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By Murat SULTANGALIYEV
Future Growth Project of Tengizchevroil will lead to loss of Tengiz, thinks Makhash Rakhmetov, the honoured oilman and a member of the RoK Academy of Natural Sciences. The scientist calculated that once this project is put into operation, the drop of resevoir pressure will lead to sharp decrease of oil production in 8-10 years.
According to him, TCO started developing Tengiz field in 1993 without maintaining reservoir pressure, i.e. the company did not re-inject water back to the reservoir in place of extracted oil, or, at least, it failed to re-inject a sufficient volume of associated gas.
As a result at the end of ‘90s TCO faced reservoir pressure dropping by 109 atm compared to its initial level of 824 atm.
In 2000-2001 when the oil extraction increased against 1993 by 25%, the reservoir pressure dropped by another 64.6 atm and that was the lowest and a sharp decrease of formation pressure since the start of Tengiz field development.
TCO announced that during 5 years of SGI/SGP projects implementation the company managed to double its oil production in the field, maintaining the stability of production the following years, and that by launching FGP, it plans to increase annual oil production from 25mln up to 37.8mln tons, i.e. by 50 %.
It is a common knowledge that in order to maintain reservoir pressure, the total volume of the hydrocarbons extracted from reservoir should correspond to re-injected volume of gas. It is even better, if re-injected gas volume is 20-30 % higher than the extracted volume of oil.
From the beginning of development till early 2012 over 224mln tons of oil and 126bn cubic meters of gas were extracted, but the volume of re-injected gas is only 2bn cubic meters. In order to compensate reservoir power, it is necessary to re-inject at least 70-80% of its initial level, i.e. not less than 126,5bn cubes of gas, based on the summarized volume of produced hydrocarbons.
But actually, only 2% of a required gas volume has been re-injected.
TCO uses the experience of Russian scientists, who were the first to use this method and achieved high pressure in a reservoir and increased oil production by means of liquid solvents, enriched and dry gas.
According to their theory, if oil contains more of intermediate C2-C6 components (oil’s “fat”), more oil is produced during gas re-injection. And Tengiz oil is very “fat”.
But when a reservoir pressure decreases below saturation pressure, a pressure drop occurs in “a gas cap” that makes an ingress of oil into it possible, which leads to irrecoverable loss of a third of an oil filed stock. Besides, decrease of reservoir pressure has a risk of technogenic earthquakes, not to mention the fact that there will be no gushing oil in Tengiz.