LOS FAXINAIS: ¿UNA PRÁCTICA SOCIOAMBIENTAL DEL PASADO?

As mentioned earlier, a distinction is traditionally made between conventional and non-conventional hydrocarbons. We will not deal with the case of condensates —light liquids sometimes associated with natural gas— because these reserves are generally included in the figures for the gas reserves, except, usually, in the U.S. and Canada. It should be noted however that condensates account for up to 20%, in terms of energy content, of the reserves of the field.

3.2.1 Conventional and non-conventional hydrocarbons

In this area also there is not a clear and precise definition of which hydrocarbons are conven-tional and which are not. A qualitative description of petroleum was given in Chapter 1.

Natural gas is described less in terms of quality parameters (calorific value, content of sulphur or inert gases such as CO2, etc.) than in terms of its origin. A distinction is made, therefore, between gases associated with oil or condensates and so-called dry gases (which account for two-thirds of present world gas reserves). Whether a particular gas deposit is considered conventional or not depends on how difficult it is to extract and put into production.

Colin Campbell, Alain Perrodon and Jean Laherrère (1998) regard conventional hydro-carbons as being hydrohydro-carbons which can be produced in the technical and economic condi-tions of the present and the foreseeable future. This definition, which is very close to McKelvey’s definition of proven reserves (see Section 3.1), allows however for technological progress and future economic circumstances. Non-conventional hydrocarbons therefore become, putting it somewhat simplistically, those which are difficult and costly to produce.

But it is extremely difficult to know what the technical and economic conditions will be in the future. The impact of a new technology on the extraction of hydrocarbons can be measured post hoc, but how can we predict where technology will be in 20 years?

This is well exemplified by the deep offshore sector. At the end of the 1970s all offshore hydrocarbons situated in water at a depth greater than 200 metres were considered non-conventional (and therefore not included in estimates of proven reserves). The technology of the time was simply not able to put these resources into production profitably. Nowadays

Chapter 3Hydrocarbon reserves

we commonly envisage producing from reservoirs in depths of water 5 or 10 times as great, i.e. at depths of 2 000 metres. The boundary between conventional and non-conventional hydrocarbons has retreated considerably over time.

Heavy and extra-heavy hydrocarbons furnish another example. The Orinoco basin in Venezuela, which has been known since the 1930s, contains extra-heavy crudes (8–10°API).

In 1967 a first evaluation of the total resources present there arrived at an estimate of 693 Gbbl (i.e. equivalent to more than half of the world’s proven reserves of conventional oil). The position in 1967 was therefore: resources = 693 Gbbl, reserves = 0! A new evalu-ation in 1983, however, estimated the resources to be 1 200 Gbbl and the reserves (these were strictly speaking not proven reserves) to be of the order of 100 to 300 Gbbl.

It can be seen, therefore, that the boundary between conventional and non-conventional tends to be pushed back over time in the direction of hydrocarbons which are more and more difficult to produce in terms of production conditions, situation, quality and overall, in terms of extraction costs. However geopolitical factors also come into play, modifying this picture somewhat. In the Middle East, for example, oil tends to be easy to produce and abundant.

One of the consequences of the oil price shocks², however, was to enable the discovery and commercial production of less accessible petroleum throughout the world. The oil which is cheapest to produce is therefore no longer necessarily the only or even the first resources to be exploited.

Non-conventional hydrocarbons are therefore the reserves of the future. This shifting of the boundary is referred to by some authors as the fossil carbon continuum. When the reserves of a certain type of hydrocarbon which can be produced are exhausted, other types are sought, including non-conventional hydrocarbons. Gradually, and with the help of tech-nological progress and political exhortation, the production of these new hydrocarbons becomes the norm, becomes conventional or “conventionalised”. We have therefore grad-uated from oils in the U.S., Algeria and the Middle East which are easy to produce, to offshore, and are now turning to extra-heavy oils and ultra-deep offshore hydrocarbons.

The main families of non-conventional hydrocarbons are considered in the sub-sections below.

3.2.2 Deep and ultra-deep offshore

A distinction is generally made between deep offshore (between 400 meters and 1 500 meters water depth) and ultra-deep offshore (up to 1 500 meters). The former can nowadays be easily accessed, thanks to advances in data processing and their application to 3D seismic data.

Deep and ultra-deep offshore reserves are estimated between 160 Gboe and 300 Gboe (IEA, 2005). More than 70% of these reserves are located in Brazil, Angola, Nigeria and United States. Today, most of the production comes from the Gulf of Mexico but the growth is expected from Angola and mainly Brazil with the pre-salt discoveries.

3.2.3 Heavy, extra-heavy oils and oil sands

An oil is termed heavy if its API gravity is less than 22°. Below the range 12 to 15°API it is referred to as extra-heavy. Many of these deposits are referred to as oil sands. These

Chapter 3Hydrocarbon reserves

2. Term referring to large and abrupt changes of price, see Chapter 1.

substances are genuine petroleum, having passed through the entire cycle which characterises the formation of petroleum. They originate from hydrocarbons expelled from a source rock into a reservoir (generally sand), often very large in size. Long oxidation and the gradual disappearance of the lighter fractions have resulted in extra-heavy and extremely viscous oils.

The two main examples of deposits of this kind are the oil sands of Athabasca in Western Canada and the Orinoco belt in Venezuela.

The total resources of these oils are considerable: of the order of 4 700 Gbbl, i.e. four times the proven reserves of conventional oils! More than one-third (1 700 Gbbl) of these resources are found in Canada, with 870 Gbbl in Athabasca alone. Russia may have 1 500 Gbbl of heavy oil resources, although the official statistics do not indicate the densities involved, which makes classification risky. After Russia, Venezuela possesses 1 200 Gbbl in the Orinoco belt. The U.S. and Indonesia also have large resources.

Oil sands have so far remained within the domain of non-conventional oils, despite the vast resources involved. Today, only 5% of these resources appear to be economically viable. By 2025–2035 the recovery ratio may have reached a threshold of 15–20%, whereby oil sands could be regarded as a conventional hydrocarbon.

3.2.4 Oil shales

Oil shales are not oils in the same way as the aforementioned hydrocarbons. They do not originate from the migration of oil from source rock to a reservoir, but remain in the source rock. The source rock is usually a clayey sedimentary rock which can produce oil after under-going crushing and pyrolysis at a temperature of about 500°C. The production of oil from shale requires heavy industrial installations. Shale can claim a first in petroleum history: at the beginning of the 20th century there were numerous sites where shale was quarried throughout the world. These shales produced surface outcrops which were of course exploited. At a time when petroleum geology was virtually non-existent, no exploration was needed to find these deposits.

Shale can be found on all five continents, as can be seen from Table 3.2, but the largest deposits occur in the U.S.

Except in the U.S. and in Estonia, the oil produced from shales is currently confidential.

The process produces large volumes of solid waste and CO₂, and these will lead to additional environmental protection costs. Furthermore, enormous quantities of water are required.

For example it has been calculated by the company Unocal that it would be necessary to use the entire flow of the Colorado river in order to produce commercially from the Green River Canyon shales.

Chapter 3Hydrocarbon reserves

Table 3.2 World resources of oil shales (Gbbl).

US South Australia Africa Former USSR Asia

America (unofficial) (unofficial)

200

Resources 2 200 800 (of which 20 of 115 1 400 2 800

Stuart shale oil)

3.2.5 Synthetic oils

The Fischer-Tropsch process for converting gas or coal into synthetic oil was developed in Germany during the second world war (see Chapter 1), where it was the only source of motor fuel. The process remains a difficult one. The market for synthetic oil produced from gas could grow. Until recently, there were only a few units which convert gas into oil —a production capacity of 100 kbbl/d from 30 Mm3/d of gas— notably in Malaysia (Shell experiment) and South Africa (a remnant from a boycott by producing countries provoked by the policy of apartheid. Things have changed with the new market conditions based on a higher crude oil price. New projects are now under consideration. In the Pearl Gas to Liquids project, Shell and Qatar Petroleum are investing hugely to build two 70 kbbl/d trains dedicated to convert gas into oil. China has turned its attention to coal liquefaction technology. In 2004, Shenhua Group, the country’s largest coal producer, was assigned a project to build a coal liquefaction plant in northern China. The first phase is intented to bring on stream annual production capacity of 1 Mtoe output by 2008. A second phase could then raise the project to its full design capacity (100kbbl/d of oil equivalent output). South African Sasol sees also coal to liquids potential in China (feasibility studies are conducted for two 80 kboe/d plants) and in the US (in Montana, Illinois and Wyoming).

Chapter 3Hydrocarbon reserves

3.2.6 Non-conventional gas

The resources of non-conventional gas are thought to be considerable, but are not yet well charted. Reservoirs of non-conventional gas are characterised by low recovery rates: of the order of 10–20%, against about 80% for conventional gasfields. These are reservoirs in which the entrapment mechanism is very different from that of conventional reservoirs.

The three main types of non-conventional gas originate from:

– Coal deposits (coalbed methane);

– Shales and formations with a low permeability (tight sands);

– Gas in solution in aquifers and zones of geopressure.

Gas obtained from coal deposits in the U.S. are the best known. But estimates of US resources vary between 2.8 and 9.8 Tm³. The other countries with large resources are China (30–35 Tm³), Russia (20–100 Tm³) and Canada (5–75 Tm³). The figures tell their own story

Figure 3.3 Possible applications of the Fischer-Tropsch process.

as to the uncertainty attaching to the estimates. Production remains limited but is growing significantly in the US —where 45 Bcm were extracted in 2004— and in China where 10 Bcm could be produced in 2010.

Tight gas sand reserves figures remain unknown. Canada estimates vary in the range 2.5–42 Bcm. US ressources are estimated to 7 Bcm. Production is growing. In 2005, 100 Bcm of natural gas were extracted from tight gas sand reservoirs in the US.

As far as shale gas is concerned, figures of 100 Tm³have been suggested, but 40 Tm³is probably a more realistic figure. In any case, production is mainly located in the US (17 Gm³ per year in 2005).

The solubility of methane in water depends greatly on pressure and temperature (for example 17 m³per m³of water at a depth of 6 000 m and up to 170 m³at 10 000 m). Because of the sensitivity of the calculation to the conditions within the trap, estimating the resources present can be a perilous undertaking, and the figures which follow are of a highly specu-lative nature. Russia has estimated that its resources are 1 000 Tm³, and U.S. estimates vary in the range 30–200 Tm³(including 150 Tm³for the Gulf of Mexico alone). In the early 1980s an estimate of 1 000 Tm³were made for a single reservoir in the Gulf of Mexico!

The production of non-conventional gases is growing fast in North America and China.

In any case, production remains limited compared to conventional gas extraction..

3.2.7 The polar zones

Several fruitful exploration programmes have been carried out in the Arctic, and these have identified some 10 basins with real potential. Most of these basins are in Alaska, Greenland and Russia, the latter looking the most promising. In the Arctic as a whole, resources of 8 700 Gbbl of oil and up to 20 Tm³ of gas have been discovered. However the fields concerned probably contain much more gas than has been announced. It should not be forgotten when considering these figures that production of these resources will be particu-larly difficult given the very harsh climate, the ice cover, the lack of infrastructure and the remoteness of the site from existing markets.

The Antarctic, on the other hand, looks very much like being the poor relation of its Northern counterpart. The geology of Antarctica seems unpropitious for the discovery of significant deposits of oil. Furthermore, quite apart from the difficulties associated with the extreme climate and inaccessibility, all industrial activities on this continent have been forbidden since 1991, in order to preserve its environment.

3.2.8 Other types of non-conventional hydrocarbons

There are many other categories of non-conventional and other hydrocarbons, for example:

• Very small fields (less than 10 Mboe) are classified as non-conventional. There are very many such fields. But their small size makes them difficult to find. Furthermore there needs to be pre-existing infrastructure nearby. Development costs must be kept low if very small fields are to be remotely profitable.

• Oils won by assisted recovery techniques are themselves sometimes treated as being non-conventional products, although most of these techniques are becoming standard.

• High-pressure, high-temperature (HP-HT) reservoirs are subject to the same kind of inconsistencies because the various record-keeping agencies do not use the same pressure and temperature criteria (these vary around 700 bar and 150°C) for classification. This

Chapter 3Hydrocarbon reserves

means that fields with the same pressure and temperature characteristics may sometimes be classified as conventional and sometimes as non-conventional.

• Gas hydrates are very important potential sources, and some authors consider that these may exceed in magnitude the total known reserves of hydrocarbons. These are gases in a solid form which occur in the form of crystalline hydrates. It is impossible to say now whether we will one day be able to transform these resources into reserves. Two hurdles will have to be overcome to make the production of these substances viable: their low energy density and the considerable input of energy needed to transform them from a solid into a gas.

3.3 THE PRODUCTION OF RESERVES