Field Results and Experimental Comparative Analysis of Sodium and Nonsodium Chelant-Based HF Acidizing Fluids for Sand Control Operations

Abstract

Abstract Field results and laboratory data are presented for the purpose of identifying best practices for two different acidizing fluids based on chelating agents containing hydrofluoric (HF) acid employed in clean-up treatments in high-rate water pack completions (HRWP). The HF fluids are a newly introduced aminopolycarboxylic acid (APCA), pH 2.5 to 3 that contains sodium ions, and an established hydroxycarboxylic acid (HCA) fluid, pH 3, sodium-free. Flow testing was conducted at the anticipated bottomhole static temperature (BHST) of 270°F in synthetic packed columns with formation sand. However, the field conditions at which the treatments were run corresponded to a BHST of 202 to 216°F and a bottomhole pressure (BHP) of 1,800 to 2,000 psi. The permeability of the sands was 89 to 162 md. Comparative data and results stemming from laboratory testing and field use of the HF/chelant fluids are analyzed for concentrations of 1 and 1.4% HF and APCA at 0.6 M, and 1% HF with HCA. Field data and production results are discussed for two set of wells treated with each type of HF fluid. The chemical differences, reactivity and characteristics among the APCA/ and HCA/ -HF fluids on formation sand and on formation core are described. Fluid testing excluded acid preflush and NaCl or KCl was the sole brine employed. Laboratory results indicate that both HF fluids are compatible with the brines used within the scale of the experiment and provide full or increased relative permeability. The field application of the APCA/HF fluid in HRWP appears to perform less efficiently, requiring longer pumping times, than the HCA/HF fluid. A salient observation from laboratory testing indicates greater effectiveness at pH 2.5 vs. 3 for the APCA/HF fluid. A differentiating characteristic is that the APCA/HF fluid can be used to treat heterogeneous sandstone with moderate carbonate content and HCA/HF is mostly compatible with clean sandstone unless an acid preflush is incorporated. The operational outcomes observed during the field use of the APCA/HF fluid appear to indicate significant differences in laboratory vs. field performance requiring further assessment to identify appropriate practices in HRWP. The APCA/HF fluid can stabilize problematic ions in the spent fluid without the need for acid preflushes and without maintaining highly acidic conditions. The effective field use of the newly developed APCA/HF fluid containing Na+ with and without an acid preflush indicates that future work with this type of stimulation fluid is viable in matrix acidizing.