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Sofala
Mozambique is located in southeast Africa with an extensive area of 306,642 sq miles (approximately 800,000 sq km). The major cities include the capital city of Maputo, Beira, Matola, Nampula, Quelimane, Tete, Nacala, and Pemba. The terrain varies from lowlands to high plateau with a climate range from tropical to subtropical. Mozambique has an enormous energy potential, which provides the country with favourable means to fulfil its domestic and regional energy needs for southern Africa and beyond. The latest discoveries of natural gas, estimated at 277 trillion m3, puts Mozambique in a very privileged position both in the region and in the world.
Country:
- Africa > Mozambique > Maputo City > Maputo (0.26)
- Africa > Mozambique > Cabo Delgado > Pemba (0.25)
- Africa > Mozambique > Zambezia > Quelimane (0.24)
- (4 more...)
Oilfield Places:
- Africa > Mozambique > Temane Field (0.99)
- Africa > Mozambique > Pande Field (0.99)
- Africa > Mozambique > Mozambique Basin (0.99)
- (2 more...)
SPE Disciplines:
Introduction Summary We lay out a case history of a multi-method airborne geophysical survey performed to assist a hydrocarbon exploration project in central Mozambique. The dedicated targets of the survey are near surface resistivity anomalies caused by hydrocarbon seepage plumes. The geophysical survey concept includes the use of time-domain electromagnetics, magnetometry and gamma-spectrometry applied from rotary and fixed wing aircraft. Preliminary data interpretation, closely tied to 2D seismic and regional geological information, results in the successful delineation of a seepage alteration zone just one month after survey completion. Airborne Electromagnetic (AEM) resistivity mapping has been used by the oil industry to some extent since the 1990´s when airborne multi-method surveys were conducted to outline near surface alteration zones caused by hydrocarbon seepage plumes (Smith & Rowe, 1997). The correlation between hydrocarbon seepage and anomalies of the electrical properties of near surface sediments has been investigated broadly using of land-based EM and resistivity methods (Sternberg, 1991 and Hughes, 1983). No significant activities in this field have been reported since then, however. AEM exploration for base metals has been booming over the last decades, mainly driven by a steady rise in commodity prices. Although oil and gas prices have increased significantly as well, few AEM developments have been reported in this field. Nevertheless, high energy-prices enabled oil and gas companies to widen their horizons and investigate the use of unconventional methods such as AEM for hydrocarbon exploration. In early 2008 we had the opportunity to initiate a multi-method airborne geophysical survey in a petroleum exploration license in Mozambique based on the evidence of gas seepages in the area. As a multidiscipline group consisting of a Norwegian oil & gas exploration and production company, a geoscience research and consulting institute as well as geophysical service and software development providers in Canada, we planned and successfully conducted this survey over an area of some 2000 km2. This survey combined helicopter-borne time-domain EM with a magnetic and gamma-spectrometry survey. Here we describe the survey planning, processing and initial interpretation phases highlighting the findings and value we obtained from the data. Survey area The AEM survey area is located in the Republic of Mozambique within the onshore Inhaminga block situated north of Beira and south of the Zambezi River. The Inhaminga block covers an area of 16,500 square kilometers and is located some 200 km from the Pande and Temane gas fields. The AEM survey covers an area of roughly 50 x 40 km located in the northern area of the license, close to Inhaminga (Figure 1). Main flight lines are about 45 km long heading NW-SE with 500 m line spacing. Geology The Urema Graben was formerly interpreted to represent the southernmost part of the East African Rift, but new seismic surveys show the main rift period to be Mesozoic in origin. Only a thin portion of the graben fill can be ascribed to the East African Rift episode (the sequence above the Oligocene in Figure 2). The Urema Graben forms a half-graben with the main fault located just west of the Inhaminga High.
Geologic Time:
- Phanerozoic > Cenozoic > Paleogene (0.35)
- Phanerozoic > Mesozoic (0.34)
Geophysics:
- Geophysics > Electromagnetic Surveying (1.00)
- Geophysics > Seismic Surveying > Surface Seismic Acquisition (0.35)
Oilfield Places:
- Asia > China > Hubei > Jianghan Basin (0.99)
- Africa > Mozambique > Temane Field (0.94)
- Africa > Mozambique > Pande Field (0.94)
SPE Disciplines: Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
This paper presents an equipment to perform shear tests under low constant normal stresses. This equipment maintains a normal stress during the whole joint sliding by means of a lever arm and dead weights. For common joint samples (around 100 to 150 cm), the applied normal stresses can range from 20 to 200 kPa. The results of some sets of joint tests are presented. The joints came from road cuts in the central part of Portugal. One of the sets is from quartzite discontinuities and the remaining are from schistous discontinuities. A description of the geological characteristics of the joints and the analysis of the results of the tests are presented. 1. GENERAL REMARKS Rock slope stability analyses require the knowledge of the shear strength of the most relevant discontinuities. The determination of the strength parameters should be evaluated by shear tests. These tests should reproduce as close as possible the features that occur in the field. In this case, normal stresses are low, typically smaller than 0.2 MPa, and should be kept constant during the sliding. In the proposed paper, a new equipment to perform shear tests under low constant normal stresses is presented. This equipment maintains a normal stress during the whole joint sliding by means of a lever arm and dead weights. For common joint samples (around 100 to 150 cm), the stresses used can range from 20 to 200 kPa. These values of normal stress cover the range of stresses that can commonly be found in road cuts. The height of this kind of slopes, which are particularly frequent in mountain roads, can go from 10m to around 40 m. This paper presents the results of some sets of joints. The joints came from road cut slopes in the central part of Portugal. One of the discontinuity sets is from jointed quartzite discontinuities and the remaining sets are from schistous discontinuities. A description of the geological characteristics of the joints is presented and an analysis of the results of the tests is also put forward. 2. GEOLOGIC FRAMEWORK The shear tests were performed on joints prepared from rock material collected in 4 rock slopes from road cuts in the central part of Portugal. The roads are the IP3 (Itinerario Principal n3) and the EN 234 (Estrada Nacional n° 234), near Coimbra. In both cases, they are located in the Buçaco Ordovician-Silurian Syncline and in the Schist-Greywacke pre-Ordovician Complex (Beiras Group). Slope 1 is located at km 55 of the IP3. It develops along 150 m and is placed close to the central zone of the Buçaco Palaeozoic Syncline. This slope is composed mainly by impure quartzites, though schists and carbonaceous schists are also present. The latter display a dark colour and are very weathered (W5). The impure quartzites are set in persistent benches with a weathering degree ranging from W2 to W4. They present purplish, greyish and whitish colours and are composed primarily by quartz (more than 75%) and white mica and ferrous oxides.
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