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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.

Acidizing is an important measure to increase production and injection in oil and water wells. Mud acid (hydrochloric + hydrofluoric) is usually used as acidizing fluid in sandstone reservoir. However, there are some problems such as too fast reaction of acid-rock, secondary deposition of residual acid and metal ions, formation pollution and residual acid need to flow back. A new type of retarded acid system is synthesized by experiments, which is mainly composed of isopropyl phosphate polymer and fluorine. Isopropelphosphoric polymer is synthesized from phosphorus trichloride, acetone and other materials, and then polymerized with acrylic under the action of initiator to form isopropelphoric acrylic copolymer. The 1H-NMR and the 31P-NMR are adopted to detect and analyze the position and connection mode of hydrogen and phosphorus in the molecular skeleton. The results show that the molecular structure of the synthesized retarded acid contains isopropelphosphoric-acrylic copolymer and polyisopropelphosphoric. Through the evaluation of corrosion performance and scale inhibition performance, it is further verified that the corrosion inhibition performance of the acid system can release hydrogen ions slowly by multistage ionization and inhibit the secondary precipitation. The synthesis process of a new tape of environment friendly none-flowback retarded (EFNR) acid liquid is formed through experimental research. The H+of the molecular structure of the synthesized retarded acid has a multi-stage characteristic of ionization. The carboxylic group and phosphoric group can complex Ca2+ and Mg2+ plasma, and the residual acid does not need to flow back.