The JG field is an oil & gas producing field located in Abu Gharadig Basin. The Lower Safa Member is the main reservoir representing the lower member of Khattatba Formation and it is subdivided into two reservoir units "A and C" separated by non-reservoir unit "B". During the next development phase of Lower Safa "A" by it is necessary to avoid drilling dry holes or wells with low reservoir quality, and so, it was essential to understand the reason behind drilling 6 wells with low reservoir quality and the re-evaluation of the available data used to re-identify geometry was of high importance.
Lower Safa "A" had been cored in three wells with total length of about 46m. The sedimentological description of these cores highlighted several features pointing to a tidal dominated estuarine environment of deposition as abundance of carbonaceous material, channel erosion surfaces and paleosols, rapid changes of lateral and vertical facies, and mix of terrestrial and marine micro fossils.
The previous development strategy of JG field was to drill wells on crestal position along the main bounding fault which extended about 8 km in the East-West direction, assuming extension of estuarine system in the North-South direction.
Based on this study after re-evaluating available data estuarine system subdivisions clearly reflected in Lower Safa "A" unit and delineated from log characters and core features, it was proven that this unit was deposited in tidal dominated estuarine environment but extended in the East-West direction parallel to the fault, and the wells which encountered low reservoir quality were drilled in the low energy central zone and marches of estuary.
According to this study, it is recommended while developing Lower Safa "A" unit to drill within eastern and western areas i.e. the inner and outer parts of the estuarine system, which are characterized by good reservoir quality and to avoid drilling in the central part where the reservoir is low quality.
Ghanima, Ahmed (Bapetco) | El Bendary, Ahmed (Bapetco) | Taha, Ahmed (Bapetco) | Farag, Yasser (Bapetco) | Gamal, Ahmed (Bapetco) | Abbas, Sabry Aboel (Bapetco) | Samantray, Ajay (Bapetco) | Ibrahim, Haitham (Bapetco)
Histrorically, Upper Safa is considered to be the source rock of the gas and condensate accumulated in Lower Safa stratum in Obaiyed Field. Both of Upper and Lower Safa units are parts of Khatatba formation "Jurassic age, Western Desert coulumn, Egypt". The integration of all petrophysical and geochemical data indicated that, there is a rich organic Carbon embedded in the formation with a high britteleness ratio. As a result of the opportunity identification, there is an operational scope being studied now to proceed with a haydrulic fracturing stimulation targeting the sweet intervals "Intervals of high TOC and high Britteleness ratio" aiming to maximize the whole gas and condensate production of the field. This paper is summarizing the opportunity identification process and results using available petrophysical and geochemical data.
Six wells had been used in this study where there is a complete set of well and continuous petrophysical data exist in all of them supported by geochemical analysis reports. Specific interpretation techniques were utilized to identify the opportunity from the logs. The property of Total Organic Carbon was estimated from logs using standered DeltaLogR Passey Technique and then verified using measured data. The rock briteleness property was estimated from avilable acoustic sonic logs "Compressional and Shear slowness". The type of Kerogen and level of Maturity were recognized from geochemical sources. The data integration provided a well identification of the shale gas opportunity.
As a part of complete assessment study of unconventional resources, a dedicated subsurface team was formed in order to evaluate the connectivity of Upper Safa, estimate the in place volumes and define the development options. The team also proposed on short term scale performing a vertical hydraulic fracturing in one of the sweet wells in order to prove the evaluation concept and increase total field production.
The success of this project is measured by three aspects: first, proving the presence of commercial shale gas plays in Upper Safa unit, second, maximizing the gas and condensate production from the field and finally, on the long term scale, unlocking commercial unconventional gas resource for future generations in Western Desert, Egypt.
Moneim, M. A. (Shell Egypt) | Ahmad, M. F. (Shell Egypt) | Hanafy, O. (Smith Bits, a Schlumberger Company) | Fayez, S. (Smith Bits, a Schlumberger Company) | Eloufy, M. (Smith Bits, a Schlumberger Company) | Aguib, K. (Smith Bits, a Schlumberger Company)
Drilling the deep lithology column using PDC bits in the Obayied field of Egypt's Western Desert has been extremely difficult. The field's lithology column represents an amplification of all of the typical lithology characteristics in the Western Desert. The highly interbedded sandstone, siltstone, and shale—along with the variance of such interbedding across the field—has been a significant challenge for well planners and has adversely affected cost per foot. The application is characterized as predominantly abrasive and impact-intensive in the same section, hence challenging for PDC bit durability. To efficiently drill the 8½-in interval, a fundamental change in PDC bit design is required.
Considering these formidable challenges, service providers had to evolve PDC bits to meet the constant demand of improving performance and reducing costs. Focus was concentrated on balancing new technology developments and the willingness to invest on field trials. To accomplish these objectives in the Obayied field, the operator and the service provider identified two main problems—developing an in-depth understanding of rock strength characteristics of each individual formation in the deep rock column and its variance across the field, and developing PDC bits that can survive such a challenging rock column with improved durability and ROP.
Recently, a novel conical diamond element (CDE) with extreme impact- and abrasion-resistant characteristics has been developed. The CDE has been incorporated at bit center in a new and innovative PDC design, solving the traditional challenge of the inefficient characteristic of PDC bit central area. In addition, a field-wide rock strength study based on sonic and gamma rays logs provided the transparency required for better planning and risk management to resolve the operational inefficiencies traditionally seen in the Obayied field.
The new PDC bits utilizing the CDE technology has been deployed in Obayied and has reduced consumption to just 3–4 bits per section in 2014, whereas that number was 8–10 bits per section averaged in 2006. The new bit has also reduced the average number of days to drill the section from as low as 6 days to reach TD instead of 20 days. Performance gains were achieved both in ROP and footage totals in the most challenging formations, including Alam Al Buwaib, Upper Safa, and Lower Safa. The authors will discuss the benefits of this industry collaboration that achieved exceptional performance improvement leading to dramatic cost savings in the Obayied field.
A review of the available data of the Obaiyed field was carried out by Bapetco as part of the 2002 FDP update and the last review of Oct.2004. The Obaiyed field is a complex field, characterized by large uncertainties in permeability distribution and accordingly connected GIIP. The objective was to produce an integrated diagenetic and sedimentological model that can be utilized in 3D reservoir modelling. The study has resulted in a comprehensive 3D model of an estuarine, incised valley depositional system. Geological, Petrographical, sedimentological and Reservoir Engineering data have been integrated to create model realizations reflecting extreme scenarios of the permeability distribution within the field in an attempt to define their connectivity. The majority of the sandstone were deposited as bars within the estuary. The occasional higher permeability layers correspond to petrographic differences in the sandstones that relate to depositional sub-environment. Rock samples have been taken from the Paleozoic/Mesozoic in order to assess the diagenetic history, its impact on reservoir quality, and potential petrographic criteria by using the following analyses:
• Rock composition, Thin section petrography, SEM-analysis, XRD;
• Clay Mineralogy and Illite crystalinity;
• Age dating and Age of diagenesis: K/Ar-dating of Illite/Kaolinite concentrates.
The permeability and saturation distribution are a function of the diagenetic history of the field, causing the Paleozoic sandstones, which underlie the Mesozoic Lower Safa, to have a markedly lower permeability and generally lower saturation.
The Obaiyed gas/condensate field presents the challenging combination of a complex subsurface and a short timeframe to fully develop the field and to deliver committed daily quantities. The field was discovered in 1992, subsequently 4 appraisal wells were drilled between 1994 and 1996. After issuing the initial FDP in 1996 a development campaign was started in 1997, first gas was produced in 1999.
After drilling 28 wells in the area subsurface uncertainties have been reduced significantly, the current updated FDP focuses on the development of reserves locked in the tight parts of the field as a means to maximize profitability of the field. Currently over 50% of the in-place gas is locked in tight gas sandstones in the Obaiyed field.
In order to rule out other causes of poor productivity, the formation damage is the mechanism responsible for poor productivity. As this can only be done by ensuring no damage during drilling
Over the next two years, drilling activity in Bapetco will be increased, mainly because of the upcoming drilling campaign to develop the NEAG field In Abu El Gharadig Area and Obaiyed Area. Initial development plan will comprise drilling of 8-10 development wells in both Areas.
The Obaiyed gas/condensate field is located the Western Desert 50Km South of Marsa Matrouh. The Jurassic Lower Safa member (the reservoir bearing unit) consists of massive sandstones, which after deposition were subject to extensive deformation. A wide range of reservoir qualities is found in the field, with permeabilities ranging from tight (sub 0.1 mD) to high (up to 600 mD). Even after drilling 11exploration/appraisal and 30 development wells in the Obaiyed area, there are still significant subsurface uncertainties in the reservoir quality and extension, as shown by the 20% failure rate of the development wells. In order to improve our understanding of the Lower Safa reservoir, EREX Egypt was asked to make core descriptions for 15 wells in the Obaiyed field. They described 824m out of 1300 m total core length, to determine the depositional model of the Lower Safa. The conclusion of the study was that the main reservoir can be described as an estuarine deposit, with strong tidal influences in the earlier sequences, that evolved vertically into a wave-dominated deposit. The sedimentological study resulted in a simplified facies scheme that was used in Petrel to generate a 3D model for history matching. Unfortunately, it proved impossible to make a core-log correlation that could guarantee the successful production of new development wells. It was decided to take the reservoir quality uncertainty as a given and develop a completion strategy that would enable BAPETCO to produce the wells in any case. Therefore BAPETCO is planning a staged massive frac strategy in the coming years in parallel to the infill drilling campaign to maintain our production plateau and increase the ultimate recovery from the field.
The JG field is located in the North East Abu Gharadig (NEAG) Basin of the Western Desert in Egypt. With first production in 2002, it is the first commercial discovery in the
Middle Jurassic Lower Safa Reservoir Units in this basin. Oil and gas are produced from the tidally influenced estuary channel deposits in the Lower Safa A Unit and oil from the massive braided fluvial channels in the Lower Safa C Unit.
At first, the field was believed to consist of one single hydrocarbon column. However based on production behavior and additional well information it became apparent that the
field was highly compartmentalized in the vertical and horizontal domain. Since then multiple data sources have been leveraged in order to obtain better compartment definitions: 3D seismic, logs, PVT data, geochemical fingerprinting, repeat pressure surveys and production data.
The boundaries between the reservoir compartments are defined by a combination of faults and stratigraphic heterogeneities. Although clear in places, some compartment
boundaries can only be defined from non-geological data sources. Understanding these heterogeneities and compartment boundaries is essential for optimizing the field development.
Like so many fields the JG field proved to be more complex than initially expected. It is argued that extensive data gathering, in particular in the early field development, is essential in helping to timely identify and properly define such complexities.
A fully integrated study was required to solve the puzzle of the rapidly declining reservoir pressures in the Obaiyed Field. A more regional sedimentological and structural approach formed the basis for a new reservoir model. Consequently the field is now subdivided in a number of discrete blocks, each with its own static and dynamic parameters to predict reservoir properties.
The Obaiyed Gas Field is situated in the Western Desert of Egypt, approximately 450 km WNW of Cairo (Figure 1). It is operated by BAPETCO (a Government-Shell joint venture) and is the largest onshore gas field in Egypt. It commenced production in late 1999 and produces from tight Middle Jurassic sandstones at a depth of some 4000 m.
The field was contracted to supply a DCQ (Daily Contractual Quantity) of 300 MMscf/d for seven years. Very early into production wellhead pressures began dropping sharply. Static surveys confirmed reservoir pressures were declining rapidly suggesting the field would fail to meet DCQ by mid 2001.
To safeguard the DCQ, a study team was set-up with Shell Technology E & P in Rijswijk, The Netherlands to identify the reasons for the decline and recommend remedial action. The resulting Obaiyed recovery study was successfully completed in November and the main results are discussed in this paper. The appraisal and development phases of the field encountered so many unexpected well results that they may be best described as ‘EWD': ‘Exploring While Developing'.
The main reservoir succession is part of the Middle Jurassic Khatatba Formation (Figure 2) overlying the Base Mesozoic Unconformity and Palaeozoic sands of the Shifah Formation below. The reservoir section of the field is interpreted as the proximal sandy facies of the Lower Safa Member of the Khatatba Formation, representing fluvial/alluvial estuarine -incised valley- sediments. Deposition of the Lower Safa Member was affected by palaeo-topography and possibly also by syn-sedimentary tectonics, with onlap / non-deposition / erosion on palaeo-highs.
The field is situated in a large structure, charged with gas but reservoir quality is lacking in a number of wells and for a variety of reasons.
Find the Sweetspots
Production appears to be mainly from relatively few permeable units (tidal channels of some 1-20 m thickness) in the otherwise massive tight Lower Safa sandstones. The permeable zones have permeabilities in the order of 10-100 mD, in contrast to a tight background with permeabilities of 0.01-1 mD.
Predicting the presence of well connected permeable reservoir has been difficult. Complexities in primary deposition, diagenesis and structural overprint interplay and the poor seismic resolution at reservoir level hampered the mapping of non-depositional areas and reservoir thickness. Reservoir diagenesis has been studied in detail, based on a good set of core data but the results can not be used in a predictive way. Quantitative seismic studies failed to predict reservoir development because of poor seismic resolution and small impedance differences at the main objective level. Well correlation at reservoir level is difficult mainly because of poor biostratigraphical control in the barren sandstones.
Exploration and development in Obaiyed are therefore very much a matter of finding the sweetspots in terms of reservoir development against a complex geological background.