Development of New Seawater-Based Formulation to Stimulate Sandstone Formations
- Abdulazeem Ahmed (King Fahd University of Petroleum and Minerals) | Mahmoud Mohamed (King Fahd University of Petroleum and Minerals) | Elkatatny Salaheldin (King Fahd University of Petroleum and Minerals) | Barri Assad (King Fahd University of Petroleum and Minerals) | Abdulrahim Muhammadain (King Fahd University of Petroleum and Minerals)
- Document ID
- Society of Petroleum Engineers
- SPE Kingdom of Saudi Arabia Annual Technical Symposium and Exhibition, 24-27 April, Dammam, Saudi Arabia
- Publication Date
- Document Type
- Conference Paper
- 2017. Society of Petroleum Engineers
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- 42 since 2007
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When carbonate in sandstone rocks exposed to seawater based acids, calcium sulfate will precipitate. Recently, chelating agents/seawater solutions were introduced to prevent scaling problem in sandstone formations. The objective of this study is to introduce DTPA (diethylene tri-amine penta-acetic acid)/ seawater solution combined with potassium carbonate as a clay stabilizer and catalyst to stimulate sandstone reservoirs.
Solubility tests of Bandera sandstone (10 % illite content) in high pH DTPA solutions diluted with seawater were performed to determine the optimum concentration of DTPA and potassium carbonate. Computed Tomography (CT) scan was conducted before and after the acidizing process to assess the performance of the new formulation. Coreflooding experiments were carried out on Bandera sandstone cores to investigate the ability of the new formulated fluid to stimulate sandstone formations. Inductively coupled plasma (ICP) was used to analyze the collected effluents to understand the mechanism of seawater and potassium carbonate effect on the reaction of DTPA with sandstone rocks.
The results showed good compatibility between DTPA seawater based fluids and Bandera sandstone cores. No precipitations were detected during the solubility tests. 20 wt. % DTPA at pH of 11 combined with 3 wt. % potassium carbonate gave the optimum solubility ratio. Reduction in CT-number in the treated sandstone cores indicates the porosity enhancement after treatment. Permeability measurements showed about 40 % increase in permeability improvement ratio of Bandera sandstone cores after injecting 6 pore volumes of 20 wt. % DTPA at pH of 11 diluted using seawater combined with 3 wt. % of the catalyst at 250°F and the injection rate was 5 cm3/min.
The obtained results of this work will enrich the outcome of sandstone acidizing using seawater based fluids without calcium sulfate precipitation in offshore operations at high temperature and also will prevent the problems associated with high illite content formations.
Offshore stimulation jobs are expensive operations due to the cost of transporting fresh water to the offshore platforms. Generally, engineers use fresh water to formulate acids to make stable solutions that can effectively enhance formation permeability without any further problems. Seawater was introduced to prepare and flush acids to minimize the cost of logistic supply of the fresh water. However, seawater has the problem of scale precipitation. Sulfate ions from seawater combine with calcium, barium, or strontium ions in the formation brine or with calcium in the spent acid to produce sulfate scale. He et al. (2011) found out that calcium sulfate precipitated at different stages of the acidizing process after using HCl prepared using seawater. Oddo et al. (1991) reported the same phenomena when seawater and KCl were used to post flush the mud acid from offshore wells after treatment. So to come up with cost effective seawater based acid for sandstone acidizing we have to consider many factors. At first, main acid should be compatible with seawater to have proper solution without precipitations. Furthermore, this formulation should be able to remove the damage, improve the permeability and maintain sandstone formation stability.
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