VI. Ask and answer

1. – When …?

– When a large part of the crude oil cannot be recovered simply by ….

2. – What does the injected fluid …?

– It replaces the produced oil and maintains ….

3. – What happens to the gas …?

– It collects to form ….

4. – When is … realized?

– When gravity segregation of ….

5. – What is another …?

– … water flooding.

6. – When is … made more viscous?

– By the addition of ….