Propagation of Regular HCl Acids in Carbonate Rocks: The Impact of an In Situ Gelled Acid Stage

Abstract

Recent laboratory and fleld studies indicated that polymer-based in situ gelled acids can cause formation damage. Coreflood experiments using single-stage and multistage acids were conducted at 250 °E. 15 wt. % regular HCI and 5 wt. % in situ gelled acid-based on Ee(UI) as a crosslinker were the acids that were used in this study. Propagation of acids and crosslinker inside 20 in. long cores was examined for the flrst time in detail. Stage volume and injection rate, which were the parameters that affect the propagating of various chemical species, were examined. Samples of the core effluent were collected and the concentrations of calcium, crosslinker, and acid were measured. Material balance was conducted to determine the amount of cross-liker that retained in the core. The results show that in situ gelled acid should be pumped at low injection rates. In situ gelled acid at low injection rate instantaneously plugged the tip of the wormhole and did not create additional wormholes inside the core. Therefore, when the flnal regular acid stage bypassed the gel, it started to propagate from nearly the last point that the flrst stage ended. In site gelled acid stage volume should not exceed 0.5 PV. No beneflts were gained by increasing the volume of in situ gelled acids. Retention of total iron in the core increased in multistage acid treatments, especially at low acid injection rates.

Challenges During Shallow and Deep Carbonate Reservoirs Stimulation

“…Heterogeneous carbonate reservoirs can be stimulated using gelled HCl acid in order to divert the acid from high permeability to low permeability layers in the reservoir to achieve uniform acidizing treatment. To achieve uniform acid treatment, the gelled acid should be injected at low injection rates [5], Penny et al [6] developed a new microemulsion additive that is effective in treating the damaged wells and is very effective in fluid recovery and relative permeability improvement when used in drilling and stimulation jobs at low concentrations. The microe mulsion is a blend of biodegradable solvent, surfactant, cosolvent, and water.…”