Ensuring Better Well Stimulation in Unconventional Oil and Gas Formations by Optimizing Surfactant Additives
- Liang Xu (Multi-Chem/Halliburton) | Qiang Fu (Multi-Chem)
- Document ID
- Society of Petroleum Engineers
- SPE Western Regional Meeting, 21-23 March, Bakersfield, California, USA
- Publication Date
- Document Type
- Conference Paper
- 2012. Society of Petroleum Engineers
- 2.5.2 Fracturing Materials (Fluids, Proppant), 1.8 Formation Damage, 5.4.7 Chemical Flooding Methods (e.g., Polymer, Solvent, Nitrogen, Immiscible CO2, Surfactant, Vapex), 4.1.2 Separation and Treating, 1.6.9 Coring, Fishing, 3 Production and Well Operations, 4.1.5 Processing Equipment, 5.1 Reservoir Characterisation
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Proper application of surfactant is critical to the completion process. It not only enhances initial production (IP), but helps sustain long-term production. Conventional wisdom suggests that the use of a nonemulsifying surfactant will work appropriately across most low-permeability reservoirs. Laboratory and field results, however, suggest that a weakly emulsifying surfactant is, in fact, far more efficient in solubilizing and mobilizing oil globules.
In this paper, an experimental toolbox and key strategies are presented for properly selecting surfactants for specific reservoir conditions. Dynamic surface tension, emulsion tendency, oil recovery, wettability and adsorption tests were all considered to select the proper surfactant for the case study. On the basis of these results, the field performance of both the nonemulsifying and weakly emulsifying surfactants are evaluated using production data from the Eagle Ford. The production-enhancement data appears to correspond well to lab results and strongly suggests that weakly emulsifying surfactants are superior at enhancing production.
Surfactant is just a chemical component in the completion procedure, but it can be crucial to enhancing IP and sustaining long-term production in unconventional reservoirs. Surfactants are primarily used to reduce formation damage and restore permeability by opening additional areas for oil and gas flow (Rickman and Jaripatke 2010). More importantly, aqueous surfactant solutions solubilize oil globules and help mobilize them to the propped fractures. In many field applications, however, the IP of producing wells is not as high as expected, although they have been fracked with some surfactant additives. The primary cause for the lower IP, determined after laboratory testing and field validation, is usually the surfactant itself. Without comprehensive understanding and careful selection, some surfactants not only contribute to lower than expected IP, but can potentially decrease the mobility of oil globules in propped fractures, resulting in diminished oil and gas production over time.
In this paper, the attributes a surfactant should possess for enabling effective oil extraction are presented. As previously demonstrated (Xu and Fu 2012), a weakly emulsifying surfactant is capable of solubilizing and mobilizing additional oil globules; that is, a temporary emulsification process of the oil molecules is desired, without formation of tight-emulsion blocks. On the basis of this strategy, a toolbox composed of a series of experimental analysis is presented. This analysis allows one to select and modify a surfactant to specific reservoir conditions to maximize production and reduce risk of formation damage.
Experimental Results and Discussion
• Dynamic surface tension measurements were run using a bubble pressure tensiometer (Kruss BP100).
• Interfacial surface tension measurements were run using a spin drop tensiometer (Kruss SITE100).
• Oil recovery tests were conducted with a specially designed procedure for the unconventional formation cores.
• The wettability/imbibition tests were run according to the Washburn method (Kruss K100).
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