What would be the GDP of Algeria without Oil & Gas?
If I interpret your question correctly, you're asking what percentage of Algerian national income is derived from oil and gas extraction. The answer appears to be 30% from the website. 

I think the problem is you're assuming that the 30% figure means something like '30% of private spending', and so you're trying to account for government spending as well.

The website says 30% of GDP comes from oil and gas, that means 30% of income in Algeria is derived from oil and gas. It should already include government spending, which is taxed from income. And government spending should already include the fake jobs you mention.