Summary:

This study aimed to re-evaluate, update and adjust the structural model of Ras Budran field not only emphasizing on the productive area to provide infill development locations but also on the non-productive areas located within the lease concession to identify new potential areas that may lead to new discoveries targeting to increase the field recoverable reserves and production level.

New structure contour maps at reservoir levels had been constructed. The new set of maps will be used as the basis for building a new static and dynamic model for the Field in addition to considering them as the common basis for future wells’ planning.

Several infill target locations had been identified for further drilling in addition to another appraisal prospects believed to be hydrocarbon bearings within the well-known stacked reservoir were identified and mapped.

Introduction:

3D geological modeling has become one of the most reliable and effective means of displaying geological structures of any oil or gas field. Building a coherent 3D geological model of a heavily tectonized area is a kind of challenge in terms of field development and reservoir management scheme. Over long years of production and field maturity geological interpretation combined with production behavior have of significant importance to increase production and lower operational cost.

In this study, geological and geophysical re-interpretation besides modeling not only opens new windows of development but also highlight areas of further exploration activities outside the mature field areas. As a result of tremendous task forces that required multidisciplinary effort, all geological, geophysical, petrophysical and production data were used.

General Outline about Ras Budran Field:

Ras Budran oil field is one of the Gulf of Suez fields which are located in the central province of the eastern coast of the Gulf of Suez where the dip regime of the pre-Miocene is to the North-East. It is in the North of Belayim offshore concession area, approximately 4 km west to Sinai coast of Gulf of Suez and 13 km northwest of Abu Rudeis.

Structure

Ras Budran structure is trending to the northeast – southwest direction. This trend is nearly at right angle to the main Gulf of Suez trend. On top Kareem Formation, the structure seems to be broken into several parallel panels by a set of nearly northwest-southeast trending faults.

The pre-Miocene structure of Ras Budran is very complex as it is severely disturbed by many faults at different levels and aligned in various directions (North West-South East, North/North East-South/South West and East North East-West South West).

Further the structural complexity is enhanced by the presence of two major erosional unconformities in the stratigraphic section, one post-Eocene and second intra-Rudeis. In addition to these, a post-Paleozoic unconformity is also recognized.

In 2008 and based on the interpretation of faults regarding their alignment, throw and from well data and diameter analysis, a structure contour map on top of Nubian “A” Formation (Reservoir unit III) had been constructed.

The structure of Nubian “A” consists of a northeast dipping flank (14-15o) broken into several blocks by a system of faults down stepping to the South and South West, and is finally bounded to the south by a major antithetic fault aligned nearly East West.

Stratigraphy

A sedimentary sequence ranging in age from Paleozoic to Recent with non-depositional and erosional hiatuses are present in Ras Budran. The stratigraphic sequence is similar to the normal Gulf of Suez one.

The Pre-Cambrian Basement was penetrated in RB-A2 well within a fault contact with sedimentary sections and intruded by younger intrusive of Oligocene age along the fault planes.

Oil Reservoir

Nubian Sandstone of Paleozoic to Lower Cretaceous age forms the main reservoir in the Ras Budran field.

These reservoirs are divided into four units: –

U-I, U- IIa, U-IIb and U-III.

In addition to these, some reservoirs of secondary importance are present in sandstone of reservoir Raha and Matulla formations and Thebes Formation.

Currently, the main producing unit is Raha formation (Upper and Lower).  

Methodology and Workflow

Seismic Re-Evaluation

Walk above (VSP)

Geological Re-Evaluation

Various available logs of all wells, paleontology, paleonology, cutting description and dipmeter logs had been used to construct a correlation among the drilled wells to be used as a base for constructing maps and consequently structure contour maps.

The major missing sections in Ras Budran area can be interpreted due to the presence of either unconformities or faults. So, it is too difficult to distinguish from log evidence only. Therefore, special attention had been paid concerning that aspect.

• Well to Well Correlation

Geo-Seismic Interpretation

The latest (pre-stack depth migration) resulted from the 3D seismic reprocessing that conducted in 2010 combined with all available geological well data had been used simultaneously to construct structure contour maps at all reservoir levels. That combination led to have a good picture for the structure of the field and the following figures show the comparison between initial seismic interpretation and final Geoseismic one after well data calibration.

Fault Detection

The interpretation reveals the presence of two fault systems , one of them has the direction of (North West – South East) which is Clysmic faults and the other one has the direction of (North East – South West) which is interpreted as transfer faults.

Results and Conclusions

That study assures that the structure of Ras Budran is very complex as it is severely disturbed by many faults at different levels and aligned in various directions. The structure is trending to the northeast – southwest direction. This trend is nearly at right angle to the main Gulf of Suez trend.

Two major erosional unconformities in the stratigraphic section, one post-Eocene and second intra-Rudeis had been identified. In addition to these, a post-Paleozoic unconformity is also recognized

New structure contour maps at reservoir levels had been constructed. The new set of maps will be used as the basis for building a new static and dynamic model for Ras Budran Field in addition to considering them as the common basis for future wells’ planning.

Recommendations:

It is recommended to conduct 3D static and dynamic models using the new constructing structure contour maps.

Evaluate, calculate the volumetric and risk assessment of the identified potential areas.

Conduct either VSP in the upcoming drilled wells to help the interpreters in better understanding of the existed seismic cube or acquire new seismic.

Use the recently updated technology and techniques of either wire-line or logging while drilling in the new upcoming drilled wells.

Conduct a sedimentological study aiming to construct sedimentological and depositional models at reservoir levels to allow good reservoir characterization and facies modelling.

Re-visit the volumetric and risk assessments calculations for the new appraisal prospects upon the results of 3D static and dynamic model

By Saber Moustafa Selim*, Suez Oil Company, EGYPT
Saber.Moustafa@suco-eg.com