Proper Selection of Surfactant Additive Ensures Better Well Stimulation in Unconventional Oil and Gas Formations
- Liang Xu (Multi-Chem A Halliburton Service) | Qiang Fu
- Document ID
- Society of Petroleum Engineers
- SPE Middle East Unconventional Gas Conference and Exhibition, 23-25 January, Abu Dhabi, UAE
- Publication Date
- Document Type
- Conference Paper
- 2012. Society of Petroleum Engineers
- 5.8.7 Carbonate Reservoir, 2 Well Completion, 3 Production and Well Operations, 4.1.2 Separation and Treating, 1.8 Formation Damage, 5.8.2 Shale Gas, 5.2.1 Phase Behavior and PVT Measurements, 2.5.2 Fracturing Materials (Fluids, Proppant), 4.3.4 Scale, 5.3.2 Multiphase Flow, 4.1.5 Processing Equipment
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A typical assumption for promoting the use of surfactants is that traditional surfactants will work appropriately across a large gamut of fields, but our laboratory tests show that inappropriate application leads to much lower efficiency of the oil recovery and thereby diminished production. Operators must understand how surfactants extract the oil and then select surfactants cautiously in order to maximize recovery and minimize risk.
This paper presents a study on surfactant chemicals and their most relevant parameters. In particular, the key characteristic of surfactant additives in unconventional oil and gas formations was found to be the emulsion tendency. It was found that a weakly emulsifying surfactant was more capable of solubilizing and mobilizing additional oil globules via self association. In stark constrast to a conventional non-emulsifying surfactant, the correct application of a weakly emulsifying surfactant led to better well cleanup and a higher ultimate oil recovery.
It is not an easy task to recover oil and gas from the low permeability unconventional reservoirs. To enhance initial production (IP) and minimize production problems, surfactants, friction reducers, scale inhibitors, biocides and sometimes clay stabilizers are typically pumped together. The surfactant used in a completion procedure is just one component, but it can be crucial to enhancing IP in the unconventional oil and gas formations. Our field production results in the Barnett, Eagle Ford, Bakken, Avalon, Woodford and Utica shale, etc., all suggest that there is a significant difference if correct application of a surfactant is executed. In this paper, some parameters are highlighted to keep in mind when selecting a surfactant chemical. Most importantly, an effective surfactant must be capable of temporarily emulsifying the oil globules and thereby enabling them to mobilize to the propped fractures, without forming tight emulsion blocks (Cobos et al, 2009). We also attempt to look into the mechanism of how surfactants extract the oil globules.
The porosity and permeability tend to be extremely low in the unconventional formations (Rickman et al, 2010). It is thought that oil and water emulsions generated during the production can plug those tiny pores and severely impair production. Consequently, emulsions should be avoided at all cost. In fact, a few commercially available surfactants consist primarily of non-ionic surfactants and de-emulsifiers. The purpose is probably to suppress the formation of oil and water emulsions during the multiphase flow. Our laboratory testing in conjunction with the field production data, however, prove otherwise that a weakly emulsifying surfactant is needed to temporarily solubilize and mobilize oil globules, and thereby aid in additional oil production, without generating emulsion blocks. For the first time for the unconventional rerservoirs (to our knowledge), we present evidence that differentiate and quantify the emulsion behavior and the oil and aqueous phase separation rates, between a weakly emulsifying surfactant (surf2) and a non-emulsifying one (surf1). In contrast, the weakly emulsifying surfactant enabled significantly more oil and gas productions in the field.
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