Abstract
Sandstone reservoirs in Huabei Oilfield are characterized by low porosity, low permeability, high clay content, strong heterogeneity and high reservoir temperature. In order to solve the problems of rapid reaction, short effective penetration distance and secondary precipitation in conventional acid system, a new composite acid system is studied. The experimental results show that the acid-rock reaction speed of the new composite acid system is lower than that of the conventional acid system; the chelating ability of Ca2+, Fe3+ and Mg2+ ions is stronger; the corrosion rate of N80 steel is 1.57g/m2•h, far below the industry standard (10-20g/m2•h); the permeability of the core after acidizing increased by 3.5 times. This new type of composite acid system with slow reaction speed, scale inhibition and deep penetration is of great significance for acidizing low porosity and low permeability sandstone reservoirs in Huabei Oilfield.
Highlights
The reserves abundance in Huabei Oilfield is low, some sandstone reservoirs are characterized by low porosity and low permeability, high reservoir temperature and high clay mineral content, which make it more difficult to further improve oil recovery
The surface tension tests were performed on different types and concentrations of surfactant
The surface tension of 2%ZPJ-A is as low as 20.18 mN/m, and the surface tension of 3%ZPJ-A is only 0.03 mN/m lower than that of the 2% ZPJ-A, so considering its performance and economy, 2% of ZPJ-A is preferred as the cleanup additive
Summary
The reserves abundance in Huabei Oilfield is low, some sandstone reservoirs are characterized by low porosity and low permeability, high reservoir temperature and high clay mineral content, which make it more difficult to further improve oil recovery. For the acidizing of sandstone reservoirs, many scholars have proposed different types of low-damage acidizing fluids. The chelating agent has high chelating ability for metal ions such as calcium, iron and magnesium. It can effectively inhibit secondary precipitation; at the same time, the permeability of reservoir is improved[8-9]. The molecular structure, retardation, corrosion inhibition and chelating ability and application were comprehensively evaluated. The mechanism of measuring the molecular structure by NMR: under the irradiation of electromagnetic waves, the frequencies of carbon atoms and hydrogen atioms are different due to resonance absorption. The analysis of the molecular structure of the main agent AH indicates that the molecule belongs to the aminocarboxylic acid chelate compound. When the hydrogen ion is ionized, AH maintains a lower pH, achieving better retardation; forming a plurality of ligands with the metal ions to exert chelation
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