data testing

7/27/2019 Data Testing

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Decision to test: First Evidence

Wellsite geologists (highly experienced team with local experience)document evidence for good reservoir and some minor oil fluorescence

Gas chromatography readings show best response within the bestreservoir section . Depth fits approximately with seismic flat spot.

Schlumberger wireline logs confirm reservoir in Bireno dolomite andBireno limestone sections. (This reservoir section produces oil in theclose by Guebiba field)

Schlumberger wireline logs allowed the interpretation of the presenceof hydrocarbons in analogy to the low resistivity log response withinsimilar carbonate rock formations of nearby oil fields.


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Data Gathering

Long edge 1.3mm

permeability

DOLOMITE

LIMESTONE

G A S S H O W

S

CAP ROCK (MARL)porosity


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More Data - More EvidenceASX anno unc ement , 26 Septemb er 2011

With the good reservoir indication just beneath the regional seal (ElHaria shale) and some evidence for hydrocarbons the decision wasmade to obtain additional information and run Schlumbergers XPT and

MDT test tools (pressure data, formation fluid sample) .

The XPT pressure data confirmed the presence of good reservoir sections and led to the interpretation of an oil column.

An oil sample with mud filtrate could be retrieved from the excellentquality Bireno Dolomite reservoir with Schlumberger MDT tool.

The sample was analyzed by Corelab in Aberdeen (Scotland) andfound to be typical of crude oils in the area around the Chorbane block.


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MDT sample analysis result byCorelab (Aberdeen) : crude oil

Oil Water column interpretationfrom pressure data

MDT (Schlumberger mini DST tool) oil sample onsurface

Data Evidence: Oil found

3200

3300

3400

3500

3600

3700

3800

1500 1550 1600 1650 1700

D e p

t h [ f t T V D m s

l ]

Formation Pressure [ psia ]

X PT 2 01 1- 09 -2 4 M DT /X LD M DT /PA

Optimistic OWC

30 meter oil columninterpreted as most likely

Oil GradientWater Gradient

conservative OWC

MDT oil sample

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Decision to test: Conclusions The existence of a possible oil discovery was supported by:

Presence of good reservoir (Bireno Dolomite)Oil samplePressure data

Uncertainties were:Wireline log interpretation in relation to oil and water saturation

because of low resistivity and missing information on water salinitiesand rock properties.

Depth position of possible Oil water contact.Reservoir quality of Upper Reservoir (Bireno Limestone).

DECISION UNDER UNCERTAINTY:ON THE 30th NOVEMBER 2011 THE JOINT VENTURE JOINTLY DECIDED TOPERFORM A WELL TEST. THE POSITIVE INDICATIONS DURING THE DRILLING

AND LOGGING PROCESS JUSTIFIED THE INVESTMENT. THIS DECISION WASSUPPORTED BY ETAP (Entreprise Tunisienne d'Activits Ptrolires).


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Test and perforate the deeper Bireno dolomite reservoir in order to achieve high flowrates from the best reservoir encountered during drilling

In case the lower good quality Bireno dolomite reservoir is mainly water bearing avoidthe risk of water break through (= only water flows from the high quality reservoir) andprotect any potential oil flow from the shallower lower quality Bireno limestone reservoir against water break through.

This was achieved by planning for a possible cement squeeze off and gap in theperforations.

FORMATIONWATER

Conservative OWC Best reservoir with fractures but possibly mainly water bearing

i so lat ing cement

CAP ROCK (SEAL)

OIL

Test Design: Objectives


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CAP ROCK(SEAL)

What happened?

Test 1:Perforate both reservoir zones and establish flow

Highpermeabilityfracturedreservoir

16 meters

5 meters

16 meters

5 meters

The perforations through the casing were successfullycompleted and connection between the wellbore and the tworeservoir sections were established.

The fluid analysis of the produced fluids (approximately 90barrels) revealed that a mixture of drilling mud filtrate, well

test fluid and possibly some formation water was produced.

Since the well flowed without any acid stimulation it wasconfirmed that good reservoir had been encountered.

The Lower Bireno Dolomite reservoir was mainlycontributing to the influx of mud filtrate and some formationwater either because of the OWC in reality being close tothe conservative interpretation, or because of a fracturenetwork extending into the water leg.


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CAP ROCK(SEAL)

Cement Job after Water inflow

Due to the (much) higher permeability of the lower reservoir, any oil in the lower permeability upper reservoir would be inhibited from flowing. (Analogy: 100% water cut well after water break through inside an oil field)

Therefore the Joint Venture decided to cement off the

lower reservoir as per well test design plan in order toprevent water influx from the good quality fractured lower dolomite reservoir.

Following acid stimulation the upper limestonereservoir started to flow with the help of nitrogen lift.

After approximately 680 bbls of fluid production over 35 hours with no oil flow the test was abandoned.

Any oil left behind would be non commercial.

water

Highpermeability

fracturedreservoir

oil sample

Test 2:Flow for 35 hours


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CAP ROCK(SEAL)

Explanation: Water break throughand low oil Saturation

Water saturation

R e

l a t i v e p e r m e a

b i l i t y OIL

WATER

100% water flow

Source: Schlumberger

Different wettabilities

Relative flow capacities of oil versus formation water

The good quality Bireno dolomite was perforatedalso into the water leg. Therefore only mud filtrate andhighly mobile formation water could enter the wellbore(only 90 bbls). This situation might have been amplifiedby fractures.

The small oil column in the uppermost Birenodolomite proven by the MDT oil sample was unable toflow against the highly mobile water.

The revised petrophysics based on the newformation water salinity data indicated LOW OILSATURATIONS . In combination with the reservoir being possibly more oil wet than water wet (commonin carbonate rocks) this causes the trapped oil to beIMMOBILE and only water can flow.


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CAP ROCK(SEAL)

Conclusion: Sidi Dhaher is anon-commercial Oil Discovery

The combination of low oil saturation and water influx from the lower good quality reservoir due to theOWC being shallower than assumed explains both thetest results and data obtained in the drilling phase:

1. Thin oil column in Lower Bireno reservoir

section2. Water Break Through3. Preferential flow of water over oil in lower

quality reservoir because of lower oilsaturation and possible oil wet carbonate.

With this additional information obtained during thewell test it can be concluded to date that the Birenodolomite reservoir has only a small non commercial oilcolumn and that the upper Bireno limestone reservoir would not be able to flow freely at commercial rates.

MDT oil sample

Low OilSaturation

Water

LowPermeability

Rock

HighPermeability

Rock

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