Abstract
The reservoir of Daqing Heidimiao Oilfield (permeability 1736×10−3μm2) contains heavy oil, with the average viscosity of 3306 mPa•s. It is developed by steam flooding and steam huff and puff, however, the recovery rate is only 14.6%. Therefore, the multi-component thermal fluid huff-and-puff technology is applied to, dealing with pertinent problems such as gas channeling, corrosion and oil pump lock in the process so as to improve oil recovery and production.
Mechanism: Cooling by water, the ultra-high temperature gas generated via combustion of diesel or natural gas with air produces a multi-component thermal fluid containing CO2,N2 and vapor, combining the advantages of gas absorption and thermal recovery. Simulation: A multi-component and multi-phase percolation model is built to optimize the huff-and-puff parameters including composition ratio, temperature and injection volume.
Supporting techniques:
a high temperature oil-and-acid resistant foam system to form a precedent-blocking slug and automatically adjust the huff-and-puff profile. a dedicated low-cost and high-efficiency corrosion inhibitor system to realize corrosion-resistance. a four-node down-hole gas-liquid separation device to increase efficiency.
The comprehensive reduced-viscosity rate is more than 30%; high-pressure air chambers, ranging from 0.2 to 2.0MPa, are formed for elastic energy replenishment. Field tests show the average annual oil increase per well is about 3800 barrels, with the highest being about 7200 barrels.
The numerical simulation results show that the optimal composition ratio (N2: CO2: vapor) is 5:1:1.5, that the best injection amount is 30∼50×104Nm3 and that the injection temperature is preferably 280 ∼ 300 °C.
The oil-and-acid resistant foaming agent has improved recovery efficiency, as a significantly improved profile of gas absorption, and the oil extraction degree increases by about 31.5%.
High temperature corrosion is prevented, through intermittent injection of high-temperature-resistant corrosion inhibitor (corrosion inhibition rate 70.5% at 350 °C), and the frequency of pipeline corrosion is reduced averagely by 98.5%.
Air-lock in pump vanishes via gas-liquid separation devise, with the average indoor pump efficiency increases by more than 50% (gas-liquid ratio ≤3000m3/m3)and the one in field test increases from less than 20% to over 45%. More importantly, the maintenance period has reached 662d.
This technology has been applied to 98 wells in Daqing to date, 95 of which are stimulated successfully.
The multi-component thermal fluid huff-and-puff technology solves the problems such as gas channeling, corrosion and air-lock in pumps through supporting techniques and the synergism of steam flooding and thermal recovery to enhance oil recovery and can be used as a superseded technology after steam huff-and-puff treatment to increase the EUR, especially for heavy oil reservoirs with medium and high permeability.
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