Mohammedberhan's Hompage
Freelance Geophysicist
I am a senior geophysicist with experience of over twenty years from geophysical field data acquisition to processing and interpretation as well as supervision and petroleum negotiations. Currently, I am an adjunct instructor at Columbus State Community College teaching physics.
I have Master’s degree in geophysics from the University of Oklahoma – School of Geology and Geophysics and a Bachelor’s degree in physics from the University of Addis Ababa. I have also attended a postgraduate level advanced training and research in geothermal technology at the United Nations University in Iceland and Petroleum Policy and Management intensive studies in Norway. In addition, I have attended numerous condensed courses, including petroleum economics, petroleum accounting, computer science, geophysics related softwares, etc. I have visited a number of countries both on business trips and on training programs.
Why I am a geophysicist
Upon successful completion of my high school education at Bede-Mariam Laboratory School in Addis Ababa in 1978, I joined the Addis Ababa University Science Faculty College and graduated with Bachelor’s degree in physics in 1982. Then, I was employed by the Ethiopian Institute of Geological Surveys as a trainee geophysicist in geothermal exploration. Following a number of years experience and on-job training as well as formal training programs, I was promoted through junior geophysicist, full geophysicist and senior geophysicist positions until the end of 1992. After the independence of my country, Eritrea, I joined the Ministry of Energy and Mines of the State of Eritrea to contribute to the nation building program and served as a senior geophysicist and petroleum negotiator. I was also involved in petroleum related management tasks, petroleum economic evaluation related tasks, in writing geothermal exploration proposals, in restructuring committee, in network system administration, in evaluating petroleum related reports submitted by oil companies and in many other tasks related to petroleum exploration. In August 1997, I have been hired by the University of Oklahoma as adjunct research scientist and conducted a research work on seismic data processing and interpretation with special emphasis on seismic multiple attenuation. In January 1999, I joined the Graduate College of the University of Oklahoma and graduated with Master’s degree in geophysics in 2000. Then I went back to Eritrea and served the Ministry of Energy and Mines as a senior geophysicist and petroleum negotiator until September 2006. Currently, I am a Freelance Geophysicist and reside in Reynoldsburg - Ohio, USA.
The first time I conducted a geophysical survey as a party chief and a team leader was back in early 1983 when I acquired a Vertical Electrical Sounding (VES) data at Aluto-Langano Geothermal field, Ethiopia. This VES point was located at the site where a Temperature Gradient well (TG 29) was drilled and was named TG 29 after the name of the well. The data were acquired with a maximum current electrode spacing of 7200 m with 6 samples per decade. The data acquisition took about ten hours and the crew went back to the camp at sunset. Few hours later, I plotted the data on a log-log paper and began to interpret the curve using partial curve matching method with only interpretation experience as part of my physics of the earth course at the University of Addis Ababa and with the help of geophysics text books. I determined the electrical layers at the site to the best of my knowledge. I was so excited and began to love my job. Months later a successful exploratory well was drilled at about 300 m southeast of TG 29. I am not claiming that this successful well was drilled based solely on the results of TG 29 VES data. The credit for locating this well goes to all geoscience staff members of the Geothermal Project and other consultants of the time. But, the electrical layers I got from my partial curve matching interpretation were in good agreement with the geological log result of the successful well. This was a turning point in my career. I became interested in geophysics and made a decision to stay in it. Since then until December 1992, I conducted geophysical surveys including VES, conventional profiling, head-on profiling, self potential, gravity, heat flow and microseismic methods for geothermal exploration at different geothermal prospects in Ethiopia. I was also involved in the Ethiopian regional gravity survey program. I was awarded the United Nations University fellowship in 1984 to attend an advanced training and research program on Geothermal Technology in Reykjavik, Iceland. I specialized in Schlumberger Soundings and Head-on Profilings.
I joined the Ministry of Energy of Eritrea in January 1993 as a senior geophysicist. My first task was to participate in drafting a proposal for geothermal exploration. I have also prepared a manual for geophysical field crew to serve as a guide in geothermal exploration. I presented a paper on the role of geophysics in geothermal exploration in effort to convince the higher officials on the need of geophysical survey and motivate fellow geophysicists.
In June 1993, I was instructed by the Minister of Energy of Eritrea to get involved in petroleum policy issues and drafting petroleum laws, regulations and model contract. This was a second turning point in my career. I had to study the evolution of petroleum laws and contracts. I studied different laws of different countries and the different types of the contracts. I have also attended an eight-week intensive course in Petroleum Policy and Management given by PETRAD in Stavanger, Norway. In addition, I took petroleum accounting and economics condensed courses.
I negotiated the first Petroleum Contract my country signed with an international oil company (Anadarko Petroleum Corporation) on September 28, 1995.
Following the signing of the contract, the head of the hydrocarbon division of the Ministry of Energy and I proposed to compile the existing reports and got Robertson to do it. By mid-1996 we got both technical and contractual documents ready in effort to create a favorable condition for petroleum exploration in Eritrea. We produced promotional documents (brochures and power point presentations) and attended at many Conventions and Seminars conducted by the Society of Exploration Geophysicists, American Association of Petroleum Geologists and Africa Upstream.
In 1996 Curson conducted aerogravity and aeromagnetic surveys for Anadarko on which I played an observer role representing the Government at all stages of the survey.
In late 1996 and early 1997 Anadarko and the Ministry of Energy and Mines conducted seismic survey in the Zula and Edd blocks (Eritrean Red Sea) respectively. I followed up the whole process and took the Seismic Data Processing Concepts course given by Western Geophysical so as to be able to follow the processing program. In August 1997, I took the seismic stratigraphy courses given by Oil & Gas Consultants Inc. and joined the University of Oklahoma – School of Geology and Geophysics as Adjunct Research Scientist. This is another turning point in my career during which I noticed that one of the major problems with the Red Sea seismic data are strong seismic multiples. I conducted test runs on a portion of strike and dip seismic sections of the data acquired in 1997 using Western Geophysical - Omega Seismic Processing software but I found it hard to justify the improvement. Thus, I interpreted an old seismic Shell line acquired in 1974 with a well on it and generated a 2D-model using GX2 modeling software. Then I generated synthetic seismic section that includes primaries and possible multiples involving the water bottom and salt boundaries using GX2. I applied different methods of seismic attenuation procedures using Omega on the synthetic seismic sections until I achieved the best method of attenuation. I applied the processing flow on the real data and excellent results were obtained. Encouraged by the results, we applied the procedure on 1200 km 2D seismic data with Spectrum-Geopex in Cairo. The output seismic sections were evaluated and interpreted by TGS-Nopec.
In 2001 I negotiated another contract signed between the Government of Eritrea and CMS Oil and Gas on May 4, 2001. I was also an active member of a joint Management Committee established between the Government of Eritrea and CMS Oil and Gas.
In 2004, I conducted land gravity survey for Perenco Eritrea Ltd. in its Contract area in Eritrea.
I have also served as a geophysical advisor to Eritrean-Geoserve Geological and Groundwater Consultants and conducted hydrogeophysical surveys at different localities in Eritrea.
My interest areas include:
1- Seismic Multiple Attenuation
2- Non-conventional Electrical Methods
3- Gravity Survey
I am associate member of the Society of Exploration Geophysicists.
The above is a summary of my career life. Please, email me at mohammedberhan@gmail.com if you have any comment.
Thank you for visiting my Homepage.
Brief Hydrocarbon Exploration History of the Eritrean Red Sea
In 1921 the Italian company Societa Mineraria dell’Africa Orientale, attracted by the prominent oil seepages in the Eritrean Red Sea, drilled a shallow well on Bu el Issar Island located southeast of Dahlac Kebir islands. The well bottomed in the uppermost Miocene/lowermost Pliocene Desset Formation, at 650'.
From 1935 to 1940 Agip made field geological investigations in Eritrea and drilled a number of holes on the Dahlac Archipelago. These wells are of interest because some had significant oil shows and proved the existence of an offshore evaporite basin. However, none of these wells was deep enough to penetrate below the salt.
From December 1958 until April 1960 Naftaplin of Zagreb, under contract to the Ethiopian Government, carried out geological, gravity and magnetic investigations in coastal Eritrea and in the Danakil Alps.
Early in 1962, Mobil acquired a block on and offshore, north of Massawa, running to the border with the Sudan. After an aeromagnetic survey, a shallow penetration seismic gas exploder survey was completed in 1964. The Amber-1 well was located and drilled on the basis of these data. Approximately 11000' of salt were penetrated and the well bottomed in slightly metamorphosed sediments thought to be of Jurassic age.
In 1969 Mobil drilled an unsuccessful well, B-1, on a structural feature further out to sea, east of Amber-1, on the eastern platform boundary of the evaporite basin.
Early in 1964, Gulf acquired a large block south of Mobil. Gulf then conducted an aeromagnetic survey. After a seismic program, Gulf spudded Dhunishub-1. At 12688', the well was still in the evaporite sequence and was abandoned. Esso, by financing the drilling costs, acquired a 50% interest in the acreage. Mobil's Amber-1 and Gulf’s Dhunishub-1 both indicated the presence of a huge evaporite basin in the Eritrean Red Sea. The pre-evaporites, so prospective in the Gulf of Suez, remained untested.
Gulf drilled Secca Fawn-1 well in 1969 on a structure connected with the step-faulted, collapsed, western edge of the Red Sea depression.
Mobil drilled C-1 well in 1970 on a feature within the marginal deep. After encountering considerable quantities of gas in a reservoir apparently below the salt, it blew out and had to be abandoned. Mobil decided to abandon the play and relinquished its holdings in 1970.
In 1966, Baruch-Foster acquired acreage south of Gulf’s and carried out an aeromagnetic survey, and acquired seismic. The holding was revoked by the Government in April 1970.
Secca Fawn-1, after penetrating clastics and volcanics, reached a salt tongue in which drilling was suspended because extremely high temperatures raised the mud to boiling point. This was an unfortunate situation since gas shows had already been noticed and drilling is thought to have been near pre-salt objectives.
Gulf obviously concluded that the Red Sea was ‘hot and gas prone’ and relinquished their acreage in 1970.
In 1968, Oil Organization Ltd. (later Ethiopian Oil Corporation, EOC) acquired part of the Gulf and Mobil acreage and also acreage south of the Dahlac Islands and in the vicinity of the Danakil Depression. They farmed out part of their northern contract area to Signal who conducted a seismic survey and then withdrew. The Signal seismic revealed a series of pre-salt highs, not too well defined individually, but occurring in the region where Miocene reservoirs and source rocks might be developed. Aeromagnetic information and data from a regional seismic line convinced the company that prospectivity could be greater in the northern area.
Notwithstanding the rather unsatisfactory results of Gulf’s and Mobil’s holes, EOC surrendered the area in the south, but retained a narrow strip of acreage along the coast, both on- and offshore, including the C-1 gas discovery. At this stage, conditions were favorable for EOC to negotiate a further farm-out agreement to assist in financing the drilling.
General American Oil of Texas drilled two wells (J-1 to the north, MN-1 to the south) on the same trend as Mobil’s C-1 gas discovery. Unfortunately, both wells were abandoned with only a very slight oil show in their pre-evaporite targets.
In 1972 Signal acquired two small contract areas offshore and just to the south of the Sudanese border from Ethiopian Oil Corporation. Signal acquired 461 line-km of seismic and then withdrew from their acreage.
Shell entered the Eritrean oil search in the Red Sea early in 1974 when it was also exploring the opposite coast of the Red Sea in the Yemen. The company took a large contract area covering the southern part of Gulf’s former holding, consisting of the relinquished Baruch Foster concession and the former Assab block of Ethiopian Oil Corporation. Marine seismic and gravity surveys were conducted. The 1974 -1975 results were of good quality and led to a detailed survey over a domal uplift in pre-salt formations.
Thio-1 well was drilled on this structure in 1977 to a total depth of 10233'. The objective pre-salt formations were investigated over a considerable interval but this well failed to discover hydrocarbons. Shell surrendered the acreage late in 1977.
International Petroleum Corporation acquired a Production Sharing Agreement from the then Ethiopian Government in 1989. This covered 34000 km2 in the on- and offshore Danakil area down to the now Eritrea/Djibouti border. Amoco farmed-in, assumed the operatorship and acquired 374 line km of new seismic. In 1990 Force Majeure was declared and Amoco ceased operations.
After the Declaration of Independence, negotiations with the Eritrean Government were initiated, but Amoco and its partners no longer retain interests in the State of Eritrea.
BP acquired Ethiopian/Eritrean Red Sea acreage in 1989 surrounding the Dahlac Islands which consisted of 30700 km2. The International Finance Corporation (IFC, the commercial arm of the World Bank) entered the partnership.
BP acquired 1114 line km of seismic. The initial exploration period included an optional well which was never drilled and BP no longer holds interests in the Eritrean Red Sea.
On September 28, 1995, Eritrea signed its first Petroleum Sharing Agreement with Anadarko Petroleum Corporation for Zula Block. Anadarko acquired aerogravity, aeromagnetics and seismic data. The Ministry of Energy and Mines of Eritrea in its part conducted seismic with similar acquisition and processing parameters to those used by Anadarko in effort to fill the gaps and promote the southern portion. Later, Andarko bought some of this data and signed another contract for the Eddy Block.
Anadarko drilled three wells in 1998 – 99 in Zula and Eddy blocks. The wells encountered oil and gas shows; but did not discover hydrocarbon. Anadarko Petroleum Corporation relinquished both Zula and Eddy blocks in 1999.
Government signed a Production Sharing Agreement with CMS Oil and Gas for the Defnin Block on May 04, 2001. CMS Oil and Gas conducted a 120 fold 2D seismic survey of 3,377 km. CMS Oil and Gas transferred its interest in Zula Block to Perenco in 2003. Perenco drilled Chita-1 well and relinquished its holding in 2006.
Tectonic Evolution of the Red Sea
Pre-rift arching and break-apart of the continental crust of the Afro-Arabian shield during Oligo-Miocene times led to the formation of the Red Sea in its present shape, with its marked block faulting on the flanks and strong subsidence in its central part. Rifting was transtensional and involved block faulting with both normal and strike-slip faults, which generally trend NW-SE to NNW-SSE. By the Late Miocene – Early Pliocene, about 5 Ma ago, small pull-apart basins along the axis of the Red Sea and Gulf of Aden were developing oceanic crust. As extension continued, these coalesced to form a continuous strip of oceanic crust, and the passive margins seen today developed on the flanks of the deep water axial trough.
Stratigraphy
PRE-RIFT
During the period of the Late Precambrian/Eocambrian, the Afro-Arabian craton was peneplaned and tilted to the north and east. Onto the eroded Precambrian / Eocambrian basement Complex was deposited a sequence of Middle to Upper Paleozoic glacial deposits and the Upper Paleozoic to Mesozoic sequence of the continental Nubia Group. Mesozoic rifting in central Sudan, Kenya, Ethiopia and Eritrea allowed the accumulation of a thick sequence of marine to fluvio-lacustrine shales and sandstones, partially time equivalent to the Nubia. Deposition of marine shales and carbonates and of more marginal sandstones continued through the Mesozoic and into Cenozoic forming the Eritrean and Ethiopian Adigrat, Antalo, Agula Shale and Amba-Aradom Formations of Jurassic and Cretaceous ages.
RIFT STAGE
Pre-rift arching and break-apart of the continental crust of the Afro-Arabian shield during Oligo-Miocene times led to the formation of the Red Sea in its present shape, with its marked block faulting on the flanks and strong subsidence in its central part.
Sedimentation into the newly subsident Gulf of Suez-Red Sea graben commenced with fluviatile-lacustrine sandstones and shales of the Dogali Formation which were accompanied by an outpouring of Oligo-Miocene basalts. This earliest syn-rift sequence was followed by the fine and coarse clastics of the shallow marine Lower to Middle Miocene Habab Formation. Restriction of the Gulf of Suez-Red Sea system led to the deposition of the evaporitic / clastic /carbonate sequences of the Belayim Formation of the Gulf of Suez and the top most Habab Formation of the Eritrean Red Sea. Finally the Gulf of Suez-Red Sea Graben desiccated completely and the thick halites of the South Gharib (Gulf of Suez) and Amber Formations (Eritrean Red Sea) were deposited. Rifting continued throughout the latest Miocene, accompanied by horst-graben faulting and consequent fault block rotation.
POST-RIFT STAGE
Post-rift stage is marked by the separation of continental blocks and the generation of the oceanic crust in the axial trough. This stage resulted in an important subsidence during Upper Miocene – Quaternary time, with the Desset and Dhunishub Formations developed in the Coastal basin and restricted depocenters of the salt basin.
Hydrocarbon Potential of the Eritrean Red Sea
Abstract
From the very limited exploration activities carried out in the Eritrean Red Sea encouraging results have been obtained. A number of prospects have been identified both in the syn-rift and post-rift formations. Hydrocarbon shows have been observed in both post-rift and syn-rift units. These include gas shows in Desset Formation in Secca-Fawn-1 well, Oil and gas shows in Amber Formation in the Adal-1 and 2, Suri-1, Dhunishub-1, Amber-1 and B-1 wells and gas show in the boundary between Amber and Habab Formations in Secca-Fawn-1 and C-1 wells. The 55-day blowout of well C-1 which occurred at 9865¢ is the most important occurrence in the Eritrean Red Sea. The zone was not cored, tested or logged.
The blowout zone is interbedded in the lower part of the massive salt or located at the top of Habab. The gas consists of C1(91%), C2(5.5%), C3 (2%) and C4 (1.5%) hydrocarbons, combined with small amount of distillate, and was produced at an estimated pressure of 7700 psi and volume of 5-20 MMCFGD. Gas shows were recorded at the Secca Fawn-1 well in the Amber Formation near TD. Oil and gas shows were also recorded at one of the recent wells – Bulissar #1.
Flat spots have been observed in some of the seismic lines. Moreover, several surface oil seepages were recorded in the reefal limestone of Dhunishub Formation, on Dahlac Island and along the Eritrean Coast north of Massawa and Defnin Islands.
Petroleum System of the Eritrea Red Sea
Source Rocks
Oil and gas seeps on and around Dahlac Islands, as well as oil impregnated sands on Difnein Island and the Red Sea Coastline of Eritrea are conclusive proof that hydrocarbon generating systems have been working in this area. Shows encountered during drilling have confirmed this.
The Late Jurassic organic rich shales and marls of the Antalo limestone and Agula Shale represent the pre-rift potential source rocks.
The results of rock-eval analysis revealed several organic rich horizons in a number of Eritrean offshore wells in both syn-rift Habab and Amber Formations.
Some intervals with fair to good TOC were encountered in wells J-1 and Thio-1. A 305 m thick source rock within the syn-rift sediments with a TOC of 3 to 8.65 kg HC/ton, kerogen type II, oil prone source rock was encountered in well J-1.
BEICIP had predicted, from the results of seismic interpretation, the presence of shaley inter-beds displaying the qualities of source rock within Desset Formation. This prediction has been proven by the recent wells drilled by Anadarko Petroleum Corporation. The wells encountered alternating layers of salt and shales which are high quality source rocks.
Maturity
Geothermal gradients in the Eritrean Red Sea vary from 2.56 °C/100m in Du Rig Rig #1 well to 6.18 °C /100m in well Secca-Fawn-1.
Regionally, geothermal gradient shows a tendency to increase form the Red Sea rift margins to its center (Axial trough). However, geothermal gradients measured at a point location are probably local phenomena and are affected by local salt tectonism and structural setting. Thus, the geothermal gradient maps prepared with only few wells’ data in such a vast area can not be reliable.
The highest geothermal gradients are found in wells with volcanic intercalation within the syn-rift or post-rift sequences, e.g. B-1 has volcanics within the Amber Formation which appear to be related to volcanism in the axial trough. Secca Fawn-1 has volcanics in the Desset Formation which may be related to normal faulting between the Danakil Block and the salt basin. Of the five wells analyzed for thermal maturity, three (MN-1, J-1 and Thio-1) enter the oil window in the middle or lower Habab, while the other two (Secca Fawn-1 and C-1) enter the oil window in the Desset and Amber Formations respectively. Wells closer to the Axial trough which have not been analyzed for thermal maturity (Amber-1, B-1 and Dunshb-1) have evidence, in the form of shows, that the Amber Formation is in the oil window.
Reservoir Rocks
The potential reservoirs in the Eritrean Red Sea are in clastic successions, but potential carbonate reservoirs have also been identified. Potential reservoirs occur in all three megasequences.
Pre-rift:
All potential pre-rift reservoirs are unproved by drilling in the offshore, but are likely to occur on the downdip areas of tilted fault blocks, where they have avoided erosion. They include the fluvio-glacial sandstones of the Paleozoic Enticho sandstone, fluvio-deltaic to shallow marine sandstones of the Jurassic Adigrat sandstone and fluvial sandstones of the Cretaceous Amba Aradom sandstone. Potential reservoirs may also occur in the Jurassic Antalo Limestone, especially where it is fractured and/or dolomitised. Of these potential reservoirs, the best are likely to be in the Adigrat sandstone, which has good porosity when seen at outcrop.
Syn-rift:
Potential syn-rift reservoirs occur both in the pre-salt Habab and Dogali Formations and in the salt-bearing Amber Formation.
Sandstones in the transgressive Habab Formation are generally thin, and the sandstones commonly contain a high proportion of volcanic fragments. However, some thicker sandstones (20-60m) occur locally (e.g. in well J-1) and these have average porosities of approximately 14%.
A blowout in well C-1 is thought to have been from sand near the top of the Habab Formation. At outcrop, the laterally equivalent Dogali Formation includes texturally and mineralogically mature lenticular sandstones, which are likely to have good reservoir quality. The overlying Amber Formation is dominated by evaporates, but also includes marginal clastics, which may have extended further into the basin during periods of evaporative drawdown. These clastics are likely to include fluvial, eolian and beach sandstones, some of which are likely to have good initial reservoir quality. The associated salt will form good intraformational seals, but it may also have led to the cementation of some of the sandstones by evaporite minerals. Sandstones of possible Amber Formation age may also occur in topographic lows on the top surface of the salt.
Post-rift:
The transgressive Desset Formation contains continental sediments near its base, which may have lenticular geometry. They have good interpreted log porosity (12-13%, possibly exaggerated due to caving problems). These lower sandstones are likely to extend further into the basin than higher sandstones. The laterally equivalent and overlying Dhunishub Formation consists mainly of limestones, with sandstones in the more proximal (i.e. western) areas. The limestones include local reefal limestones. Due to its shallowness, sealing may be a problem for potential reservoirs in the Dhunishub Formation.
Seal
For the pre-rift reservoirs Agula shale, the Upper Habab (silts and shales) and where the pre-rift succession has been intensively eroded the Upper Miocene evaporites can be good seals.
Amber salt can provide good reservoir seal for the underlying Habab and the intra-salt sand lens reservoirs.
Locally Upper Desset Formation could serve as seal for Upper Amber and Lower Desset Formations. The reef buildups in the Dhunishub Formation are also important seals.
Trap styles
Two hydrocarbon play systems are clearly apparent, pre- and post-evaporite, and play types differ according to the system being targeted. Pre-evaporite of Suez, form the most attractive plays where geothermal gradients are moderate. Where increasing heat flow and higher sediment load generally result in an over-mature pre-evaporate section, maturation and halokinetic control and post-evaporite Miocene tilted fault blocks, similar to the Gulf sedimentation has resulted in a number of other play types.
Tilted fault blocks, rotated fault blocks, horsts and compactional drape are the most likely traps in both the pre-rift and syn-rift pre-salt units. Whereas structures related to the salt tectonics such as rollover anticlines, ramp anticlines, stratigraphic pinchouts, turtlebacks, salt diapers and salt canopies or pillows prevalent in the salt basin are principal style traps for the post-rift units. Frequent glide planes and growth faults due to gravity tectonics are prominent along the basin borders, which could constitute likely traps in the post-rift units.
The facies changes in the syn-rift and post-rift units might also provide a possible stratigraphic trap. Moreover, regressive transgressive surfaces in the Mesozoic successions (pre-rift) and the regional Unconformity surface between the Mesozoic and rift sequences can be also considered as subordinate traps.
