DEPARTMENT OF THE INTERIOR 

U.S. GEOLOGICAL SURVEY

Petroleum exploration in Malawi

by

V 

R. E. Mattick

Open-File Report 84-

Prepared in cooperation with the Government of Malawi, under the auspices 

of the U.S. Agency for International Development, U.S. Department of State,

This report is preliminary and has not been reviewed for conformity 

with U.S. Geological Survey editorial standards and stratigraphic nomenclature,

J_/ U.S. Geological Survey, 

Reston, VA 22092

1984
CONTENTS

Page

Abstract....................................................... 1

Introduction................................................... 2

Past Exploration............................................... 3

Future Exploration............................................. 7

Northern Lake Malawi Area...................................... 8

Lower Shire Valley............................................. 11

Addi ti onal Work................................................ 12

Summa ry........................................................ 13

References Cited............................................... 14

ILLUSTRATION 

Figure 1.-- Map of Malawi and adjacent areas.................. 9
PETROLEUM EXPLORATION 

IN MALAWI

by

Robert E. Mattick 

U.S. Geological Survey

ABSTRACT

Sedimentary rocks, which could contain petroleum accumulations, are present 

in two areas of Malawi: (1) beneath the northern part of Lake Malawi and (2) 

in the Lower Shire Valley. The first named region encompasses an area of 

about 2,000 km 2 and last named region encompasses an area of about 700 km2.

In the northern part of Lake Malawi, where the sedimentary section is 2.5 

to 3.5 km thick, shallow cores (< 10 m) from the lake bottom indicate that organicrich sediments are being deposited today under highly anoxic conditions. Seismic 

reflection surveys indicate that large structural features capable of trapping 

migrating petroleum are present. Seismic-stratigraphic interpretations and 

field surveys suggest that potential reservoir rock, in the form of deltaic 

sandstone, is being deposited locally along the lake margins and extends into the 

lake. At the present time, however, there is no evidence to suggest that petroleum 

has been thermally generated at depth. Geologic interpretations suggest that 

Lake Malawi is a relatively young geologic feature (less than 4 m.y.b.p.) and 

heat flow measurements are about average for continental areas.

In the Lower Shire Valley, there is no direct geologic evidence that indicates 

the presence of source rock although some authors have speculated that Cretaceous 

age marine shales exist at depth.

Based on the lack of geologic evidence for thermal maturity and a large 

areal extent of potential sedimentary rocks., the petroleum potential of Malawi 

must be considered poor. Industry, therefore, has not been able to justify 

the high expenditures (probably greater then $500,000,000 U.S.) that would be

1
required to test drill in the extreme water depths (greater than 500 m) of Lake 

Malawi.

Despite the fact that its petroleum potential is rated as poor, Malawi 

may decide that further exploration is warranted. The author, therefore, has 

outlined a low-cost, small-scale geophysical and drilling program that, although 

not designed to actually discover petroleum accumulations, is intended to give 

further insight to Malawi's petroleum potential, increase the knowledge of the 

subsurface geology, and, hopefully, thereby attract industry to explore further. 

The geophysical program is designed to be coordinated with coal exploration 

in the northern part of the country, water resources studies in the southern 

part of the country, and to develop geophysical capabilities in the Malawi 

Geological Survey.

INTRODUCTION

In September of 1982, the Government of Malawi requested from the United 

States Agency for International Development (USAID) the technical assistance 

of a petroleum geology consultant. The consultant was to advise the Malawi 

Government on its possible role in promoting and monitoring oil exploration 

in Malawi. In particular to look at the possibility of setting up, within 

the Geological Survey Department, a small petroleum geology unit to monitor 

company operations and provide expert advice to the government. At the 

time that this request was made, the Government of Malawi had signed an 

agreement to enable Shell Exploration B.V. to carry out an airborne geophysical 

survey of Lake Malawi and the Lower Shire Valley. In anticipation of further 

exploration and possible petroleum production, an exploration and production 

bill was being prepared by officials of the Malawi Government.

In February of 1983, when the author, under the auspices of USAID, arrived 

in Malawi, the role of the petroleum consultant was somewhat revised. By that

2
time, Shell had discontinued all exploration and had dropped their exclusive 

option to negociate further exploration rights. In discussion with officials 

of the Malawi Geological Survey, it was decided that the petroleum consultant 

should investigate the possibility of small-scale exploration projects involving 

foreign consultants working in cooperation with the Malawi Geological Survey - 

such projects would be geophysically oriented toward obtaining further knowledge 

of Malawi's petroleum geology and the results might attract foreign oil companies 

to explore further.

The suggested projects that resulted were based on discussions and field 

reconnaissance surveys with Malawi geologists during a three week period beginning 

February 1, 1983. The author wishes to thank Dr. Richard Johnson, Chief Geologist 

and Mr. James C. Chatupa of the Malawi Geological Survey for their helpful explanations of the regional geology, their many useful suggestions, and their assistance 

in obtaining transportation to visit field sites.

The author spent approximately 2 weeks at the Geological Survey in Zomba 

reviewing aeromagnetic, seismic, and gravity data. The remaining week's time was 

split between reconnaissance surveys of the northwestern shore of Lake Malawi and 

the Lower Shire Valley and report writting in the USAID office in Lilongwe.

PAST EXPLORATION

The history of petroleum exploration in Malawi has been reviewed by Crow 

(1982) and part of the following is a brief summary from his report. After 

completion of a regional mapping program by the Malawi Geological Survey in 

1970, it was established that sedimentary rocks which could contain petroleum 

accumulations are present in only two areas - (1) the Lake Malawi area, where 

lacustrine sediments are presently being deposited and (2) the Lower Shire 

Valley in the southernmost part of the country. At that time, however, the 

petroleum industry showed little interest in Malawi because the potential
areas are of small areal extent and the sedimentary sections were thought 

to be relatively thin and composed of relatively young rocks.

Lake Malawi and the Lower Shire Valley are parts of the East African 

Rift System which extends from the Red Sea to Mozambique. The rift system 

in its present form is a Tertiary feature (Crow, 1982) and individual grabens 

and tilted fault blocks are filled by terrestrial and lacustrine sediments. 

At the present time, sediments with a high organic carbon content are being 

deposited in those areas occupied by deep-water lakes with highly anoxic bottom 

conditions such as Lake Malawi and Lake Tanganyika. In Lake Albert where bitumen 

seepages occur (Harris and others, 1956) and in Lake Tanganyika where bitumen 

balls are reportedly washed ashore (Crow, 1982) petroleum apparently has been 

thermally generated from organic-rich rocks at depth. Lakes Albert and Tanganyika, however, probably are much older geologic features than Lake Malawi.

In 1974 the Institute of Geological Sciences of Great Britain published 

the results of a gravity survey that covered the land area of Malawi (Andrew, 

1974). Later the Superior Oil Company (Soule, 1976) interpreted the gravity 

data and showed that there were possibly 3 km of sedimentary rock beneath the 

Lower Shire Valley. The company, however, did not follow up this study.

In 1980, Dumestre (1980) reviewed the petroleum geology of Malawi and 

concluded that the existence of petroleum accumulations beneath Lake Malawi 

and the Lower Shire Valley would depend on the presence of thermally mature 

source rock. The author of the present paper reached the same conclusion 

and estimates that the possibilities are low that thermally mature source 

rocks exist beneath Lake Malawi. Geologic interpretations (Crossley and 

Crow, 1980) suggest that the Lake Malawi graben is a relatively young feature 

(less the 4m.y.b.p.). Heat flow measurements in Lake Malawi sediments (Von 

Herzen and Vacquier, 1967) indicate that terrestrial heat flow in southern
Africa is about average for continents; however, these authors did record 

higher than average heat flow measurements in the central part of the lake 

where shallow igneous intrusions are believed to be present. In the Lower 

Shire Valley, however, Dumestre (1980) speculated that thermally mature source 

rock, in the form of marine shales of Cretaceous age, might be present at depth 

in the Shire Trough. These rocks, if they exist, would be a continuation of 

marine, Upper Cretaceous deposits of the Urema Graben on the east coast of 

Mozambique where natural gas seeps and natural gas production occur. Although 

there is structural evidence that the Shire Trough is connected to the Urema 

Graben there is no direct geologic evidence to indicate that Cretaceous marine 

rocks are present in the Lower Shire Valley.

In early 1982 interest in Malawi's petroleum potential was stimulated by 

an announcement by the National Science Foundation of America that a seismic 

reflection survey indicated a considerable thickness of sedimentary rock 

beneath Lake Malawi and that shallow cores showed that the lake sediments had 

a high organic carbon content. The scientific expedition that collected the 

data was from Duke University, North Carolina and a preliminary report was 

filed with Malawi, by Rosendahl (1981).

According to Crow and Chatupa (1982), the Duke University seismic data were 

difficult to interpret because of interference from water-bottom multiples which 

limited stratigraphic interpretation, in general, to the upper 1 km of sedimentary 

rock. Water-bottom multiples result from seismic energy that is reflected more 

than once from the water-sediment interface. In this case these multiples are 

of higher amplitude than seismic waves reflected from deeper rock layers. On 

some profiles, however, the sedimentary section appeared to be greater than 2 km 

thick. Although the seismic survey could not distinguish the age of the sedimentary rocks beneath the lake, it did indicate that a complicated pattern of
faults and folds was present. Some of the larger structures appeared to form 

potential petroleum traps if cap rock and adequate reservoir rock were present. 

Seismic-stratigraphic interpretations by Rosendahl (1981) suggest that potential 

reservoir rock, in the form of deltaic sandstone deposits, is being deposited in 

areas where large rivers empty into the lake. A reconnaissance survey of the 

mouth of the South Rukuru River area and a review of seismic records by the 

author of this report confirm the interpretations of Rosendahl (1981) concerning 

the probable presence of reservoir rocks.

In 1981, Shell Exploration B. V. explored the Lake Malawi and Lower Shire 

Valley areas with an aeromagnetic survey. In 1983, the company submitted 

to the government of Malawi a report of their results which has added much 

to the knowledge of the general geology of the rock layers buried beneath Lake 

Malawi. The data indicate that basement rocks lie at relatively shallow depths 

over much of the surveyed area. However, in the lake area between 10°30'S 

and 11°30'S latitudes, the sedimentary section is interpreted to be 2.5 to 3.5 

km thick over an area of approximately 2,000 km 2 . The area of thick sedimentary 

rock coincides approximately with Lake Malawi's deepest water depths--in excess 

of 500 m. Similar thicknesses of sedimentary rock may also be present in parts 

of the Lower Shire Valley although, in this area, the presence of a thick intrasedimentary layer of volcanic rock precluded accurate depth estimations. Following 

submittal of their report, Shell dropped their exclusive option to negotiate futher 

exploration rights. The company apparently felt that the quantities of oil and 

gas likely to be discovered in the Lake Malawi area did not justify the high 

expenditures (probably greater than $500,000,000 US) required to test drill in 

the extreme water depths of Lake Malawi. At the present time, the deepest 

water depths from which oil is produced is about 330 m; however, the technology
is available to test drill from large ocean-going vessels in water depths in 

excess of 2,000 m. The extreme high costs of drilling in Lake Malawi would be 

associated with costs of transporting a drill ship to the land-locked lake.

FUTURE EXPLORATION

The fact that large oil companies, at the present time, essentially are 

not interested in test drilling leaves Malawi facing a dilemma. On one hand, 

the import of petroleum, their derivatives, and nitrogenous fertilizer that 

can be made from natural gas is straining the economy of Malawi. On the other 

hand, to actually test Malawi's petroleum potential, drilling eventually will 

have to be done in deep water at extremely high costs. Malawi presently does 

not have the economic resources to undertake such a project and the possibility 

of its obtaining grants or loans of sufficient amounts for deep-water drilling 

is highly unlikely considering that petroleum, if discovered, will probably 

occur in relatively small quantities. Although low-cost techniques for subsea 

production in deep water may be available in the next few years, the cost of 

initial test drilling in deep water is not expected to decline. In fact, if 

oil prices continue to fall over the next 10 years as predicted by some economists, 

deep-water drilling worldwide will probably be limited to fields of super-giant 

size. However, if there is any chance of discovering oil and gas accumulations, 

Malawi may decide to pursue such possibilities.

In light of the above discussion, it may be in the best interest of Malawi 

to undertake small-scale geophysical and drilling operations, possibly with the 

help of foreign aid, in land areas immediately adjacent to Lake Malawi and in 

the Lower Shire Valley. Although it is unlikely that these operations will 

actually discover petroleum accumulations, the increase in knowledge gained of 

the subsurface geology could induce industry to explore further. For instance, 

if such small-scale projects were to show that sedimentary rocks of Miocene age
underlie Lake Malawi, the area would become much more attractive to industry from 

a viewpoint of petroleum potential. Similarly, if marine Cretaceous rocks exist 

in the Lower Shire Valley, the prospects for the occurrence of natural gas would 

be greatly echanced. Another possibility is that coal measures or black shale 

fades of the Karroo System may prove to be relatively thick at depth beneath 

Lake Malawi--such beds could provide rich source rock for the generation of 

natural gas.

In addition to providing insight into the subsurface geology of local 

areas, small-scale geophysical operations performed by foreign consultants in 

cooperation with the Malawi Geological Survey would provide a much needed learning 

experience for Malawi geologists in the techniques of obtaining and interpreting 

geophysical data. The Malawi Geological Survey at present has no capabilities 

for geophysical exploration. Furthermore, judical planning of such surveys could be 

done so that work would be performed in conjunction with further exploration 

for coal and water resource studies.

In the following sections of this report, suggested low-cost projects are discussed for the Lake Malawi area and the Lower Shire Valley.

NORTHERN LAKE MALAWI AREA

The results of the aeromagnetic survey flown by Shell indicate that significantly 

thick sections of sedimentary rock in the Lake Malawi graben are limited to two 

centers: one north of 11°00'S latitude and other south of 12°00'S latitude. It 

is reasonable to hypothesize, as was done by Crow and Chatupa (1982), that these 

depositional centers represent early stages of the graben's history and that they 

contain the oldest lake sediments. Therefore, if petroleum accumulations underlie 

Lake Malawi (fig. 1), they more than likely would occur in the vicinity of the 

depositional centers and it is in these areas that further studies should be 

concentrated.
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In addition to the seismic refraction survey on land, at least one seismic 

refraction profile should be recorded on the lake where aeromagnetic data 

indicate the thickest section of sedimentary rocks. Here again the objective 

should be to map the thickness of post-Karroo and Karroo rocks. This data would 

greatly supplement the Duke University seismic reflection data which did not 

differentiate post-Karroo from Karroo rocks. It is suggested that this survey 

be done in cooperation with future work by the university and possibly 

corrdinated with heat flow measurements on the lake to locate present-day 

hot spots in the northern part of the lake.

Thought should be given to coordinating onshore seismic refraction 

surveys for petroleum purposes with surveys designed for coal exploration in the 

nearby Karonga area. Such surveys should be designed to measure the dip 

and changes in thickness of Karroo beds beneath coastal-plain sediments.

Following the geophysical surveys, a hole should be drilled to test 

post-Karroo rocks. The primary objectives of the drilling should be:

(1) micropaleontological and palynological studies to establish 

the age of the oldest lacustrine sediments,

(2) temperature measurements to establish the geothermal gradient, 

and

(3) geochemical analysis of potential source rocks. These analyses 

can probably be performed on drill cuttings and continuous 

cores would not be required unless coal measures are penetrated. 

Thought should be given to obtaining a suite of geophysical logs 

from the test -- costs, however, may be prohibitive.

10
LOWER SHIRE VALLEY

The main objectives of further studies in the Lower Shire Valley (fig. 1) 

should include at least the following: (1) map the top and base of rocks of the 

Karroo system, (2) map the thickness of Cretaceous sedimentary rocks and 

determine their environment of deposition (marine, lacustrine, or terrestrial), 

(3) measure the geothermal gradient, and (4) map the extent of basalt flows.

Basement rocks, Karroo rocks, and post-Karroo rocks more than likely have 

large differences in velocity so that the top and base of the Karroo system 

can be mapped by simple seismic refraction techniques. The possibility of 

mapping the thickness of Cretaceous rocks and basalt flows will depend on 

measurements made during the actual field surveys.

It is suggested that at least 3 seismic refraction profiles be recorded-- 

2 perpendicular to the regional strike of the graben and one along the graben 

axis. Good road systems and easy access for cross-country profiles during the 

dry season would facilitate such profile orientation. In addition velocity 

measurements should be made on outcrops of the Cretaceous Lupata series, the 

Karroo system, and the basalt flows. The actual length of profiles and shotpoint 

locations should be determined as field work progresses.

Following completion and interpretation of the geophysical surveys and 

depending on the results of the survey, a test hole should be drilled with the 

objective of testing Cretaceous deposits, determining their environment of 

deposition, measuring the geothermal temperature gradient, and analysing samples 

of potential source rock. These analysis probably can be performed on drill 

cuttings and would not require more expensive coring.

Thought should be given to coordinating all geophysical work done in Lower 

Shire Valley with deep aquifer studies. Adequate water supply for irrigation in 

the valley is a serious problem and any knowledge of deep aquifer systems that

11
might be gained through geophysical work would be of great help to Malawi in 

formulating water resources programs.

ADDITIONAL WORK

In addition to the geophysical surveys outlined above, it is suggested 

that measurements of crustal thickness be made across the entire Malawi Graben. 

Such measurements would involve a single seismic refraction profile oriented 

approximately east-west across the entire country. Through such measurements, 

knowledge would be gained of the overall geologic structure of the Malawi 

Graben and provide information pertaining to past and present thermal regimes. 

This survey could be performed with the same equipment used in the other seismic 

refraction surveys.

The geophysical system employed should use geophones independent of cables 

or wires. This would involve the use of radio controlled geophones or systems 

with internal clocks that could measure travel times (shotpoint to geophone) 

with an accuracy of at least 2 milliseconds. Employment of such equipment 

would facilitate field work and allow access to regions otherwise inaccessible 

by roads.

In order that Malawi receive maximum benefit from a geophysical program 

the following suggestions are offered:

(1) Prior to the start of field work, a short course in theory and field 

techniques of seismic refraction methods should be given to the Malawi 

Geological Survey.

(2) Provide the opportunity for at least one Malawian geologist to work 

on data interpretation.

(3) Coordinate geophysical work for petroleum exploration with coal 

exploration in the northern Lake Malawi area and with water resources studies 

in the Lower Shire Valley.

12
(4) Take advantage of Malawian technical expertise as far as logistics, 

surveying, explosives technicians, labor, etc. when planning geophysical 

exploration.

(5) The Malawi Geological Survey should obtain field tapes from any future 

seismic reflection surveys done on the lake. Reprocessing of the data, such as 

removal of water-bottom multiples, could prove useful in further petroleum 

exploration.

SUMMARY

A relatively low-cost program aimed at increasing Malawi's knowledge 

of its petroleum potential should contain the following:

1) Onshore seismic refraction surveys in the Youngs Bay area and 

the Lower Shire Valley with the objective of mapping at least the top and 

base of Karroo rocks.

2) A single offshore seismic refraction profile in the northern part 

of Lake Malawi also to map the top and base of Karroo rocks.

3) An east-west oriented seismic refraction profile across the width of 

the country to measure crustal thickness.

4) Following interpretation of the geophysical data, it may be decided 

to drill test holes in the Youngs Bay and Lower Shire Valley areas. The 

objective of the Youngs Bay drilling would be to document the age of earliest 

Lake Malawi sedimentation and to measure the geothermal gradient. The objective 

of the Lower Shire Valley drilling would be to test for the presence of marine 

Cretaceous rocks.

5) The program, as outlined, should be coordinated with coal exploration 

in the Karonga area and water resources studies in the Lower Shire Valley. Such 

small-scale additional surveys, while the equipment is available within the 

country, would be useful to coal and groundwater studies in these areas.

13
REFERENCES CITED

Andrew, E. M , 1974, Gravity Survey of Malawi: field work and processing: 

Institute of Geological Sciences of Great Britain. Report No. 74/75.

Crossley, R., and Crow, M. J., 1980, the Malawi Rift in Geodynamic Evolution 

of the Afro-Arabian Rift System: Accademia Nazionale dei Lincei, Rome, 

Italy, p. 78-87.

Crow, M. J., 1982, The geological background and the start of the search or 

oil in Malawi: Geological Survey of Malawi Report MJC/33, 13 p., 9 figs.

Crow, M. J., and Chatupa, J. C., 1982, An Account of the Stratigraphy,

Structure, and Evolution of the Lake Malawi Graben: Report available

from Geological Survey of Malawi, 22 p., 9 figs.

Dumestre, A., 1980, Evaluation of Petroleum Exploration Possibilities in

Malawi: unpublished report available from the United Nations, N.Y. 17 p., 

3 figs.

Harris, N. J. W., Pallister, J. W., and Brown, J. M. 1956, Oil in Uganda, 

Geological Survey of Uganda Memoir.

Rosenthal, Bruce, 1981, Cruise Report: Rosendahl/Livingstone Seismic Surveys 

of Lake Malawi, June-July 1981, unpublished data available in files of 

Malawi Geological Survey.

Soule, R. P., 1976, Gravity interpretation, Malawi Africa: Report of Exploration 

Data Consultants Inc. for Superior Oil Company, 4 p.

Von Herzen, R. P., and Vacquier, v., 1967, Terrestrial Heat FLow in Lake 

Malawi, Journal of Geophysical Research, v. 72, No. 16, p. 4221-4226.

14