The Fracturing and Acidizing Technical Service Center (FATSC) of CNPC and STIM-LAB Inc.jointly studied "Xiando"( XD) and "Zhaoren" ( ZW) polymers to understand their theological properties and their proppant transport capabilities when crosslinked with borate ions. A series of bench top tests were conducted on XD, ZW, and guar, including residue measurement, base gel viscosity, and single particle settling, to help define the crosslinker concentration required to optimize the fluid systems. A rheometrics pressure rheometer(RPR)was used to measure the viscoelasticity of the borate crosslinked fluids, anda large scale rheology simulator was used to observe the dynamic proppant transport under shear conditions.

In the steady shear mode, the RPR measured three different regions in the shear stress-shear rate plots, including a shear thinning region at low shear rates, a shear thickening region at intermediate shear rates, and a shear thinning region at high shear rates. The 0.6%(50 1b/1000 gal) XD and ZW base gel showed the same characteristics as typical thin polymer solutions. When crosslinked with borate at low temperature, the storage modulus G' values showed good elastic properties for the fluids. At temperatures up to 66 °C, the G’Values are higher than 19 dynes/cm2, which is proposed by de Kruijf[1]

to be the minimum for a crosslinked fluid to have good proppant transportcapability.

Large scale rheology simulation and proppant transport visualization showed the XD-borate crosslinked fluid system caused very low pressure drops in the pipe rheometer, indicating XD's good friction reduction characteristics. The friction of XD base fluid is only 20% of that of water. The observation in the slot rheometer indicated excellent proppant transport capability. There was no observed bulk settling and little movement between particles. The pressure drops of ZW-borate system in pipes and slot were higher, although the proppant transport was almost perfect. There was slight interparticle movement but no bulk settling observed.

Two case studies are presented to show the successful applications of XD-zirconium-borate and ZW-borate systems to Chinese oilfields.

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