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HCl/Formic In-Situ-Gelled Acids as Diverting Agents for Carbonate Acidizing
- Ahmed I. Rabie (Texas A&M University) | Ahmed M. Gomaa (Texas A&M University) | Hisham A. Nasr-El-Din (Texas A&M University)
- Document ID
- Society of Petroleum Engineers
- SPE Production & Operations
- Publication Date
- May 2012
- Document Type
- Journal Paper
- 170 - 184
- 2012. Society of Petroleum Engineers
- 1.6.9 Coring, Fishing, 5.4.10 Microbial Methods, 4.2.3 Materials and Corrosion, 3.2.4 Acidising, 5.8.7 Carbonate Reservoir, 5.5.2 Core Analysis, 1.10 Drilling Equipment, 2.5.2 Fracturing Materials (Fluids, Proppant)
- HCl/formic acids, formic acid, carbonates, diversion, acidizing
- 4 in the last 30 days
- 959 since 2007
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In highly heterogeneous carbonate reservoirs, several acid systems have been used to enhance acid diversion during matrix acidizing such as surfactant-based acids and in-situ-gelled acids. In-situ-gelled acids are also used to reduce leakoff rate in acid fracturing. The main acid used in this system is hydrochloric acid (HCl). However, high reaction rates and severity of corrosion problems, especially for wells completed with Cr-based tubulars, limit the use of HCl at high temperatures. On the other hand, mixing organic acids with HCl either increases the acid penetration or reduces the necessary strength of HCl and the necessary load of the corrosion inhibitors. A few studies addressed the systems that use both advantages.
The objective of this work is to investigate the behavior and the performance of different in-situ-gelled HCl/formic acid blends as diverting agents by conducting viscosity measurements and reaction-rate measurements using the rotating-disk apparatus, and through coreflood study.
Formic acid was blended with HCl, and four in-situ-gelled acids were examined. Formic acid concentration varied from 0 to 6.31 wt%, and HCl concentration ranged from 0 to 5 wt%. Pink Desert limestone was used for reaction-rate and coreflood experiments. The rotating-disk apparatus was used to measure the reaction rate at 250degF at disk rotational speeds of 100 and 1,000 rev/min. The effect of formic acid concentration and zirconium crosslinking on the reaction rate was examined. Coreflood experiments were conducted at 250°F using two different rates of injection (2 and 10 cm3/min), and the core samples were imaged using a computed-tomography (CT) scan technique after each coreflood experiment.
Increasing formic acid concentration decreased the reaction rate of in-situ-gelled HCl/formic acid with calcite at both low and high disk rotational speeds. This was confirmed by viscosity measurements, which showed that increasing formic acid concentration increased the viscosity of the live acids and decreased the viscosity of the spent acids. Coreflood results showed that increasing formic acid concentration in HCl/formic acid blends reduced acid ability for diversion. In the selected range of acid concentration and for the type of polymer and crosslinking agent used, the in-situ HCl/formic acid behaved more like gelled acid and reached a breakthrough in all coreflood experiments. The higher the formic acid concentration, the higher the pore volume of the acid required to break through.
The objective of this work is to investigate the behavior and the performance of different in-situ gelled HCl-formic acid blends as diverting agents by conducting viscosity measurements, reaction rate measurements using the rotating disk apparatus, and through core flood study.
Formic acid was blended with HCl and four in-situ gelled acids were examined. Formic acid concentration varied from 0 to 6.31 wt% and HCl concentration ranged from 0 to 5 wt%. Pink Desert limestone was utilized for reaction rate and core flood experiments. The rotating disk apparatus was used to measure the reaction rate at 250°F at disk rotational speeds of 100 and 1000 rpm. The effect of formic acid concentration and zirconium crosslinking on the reaction rate was examined. Core flood experiments were conducted at 250°F using two different rates of injection (2 and 10 cm3/min) and the core samples were imaged using a CT scan technique after each core flood experiment.
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