Youqi dizhi yu caishoulu (Jan 2024)
Evaluation of thermalchemical fluid huff and puff to relieve retrograde condensation damage in reservoirs
Abstract
In order to effectively eliminate the reservoir damage caused by retrograde condensation in condensate gas reservoirs， a new method for removing the plugging pore throat of condensate oil by thermochemical fluid huff and puff was proposed. For tight sandstone， carbonate， and shale reservoirs， a core oil displacement experiment of thermochemical fluid huff and puff was carried out to evaluate the feasibility of removing condensate plugging by thermochemical fluid. Based on nuclear magnetic resonance technology， the change characteristics of the micro-pore structure of the three types of reservoirs before and after huff and puff were analyzed， and the mechanism of removing retrograde condensate damage by thermochemical fluid was clarified. The experimental results show that thermochemical fluids （NH4Cl and NaNO2） can rapidly release a large amount of gas and steam under the catalysis of acetic acid， increase the core pressure and temperature， reduce the viscosity of crude oil， make the condensate change from liquid to gas， and reduce the flow resistance. The cumulative condensate recoveries of tight sandstone， carbonate， and shale cores by thermochemical fluid huff and puff are 65.7%， 73.9%， and 46.3% respectively. Among them， two rounds of huff and puff can effectively remove 55.5% and 67.6% of condensate plugging in tight sandstone and carbonate samples respectively. However， the shale core needs to extend the soak time and increase the number of huff and puff to improve the recovery of condensate. After the thermochemical fluid huff and puff， the average pore size of tight sandstone， carbonate， and shale cores increases from 0.37， 1.04， and 0.002 1 μm to 0.84， 2.04， and 0.005 8 μm respectively. The thermochemical fluid huff and puff effect is 1.85 and 1.32 times that of CH4 injection and methanol injection respectively.
Keywords
