Sandstone acidizing

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Sandstone Acidizing

Behzad Hosseinzadeh

Spring 2015 Number of slides : 33 Supervisor: Dr. Aghighi

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IntroductionSandStone Acidizing

The main aim of matrix acidizing is to improve production and reduce skin by: Dissolving formation damage Creating new pathways around the wellbore

Matrix acidizing should be below fracture pressure. Sandstone acidizing is performed for two primary purposes:

Perforation breakdown (The fracturing of a perforation tunnel ) :It is sometimes necessary to break down perforations by temporarily pumping acid above fracturing pressure to initiate production or injection of a subsequent treatment,such as hydraulic fracturing. Typically, HCl is used in concentrations ranging from 5% to 20%, with 15% HCl being standard.

Near-wellbore formation damage removal :The primary purpose of matrix acidizing in sandstones is to remove formation damage caused by clay and other siliceous fine particles

plugging near-wellbore permeability.

Introduction

History

Chemistry

General Procedure

Six Steps

Field Operation

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HistorySandStone Acidizing

Because of the growing excitement surrounding acid treatment of limestone (Carbonate rocks) formations throughout 1932, interest in developing treatments for sandstone formations began growing too.

In May 1933, Halliburton conducted the first sandstone acidizing treatment using a mixture of HCl and hydrofluoric acid (HF).

Unfortunately, the results of this first attempt were very discouraging. The reaction of the strong acid solution in the formation caused substantial sand production into the wellbore.

Consequently, use of HCl-HF was not very popular for the next 20 years. Many sandstone acidizing treatments have been pumped since, without such

understanding of purpose and potential. In 1965, the study by Smith and Hendrickson removed much of the mystery in HF

acidizing for petroleum engineers and led the way to improved design practices. The most important result of this work was the development of tapered HF treatments, with HCl preflush and overflush, to inhibit deposition of plugging reaction products.

Introduction

History

Chemistry

General Procedure

Six Steps

Field Operation

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Chemistry SandStone Acidizing

Matrix acidizing of carbonates and silicates are worlds apart. sandstone acidizing, the reaction between HF and sandstone is much slower. In sandstone formations, matrix acidizing treatments should be designed primarily

to remove or dissolve acid-removable damage or plugging in the perforations and in the formation pore network near the wellbore.

Matrix treatment of an undamaged formation cannot be expected to significantly increase production.

In carbonate formations, matrix acidizingworks by forming conductive channels, called wormholes, through the formation rock. These penetrate beyond the near-wellbore region,or extending from perforations.

If a carbonate formation is undamaged, a matrix acidizing treatment probably cannot be expected to do more than double theproduction rate.

Introduction

History

Chemistry

General Procedure

Six Steps

Field Operation

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Don’t ever touch a sandstone unless you know about the mineralogy of the rock. It is better to leave the well as it is

In carbonates, we dissolve the rock itself by acid to generate wormholes. In sandstones, we remove the damaging material and not dissolve rock matrix as it will require huge volume of HF.

Carbonates (Calcite or Dolomite) may be present up to 20-30% by weight in sandstone. It is very complicated to acidize such formations containing >20 wt% carbonates as we should not use HF as CaCO3 or CaMg(CO3)2 will react with HF to form Calcium Fluoride and Magnesium Fluoride respectively, which precipitate.

Introduction

History

Chemistry

General Procedure

Six Steps

Field Operation

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Sandstone

QuartzReacts with HF

Clays, feldspar and micas

Precipitate in reaction with HF

The m

ain pro

blem is

to so

lve th

is

precip

itation

HF + these minerals = CaF2 (precipitates easily)

Introduction

History

Chemistry

General Procedure

Six Steps

Field Operation

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Sandstone Acidizing General ProcedureSandStone Acidizing

A preflush of 15% HCl with additives of at least 50 gal/ft to scrub away all CaCO3 ahead of the HF mix to prevent calcium flouride precipitants.

Follow with correct HF/HCL mix at a minimum of 50 gal/ft or 25 gal/perforation with correct corrosion, anti-sludging, and iron sequestering additives.

Post flush with 15% HCL with additives in a volume of at least twice the HF mixture volume. This prevents precipitants forming with displacement fluids. These fluids could be diesle, brine, or weak HCl to displace the main flush from the wellbore

Oil reservoir post flush is either 15% HCL or diesel followed by field brine or 2 % KCL diesel, followed by field brine or 2 % KCL.

In gas reservoirs or injection wells it is 15% HCL followed by field brine or 2% KCL.

Flow or swab the acid volume out immediately to prevent damage.

Introduction

History

Chemistry

General Procedure

Six Steps

Field Operation

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Main FlushSandStone Acidizing

Introduction

History

Chemistry

General Procedure

Six Steps

Field Operation

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Six Steps to Successful Sandstone Acidizing

SandStone Acidizing

Success rate in carbonate acidizing is >95 while in sandstone, it is barely 40% as there are so many minerals in sandstones as compared to carbonates.

1. Determine Whether Acid-Removable Skin Is Present 2. Determine Appropriate Fluids, Acid Types,

Concentrations, and Treatment Volumes3. Establish a Proper Treatment Additive Program4. Determine Treatment Placement Method5. Ensure Proper Treatment Execution and Quality Control6. Evaluate the Treatment

Introduction

History

Chemistry

General Procedure

Six Steps

Field Operation

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SandStone Acidizing

ONE. Determine Whether Acid-Removable Skin Is Present Skin damage must be present, but it must be acid removable

Introduction

History

Chemistry

General Procedure

Six Steps

Field Operation

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SandStone Acidizing

TWO. Determine Appropriate Fluids, Acid Types, Concentrations, and Treatment Volumes

The injection string (production tubing, drill pipe, and coiled tubing) should be pickled prior to pumping the acid treatment.

This stage is applicable in oil wells in which the crude may not be compatible with acid mixtures used or in which organic deposition is believed to be present. It

calcium chloride in solution mixes with formation brine.

this is the case, a separate acetic acid stage may be needed to reduce iron precipitation potential.

The main purpose of the preflush is to dissolve carbonate minerals in the formation prior to injection of the main HF mixture.

The purpose of the main acid stage is to dissolve siliceous particles that are restricting near-wellbore permeability, plugging perforations or gravel packs.The purpose of the overflush is to displace the HF phase away from the wellbore

Introduction

History

Chemistry

General Procedure

Six Steps

Field Operation

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SandStone Acidizing

THREE. Establish a Proper Treatment Additive Program With respect to acid additives, the following are common causes of

treatment failure: Additive misuse Additive overuse

Corrosion inhibitor and inhibitor intensifier Iron control agent Water-wetting surfactant Mutual solvent Alcohols Nonemulsifier/demulsifier Antisludging agent Clay stabilizer Fines-stabilizing agent Foaming agent Calcium carbonate/calcium sulfate scale inhibitor Friction reducer Acetic acid (additive to HCl-HF)

Introduction

History

Chemistry

General Procedure

Six Steps

Field Operation

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SandStone Acidizing

FOUR. Determine Treatment Placement Method There are two basic methods of acid placement to achieve full

coverage of the desired treatment interval: Mechanical placement

isolation (packers), ball sealers, coiled tubing Chemical diversion

Polymer gels, foams, oil-soluble resins, rock salts, and surfactant gels

Introduction

History

Chemistry

General Procedure

Six Steps

Field Operation

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SandStone Acidizing

• FIVE. Ensure Proper Treatment Execution and Quality Control(Safety at the job site, Quality control during rig-up of equipment, Quality control before pumping, Quality control during pumping, Quality control after pumping /during flowback) (produced a booklet BY King and Holman of the Amoco Production Company)

• SIX. Evaluate the Treatment Treatment evaluation involves the following:

Pressure monitoring during injection Flowback-sample analysis Production-rate comparison and analysis Well test analysis (skin removal) Payout and return on investment (ROI)

Introduction

History

Chemistry

General Procedure

Six Steps

Field Operation

Sandstone acidizing

Engineering

Transcript of Sandstone acidizing