Polymer Reduction Leads to Increased Success: A Comparative Study
- Natasha Helen Kostenuk (Trican Well Service Inc.) | Pierre J. Gagnon (Conoco Phillips Canada)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- March 2008
- Document Type
- Journal Paper
- 55 - 60
- 2008. Society of Petroleum Engineers
- 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 1.6 Drilling Operations, 1.8 Formation Damage, 2.5.2 Fracturing Materials (Fluids, Proppant), 4.1.2 Separation and Treating, 1.2.3 Rock properties
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Recent advances in guar and crosslinker technologies have resulted in the development of high-viscosity crosslinked borate-fracturing fluids without increasing polymer loadings. These low polymer (LP) borate fracturing fluids are being used successfully in various formations previously believed to be too hot and or too deep for LP fracturing fluids.
Historically, polymer loadings of 3.6 to 4.2 kg/m³ (30 to 35 lbm/1,000 gal) were commonly pumped in the Western Canadian Sedimentary basin (WCSB) for formations deeper than 2500 m and bottomhole temperatures greater than 80°C. These same formations are now fracture stimulated using the LP fluids with loadings as low as 1.8 kg/m³ (15 lbm/1,000 gal) with exceptional results.
This paper demonstrates that LP fracture fluids can be used in place of fluids requiring higher polymer loadings with minimal changes to the overall design of the fracture treatment. The new fluid can be pumped on-the-fly at conventional pump rates and proppant concentrations because of the fluid's improved shear and temperature stability.
The advantages of using a reduced-polymer fracturing fluid include increased production, lower treatment costs, and lower frictional pressure loss.
This paper illustrates these advantages as it compares the LP fracture fluid with HP fracture fluids in more than 200 wells in the WCSB. The formations where LP fluids were used have depths of up to 3250 m and reservoir temperatures reaching over 100°C.
Low-permeability gas wells in the WCSB often require hydraulic fracturing to be ecomonic (such fracturing treatments are considered to be a critical step in the completion process). The choice of fracturing fluid is a major component and concern when designing optimal fracture stimulations. The primary roles of the fracturing fluid are to initiate and extend a hydraulic fracture and to distribute proppant. The majority of fracture treatments use crosslinked water-based fluids. Fluid viscosity is attained by adding some type of guar polymer to the water. Many types of guars can be and have been used, including derivatized guars, xanthan gum, and polyacrylamides. For the LP fluids discussed in this paper, a nonderivatized guar crosslinked with borate was used. For the purpose of this paper, LP fluids are described as those with polymer loadings of 1.8 to 2.4 kg/m³ (15 to 20 lbm/1,000gal). Conversely, HP fluids are those containing polymer loadings of 3.0 to 4.2 kg/m³ (25 to 35 lbm/1,000gal).
Recent advances in guar processing have made the LP systems achievable. Historically, guar has been known to contain 8 to 12% residue (Gidley et al. 2001), but newer, more-processed guars available today contain 1 to 5% residue. This enhanced guar has a higher molecular weight than previous guars (Dawson et al. 2004), thereby increasing the yield of the polymer that, in turn, increases viscosity. The shear and temperature stability of the resulting fluid is superior to other guars, leading to a wide range of applications.
Why Reduce Polymer Loadings?
As stated previously, polymer is required to create enough viscosity for the fracture fluid to initiate and to extend the fracture, as well as properly place the proppant along the fracture. Unfortunately, polymer is also known to be damaging to the proppant pack (Kim and Losacano 1985; Roodhart et al. 1988). This damage adversely affects proppant-pack conductivity and, therefore, production potential. There can also be damage from filter-cake buildup on the formation face, which can also reduce the fracture's effectiveness (Volk et al. 1983).
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Dawson, J.C., Cramer, D.D., and Le, H.V. 2004. Reduced Polymer Based FracturingFluid: Is Less Really More? Paper SPE 90851 presented at the SPE AnnualTechnical Conference and Exhibition, Houston, 26-29 September. doi:10.2118/90851-MS.
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