Modeling of the Flow of Chelating Agents in Porous Media in Carbonate Reservoirs Stimulation
- Mohamed Ahmednasreldin Mahmoud (Texas A&M University) | Hisham A. Nasr-El-Din (Texas A&M University)
- Document ID
- Society of Petroleum Engineers
- North Africa Technical Conference and Exhibition, 20-22 February, Cairo, Egypt
- Publication Date
- Document Type
- Conference Paper
- 2012. Society of Petroleum Engineers
- 3.2.4 Acidising, 1.8 Formation Damage, 5.5.2 Core Analysis, 1.10 Drilling Equipment, 4.1.2 Separation and Treating, 1.6.9 Coring, Fishing, 4.3.4 Scale, 5.4.10 Microbial Methods, 2.5.2 Fracturing Materials (Fluids, Proppant), 5.8.7 Carbonate Reservoir, 5.2 Reservoir Fluid Dynamics, 4.2.3 Materials and Corrosion
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Different fluids have been introduced in the oil industry to be used as alternatives to HCl. Chelating agents such as EDTA (ethylenediaminetetraaceticacid), and HEDTA (hydroxy ethylene diamine triacetic acid) have been used as stand-alone stimulation fluids. These fluids can be used to stimulate water injectors, oil, or gas producers, therefore, the effect of the type of reservoir fluid on the stimulation process should be investigated.
In this study, an analytical model was developed to describe the flow of HEDTA and EDTA chelating agents and propagation inside carbonate formations. The analytical model can be used as a pre-design tool before the treatments. The developed model can be used to predict the volume of the chelant solution required to create wormholes in calciteformations at different temperatures. The temperature affects the diffusion coefficient of the chelating agent, wormholing rate, and wormhole shape and size. The dissolving power of different forms of HEDTA chelating agent can be determined using the model. The optimum injection rate based on optimum wormholing conditions was identified for the chelating agents. Also, the model can be used to predict the wormholing rate of different chelating agents in carbonate formations.
The analytical model can be used to predict the performance of the chelating agent in carbonate stimulation. The volume of chelating agent required to stimulate carbonate formation per foot thickness was determined using the developed model. The optimum injection rate was determined for different chelating agents using the model and the results were compared with experimental results from previous work and there was a good agreement between the measured and the predicted values. The model can be used to determine the best stimulation fluid based on the temperature and fracture pressure of the target zones.
There are certain cases where regular HCl or HCl-based fluids cannot be used to stimulate carbonate formations. HCl is very corrosiveto low carbon steel at high temperatures. Some of well tubular are made of Cr-13 based tubing with Cr2O3 acting as a protective layer, which is soluble in HCl. Wells completed with such way cannot be treated with concentrated HCl acids. At higher temperatures the corrosion problems with HCl become severe and corrosion inhibitors and inhibitor intensifiers are needed to minimize these problems.
An ideal stimulation fluid should be available to treat the entire productive interval of the formation. As the stimulation fluid is pumped into a long lateral of a heterogeneous reservoir, it will naturally flow to the intervals of high permeability and not readily flow to the low permeability intervals. In such cases diverting agents should be used to stimulate the formation effectively. Mechanical and chemical diverters such as ball sealers, polymers, and surfactants have been used to redirect flow to low permeable zones (Zeiler et al. 2006).
Ethylene diamine tetra acetic acid (EDTA) is an alternative fluid that is capable of stimulating carbonate reservoirs. EDTA is a chelating agent that stimulates by means of complexing the metal components of the carbonate matrix. The dissolution mechanism is different from that of HCl. Dissolution of calcite can be enhanced at low pH through a combination of hydrogen ion attack and chelation. EDTA was first used for the removal of calcium carbonate scale from sandstone reservoirs at the Prudhoe Bay field (Tyler et al. 1985).
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