Geology Field Trip Jebel Hafeet

8/18/2019 Geology Field Trip Jebel Hafeet

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Introduction

The Jebel Hafeet is an asymmetrical anticlinal structure in The East of Abu Dhabi Emirate, in theborder between the UAE and Oman. The north –northwest – south-southeast oriented structure is 29 km in

length, up to 4.2 km wide and reaches a maximum elevation of 1,168 m.The goal of the geology field trip is understanding the complexity of the surfaces in order tounderstanding the complexity of the sub-surface. This prominent mountain exhibit a carbonates textures andfossil assemblages that can give us an idea of the depositional settings of the unit and also exhibit manylarge and small scale structural features where we can imagine and contemplate their role like a trappingmechanisms. The carbonate is one of the most common source rock of the Petroleum System in the world,as a first part of this report I will show it some important pictures taken it during the field trip and at the endof the report I will give it a brief description about the permeability and porosity about the two formationsvisited during the Jebel Hafeet field trip, as well as Suggestions about tools that we would include in the BHA(Bottom Hole Assemble) to get Porosity (Primary and Secondary) and Permeability and identify Traps ormigration paths, possible traps of the Petroleum system element, how we can determine the presence of

petroleum system elements using GR, how the lithology would be interpreted from seismic, logs and cores,and what are the problems we would have to watch out for if we come across such formation when viewingit in well logs or seismic. During the field trip we were able to visit two formation: Rus Formation (Lower andUpper) and Dammam Formation (Mudstone and Limestone).

Stopped 1 – Lower Rus Formation.

Figure 1. Lower Rus Formation. Fractures

The Lower Rus formation, it is a Calcareous Rudstone of shallow water environment. In both part ofthe (Figure 1) we can see the presence of silts and fractures, on the left a closed asymmetrical fracture whichmeans cero permeability-high porosity and in the other hand on the right an opened symmetrical fracturewhich means high permeability-high porosity, this fracture have a direction NS-EW.

Figure 2. Lower Rus Formation Calcareous Rudstone


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A brief demonstration about high and low porosity (Figure 2), the bottle in the picture represent thescale. On the left side we can see the fluid pathway in an opened fracture that represent a high porosity. Withregard to the other side of the picture we can see Calcite crystals filled or cemented which means a low ocero porosity. This part of the formation has presence of fossil content with a flat morphology.

Stopped 2 - Upper Rus Formation

Figure 3. Upper Rus Formation

Reverse Faults in the Upper Rus Formation (Figure 3), deep water marine environment withinterlayer laminated. In this part of the formation there is not presence of fossil content.

Stopped 3 – Dammam Formation

Figure 4. Dammam Formation.

Samples of Foraminifera from the Dammam Formation (Figure 4). The Dammam is an EoceneFormation of shallow water environment.

Petroleum system element – possible trapsIt's known that the Rus Formation is a sequence of well bedded massive limestone, nodular

limestone with chert bands and nodules of Early Eocene age, divided in two units, the lower unit is dominatedby nummulitic packsotnes and rudstones with poorly defined meter- to decameter-scale bedding andnodular appearance, interpreted as representing deposition in a shallow water marine environment. Theupper unit comprises thinly bedded wackestones and mudstones hosting bands of irregulary-shapednodules of chert. This unit is inferred to have been deposited in a relatively-deep marine shelf environment.


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With regard to the Dammam Formation is a Middle to Late Eocene formation with alternatingsequence of thin bedded hard nummulitic limestones (grainstones) and marls.

Three mainly carbonate formations were deposited in Jabal Hafeet area within the Arabian Peninsuladuring the Tertiary, The Rus and Dammam formation belong to these mainly formations. During thePeleocene to Early Eocene active compression ceased, and sediments were deposited within the remnant

foredeep-setting, where the carbonate Rus formation has been deposited. This has been followed by thedeposition of the Dammam formation in a structural setting. Both formation can be a good representations ofa possible reservoir rock.

Porosity and PermeabilityThe carbonate formation is one of the most common reservoir in the world. The sediments in these

formation is composed of particles with a wide range of sizes and shapes mixed together forming a multitudeof depositional textures. All carbonate sediments have sufficient porosity and permeability to qualify asreservoir rocks. It can be classify like a Carbonate formation with a complexity porosity structure.

Suggestion of tools to get Porosity (Primary and Secondary) and Permeability

Density Tool is the primary indicator of porosity, the tool can be used by itself or can be run incombination with other tools, such as the compensate neutron, which is a good combination to obtain porosityaccurately. Another tool that can be used for identify permeability is the sonic Tool. Regarding with thepermeability we have to calculate using these log, but is not measured directly by them.

How can you determine the presence of any PS elements using GR. Any suggestion on the tools thatcan help identify Traps or migration paths?

Gamma ray logs measure the natural gamma ray emissions from subsurface formations. The cleansand (free of shale) and the carbonates has low concentrations of radioactive material, therefore, they givea low lectures of gamma ray. When the shale content increase, the profile of gamma ray increase due to theconcentrations of radioactive material in shale. In that way we can identify the presence of a PetroleumSystem using Gamma ray. The presence of faults can be identify by the repetition of strata in the sameborehole.

How would the lithology be interpreted from seismic, logs, core?The lithology can be interpreted from the logs using special tools, for example Gamma ray that can

be measure the natural gamma ray emissions from subsurface formations, or electrical logs like Spontaneouspotential. The seismic can be used for identify the different caps of the subsurface due to the density of eachlithology. The core are samples taken from the subsurface and is the way more accurate for identify lithology.

What are the problems you would have to watch out for if you come across such formation whenviewing it in well logs or seismic?

The quality and resolution of the reflection seismic data from rocks suffer from their structuralcomplexity. The complexity of carbonate rock’s seismic responses is related mainly to their much morecomplex porosity structure like in our formations and fluid heterogeneity. Carbonate rocks are often denselyfractured, which adds heterogeneity to their porosity and permeability structure, but also add complexity tothe reservoir properties and fluid flow pattern.

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Geology Field Trip Jebel Hafeet