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How is a conventional hydrocarbon deposit exploited?

We saw in the previous blog post (#5) what a conventional hydrocarbon deposit is, and above all that this kind of deposits could be present in importance in Quebec.  Let us remember that they do not require fracturing for their production.

Here is a simple description of the production processes used:

This operation requires the drilling of a hydrocarbon production well down to the depth of the resource to be extracted. In order for this well to be completely independent and insulated (i.e. without any communication between the hole and the host rocks), sealed steel pipes (“casing “) are inserted and cemented in place:

            -A first one, from the surface up to about 10% of the total depth of the well (Conductor pipe),

            -A second, in the conductive pipe from the surface up to about 100 meters above the zone to be            produced (Intermediate casing),

            -A third, from the surface to the bottom of the production zone (Production casing).  

These pipes are cemented in a perfectly watertight way in the hosting rock and one in the other.  They are put in place to first isolate and protect the groundwater but also to prevent any contamination of other porous zones that may be present between the surface and the area to be produced. In order to be able to exploit the resource, the production pipe is perforated within the porous levels of the reservoir enabling the hydrocarbons to flow freely because of the simple action of the pressure differential (pressure caused by the weight of the rock column in the reservoir and atmospheric pressure in the hole). A series of valves installed at the well head (“Christmas tree”) control pressure and flow to prevent and compensate for any contingencies.

As the reservoir is already naturally porous and permeable by definition, the well responds to natural mechanisms: the inside of the well being more or less at the surface atmospheric pressure, a phenomenon of suction occurs in the well causing the oil to flow to the surface.  As the oil is floating over the formation water and is also covered by a lighter gas cap which is tending to expand, the oil can be produced until the time when the gas and/or the water will take over. Generally, one can hope to produce the oil present in this type of reservoirs with a recovery rate varying between 5 and 30%. Recovery rates are a direct function of the average porosities and permeabilities encountered in the reservoir.

Throughout the production period, the pressure in the reservoir is dropping and natural recovery becomes less effective. To maintain a better production, fluids are injected into the reservoir: Such as water below the oil production zone or natural gas above the oil zone in the gas cap.

When the possible recovery rate of the resource becomes unprofitable and no other hydrocarbon zones in the well can be produced, the well is abandonedby installing cement plugs at different intervals up to the surface so that it becomes closed in a watertight and permanent way.

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