anglais gas shale.docx

8/11/2019 Anglais gas shale.docx

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Shale gas exploitation worldwide

Shale gas is natural gas, it is not retained in an impermeable layer, so-called

"conventional" gas or oil deposits, but trapped within the rock itself.Shale gas is usually embedded very deep (1500-3000 meters) in sedimentarybasins, in compact and impermeable rock. It is estimated that its reservescould provide 120 to 150 years of current consumption of natural gas.Shale gas is the gas source rock is an unconventional gas.

In the past, the oil and gas industry considered shale gas uneconomical toproduce. However, advances in directional well drilling and reservoirstimulation have dramatically increased gas production from unconventionalshales.

Recent high natural gas prices have also stimulated interest indeveloping gas shales. The decision to exploit a field result of several yearsof study :

Gas shale is characterized by a very less permeability and moderateporosity.

Gas shale log is a high Gamma-ray, a high resistivity, a low density, a high

neutron and sonic porosity and low Pe.

Identification and development of shale gas resources by collection of coresamples from drilled wells or through drilling of selective coreholes into suchshales to generate the following data :

- data on shale lithology : mineralogy and thickness- Extension of high gamma ray zones and intercalation of sandstones orsiltstones

- rock property data : porosity, permeability, density- Pyrolysis data to identify the type and maturity of organic matter and todetect hydrocarbon potential in sediments.- gas content data.

Recording, analysis and interpretation of different log data.

Developing data base, building geologic models and assessment of

resource potential of basins, also assessing the recoverable resources inshale gas.



The research aims to optimize the exploration of basements.The main objectives is to improve the efficiency of fracturing techniques andreduce water consumption.

Optimal shale gas exploitation require modern technologies such as :

- Drilling horizontal wells- Introduction of modern rigs- Hydro fracturing

It’s require large volumes of water to hydraulically fractures

require high density drilling, well spacing

To extract shale gas must make a fracturing of the rock, and the gasobtained after water injection pressure: this is called hydraulic fracturing.

horizontal drilling and well completion technologies, including multi stagehydraulic fracturing

a typical gas well require 7-10 stages of hydrofracturing and 3-5 lacsgallons of water for 1 stage of hydrofracturing

The frac water is recycling for reuse in other wells after a little chemical

treatment

Gas in shale is stored in three ways in the shales :

- free gas in the rock pores- free gas in the natural fractures- absorbed gas on organic matter and mineral surface

Shale gas wells are not hard to drill, but they are difficult to complete.

In almost every case, the rock around the wellbore must be hydraulicallyfractured before the well can produce significant amounts of gas. Fracturinginvolves isolating sections of the well in the producing zone, then pumpingfluids and proppant (grains of sand or other material used to hold the cracksopen) down the wellbore through perforations in the casing and out into theshale.The pumped fluid, under pressures up to 8,000 psi, is enough to crack shaleas much as 3,000 ft in each direction from the wellbore. In the deeper high-pressure shales, operators pump slickwater (a low-viscosity water-basedfluid) and proppant. Nitrogen-foamed fracturing fluids are commonly pumpedon shallower shales and shales with low reservoir pressures.



Exploitation of these deposits is expensive and poses risks to theenvironment, in the underground, in groundwater and at the surface.

The hydraulic fracturing treatments used to stimulate gas production fromshale have stirred environmental concerns over excessive water

consumption, drinking water well contamination, and surface watercontamination from both drilling activities and fracturing fluid disposal.The saline “flowback” water pumped back to the surface after the fracturingprocess poses a significant environmental management challenge. Theflowback’s high content of total dissolved solids (TDS) and othercontaminants must be disposed of or adequately treated before discharged tosurface waters.

the risk on the sheets of water (les nappes d’eau) : Hydraulic fracturingposes a potential risk to water wells and thus domestic drinking water supply.

The concern is that the chemicals used pose a potential risk to groundwaterquality, and the fracturing may damage aquifers.the large quantities of water that hydraulic fracturing consumes may tax localand regional water supplies and that disposing the “flowback” extracted fromthe shale after fracturing may affect surface water and groundwater quality.

Projects Gas shale is temporarily suspended for environmental risks.

anglais gas shale.docx

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