WIRELINE LOGGING RESPONSE AND TRUE CORE ANALYSIS OF …

Vol.51, No.2, 2018

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WIRELINE LOGGING RESPONSE AND TRUE CORE ANALYSIS

OF THE UPPER SHALE MEMBER OF ZUBAIR FORMATION,

RUMAILA OILFIELD, SOUTHERN IRAQ

Mohanad H. Al-Jaberi1 and

Hayder K. Al-Mayyahi*

1Department of Geology, College of Science, University of Basra, Basrah, Iraq

*Basra Oil Company, Basra, Iraq, e-mail: [email protected]

Received: 10 April 2018; accepted: 15 May 2018

ABSTRACT Sedimentary rocks can be defined from others not only by their lithology,

structures, fossil content, geometry and sedimentary but furthermore by their general

response to the wireline logs. This study involves the determination of the properties

of Upper Shale Member of Zubair Formation (Lower Cretaceous) in Rumaila oilfield

by using several log interpretation software through wireline logging response of

lithology. Many wells were chosen in Rumaila oilfield to know the lithology of Upper

Shale Member, in addition to calculating permeability for Rumaila oilfield by using

eight wells through Rumaila cross-section. The Gamma Ray log responses of clean

sand range between 30 – 40 API, while it decreased in the case of silt and clay

cemented sand grain. Sandstones are dominated in the south of Rumaila, this could

increase the porosity and permeability of the rocks. While clay and shale are

dominated in the north of Rumaila. Log responses don’t give a true representation for

formation lithology if comparison with true core lithology by using grain size

analysis.

Keywords: Electrofacies; Zubair Formation; Rumaila oilfield; Wireline log

INTRODUCTION Electrofacies analysis is important to clarify the lithological type from wire logging

responses and then to interpret reservoir limited and characterize (Schmitt et al., 2012).

The main element to determine electrofacies is log and core data integration.

Recognition of electrofacies in various types of depositional environments can be

reached through inductive and deductive practices (Marwanza and Nas, 2017(. The term

electrofacies was originally defined as a set of logs response that characterizes a bed and

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Iraqi Geological Journal Al-Jaberi and Al-Mayyahi Vol.51, No.2, 2018

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authorized it to be distinguished from the others (Serra and Abbot, 1980). Electrofacies

are based on properties taken from incessant remote measurements at scales starting

from one meter and more, while geological facies are based primarily on observational

characteristics taken at scales down to millimetres (Doveton, 1994). Electrofacies are

defined as a set of technologies used typically to provide assistance in performing

sequence stratigraphy and recognize rock types with common properties. However,

electherofacies can’t totally determine geology facies (Ramezani et al., 2017). Such a

useful lithofacies can result from orthodox core description combined with wireline log

data due to the wireline log data are related to petrophysical parameters including

permeability, water saturation and porosity (Hwan Woo et al., 2018). In this study, open

hole logs (spontaneous potential, gamma ray, caliper, shallow-medium and deep

resistivity, neutron, density, sonic, photoelectric factor and nuclear magnetic resonance)

were calibrated depending on the lithological discrepancies defined in the core samples.

The potential capability of multivariate analysis in distinguishing each electrofacies was

analysed based on recognition of geological facies within the core samples.

Encouraging results were acquired after applying such techniques mouth bars;

distributary channels, porosity-permeability relationships were established depending

on the defined electrofacies. This study is going to discuss the electrofacies application

using wireline log and true core analyse on the Upper Shale Member of the Zubair

reservoir to define the reservoir characterization.

THE STUDY AREA The Rumaila oilfield is located of about fifty Km to the northeast of North Luhais

oilfield in the Basrah city, southern Iraq. The field lies approximately between

longitudes 30° 13' – 30° 24', and latitudes 47° 14' – 47° 19' (Fig. 1). Rumaila oilfield is

located of about fifty km to the west of Basra city covering an area of 1800 Km2. The

Rumaila is the biggest oilfield in Iraq. It was discovered in 1953 and in 1972 started in

operation; it is a 6th globally, with oil reserves of about 17 billion barrels.


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Fig. 1: Location map shows the Rumaila oilfield; Permeability wells,

Core samples wells

METHODS The petrophysical data was processed by employing deductive and inductive

approaches so as to get the most from both methods (Doveton, 1994; Moss, 1997). The

first step of the integrated approach is the application of hierarchical clustering methods

to identify electrofacies groups using log curves (Saikia and Baruah, 2017). Deductive

approaches include those procedures that seek to distinguish the data by the calculation

of a set of component proportions that can be identified through linking with wireline

log data by some set of response equations (Moss, 1997). In this research, the Rumaila

wells project were examined by Petrel software for distributing net sand and calculate

the porosity for all Rumaila oilfield. The best cross-section that passes through eight

wells were chosen, four wells in the south (Ru-382, Ru-385, Ru- 387 and 456) and four

in the north (R-516, R-522, R-520 and R-564) to measure permeability through NMR

wireline log by Techlog software. The model was build taking into account the

components and variables numbers (curves of data). Generally, mismatches and gross

errors detection measurements are comprised in the practices although mathematical

constancy cannot be guaranteed of geological accuracy. This situation is well

represented by standard log analysis. On the contrary, an inductive approach establishes

their classes or transformations rely on the data set and don't rely on any pre-determined

R-572

Ru-387

Ru-215

Ru-387

R-031


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correlation between the components. These procedures tend to isolate distinctive

patterns and to derive classifications or new variables that may be interpreted with a

physical meaning. Real lithology representation with wireline log responses chose two

core samples (R-031and Ru-215) and focused on grain size analysis of Upper shale

units’ depth (Table 3) and comparison with wireline log by Geologix software.

Many companies made charts for electrofacies depending on wireline logging

response such as Schlumberger, Weatherford, Halliburton, Allied-Horizontal and Baker

Atlas (Table 1 and Figs. 2 and 3). The response of facies are not fixed values, for

example shale response from wireline logging ranges 58.8 – 143.0 in sonic log,

2.2 – 2.7 in density log, 12.0 – 4.3 in resistivity log and 4.65 in PE log. But the sandston

facies response in Sonic log is 62.5 – 86.9, 2.65 in density log, 12.58 – 8.20 in

resistivity log and 1.81 in PE log. Log value in Table (1) and Figure (2) gives indicators

of formations lithology but it cannot represent true lithology due to log values with

lithology has been different for service companies of wireline log.

Table 1: Acoustic characteristics of common formations (Schlumberger, 1989)

Material Porosity

(%)

∆t

(µs/ft)

Sound Velocity Acoustic Impedance

(MRayl) (ft/s) (m/s)

Dolomite 5 – 20 50.0 – 66.6 20,000 – 15,000 6,096 – 4,572 16.95 – 11.52

Limestone 5 – 20 54.0 – 76.9 18,500 – 13,000 5,639 – 3,962 14.83 – 9.43

Sandstone 5 – 20 62.5 – 86.9 16,000 – 11,500 4,877 – 3,505 12.58 – 8.20

Sand 20 – 35 86.9 – 111.1 11,500 – 9,000 3,505 – 2,743 8.20 – 6.0

Shale 58.8 – 143.0 17,000 – 7,000 5,181 – 2,133 12.0 – 4.3

Different minerals with different GR counts

Fig. 2: GR log responses in rock types (Gillen et al., 2007)


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Fig. 3: Atlas of log responses (2003) in (Gillen et al., 2007)


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THE RESULTS 1. Wireline logging response application in the south and north Rumaila oilfiled

The coordinates of the studied wells are tabulated in Table (2). The Wireline log

technique was applied on well Ru-215 (south Rumaila) and R-031 (north Rumaila) to

analyses and interpret the electrofacies in these oilfields. The results were compared to

the standard electrofacies (Figs. 4 and 5).

Table 2: Coordinates of wells in the study area

Well No. Easting (m) Northing (m)

Ru-215 729359.14 3338853.89

R-031 725533.05 3371289.2

2. Porosity and net sand distribution

The distribution of porosity and net sand were displayed in Figures (6 and 7)

depending on electrofacies charts that used a cross-section for several wells penetrating

the Upper Shale Member in the Zubair Formation using petrel program. The sand ratio,

sand thickness and porosity increase in the south of Rumaila. Reflecting different

petrophysics properties in both south and north Rumaila. The south Rumaila is better

and these good indicators for high producing oil where decline in the north of Rumaila.

In addition, eight wells are chosen in all Rumaila to calculate the permeability through

NMR wireline log by Techlog program which illustrated by Figure (8). Permeability in

the south of Rumaila is high and better that in the north of Rumaila which observed of

low permeability.

3. Core grain-size analysis

Core samples are a major source of information for evaluation, exploration,

development, and production of any hydrocarbon reservoir (Tavakoli, 2018). Quartz is

the greatest abundant mineral ratio among main component grains reaching more than

96% sandstone and approximately 4% mixing between silt and clay in the Upper shale

of Zubair Formation in south Rumaila (Table 3). In the north of Rumaila, the quartz

content is 75% and 15% mixing as silt and clay (Table 3). The grain size analysis for

core samples gives a true lithology interpretation for the formations plus real porosity

and permeability measurement, the accuracy of this procedure is high because it is a

direct measurement.


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Fig. 4: Electrofacies analysis of Ru-215 South Rumaila oilfield

USM= Upper Shale Member unit


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Fig. 5: Electrofacies analysis of the R-031 North Rumaila oilfield

USM: Upper Shale Member unit


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Fig. 6: Porosity distribution in Rumaila oilfield


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Fig. 7: Distribution of net sand in Rumaila oilfield


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Fig. 8: Permeability distribution (average) of the Upper Shale Member

in Rumaila oilfield

Table 3: Grain size analysis

South Rumaila

Depth Upper shale unit Sand% Clay% Silt%

3145.66 USM20 96.0005 1.675 2.3245

3175 USM30 83.621 1.625 14.754

3194 USM40 87.8535 3.4 8.7465

3203 USM50 98.267 1 0.733

3215 USM 60 92.342 3.575 4.083

3218 USM65 95.7625 1.9 2.3375

North Rumaila

Depth Sand% Clay% Silt%

3211 USM20 83.9576 6.7 9.34238

3224 USM30 74.3214 6.325 19.3536

3271 USM40 76.0129 4.25 19.7371

3277.8 USM50 80.1448 5.125 14.7302

3281 USM 60 78.3452 6.85 14.8048

3290 USM65 83.0643 5.625 11.3107

DISCUSSION The GR log doesn’t give a true representation of formation lithology because the

sand grains may be covered with clay, in this case, Gamma Ray behaviour would

indicate a response similar to shale. On the other hand, the core grain-size analysis

showed domination of the sandstone in Rumaila oilfield which doesn’t follow the log

reflection, thus in Upper Shale Member 20 (USM20) to Upper Shale Member 60

(USM60) units; The ratio of sand in South Rumaila is 96% where as in North Rumaila


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is 83%, where the electrofacies results indicated that the sand content is lower than that

of core sand, furthermore the electrofacies shale interpretations does not give a true

representation, for example, GR reading in shale is more than (70 API) but indicated

that the clay minerals give similar values of Kaolinite 80 – 130 and Illite 250 – 300 API

depending on Gillen et al. (2007) (Fig. 2).

This study recommends calibrating the wireline logs with core grain size analysis in

both south and north Rumaila by calculating sand ratio information and taking into

account the silt and clay percentage in true formation lithology.

CONCLUSIONS Generally, the properties of Upper Shale Member (porosity, permeability and net

sand) were high in the south of Rumaila oilfield and gradually decrease towards the

north. Moreover, the study presented according to wireline log analysis’s that the Upper

Shale Member has a several sand unit with higher thickness in south of Rumaila, while

in the north of Rumaila, the sand units are less and a bit thicker. For this reason,

Rumaila oilfield has high oil production in the south of the field, and less in the north.

Furthermore, the grain size analysis showed that the sand units in the north Rumaila are

covered by clay and silt which cause decreasing in the porosity and permeability of the

formation.

REFERENCES Allied-Horizontal-Wireline www.indeed.com/cmp/Allied-Horizontal- Wireline Services/reviews?

fcountry=US&floc=Pleasanton%2C+TX

Doveton, J., 1994. Geologic Log Analysis Using Computer Methods. AAPG Computer Applications in

Geology, No.2, 169pp, Tulsa.Ed. Developments in Petrophysics, Geological Society Special

Publication (122): 181 – 252.

Gillen, M., Engels, O.G., Gilchrist, W.A., Trcka, D.E., Kruspe, T. and Chen, S., 2007. U.S. Patent No.

7,301,338. Washington, DC: U.S. Patent and Trademark Office.

Hwan Woo, J., woo Rhee, C. and hwa Jin, J., 2018. Electro facies calssification of Horn River shale by

Multi Resolution Graph-based Clustering.

Moss, B., 1997. The partitioning of petrophysical data: a review. In Lovell and Harvey.

Ramezani, A.A., Rahimpour, B.H., Kamali, M., Moussavi, H.R. and Kadkhodaie, A. 2017. 2017351

depositional Environment, Electrofacies and Sequence Stratigraphy of the Fahliyan Formation

(Lower Cretaceous), Abadan Plain.

Serra, O. and Abbot, H., 1980. The contribution of logging data to sedimentology and stratigraphy. SPE.

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Schlumberger log interpretation chart, 1989. Schlumberger log interpretation charts. Schlumberger

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Schmitt, P., Veronez, M.R., Tognoli, F.M., Todt, V., Lopes, R.C. and Silva, C.A. 2012. Electrofacies

Modelling and Lithological Classification of Coals and Mud-bearing Fine-grained Siliciclastic

Rocks Based on Neural Networks. Earth Science Research, 2(1): 193.

http://www.indeed.com/cmp/Allied-Horizontal-%20Wireline%20Services/reviews?%20fcountry=US&floc=Pleasanton%2C+TX

http://www.indeed.com/cmp/Allied-Horizontal-%20Wireline%20Services/reviews?%20fcountry=US&floc=Pleasanton%2C+TX


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Saikia, K. and Baruah, C., 2017, April. A Practical Solution to Overcome Challenges in Unconventional

Reservoir Simulation and History Matching Using Integrated Petrophysical and Facies Modeling

Approach. In SPE Oil and Gas India Conference and Exhibition. Society of Petroleum Engineers.

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