API REPORT 82-45:1984

I. INTRODUCTION This is the final report on our research conducted under the American Petroleum Institute's PRAC Project 82-45 entitled 'Rheological Characterization of Fracturing Fluids'. The project was initiated by the American Petroleum Institute (API) because: 1) the expense of hydraulic fracturing makes it desirable to understand the processfully, including the rheology of the fracturing fluid, to ensure a successful fracturing operation, and 2) during a round-robin testing program by several laboratories the viscosities reported by the participants for identical gel formulations varied by 1000 %. The purpose of this report to to provide a working guide to rheology of guar gels. We first provide, in Section II, a summary of the significant results and conclusions from the first year of this investigation. In Section III dynamic oscillatory shear measurements, which are used to study guar measurements can be directly related to the number of network cross links. These measurements and their interpretation are discussed in detail, since they are probably less familiar to researcher in the oil production research area than are steady shear measurements. In Section IV we describe the rheological instruments used in this study. In Section V the preparation of guar samples is detailed. The composition of the model guar gel used in this study was specified by the API Steering Committee. Our observations on the factors controlling gel rheology, including chemical effects, sample preparation effects, and flow history effects are presented in Section VI. In Section VII a model that describes the rheology of gelling fluids is described. The model is based on the temporary network theories used to describe the rheology of polymer melts and solutions. To this theory we have incorporated the chemical kinetics of metal ion adsorption onto the guar polymer backbone and subsequent polymer-polymer cross linking. In the final sections recommendations for rheological instrumentation and for future research are presented. At the quarterly meetings with the API Committee overseeing this work several hundred pages of experimental data were distributed. All of that data are not included in this report. Rather the important conclusions drawn from those data are presented along with the relevant data that support those conclusions. The original data are on file with the API publications department and can be obtained through the API.