evaluation of hydrocarbon prospect of fareed field ... · migration path for hydrocarbon into...

_____________________________________________________________________________________________________ *Corresponding author: E-mail: [email protected];

Journal of Geography, Environment and Earth Science International

7(4): 1-8, 2016; Article no.JGEESI.29113 ISSN: 2454-7352

SCIENCEDOMAIN international www.sciencedomain.org

Evaluation of Hydrocarbon Prospect of Fareed Field, Western Niger-Delta, Nigeria

Aigbedion Isaac1* and Hafiz Abdullai1

1Ambrose Alli University, Ekpoma, Nigeria.

Authors’ contributions

This work was carried out in collaboration between both authors. Both authors read and approved the

final manuscript.

Article Information

DOI: 10.9734/JGEESI/2016/29113 Editor(s):

(1) Ioannis K. Oikonomopoulos, Core Laboratories LP., Petroleum Services Division, Houston Texas, USA.

Reviewers: (1) Angelo Paone, Pusan National University, Busan, South Korea.

(2) K. Nirmalkumar, Kongu Engineering College, Perundurai, Erode District, Tamilnadu, India. Complete Peer review History: http://www.sciencedomain.org/review-history/16457

Received 23rd August 2016 Accepted 15

th September 2016

Published 5th

October 2016

ABSTRACT An integrated 3D sesmic data and a suit of well logs of Fareed six wells located at the Fareed field Niger Delta Nigeria were analysed with Petro Tech Software for reservoir characterization and volumetric analysis. Average reservoir parameters such as porosity (0.30), hydrocarbon saturation (0.25), gross thickness (27 m), and net thickness (0.7) were derived from petrophysical analysis. Sesmic section analysis showed fault assisted anticlinal structures which served as structural traps. The volume of hydrocarbon originally in place was estimated to be 325,000 million barrels of oil within Fareed field.

Keywords: Volumetric analysis; reservoir; hydrocarbon; Niger delta; resistivity. 1. INTRODUCTION The knowledge of the character and extent of a hydrocarbon reservoir are important factors in quantifying the hydrocarbon in place [1]. The

main Information required are the thickness, pore space and a real extent of the reservoir. Other intrinsic parameters are the shale volume/ content, net to gross ratio and saturation values [2,3].

Original Research Article

Isaac and Abdullai; JGEESI, 7(4): 1-8, 2016; Article no.JGEESI.29113

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The objective of hydrocarbon exploration is to identify and delineate structural and stratigraphic traps suitable for economically exploitatable accumulations and delineate the extent of discoveries in field appraisals and development. These traps could be very subtle and complex and are therefore difficult to be mapped accurately [4,5]. Seismic and well log data are widely used in petroleum exploration to map the subsurface. The two set of data are complimentary: i.e seismic profiles provide an almost continuous lateral view of subsurface, whereas well log yield fine vertical resolution of the geology at the borehole. Seismic profile can resolve, with relatively high precision, the structural and stratigraphic changes from the arrival times and amplitudes of the reflection event. Therefore, the integration of well log and seismic data would provide a high degree of reliability in mapping subsurface structural and stratigraphic plays.

It will also provide insight to reservoir hydrocarbon volume which may be utilized in exploration evaluation and in well planning [6,7]. Understanding of reservoir characteristics,

most importantly; porosity, water saturation thickness and area extent of the reservoir are crucial factors in quantifying producible hydrocarbon [1]. These parameters are important because they serve as veritable inputs for reservoir volumetric analysis, i.e. the volume of hydrocarbon in place.

1.1 Geology of the Study Area The study area is located offshore of the Niger Delta-Nigeria, situated on the Gulf of Guinea along the west coast of Africa (Fig. 1.1). From the Eocene to the present, the Delta has prograded South-Westward, forming depobelts that represent the most active portion of the Delta at each stage of its development. These depobelts form one of the largest regressive Deltas in the world with an area of some 300,000 km

2, a sediment volume of 500,000 km

3, and a

sediment thickness of over 10 km in the basin depocenter. The Niger Delta- Nigeria Province contains one identified petroleum system, named as Tertiary Niger Delta (Akata - Agbada) Petroleum System [8,9].

Fig. 1.1. Fareed field location


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2. MATERIALS AND METHODS

The materials for the study are seismic section, well logs, base maps and check shot data for the wells in the study area. All the data were loaded on petrol Tech software workstation. The study was performed using Petrol Tech 3 Dimensional (3D) seismic interpretation modules. The cross-line (strike) and the in-line (dip) and the above mentioned data set were provided by Shell Petroleum Development Company Limited. The well logs used were those of calipher, gamma ray, resistivity, neutron, density. In a hydrocarbon bearing reservoir part of the water is replaced by oil or gas, which are also electrical insulators. If the rock is water wet, the hydrocarbon is accumulated in the centre of the pored spaces. The remaining water coats the grain surfaces. Electrical current can still travel through the reservoir, along the water layer around the grains. The total resistivity of the reservoir Rt can be orders of magnitude higher than the Ro of a similar water bearing formation, because the volume and the connectivity of the conductor (water) is smaller. Therefore in addition to the parameters of the first Archie equation, the total resistivity also depends on the water saturation Sw and the geometry of the water coating the grains. The increase of the resistivity Rt of the partly hydrocarbon filled rock

over the resistivity Ro of the fully water filled rock is called the resistivity index. It is function of the water saturation Sw.

I = ��

�� = ��

��

Similar to m, n is often constant within a particular rock, independent of Sw.

�� = ��

��∅��

��

Sh =1 – Sw

m is the cementation factor, in Niger Delta setting m = 1.8, n is most commonly 2, Rw is resistivity of nearby clean water. The combination of the first and second Archie equation describe how the actual measured resistivity depends on the water resistivity, porosity water saturation (in case of clean sands or carbonates, for which Archie equation applies).

�� = ��∅��

�� More advance technique can be used to locate more oil from thin beds or thinning laminated shaly sand like the Simandoux equation.

Fig. 1.2. Interpreted seismic section: Well 3


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Fig. 1.3. Interpreted seismic section: Well 7

Fig. 1.4. Fareed field 2002 and 2005 top G reservoir depth map comparison

The Simandoux equation is one of the most popular and successful equation in common use which include shale correction for the saturation calculation. It requires inputs to shale volume. In general the equation can be written as

S� = �.��

∅� ��

��

�

+ �∅�

�� −

��

��

where �� is the volume of shale and �� is the pure shale resistivity.

C is set for 0.40 for sand and 0.45 for carbonate. �� is water saturation, �� is the formation true resistivity, �� water resistivity.


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3. RESULTS AND DISCUSSION

The Fareed structure is a well-identified culmination controlled to the North by a major down to basin growth fault and to the west by a prominent fault which is synthetic to the fareed structure counter-regional fault. Four intra-field growth faults are present across the structure (Fig. 1.5). The presence of these faults in the study area is an indication that there is possibility of hydrocarbon accumulation. Weber and Daukora (1975) describe faults as good migration path for hydrocarbon into reservoir rocks [10].

The analysis of the all the well section revealed that each of the sand units extends through the field and varies in thickness with some unit occurring at greater depth than their adjacent unit i.e possibly an evidence of faulting. The shale layers were observed to increase with depth along with a corresponding decrease in sand layers. From the analysis, particularly the resistivity log, all the four delineated reservoirs were identified as hydrocarbon bearing units across the eight wells i.e G 2.1 A, G 2.0 B , G 2.1 and G 2.2 (Figs. 1.6, 1.7 and 1.8).

Fig. 1.5. Interpreted seismic section showing faults

Table 1.1. Average petrophysical properties estimated for hydrocarbon column of the Fareed wells

Hydrocarbon column

thickness Netpay Netpay PHI Netpay �� N:G

M M % % % Fareed-1 44.39 25.76 27.13 33.68 57.81 Fareed-2 19.69 11.58 30.82 25.75 58.82 Fareed-3 95.91 62.94 29.33 19.35 65.62 Fareed-4 34.40 20.94 30.46 27.72 60.88 Fareed-5 96.34 66.96 25.95 21.55 69.50 Fareed-6 58.49 38.03 28.02 18.59 65.03 Fareed-7 59.55 40.58 31.32 33.06 68.15 Fareed-8PH 59.66 46.78 28.52 27.78 78.41 Weighted average 29.53 24.73 65.53


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Fig. 1.6. Fareed field 2.0 reservoir

Fig. 1.7. Fareed reservoir G 2.0


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Fig. 1.8. Fareed reservoir

The petrophysical parameters for the G reservoir which is sub divided into four layers cuts across the eight wells in Fareed field. The reservoirs were penetrated between 96 to 110 m with gross thickness ranging from 19m to 96 m, Netpay 11 m to 66 m, porosity which is of the range of 28% to 32%, water saturation ranges from 22% to 28% and net-to-gross ranges from 60% to 72% of the G reservoir layers which was estimated by applying 70% V-Shale, 15% Porosity and 60% Water Saturation. The petrophysical properties estimated for hydrocarbon column of the Fareed wells is given in the Table 1.2. Netpay weighted average porosity and water saturation of the well

data was calculated to determine the average field properties. The estimated weighted averages were used for deterministic evaluation of oil in-place. The G reservoir shows very good values which is indicative of a porous sandstone. The water saturation and hydrocarbon saturation reveal that both hydrocarbon and water are present in the reservoirs with the hydrocarbon having a higher ratio. Hence the G reservoir is a hydrocarbon bearing unit. The volume of hydrocarbon originally in place was estimated to be 325,000 millions barrels of oil. From these results, we can infer that Fareed field has exploitable potential hydrocarbon.

Table 1.2. Petophysical parameters/volumentrics

Reservoir Average net

thickness(m) Area�� Average

netpay ��%

Average netpay porosity%

N/G% FVFrrl/bbl OOIP mbl

G 2.0A 1 8297.99 46.22 24.87 39.49 1.2591 8.61 G 2.0 B 12.60 6304.18 24.96 28.53 72.42 1.259 131.93 G 2.1 27.21 3879.701 24.44 28.79 86.67 1.2602 178.16 G 2.2 8.45 423.30 19.42 28.04 60.82 1.3013 6.27 Total 324.97


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4. CONCLUSION

Seismic and well log data have been used to estimate structural characteristic of the identified sand bodies within the subsurface of the fareed field in the Niger Delta, Nigeria. The G reservoir shows good to very good values which is indicative of a porous sandstone. The water saturation and hydrocarbon saturation reveal that both hydrocarbon and water are present in the reservoirs with the hydrocarbon having a higher ratio. Hence the G reservoirs is a hydrocarbon bearing unit. The volume of hydrocarbon originally in place was estimated to be 325,000 million barrels of oil. From these results, we can infer that Fareed field has exploitable potential hydrocarbon.

COMPETING INTERESTS Authors have declared that no competing interests exist.

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________________________________________________________________________________ © 2016 Isaac and Abdullai; This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Peer-review history: The peer review history for this paper can be accessed here:

http://sciencedomain.org/review-history/16457

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