Monitoring and Interpreting In Situ Combustion ProcessUSING CARBON ISOTOPE

AMBATI VENKATESH PE16M002 IITM

TABLE OF CONTENTS

INTRODUCTION OF INSITU COMBUSTION PROCESS AND TECHNIQUES INVOULED CARBON ISOTOPE CARBON ISOTOPE ANALYSIS DIFFERENT CARBON ∂ VALUES FIELD ANALYSIS AND INTERPRETATION CONCLUSION

IN-SITU COMBUSTION

In-situ combustion is basically injection of an oxidizing gas (air or oxygen-enriched air) to generate heat by burning a portion of resident oil.

PROCESS DESCRIPTION

Most of the oil is driven toward the producers by a combination of the following Gasdrive (from the combustion gases) WaterdriveBased on the respective directions of front propagation and air flow, the process can be either of the following Forward (when the combustion front advances

in the same direction as the air flow) Reverse (when the front moves against the air

flow)

PROCESS DESCRIPTIONForward combustion can be further characterized as either of the following Dry combustion Wet combustion

CARBON ISOTOPES

Carbon (C) has 15 known isotopes, from 8C to 22C, of which 12C and 13C are stable. The longest-lived radioisotope is 14C, with a half-life of 5,700 years

Carbon has two stable isotopes, 12C(98.89%) and 13C(1.11%).

The accepted unit of isotopic measurement is the ∂ value given in parts per thousand with the symbol °/00. The ∂13C value in °/00

The international standard is called Pee Dee Belemnite PDB because it is based on a belemnite sample taken from the Peedee formation of South Carolina.

Carbon isotope analysis

To determine the nature of reactions occurring during the in-situ combustion process and to identify wells in combustion communication.

Include the classic burning profile at the leading edge; super-wet or low-temperature combustion; a wide combustion zone with a secondary front, which is indicative of oxygen channeling; and carbonate decomposition in carbonate core

The carbon isotope study contributed to the understanding of the origin and behavior of CO2 and methane generated.

Carbon isotope data can assist in distinguishing the type of fuel consumed and the nature of the reactions occurring at the combustion front.

Carbon isotope measurements of CO2 and methane can be used to evaluate the communication paths between the injectors and producers in combustion projects.

Expected Carbon ∂ Values

o The figure shows the variations in the methane and Co2, ∂ values encountered for the combustion process.

o Different fields have different ∂ values depending on the composition of crude oil.

o ∂ values for the individual oil fractions can be heavier in the following order: saturates, bulk oil, aromatics, resins and asphaltenes.

HEATING PROCESS IN THE RESERVOIR

Reactions in In-situ combustion occur over a broad temperature range.

The air/oxygen then passes into the combustion zone, where it reacts with the deposited fuel to form CO2, CO, and water.

Ahead of the high temperature combustion region, thermal cracking produces a fuel, normally called coke, and volatile gases (such as methane and ethane).

Low-temperature oxidation (LTO)—heterogeneous gas/liquid reactions producing partially oxygenated compounds and few carbon oxides

Medium-temperature reactions—cracking and pyrolysis of hydrocarbons to form fuel

High-temperature oxidation (HTO)—heterogeneous H/C bond breaking reactions in which the fuel reacts with oxygen to form water and carbon oxides

In wet combustion- If the water/air ratio is increased to 2.25 to 2.81 kg/std m3 [400 to 500 bbl/MMscf], then the process is called super-wet combustion.(0.45 to 1.4 kg water/std m3 air[80 to 250 bbl water/MMscf).

Low co2 is produced in the LTO and in Super-wet combustion zone.

Carbon production during In-Situ combustion

Solution-gas methane of origin should have a ∂ 13C value near -60°/00.

Methane produced by bitumen pyrolysis should have a ∂ 13C value between -45 and -50°/00 (extensive cracking could produce methane with a ∂ 13C value of about -30 °/00.

CO2 produced from carbonates should have ∂ 13C values between +25 and -10 °/00.

CO2 produced from combustion of the oil should have a ∂ 13C value similar to that of the oil, which is near - 30° /00.

The non associated (dry) gases -25 to -45 °/00. Methane originating from bacterial

decomposition range from -60 to-80 °/00 Isotopic composition of thermally generated

methane is a function of the type of source material, the extent of thermal transformation.

Combustion-Tube Data

These runs covered different formation types (sandstone and carbonate), different oil types (heavy oil and bitumen), and different injection modes (dry, normal-wet, and super-wet).

The CO2 is analyzed with a stable isotope mass spectrometer constructed with Micro mass 903 components for carbon isotope analysis.

Field Analysis and Interpretation

Normally, the gas, oil, and water properties and rates are the only data available for interpreting a field project, without any temperature data.

whether ignition has occurred and the nature of the reactions occurring at the combustion front.

The early combustion responses are normally interpreted by gas analyses because these responses are seen within days or weeks at the production wells.

The normal parameter used to establish whether ignition has occurred is the absence of oxygen in the produced gas and an increase in the CO2 conc.

Continuation…. The H/C ratio used to indicate the nature of the

reactions at combustion. For high-temperature combustion, the H/C ratios

are normally in the range of 1 to 2. As the low-temperature reactions increase , the

H/C ratio also increases. Oxides/Nitrogen ratio is also used.(Low values low

temp. combustion). Another method is to use the oxygen/fuel or air/fuel

ratio. CO2 concentration, with a value typically in excess

of 13% showing that high-temperature combustion is occurring when air is the oxidant.

Continuation…..

Using above analyses for interpreting the reactions occurring in the field is always complicated by

The production of solution-gas methane and CO2 of carbonate origin, which dilute the combustion-produced gases and make it difficult.

The possibility of the CO2 dissolving in the oil and water.

Therefore, carbon isotope analysis used in conjunction with gas analyses.

It distinguishes the source of the methane and CO2 and the different burning characteristics.

CONCLUSION

Carbon isotopic signatures of CO2 will greatly increase confidence level in reservoir flood predictions and can be obtained at reasonable expense.

CO2 is highly mobile and detectable at low concentrations which makes it a powerful predicting tool in identifying breakthrough, well stimulation potential and injection profile

More importantly, it provides opportunities for operational changes that could result in improving the project economics

REFERENCE K. Rich and K. Muehlenbachs, “Carbon Isotope

Characterization of Migrating Gas in the Heavy Oil Fields of Alberta, Canada”.1995

Max S. Juprasert, Mark B. Haught, and Martin Schoell, Chevron Research & Technology Co. "Prediction of Steamflood Performance Using Carbon Isotope Signatures of CO2”.1999

Richard Hallam, and R. Gordon Moore etal. “Carbon Isotope Analysis: A New Tool for Monitoring and Interpreting the In-Situ Combustion Process”

http://petrowiki.org/In-situ_combustion

Enhanced Oil Recovery Proceedings of the third European Symposium on Enhanced Oil Recovery, held in Bournemouth, U.K., September 21-23,1981

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