DOC ID© Chevron 2005

Using Sensors to Monitor Biodegradation in the subsurface

Dong LiChevron Energy Technology CompanySeptember 19, 2008

Sensors© Chevron 2007 2

Why Use Sensors?

Diurnal Changes in Pressure and Concentration

-5-4-3-2-10123456

0 1 2 3 4 5 6 7 8 9Time (day)

Con

cent

ratio

n (p

pm)

Pre

ssur

e (0

.1"

H2O

)Combustable gas concentration near surfaceDifferential pressure between 0 - 40 fbg

Sensors© Chevron 2007 3

What is the Problem?

Aeration

HC

Aerobic

Anaerobic

CO2

O2

O2

Scr

een

CO2

Groundwater

Hydrocarbons degrade readily in most environment

Sensors© Chevron 2007 4

Why Monitor Biodegradation?

Hydrocarbon biodegradation process is normally not visible

There is no easy way to determine:

Is it working?

How long will it take?

Any Process adjustment?

aeration rate, water, nutrients, …

When can we stop?

Monitoring is the key to bioremediation success

Sensors© Chevron 2007 5

What to Measure?

Physical Parameters:

Temperature, Pressure, Flowrate,

Groundwater Level, ...

Chemical Parameters (for Petroleum HC):

TPH, BTEX, VOC, pH, O2, CO2, ...

Biological Parameters:

Nature and population of microorganisms,

Biological activity indicators (O2, CO2, ...)

Sensors© Chevron 2007 6

Parameters in Biodegradation of Petroleum Hydrocarbons

O2 + HnCm CO2 + H2O

Sensors© Chevron 2007 7

How to Measure?

Soil GasSensor

Sens

or in

-wel

l mea

sure

men

t

Sens

or in

-soi

l mea

sure

men

t

Soi

l gas

sam

plin

g an

d an

alys

is

SoilProbe

Sensors© Chevron 2007 8

Hydrocarbon Sensors in Monitoring Well

0

1000

2000

3000

4000

5000

0 1 2 3 4 5 6 7

Time (day)

HC

Con

cent

ratio

n (p

pm) Figaro 813

Adsistor

Sensors© Chevron 2007 9

Soil Gas Concentration vs. Depth Profiles

0

4

8

12

16

20

0 10 20 30 40

Depth (ft)

O2

(%),

CO

2 (p

pm

)B

enze

ne

(pp

m)

0

200

400

600

800

1000

H2

(pp

m)

Oxygen (%)Carbon Dioxide (%)Benzene (ppm)Hydrogen (ppm)

Sensors© Chevron 2007 10

0

5

10

15

20

9/1/95 9/3/95 9/5/95 9/7/95 9/9/95 9/11/95Time

Oxy

gen

(%) 20 ft

30 ft

35 ft

40 ft

Diurnal Changes in Oxygen Concentration

Sensors© Chevron 2007 11

Hydrocarbon Concentration Measurements During Vapor Extraction

3600

390 44

11500

190 210

2000

4000

6000

8000

10000

12000

14000

0 20 40 60 80 100

Time of Aeration (day)

HC

Co

nce

ntr

atio

n (

pp

m)

Adsistor-1Adsistor-2Probe-1Probe-2

* Li, D.X., “Soil Bioremediation Monitoring Using Chemical Sensors,” Proceedings on Field Analytical Methods for Hazardous Wastes and Toxic Chemicals, pp. 783-790, January 29-31, 1997, Las Vegas, NV

Sensors© Chevron 2007 12

Biodegradation of Petroleum Hydrocarbons

O2 + HnCm CO2 + H2O

HC degradation rate can also be measured by the rate of oxygen consumption and carbon dioxide production.

Sensors© Chevron 2007 13

In-Situ Respiration Test Using Oxygen Sensors at Air Injection Rate of 8 CFM

0

5

10

15

20

12:00 18:00 0:00 6:00 12:00 18:00 0:00 6:00 12:00 18:00 0:00

Time of Day (hour)

Oxy

gen

Con

cent

ratio

n (%

)

Oxygen Sensor @ 5 ft

Oxygen Sensor @ 10 ft

Oxygen Sensor @ 20 ft

Sensors© Chevron 2007 14

In-Situ Respiration Test Using Carbon Dioxide Sensor at Air Injection Rate of 3 CFM *

0

5

10

15

20

10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00Time

O2

Rea

ding

s (%

)

0

2500

5000

7500

10000

12500

CO

2 R

eadi

ngs

(ppm

)

O2 Sensor

CO2 Sensor

Pump onPump off

* Li, D.X. "In Situ Respiration Measurement Using A Subsurface Carbon Dioxide Sensor," Air & Waste Management Association, 96-FA158.02, Nashville, TN (1996)

Sensors© Chevron 2007 15

Biodegradation of Petroleum Hydrocarbons

O2 + HnCm CO2 + H2O

HC degradation rate can also be measured by the rate of heat generation

Sensors© Chevron 2007 16

Schematics of Sensor Installation

OxygenSensor

T-1T-2T-3

Temperaturesensor

HCSensor

Datalogger

SandPack

20

80

60

40

1 inch Geoprobe

SVE-4

6 inch HS

Sensors© Chevron 2007 17

HC

0

5

10

15

20

25

30

35

40

45

50

11/1 11/3 11/5 11/7 11/9 11/11 11/13 11/15 11/17 11/19 11/21

Time

O2

(%) /

T (C

)

0

5000

10000

15000

20000

25000

30000

35000

40000

45000

O2 - 20 ft

O2 - 30 ft

O2 - 60 ft

O2 - 70 ft

T - 20 ft

HC - 20 ft

Temperature, Oxygen, and HC at T1

Sensors© Chevron 2007 18

Oxygen and Temperature at T2

O2

60

70

80

90

100

110

120

130

140

12/2/07 12/7/07 12/12/07 12/17/07 12/22/07 12/27/07 1/1/08 1/6/08 1/11/08 1/16/08 1/21/08

Time

Tem

pera

ture

(F)

0

1

2

3

4

5

6

7

8

T 18 ft

T 28 ft

T 38 ft

T 50 ft

T 60 ft

T 80 ft

O2 40 ft

O2 70 ft

Sensors© Chevron 2007 19

What is the Opportunities and Challenges?

Sensors are available, reliable, and cheap.

Installation and data collection are expensive.

A large potential user base exist.

Innovation is slow in a mature industry and a regulatory driven world.