TYPES OF ACIDISATIONTYPES ACTIVITY

Mud Acid •Mixture of HF and HCL.•It dissolves silicate material.•Cannot be used in carbonate reservoirs because of acid reactions.

HCL Acid wash •Uses HCL solution to remove calcium based deposits around wellbore.

Fig 3. N.I. Al-Mulhem et al 2010Table 2

RECOMMENDATIONS

After in depth analysis the following course of action is recommended :• Reduction in the density of drilling fluids in order to reduce fluid invasion into the formation during completion operations.• Improve drilling fluid rheology to provide better fluid loss control, and thus better cleanup potentials.

R.F Krueger: ‘An overview of Formation Damage and Well Productivity in Oilfield Operations’: An update , SPE 17459, presented at the SPE California Regional meeting held in Long Beach, California, March 23-25, 1988 (Accessed 13th May, 2011)

N.I. Al-Mulhem et al: ‘A Smart Approach in Acid Stimulation Resulted in Successful Reviving of Horizontal Producers Equipped with ICD Completions: Saudi Arabia Case History’ SPE 127318, presented at the 2010 SPE International Symposium and Exhibition in Formation Damage Control held in Lafayette, Louisiana, USA, 10 – 12 February 2010 (Accessed 6th May 2011)

Ismail Mohammed El-Haib; ‘Production Improvement of Formation Damaged Wells by Proper Acid Treatment’; SPE 128433, presented at the SPE North Africa Technical Conference and Exhibition held in Cairo, Egypt, 14-17 February 2010 (Accessed 6th May 2011)

Farouk Civan; ‘Reservoir Formation Damage’; Gulf Publishing’; Gulf Publishing Company, Houston, Texas, 2000. (Accessed 31st May, 2011)

Bennion, D.B., et.al; ‘Remediation of Water and Hydrocarbon Phase Trapping Problems in Low Permeability Gas Reservoirs.’ CIM Paper 96-80. (Accessed 31st May 2011).