The Frontier Geology Department is aptly named as its focus is the evaluation and promotion of South Africa's unconventional gas resources, including shale gas, coal-bed methane, deep basin biogenic gas and gas hydrates. These are new and exciting areas of exploration about which relatively little is known and can therefore truly be considered 'frontier' or greenfield exploration.
Our evaluation of South Africa's unconventional gas resources is based both on geographic distribution and play-type, with a specialist geologist associated with each (see the team structure provided below).
Part of the Department's responsibilities is the assessment of the petroleum potential of the deep and ultra-deep offshore areas. As such, it is responsible for executing the Agency's mandate to delimit South Africa's claim for an extended continental shelf beyond the current 200 nautical mile limit to the Exclusive Economic Zone.
|Manager:||Sean Johnson*||Unconventional Resources Evaluation Manager|
|Geologists:||Anthony Fielies*||Gas hydrates; deep offshore beyond areas currently considered commercial|
|Tshifhiwa Thovhogi*||Deep biogenic gas; coal-bed methane; central and western Main Karoo Basin|
|Selwyn Adams||Shale gas; south and central Main Karoo Basin|
|Caiphus Motsoaledi||Shale gas; Karoo|
|Zainab Mowzer||Geologist Shale gas|
|Xavier Schalkwyk||Geologist coal-bed methane and data management|
|Sibongile Ngini*||Geologist Shelf claim, coal-bed methane|
|Admin Support:||Anthea Julius||PA: Unconventional Resources Management Department|
* Members of the Extended Continental Shelf Claim Project
The southern Main Karoo Basin is considered to be the most prospective area for shale gas in South Africa, due to the presence of deeply buried, thermally mature black shales. To date, exploration right applications have been received from Shell International, Falcon Oil and Gas in partnership with Chevron, and Bundu Gas.
Natural gas and oil shows across the Main Karoo Basin indicate an active petroleum system with multi-play potential. The widespread occurrence of pyrobitumen (pseudo-coal) in the southern part of the basin indicates an originally oil-prone source rock.
In 1968, exploration well CR1/68 in the southern Main Basin yielded a gas flow rate of 1.83 mmscf/day for 23 hours from the fractured Fort Brown shale. The Fort Brown was thought to be self-sourcing (i.e. a gas shale), but may also have been charged by the underlying Whitehill Formation.
The volume of gas in place in the Main Karoo Basin is highly uncertain, but possible scenarios suggest that technically recoverable volumes may range from 30 Tcf to 500 Tcf. A key uncertainty is the gas content of the various Karoo shale formations – this may be limited where diagenesis is particularly high.
The Permian Whitehill Formation is considered to be the most promising shale gas target in the Karoo, due to its high organic carbon content (TOC = 5 % average), high thermal maturity (Ro = 1-4 %), high quartz content (50 %), thickness (30 m average) and regional continuity (200 000 km2). However, a major exploration risk factor is the existence of dolerite intrusions, which occur in much of the Karoo Basin.
Karoo shale gas is considered to be only a prospective resource at present, and will remain undiscovered until a hydraulically fractured test well produces enough gas to be of commercial interest. The economic value of Karoo shale, in turn, will only be known once a statistically significant number of well flow rates have been measured. The long term market for gas in South Africa is likely to be strong as the country's energy needs continue to grow. However, a significant investment in infrastructure will be required before South Africa becomes a major shale gas producer.
Coal bed methane (CBM) is a source of natural gas that is generated and stored in coal beds. Coal therefore acts as both the source and reservoir rock, with the methane being produced by microbial (biogenic) or thermal (thermogenic) processes. Coal has a large surface area and can hold enormous quantities of methane. Since coal seams have large internal surfaces, they can store on the order of six to seven times more gas than the equivalent volume of rock in a conventional sandstone gas reservoir. CBM exists in the coal in three basic states: as free gas; as gas dissolved in the water in coal; and as gas "adsorbed" on the solid surface of the coal.
In South Africa, the presence of methane gas in coal is well known from its occurrence in underground coal mining, where it presents a serious safety risk. Historically, the methane was vented to the atmosphere, but is now becoming an increasingly important source of natural gas globally. The coal deposits in South Africa are found within the Karoo basin and fault bounded rift basins further north. These basins are host to large volumes of coal and where the coal concentrated with methane gas, this holds potential for significant future sources of energy
The Deep Biogenic Gas (DBG) refers to the occurrences of hydrocarbons in the deep mines within the Witwatersrand Basin in South Africa. DBG is an unconventional gas produced at great depth directly by microorganisms during respiratory and fermentative processes (microbial gas). Substantial quantities of hydrocarbon gases have been observed within the Witwatersrand Basin during both coal and gold exploration activities. The gas is composed predominantly of methane, and other hydrocarbons including helium. Gas shows were discovered in the Free State and Evander goldfields several decades ago, and are the most promising target areas for DBG exploration at present.
The methane encountered in underground gold mining of the Archean Witwatersrand Basin in the Free State and Evander goldfields was regarded only as a mine explosion hazard and flared in large quantities. As such, local gas shows at surface have also been known to burn for years without showing any evidence of depletion. Gas encountered is not generally contained in traps but rather is being continually generated at depth and migrating to surface along natural fracture systems, faults and dykes. Published data indicates that much of the produced gas is of microbial origin, generated by primitive bacteria that inhabit deep water-bearing fissures. It is thought that additional gas may be generated within the carbonaceous shale and coal-bearing Karoo strata at shallower depth. However the source and migration pathway of the gas are unusual and present significant challenges to fully define the ultimate potential of the resources as no known analogues exist for this type of gas production.
Most recently, Molopo Exploration and Production (Pty) Ltd in South Africa has been granted the Production Right in the Free State goldfields, with first proven onshore gas reserves for the region. This former mining hazard may therefore become a potential renewable future energy source for South Africa.
Frontier Offshore encompasses those areas which have seen minimal exploration up to and beyond the 200NM EEZ. Little or no geoscience data (e.g. wells, seismic), a lack of geological knowledge and understanding, are some of the key stumbling blocks in these regions. In the Orange Basin for example, ultra-deep waters in excess of 3000m adds to the challenges in investigating these areas by traditional methods alone. However, recent advances in geophysical acquisition and remote sensing techniques have made these offshore areas more accessible to exploration.
The Agency embarked on a frontier pilot project in 2010 within the Orange Basin. Existing data such as wells, seismic, etc. available on the Continental margin on the West Coast of South Africa were used to extend geoscience interpretation into frontier regions. The Orange Basin Basin Analysis (OBBA) project aims to address and aid current knowledge and understanding of the Basin, in particular the deeper parts. Ultimately the project hopes to unlock new conventional and unconventional resources.
One of these unconventional resources, gas hydrates occurs in permafrost regions of the arctic and in deep-water along continental margins worldwide. Gas hydrates are solid ice-like structures in which mostly methane are trapped within water-cage like molecules. It is important because it contains vast volumes of methane which indicates its potential as a future energy resource. Secondly extracting gas hydrates may affect sediment strength, which can initiate landslides along a continental slope and rise. Lastly the release of gas hydrates to the atmosphere can influence global climate. Gas hydrates can be studied in two ways: wells and on seismic reflection lines as Bottom Simulating Reflectors (BSRs). A BSR is formed on seismic reflection lines because of a contrast in velocity generated by the hydrate-cemented zone. The stability of natural gas hydrates is primarily affected by temperature and pressure, and secondary by pore fluid salinity, the nature of gas enclosed and the grain size of the host material.
BSRs have been recognized on multichannel seismic imagery along the South African continental margin, especially along the upper continental slope in the regions of the Orange River delta. Though no discoveries have yet been made, gas hydrate has been discovered north of the Walvis Ridge offshore Namibia. Gas hydrates along the South African margin are stable at water depths >420m and bottom-water temperatures of ~7°C.
Estimation methods to delineate and quantify the amount of gas hydrates are: acoustic impedance inversion of seismic data, Vp/Vs, Rock Physics, AVO and seismic attribute analyses. Until recently, only two methods for extracting methane from hydrates offshore were employed. One was the release of pressure of the hydrate by drilling a hole into it, the second by pumping in steam or hot water, releasing the methane from the hydrate. A third method recently introduced is CO2 injection.
The Agency initiated a gas hydrate project in 2011 along the west coast of South Africa in order to document the existence and regional distribution of gas hydrates.