Free Custom «Modern Sediments and Carbonate Systems as Analogues for Subsurface Reservoir Quality» Essay Paper

Introduction

Tukang Besi Archipelago (or Wakatobi region) is located in Southeast Sulawesi (Southeast Asia). The Wakatobi covers approximately 823 km² and the marine water area occupies around 18377.31 km². This study area includes such islands as Keledupa, Sumbano and Pulau Ndaa (Figure 1). The Sumbano reefs are on the western side of the Kaledupa island between 1230 42.008 East and 050 30.117 South. This area is spared from the reefs near seagrass areas which range from more than 300m toward the deep water. The Pulau Ndaa has a land area covering 4 km² between 1240 03 East and 050 39 South. The area lies on the Western side of a coral reef which dries about 6.5 miles Northeast of Pulau Tomea.  

The modern carbonate reservoirs powerfully influence the half of the world’s oil production. The South East Asia’s reserves are rich in carbon buildups of Neogene age. The Tukang Besi Archipelago can be a perfect area to study buildup improvement as it includes the spread of numerous carbonate depositional systems related to isolated, small-scale buildups, fringing/barrier reefs around the island, large and small-scale atolls. This project is highlighted on the main changes within the marine environment from two different local and diagenesis impacts on reservoir quality of Cenozoic carbonate depositional systems. Moreover, the influence of sediment samples such as components, textures and mineralogies analysis of subsurface reservoir are evaluated as modern sediments and carbonate systems to be associated with the local environmental events.

 

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The overall aims of the projects are: to provide analogue data to aid in reservoir characterization of comparable Neogene subsurface buildups in SE Asia.

Specific objectives of the study are: 

• To evaluate variations in components, textures and mineralogies of modern carbonate sediments from the range of local environments from reef-related SE Asian isolated carbonate systems.
• To evaluate how modern sediment characteristics may have an impact on reservoir quality (including primary porosities and the potential for diagenetic alteration and secondary porosity development). 
• To make comparisons between deposits from the fringing reef system and atoll as analogues for subsurface reservoir quality and to compare with the literature.

This paper has been divided into four sections. The first section deals with the regional setting of modern carbonate deposits, focusing on fringing reef system (Kaledupa-Sumbano: Kal) and an atoll (Pulau Ndaa: PNd). The second section examines modern sediments and carbonate systems as analogues for subsurface reservoir quality with the help of the result of the laboratory research. The third section it is interpreted and discussed how components, textures, and mineralogies are related to the local environment within transect and how sediment characteristics may have an impact on reservoir quality. This section provides a comparison between deposits from different local depositional environment between the fringing reef system (Kaledupa-Sumbano: Kal) and an atoll (Pulau Ndaa: PNd) as an analogue for subsurface reservoir quality and its comparison. Finally, general conclusions are provided as the result of the project study.  

Methodology and data

The data in this study include the total of 27 modern samples from 2 transects across.

(1)   An island – attached fringing reef system (Kaledupa-Sumbano: Kal) 15 samples.

      (2) An atoll (Pulau Ndaa: PNd) 12 samples.

For the purpose of the study 2 methods have been used:

(a) Binocular microscopy and Petrography methods are among the most practical ways of modern sediment study. For this study the Binocular microscopy and Petrography were used to explore components, sediment, textures and any alteration. Modern sediment samples were examined under the microscope. The picture of each modern sediment sample was taken by using the Binocular microscopy. In addition, with the help of a focus the picture was changed to get a higher or lower magnification in order to have a perfect picture. So, all the components were counted in each sample group of components with the Binocular microscopy.

(b) X-ray Diffraction (XRD) was used to identify the mineralogy of samples. The modern sediment samples were grinned to a fine powder. The powdered samples were packed into a glass sample holder. Moreover, the samples were determined to use a broker-Axs D8 X-ray diffract meter of centre for material research at Curtin X-ray Laboratory. The samples were scanned from 50-3000 K to cover the peaks of the different carbonate minerals, at a scanning speed of 110 2 %u03F4 steps per second. A LYNXEYE was the perfect detector for all applications in X-ray diffraction, with identical data quality. The weight percentages of the carbonate minerals (Aragonite, low and high magnesium calcite, quartz and amorphous) relative to the percentages carbonate content was measured from the peak area ration using computer based integration peak areas of spiked and un-spiked samples.      

Results

27 modern sediment samples from two transect areas (“Keledupa –Sumbano; Kal” and “Pulau Ndaa; PNd”) have been grouped into 7 categories, each having distinctive compositional properties and representing different environments such as Foreshore to back shore, Intertidal without seagrass, Seagrass area, Coral and minor seagrass, Coral on the reef, Reef crest or margin with corals and Reef slope or fore reef.

1) Foreshore to backshore

The modern sediment samples of the foreshore and backshore areas are dominated by the sand of gravel-sized grains. Both of the transect areas (“Keledupa –Sumbano; Kal” and “Pulau Ndaa; PNd”) include 6 samples (Kal 20-21 and PNd 4-7). The samples of Kal 20, from the upper foreshore to backshore sands, and Kal 21, from the lower foreshore, mostly consist of sand (Kal 20: coarse sand to very fine sand 99.36%; Kal 21: coarse sand to fine sand 99.88%). The other transect “Pulau Ndaa; PNd” shows the contents of sediments (PNd 4-7). Sediments grains of all sizes are dominated by sand to gravel-sized grains such as PNd 4: medium sand 91.64%, gravel 8.36%; PNd 5: very fine sand 94.60%, gravel 5.40%; PNd 6: medium sand 90.21%, gravel 9.79% and PNd 7 medium sand 20.66%, gravel 79.34%. The greatest number of the sediment samples in these two areas shows to be sub-angular to sub rounded. Components of the foreshore to the back shore (± 2 mm) include Coral (~10-44%), Shells (~5-55%), Coralline Algae (~15-32%), and Calcarinds (~7-40%). In contrast, the components in Kal 20 (+ 2 mm) have many of Echinodermate (40%). The alteration of these two areas is rich in Bioerosion, Abrasion and fragmentation; however, it is poor in Cementation and Encrustation adjustment. Mineralogy of two transects consists of 36-63 % Aragonite, 14.3-45%, High-Mg Calcite, 0.3-0.6% Halite, 0.5-4.6% Low-Mg Calcite, and 18-40% Amorphous content; however, there is no Quartz in the mentioned samples.

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2) Intertidal without seagrass or coral

The modern samples of intertidal sediment without seagrass or coral area are inherent to the sand of gravel-size grains, whereas the silt or clay fraction does not exceed 1% of the Kal samples. In the Keledupa–Sumbano; Kal, the samples of Kal 18 from the lower intertidal deposits with brown algae and Kal 19 from intertidal deposits within rippled show the number of sand, gravel and some silt or clay grain fraction (Kal 18: coarse sand to very fine sand 93%, gravel 6.90% and Kal 19: coarse sand to very fine sand 97.5%, gravel 1.5%). In the Pulau Ndaa; PNd, just only one sample (PNd 3) consists of the medium sand (90.1%) and gravel (9.8%). They show bi-tri modal grain size range. The amount of the samples in two transects is related to sub-angular to sub rounded, which are a well to moderately sorted. In the both areas (± 2 mm), the sediment components include Coral (~ 10-40%) and Shells (~ 15-32%). The samples (- 2 mm) in Kal 18, 19 and PNd 3, Calcarinids are common (~ 12-40%), and Coralline Algae is about 10-15%. In Kal 18 (± 2 mm) there is also Halimeda (between 20-25%). In contrast, Imperforate (~17-23%) is represented by Kal 18 and 19 in (+ 2 mm).  The alteration of the both areas is high Bioerosion, Abrasion and fragmentation; however, it is lower than the alteration in Encrustation.  Mineralogy of two transects consist of 31.3-53 % Aragonite, 24-50%, High-Mg Calcite, 0.4-0.6% Halite, 1.6-4.7% Low-Mg Calcite, and 16-19% Amorphous content; however, there is no Quartz in the samples.

3) Seagrass area

The modern sediment samples of seagrass area are dominated by the sand of gravel- size grains, whereas the silt or clay fraction does not exceed 0.1-3% of the Kal samples. Both of the transect areas include 5 samples (Kal 7, 11, 13, 17 and PNd 2). These samples are constituted by the percentage of sand, gravel and some percentage of silt or clay grains fraction such as Kal 7: very coarse sand to medium sand 95.10%, gravel 4.80% and silt/clay 0.10%; Kal 11: coarse sand to fine sand 99.10%, gravel 0.70% and silt/clay 0.20% ; Kal 13: coarse sand to fine sand 91%, gravel 8.50% and silt/clay 0.50%; Kal 17: coarse sand 20.27%, gravel 76.73% and silt/clay 3%;  PNd 2: very coarse sand to medium sand 47.25% and gravel 52.75%. The grain size of the samples in two transects is related to sub- angular to sub-rounded and is from moderately sorted (in Kal 11,13 and 17) to poorly sorted (in Kal7 and PNd 2). In addition, in the samples such as Kal 7, 11, 13, 17 and PNd 2 components (± 2 mm) include Coral (~1-25%) and Shells (~5-30%) which are most abundant. Halimeda in Kal 7, 11 (-2mm), Kal 13, 17 (± 2 mm) around 5- 50% and Imperforate around 8-25% are common. The number of seagrass sediments in Kal 7, 11, 13 and 17 (+ 2 mm) is highly abundant, it is around 5- 80 %, but the sample PNd 2 has no seagrass sediments. The total alteration in two transects includes Abrasion, Fragmentation and Bioerosion around 1-3% of the grain mounts. Mineralogy of two transects consists of 33.1-63 % of Aragonite, 14.8-49% of High-Mg Calcite, 0.4-1.5% of Halite, 2.1-5.9% of Low-Mg Calcite, and 16-20% of Amorphous content; however, there is no Low Magnesium calcite in the PNd 2 sample.             

 4) Coral and minor seagrass

The transect areas on the coral and minor seagrass includes 4 samples (Kal 3, 5, 15 and PNd 8). The samples in the coral and the minor seagrass area are dominated by the sand of gravel- size grains which is in the Kal 3 samples: coarse sand to fine sand 98.30%, gravel 1.60% and silt/clay 0.10%; Kal 5: fine sand 92.50%, gravel 7.40% and silt/clay 0.10%; Kal 15: coarse sand to fine sand 99%, gravel 0.80% and silt/clay 0.20%; PNd 8: coarse sand to fine sand 58% and gravel 42% %. The samples are sub-angular and sub rounded, and are well sorted (Kal 3) and moderately sorted (Kal 5, 15 and PNd 8). The largest samples component of Coral which is present in two transects (± 2 mm) is around 10 to 80% ,but the components in the Kal 15 sample are abundant in it (- 2 mm). There are many Shell components in the Kal 15 sample (+ 2 mm) at 75% and Halimeda (- 2 mm) is at 55%. However, there components as Perforate, Calcarinids, Coralline Algae, and Imperforate are not abundant. The alteration of Kal 3 and 15 samples contains Abrasion, Fragmentation, Bioerosion, but Kal 5 and PNd 8 samples are abundant of alteration containing Abrasion, Fragmentation, Bioerosion and Encrustation. Mineralogy of two transects consists of 42-57 % of Aragonite, 16.1-38% of High-Mg Calcite, 0.7-0.9% of Halite, 3.6-12.5% of Low-Mg Calcite, and 16-18%  of Amorphous content.       

 5) Coral on the reef

The modern sediment samples of coral on the reef area are dominated by the sand of gravel- sized grains or a fewer number of silt or clay samples. The samples of Kal 9 consist of the greatest amount of coarse sand to fine sand 95.40%, gravel 4.50% and silt/clay 0.10%. Also, the sample is considered to be very angular to sub angular which is moderately sorted. The other sample PNd 12 has a large number of very fine sand 99.80% and gravel 0.20%, and also the samples show to be sub-angular to sub rounded which are well sorted. Among the ocmponents of Kal 9sample (±2 mm) are Coral (~25-55%), Shells (~20-30%), Halimeda (-2 mm) ~12%, Imperforate (-2 mm) ~13%, Calcarinids (-2 mm) ~12%, and Seagrass (+2 mm) ~10%. Another component of the PNd 12 sample consists of Coral (-2 mm) ~40%, Perforate (-2 mm) ~15%, Calcarinids (±2 mm) ~10-20 %, Coralline Algae (-2 mm) ~15%, Shells (+ 2 mm) ~50%, and Imperforate ~30%. Both alterations in the coral reef area included Abrasion, Fragmentation, Bioerosion and Encrustation around 0.5-3% of the grain mounts. Mineralogy of Kal 9 consists of 61% of Aragonite, 18.9% of High-Mg Calcite, 0.7% of Halite, 3.3% of Low-Mg Calcite, and 16% of Amorphous content; however, there is no Quartz in this sample. The PNd 12 sample consists of 35 % of Aragonite, 41% of High-Mg Calcite, 0.9% of Halite, 3.5% of Low-Mg Calcite, 0.2% of Quartz, and 19% of Amorphous content.  

6) Reef crest or margin with corals

The modern sediment samples of the reef crest or margin with corals area are inherent to the sand of gravel- sized grains whereas the silt or clay fraction does not exceed 1% in all of the samples. Both of the transect areas at the reef crest or margin with corals include 4 samples (Kal 1, 2 and PNd 1, 11). All of the samples consist the amount of sand and gravel such as Kal 1: sand 43.13%, gravel 56.80% and silt/clay 0.07%.; Kal 2: sand 91.62%, gravel 8.30% and silt/clay 0.08%.; PNd 1: coarse sand 88.25%, gravel 11.75% and PNd 11: very fine sand 99.80%, gravel 0.20%. The texture of all samples is sub-angular to sub rounded which are well sorted. In the components of the area there is a large number of Coral (~10-88%). In addition, they are related to some component groups in this area, among them Shells, Imperforate, Perforate, Coralline Algae, Halimeda and Calcarinids. The total of alteration in two transects contains the greatest number of Abrasion and Fragmentation, but the least number of Cementation (in the PNd 11 sample). Mineralogy of two transects consists of 28.3-41 % of Aragonite, 16.6-54% of High-Mg Calcite, 0-1% of Halite, 0-5.8% of Low-Mg Calcite, 0-0.8% of Quartz, and 15-20% of Amorphous content.

7) Reef slope or fore reef

The transect areas in the reef slope or fore reef constitute 3 samples (Wsum 2, PNd 9 and 10). The samples in the reef slope or fore reef are dominated by the sand of gravel- size grains and some amount of silt or clay which is in the samples of Wsum 2 from the sandy slope bellow rubble in the “Keledupa –Sumbano” transect: fine sand 25.76%, gravel 71.24% and silt/clay 3%; PNd 9: very fine sand 99.70% and gravel 0.30% and PNd 10: very fine sand 99.78% and gravel 0.22%. The texture of samples Wsum 2, PNd 9 and PNd 10 is very angular to sub rounded which is moderately sorted in Wsum 2, but the PNd 10 and PNd 9 samples are well sorted. The components of Coral (~20-75) and Shells (~10-40) are common in this area. There are also such components as Imperforate, Perforate, Calcarinids, and Caralline Algae. The alterations in two transects include Abrasion, Fragmentation, and Bioerosion. The sample of Wsum 2 is lower in Bioerosion. Mineralogy of two transects consists of 42-55 % of Aragonite, 23.4-34.3% of High-Mg Calcite, 0.3-1.2% of Halite, 3-4.4% of Low-Mg Calcite, 0.3% of Quartz and 18-19% of Amorphous content; however, there is no Quartz in the Wsum 2 sample.                

Interpretations and discussion

The main question which should be answered when discussing the modern carbonate sediments between two transects (Keledupa –Sumbano; Kal” and “Pulau Ndaa; PNd”) are: How do components, textures, and mineralogies relate to the local environments within transects?; How do sediment characteristics such as components, textures, and mineralogies may influence the reservoir quality (including primary porosities, the potential for diagenetic alteration, and secondary porosity development)? To address these questions it is necessary to evaluate possible links between sediment distribution, porosity, permeability, and mineralogies. Furthermore, primary porosity in carbonate is controlled by the sediment characteristic conditions at the time of deposition, and the secondary porosity development was modified through diagenetic alteration of carbonate sediments by the processes because of its control of the chemical composition of the water.

How do components, textures, mineralogies relate to the local environments with transects?

1) Foreshore to backshore

Foreshore is the area between the high and low water level, in which higher energy removes material sand. This process with erosion results into a larger amount of fine sand in comparison to the backshore environment. On the other hand, backshore is the area which lacks stability and is widened from the peak water level in order to be steady up to the area. There is always lower wave energy and consequently there is a smaller possible amount to remove sand which is accumulated in the backshore environment. The greatest percentages of the components of foreshore to backshore in this study area consists Coral, Shells, Coralline Algae, Calcarinds, and Echinodermate. There are often biologically rich environments. Detailed texture analyses the modern sediment samples of the foreshore to backshore area. In the modern sediment samples of Kal 20 and 21 there is medium sand amount, the sand is very fine, sub- angular to sub rounded and moderate to well sorted. As a result, both of the samples were transported by the high and low water energy. This environment is a product of the amount of energy created by the broken wave action. So, the processes carried the sediments to be deposited in high energy. However, the samples of PNd 4,5,6,7 included medium sand to very fine sand and were transported by wind action. The results of the study show that there is a high percentage of Aragonite which is formed by biological and physical processes such as Coral. As a result, the Coral is from marine and freshwater environment.  

2) Intertidal without seagrass or coral

The intertidal area is located between the high and low tide. At high tide the sea reaches its highest position by the side of a beach, and at low tide the sea is by the side of its lowest level. The sediment components in intertidal without seagrass or coral such as Coral, Shells, Calcarinids, Coralline Algae, Halimeda, and Impeerforate were common in this environment area. As a result, environment has presented biological, physical, and chemical components because the organism in this environment has changed the conditions to become adapted to water movement, moisture, temperature, and salinity. Moreover, these sediments in intertidal without seagrass or coral are transported by high and low tide as the modern sediment samples included fine to coarse sand and moderate to well sorted. This environment has shown medium energy of environment as the texture of the modern sediment samples was sub-angular to sub rounded. Mineralogy of the intertidal without seagrass contains high percentages of Aragonite and High-Mg Calcite, as well as the components of Coral and Shell.

3) Seagrass area

Seagrass area is the area commonly found in a coral reef lagoon, salt- marshes, on the tidal mudflats in estuaries and on shallow coastal marine locations from inter to sub-tidal region low tide in this seagrass environment. The sediment components in seagrass environment such as Coral, Shells, Halimeda, Impeerforate, and seagrass were common in this environment area. As a result, the percentage of seagrass which is located in the large areas of marine habitat of shallow water in the Keledupa is higher than seaweed because their roots, along with specialized grow cells, permit them to get into greater nutritional levels obtainable in the sediment instead of water. Also, this environment provides an estuary environment which causes the development of various organisms due to the fact that tidal action transports the nutrients to other parts of the estuary and out to sea. In the modern sediment samples of 11, 13, 17 there was coarse sand to very fine sand, sub- angular to sub rounded and moderate sorted in Kal 11, 13 and 17 as a result this process carried the sediments to be deposited in medium energy. These sediments were transported by high and low water energy. However, the samples of Kal 7 and PNd 2 were very coarse sand to medium sand; sub- angular to sub rounded and poorly sorted. As a result, both of the samples might be transported by the wave action. So, the processes carried the sediments to be deposited in high energy because the sediments were coarse sand. Mineralogy of the seagrass area occurs in the intertidal to sub tidal environment due to the high percentages of Aragonite and High-Mg Calcite.

4) Coral and minor seagrass

Coral and minor seagrass area found the location in Kal 3,5,15 and PNd 8. The sediment components in intertidal without seagrass or coral such as Coral, Shells, and Halimeda were most importants environment in this area. Moreover, these sediments in Coral and minor seagrass were transported by high and low tidal.  This environment is a product of the amount of energy created by the broken wave action as the modern sediment samples were of coarse sand to fine sand, moderately to well sorted and sub- angular to sub rounded. Mineralogically, the carbonate sediments largely consist of Aragonite and High-Mg calcite Forthermore; Aragonite plays a major role in this environment because of the presence of so much Halimeda and Coral debris.

5) Coral on the reef

Coral on the reef is one of the most biologically rich areas on the earth, which have rivaled only by tropical rain forests. In this environment, coral in the reef area found the location in Kal 9 and PNd 12. The environments for reef growth are especially where the water is too cold or too turbid as a consequence the sediments are easily removed by wave action. The sediment components in coral on the reef are Coral, Shells, Imperforate, Calcarinde, Seagrass, Corelline Algae, and Halimeda were most important in this environment. As a consequence, the environment for coral on the reef is shallow and warm water with a lot of water movement, plenty of light, with salty water which has a small amount of nutrients. This environment is a product of the amount of energy created by the broken wave action because the modern sediment samples were coarse sand to fine sand, moderately to well sorted and sub- angular to sub rounded. Mineralogically, the carbonate sediments largely consist of Aragonite and High-Mg calcite, as coral debris was abundant in this environment.

6) Reef crest or margin with corals

Reef crest or margin with the coral area was found in the location Kal 1, 2 and PNd 1, 11. These locations were from the reef edge between soft corals and tabulate Acropara and also below steep drop down erosional karstic surface. The sediment components in the coral on the reef contained a large number of Coral, the area also had such components as Shells, Imperforate, Perforate, Coralline Algae, Halimeda, and Calcarinids. This environment is the best developed where regular exposure to powerful wave creates a high energy environment becausethe modern sediment samples were coarse sand to fine sand, well sorted and sub- angular to sub rounded. Mineralogy of the reef crest or margin with corals was high percentages of Aragonite and High-Mg Calcite because wave action is generally more moderate and heavy branching corals. 

7) Reef slope or fore reef

Reef slope or fore reef was found in the location WSum 2 and PNd 9, 10. The environment of WSum 2 is located below rubble and Acropora. However, the environment of PNd 9 and 10 is a wide ledge with fine white sediment cascading down the sides and in water like ‘marine snow’. In this environment, wave actions help to create different habitats for many different marine organisms because the components of Coral and Shells were common in this area. Moreover, there are some of the components such as Imperforate, Perforate, Calcarinids and Caralline Algae. These sediments in reef slope or the fore reef were transported by water depth tide between 10-14 meters, as a consequence this environment is a product of the amount of energy created by the broken wave action because, the modern sediment samples were fine sand or very fine sand, moderately to well sorted and very angular to sub rounded. Mineralogy of the reef slope or fore reef included the highest percentages of Aragonite and High-Mg Calcite due to the wave impact in this environment. 

How sediment characteristics such as components, textures, and mineralogies may influence reservoir quality (including primary porosities, the potential for diagenetic alteration, and secondary porosity development)?

The results of the project have shown that in Keledupa –Sumbano; Kal, reservoir quality is characterized by low porosity and poor permeability because the characteristics of the sediment most were commonly of much fined grains size than the silt or clay fraction in this transect.  In contrast, carbonate sediments in Pulau Ndaa; PNd are of high porosity and good permeability because of the most commonly in very coarse grain sediments and no silt or clay fraction in this transect. The components of the Keledupa –Sumbano transect have high Halimeda and Seagrass content, but no there is no data in the Pulau Ndaa. Moreover, the secondary potential porosity of Keledupa –Sumbano has more porosity development than Pulau Ndaa because, the results have shown that the mineralogy percentage of Aragonite in Keledupa –Sumbano  is ~ 64 whereas in Pulau Ndaa ~ 58%.

Comparison between deposits from Keledupa –Sumbano fringing reef system and Pulau Ndaa atoll as the analogue for subsurface reservoir quality and comparison with literature review

The overall spatial distribution of deposits as an analogue for subsurface reservoir quality is strongly dependent on size of the islands, local environments, sediment characteristics and diagenetic alteration. The size of Keledupa–Sumbano is larger than Pulau Ndaa. Moreover, the Pulau Ndaa Island does not have an impact around the island. In contrast, Keledupa–Sumbano has a big island and also has a lot of impact from the island around (Fig.) The environment of two transects has shown that Keledupa–Sumbano is more protected from the big seagrass area but the environment of Pulau Ndaa does not show the area of the seagrass. The components of the Keledu –Sumbano transect have high amount of Halimeda and Seagrass, but there is no data concerning the Pulau Ndaa. Mineralogy of Keledupa–Sumbano (~64%) has high percentages of Aragonite and High-Mg Calcite because wave action is generally more moderate and heavy branching seagrass area more than in Pulau Ndaa (~58%). The fragmentation data show that Keledupa–Sumbano is much higher than the Pulau Ndaa Island because the sediment of Keledupa–Sumbano has very fine grain size. So, the results of the study of Keledupa–Sumbano showed low porosity and poor permeability. In contrast, in Pulau Ndaa; PNd reservoir quality is high porosity and good permeability because of very coarse grain sediments and absence of silt or clay fraction in this transect.

In comparison, the Bahamas and Belize Island has a big area which is larger than Keledupa –Sumbano; Kal” and “Pulau Ndaa; PNd”. As a result of the collected research, the grain size and mineralogy distribution shapes upon Great Bahama Bank (GBB) has demonstrated a focused on sedimentation structure along with apparent variation involving the external side and the internal platform. The principal mechanism of sedimentation within the three Belize atolls could be the build-up of organic-produced particles. Moreover, in the Bahamas, reservoir quality is characterized by high porosity and good permeability because of coarse grain sediments. In contrast, in Belize carbonate sediments have low porosity and poor permeability because of finer grained sediments. The research has also shown that to the potential of the secondary porosity of the Bahamas has more porosity development than Belize due to the percentage mineralogy of Aragonite in the Bahamas which is higher than in Belize. Within the Bahamas and Belize carbonate platform systems, sediment distribution appears to be influenced by climate, tides, currents, waves and sea water chemistry. Also, the secondary potential porosity of Keledupa–Sumbano has more porosity development than Pulau Ndaa as the results have shown that the mineralogy percentage of Aragonite in Keledupa–Sumbano (~64%) is high, and it is higher than in Pulau Ndaa (~58%). As a consequence, the porosity of the Bahamas and Belize is more developed than Keledupa–Sumbano and Pulau Ndaa. In addition, it can be seen that different depositional environments, notably underlying geology, oceanography, local climate, as well as tectonic conditions strongly influence various regional carbonate systems.

Conclusion

The two study areas have a different environment setting of carbonate deposition. This is strongly dependent on the size of the island, local environments, sediment characteristics and diagenetic alteration. The results of the project have shown that in Keledupa –Sumbano; Kal, reservoir quality is characterized by low porosity and poor permeability due to the characteristics of the sediment which are more commonly of fined grains size.  In contrast, in Pulau Ndaa; PNd carbonate sediments are of high porosity and good permeability because of the great number of very coarse grain sediments and no silt or clay fraction in this transect. Moreover, the secondary potential porosity of Keledupa–Sumbano has more porosity development than Pulau Ndaa because the results have shown that the mineralogy percentage of Aragonite in Keledupa–Sumbano (~ 64%) is higher than in Pulau Ndaa (~58%). In comparison with the Bahamas and Belize it has a higher percentage of Aragonite and High Mg-calcite than Keledup–Sumbano and Pulau Ndaa. As a consequence, the porosity of the Bahamas and Belize is more developed than Keledupa–Sumbano and Pulau Ndaa because they have a larger area than Keledupa–Sumbanol and Pulau Ndaa. Also, the facies, grain size, and mineralogy distribution shapes upon Great Bahama Bank (GBB) demonstrate the dominance of sedimentation structure along with apparent variation involving the external side and the internal platform. The principal mechanism of sedimentation within the three Belize atolls could be the build-up of organic-produced particles.