Fracturing fluid systems based on the natural polymer guar, or its derivatives, crosslinked with boron or certain transition metals, such as zirconium, have become the staples of the pumping services industry worldwide. It has been estimated that in North America alone, one billion gallons of fracturing fluid were pumped in 1997. These fluid systems have been designed to operate over a wide pH range and at temperatures to 400F (about 200C) by the appropriate choice of polymer crosslinker, stabilizer and buffer. Not only has it become apparent that the same fracturing fluid composition is not suitable over such a wide range of applications, but it is also becoming increasingly apparent that seemingly identical fluid compositions yield different results. This paper is the result of a systematic effort to demonstrate some of the reasons why seemingly identical fracturing fluid compositions may produce considerably different results, and the steps that may be taken to minimize the odds of making an undesirable choice. P. 253
Me;chant, Indian Gum IndustriesLtd. -Copyrfght 1993, ScciaW c1 Petroleum ErsJi-, Ine l%is paper was ppared fcs p_esdatkm d the 199S SPE India Oil and Gas Ccmference and Exhilsition held in New Oelhi, India, 17-19 Febiuary 199S. mls pqar wassetectad fcf -Won by an SPE Progmn Ccmmttee fdlcrtmw rak%w C# Irhrnabon ccmtainad in en afxtract wt.sn Ktsd by tha authcx( s). Contents c1 tha paper, as IXUSemted, have not lSeaiI rwiewad by tfm Sm"efy d Patrdwn Er@aers and am sukjad to ccnwtian by the adhor(s). lla matertal, as prwJented does not nacaasarily raflact rny puedtcm d the Sodety of Petmlsun Er@aers, its dfii, or manbers Papers p'aaanted at SPE medngs are sukisd 10 pb!katii 'm-w by Edtwial Canmiltaes cf 6W Sceiaty cf Patroksn EWinears Eledrcmii rqwdwlion, cistn%utii, or storaga C4 any WI c# this paper fc$ canm.amaal FWPSeS witmut ths wittsm ccmsent of tha SMe4y cf Petmlmsn Eng-is prchibitad Parmiaeion to mprcska in print is ruetrided to an s&tract of not mwe than WO wwds, diust-may not ba * ma abstrad must cxxtam wrwicwwa ac+mwk@ant d wfwre end bywfwn ths papar was presanted Write Librarian, SPE, PO. 00s S3383S. RMards'al, 7x 7X833336, U. S.A., fax 01-972-952-9435. AbstractFracturing fluid systems based on the natural polymer guar, or its derivatives, erosslinked with boron or certain transition metals, such as zirconium, have become the staples of the pumping services industry worldwide. It has been estimated that in North Ameriea alone, one billion gallons of fracturing fluid were pumped in 1997. These fluid systems have been designed to operate over a w-de pH range and at temperatures to 400T [about 200W] by the appropriate choice of polymer, erosslinker, stabilizer and buffkr. Not only has it become apparent that the same fi-aeturing fluid composition is not suitable over such a wide range of application% but it is also becoming increasingly apparent that seemingly identical fluid compositions yield different results.This paper is the result of a systematic effort to demonstrate some of the reasons why seeming~y identical fi-aeturing fluid compositions may produce considerably diffit results, and the steps that may be taken to minimize the odds of making an undesirable choice.
Aqueous based zirconium crosslinked fracturing fluids have seen widespread service since the early 1980's. Today, zirconium crosslinkers are used with many types of polymer solutions, across a pH range of from less than 1 to greater than 12, at bottom-hole temperatures of from less than 100F to greater than 400F. There is no doubt among workers in the field that the same zirconium crosslinked fracturing fluid is not suitable for such a wide range of applications, and, yet, there has yet to be published a systematic evaluation of the impact first order changes in the composition of zirconium crosslinkers have on rheological performance. This study endeavors to provide such a systematic evaluation. Aqueous-based zirconium crosslinked systems can be made with a wide range of functionality to meet specific performance needs. In hydraulic fracturing fluid systems utilizing zirconium crosslinked guar or guar derivatives, changes in the crosslinker due to differences in the zirconium raw material source, the ligand to metal ratio, cation type, and pH of the system cause significant differences in rheological performance. In particular, crosslink time, temperature and stability at temperature (for a given shear regime) can be controlled by manipulation of the aforementioned factors. This study presents a systematic evaluation of these factors and discusses how an understanding of their interrelationships is essential in predicting performance of a crosslinker or designing a new fluid system. Introduction "Zirconium crosslinked CMHPG." To the ears of a production engineer, the words ring of a very specific chemical composition. The literature contains numerous references to it, as if with its very specific chemical composition, it exhibits a very specific performance response under identical conditions. It is generally accepted that the "same" fracturing fluid supplied by different service companies may exhibit some differences, but the general consensus is that these "same" fluids exhibit a kind of performance even though details of its composition may vary with the supplier. When we think of "borate crosslinked guar," or "titanium crosslinked IWO," or "zirconium crosslinked CMHPG," we have an "idea" about what to expect from each of these kinds of crosslinked fluids, and it's not just because the polymer may vary. Those experienced in the art of evaluating fracturing fluids have very different ideas about what to expect if we were to compare, for instance, a "zirconium crosslinked CMHPO" with a "zirconium crosslinked guar." It is the purpose of this study to evaluate essentially the "same" fracturing fluid system while systematically altering certain significant variables in the composition of the fluid so that we might observe the consequences of performance. We have paid particular attention to systematic variations in zirconium crosslinkers. What may have been "generally accepted" before, but not given much consideration because any differences might have been regarded as insignificant, becomes readily apparent in its significance with respect to performance. Plot 1: Same System - Different Crosslinker Loadings It is well known in the industry that variations in the crosslinker loading can produce substantial differences in the performance quality of the fracturing fluid. In this graph we have demonstrated differences based simply on crosslinker loading. The fluid is evaluated at 245 F. Curve A demonstrates an over-crosslinked condition. Curve B demonstrates an under-crosslinked condition. P. 669^
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