Tanzania has been exploring natural gas for more than 50 years.
The first natural gas discovery in Tanzania dates back to 1974 on the Songo Songo Island, located in Lindi Region, followed by a second discovery in 1982 of the Mnazi Bay gas fields located in Mtwara Region.
Natural gas was reported to be found at Kiliwani North fields, adjacent to Songo Songo island.
What is Natural Gas?
Natural gas is a naturally occurring fossil fuel mixture of hydrocarbons and non-hydrocarbon gases. It is composed primarily of methane (CH₄/C1), with smaller amounts of other hydrocarbons, ethane (C2), propane(C3), butane(C4), and trace non-hydrocarbon gases like carbon dioxide, nitrogen, hydrogen sulfide(H2S), helium, and Argon.
The gaseous compositions of this gas vary mostly depending on the field where it’s produced, with natural gas containing hydrogen sulfide (H2S) being termed as ‘Sour gas’ and ‘Sweet gas’ for the opposite.
In its original/natural state, natural gas is odorless, colorless, tasteless, non-toxic, and lighter than air.
Its Formation
Like any other fossil fuel, natural gas is found deep underground. The gas comes from living organisms, both plants and animals, which lived some time ago, died and buried over time as sediments accumulated on top of the corpse. This is why most Oil & Gas deposits are located in sedimentary rocks.
In regions with basin-like structures (i.e., valleys and rifts), sediments are well accumulated and settle, making these geological formations potential in the search for Oil & Gas.
Over millions of years, with bacteria slowly breaking down this organic matter, the heat and pressure inside the Earth turn the decaying remains into fossils, and then into natural gas or crude oil in a process known as diagenesis (cooking for short).
A configuration known as a gas trap allows the natural gas to form and collect. The trap contains three kinds of rock.
- The source rock, which is fossilized to produce natural gas.
- The reservoir rock, a porous & permeable rock formation that the natural gas seeps into as it rises due to differences in density.
- A cap rock/seal, which is the layer of a very dense rock above the reservoir rock that keeps the gas from leaking to the surface.
Classification of Natural Gas
There are several ways to classify and categorize this fossil fuel, we will focus on the specific gravity (SG). Such classification isn’t a standard practice in the industry, as natural gas is typically classified based on its composition, heating value, or sulfur content (e.g., sweet vs. sour gas).
Specific gravity can be relevant in certain contexts, such as gas processing, pipeline design, or LNG production, as it indicates the density of the gas relative to air, methane content, and the presence of heavier contents (both hydrocarbon and non-hydrocarbon).
| Specific Gravity (SG) | Gas type | Characteristics |
| 0.55 – 0.65 | Lean Gas | Lightest natural gas, close to pure methane (SG ~0.55). Low energy content per unit volume but high heating value per unit mass. Common in dry gas fields. |
| 0.65 – 0.75 | Intermediate Gas | Balanced composition, common in many conventional gas fields. Moderate energy content and density. |
| 0.75 – 0.9 | Rich Gas | Heavier and denser gas, often called “wet gas” due to high liquid content. Higher energy content per unit volume, but requires more processing. |
Tanzania’s latest estimated natural gas reserves as of 2016 was about 57 TCF in place, with the gas’s SG falling in the range 0.55 to 0.65, making it a Lean gas.
One of the best traits for such gases is that they have high methane content (90–98%), minimal heavier hydrocarbons, and low levels of non-hydrocarbons, making the gas ideal for LNG production and/or consumption with minimal cost for processing. This is what makes Tanzania’s natural gas a beauty and attraction for investment.
What does the future look like?
McGraw-Hill Companies Inc. had reported the fuel usage over the past decades as shown below.
Likelihood to see an increment in Gas usage (probably doubled or tripled) with a major turn of events as the world looks towards clean energy solutions.
Tanzania is on track, as it has witnessed more discoveries in the past decades, with plans to propel further gas exploration in both onshore and offshore.
