Nitrogen (foam) assisted thermal production technology 

Introduction 

Steam injection is a common method for heavy oil production. After the injection of high-temperature steam into the formation, the temperature of heavy oil increases, which leads to flowing capability of oil be improved. At the same time, the injection of steam can effectively restore the formation energy and greatly increase the productivity of heavy oil.

After the multi-cycles injecting high temperature steam, it is prone to form steam channels with high permeability on the top of steam-chamber, which leads to the poor thermal insulation and recovery effect. For this kind of reservoir, prior or coinjection of nitrogen foam can improve the stimulation effect of heavy oil reservoirs.

Technical principles

After nitrogen foam is injected into the formation, the steam stimulation mode transfer to the combination mode of steam, nitrogen and chemical agent by blocking the high water cut zone, diffusion viscosity reduction, top insulation, etc.

A) nitrogen plays a role in weilbore thermal insulation in order to reduce wellbore heat loss and improve steam dryness;

B) Nitrogen distributes in top of reservoir in order to reduce the heat loss by insulating overlying mudstone

C) Effectively replenish formation energy, enhance displacement pressure and prolong effective period of steam huff and puff.

D) Foam restricts the fingering of high water cut zone and the steam zone in the top of chamber, which will relatively uniformly sweep the suction profile as well as increase the steam heating radius.

Suitable reservoirs

A) Heavy oil reservoirs with medium or high permeability and large reservoir thickness;

B) The early steam huff and puff with good effect, and multi-cycles huff and puff with unwanted effect;

C) The weak edge-bottom water, and production water mainly stemming from injected water.