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Aud, W.W., Integrated Petroleum Technologies Inc.; Wright, T.B., Resources Engineering Systems Inc.; Cipolla, C.L., Union Pacific Resources Co.; Harkrider, J.D., Integrated Petroleum Technologies Inc.; and Hansen, J.T., Gas Research Inst.

SPE Members

Abstract

The success of most fracture treatments is primarily dependent on the ability to evaluate the characteristics and critical mechanisms that control how a formation hydraulically fractures. By developing an understanding of the mechanisms, it is possible to make the necessary improvements to ensure optimum proppant placement and therefore maximize economic results. This discussion presents a simple, low cost method for improving the overall fracture geometry and reducing the risk of premature screenouts. Dramatic improvements in near-wellbore tortuosity and improvements in proppant placement can be achieved by maximizing the viscosity of fluid that is used to initiate the fracture and carry proppant through the near-wellbore region. Using the approaches presented, it has been possible to eliminate premature screenouts and improve the overall proppant placement in many different environments.

Introduction

The most likely cause for poor results in most fracture treatments is ineffective proppant placement adjacent to the pay interval. Poor proppant placement is usually related to procedures that use excessive fluid volumes, small proppant volumes and low concentrations. The use of such practices is usually related to experience with screenouts that developed into interpretations and approaches that appear to be incorrect as follows:

-The interpretation that a screenout is at the tip of the fracture caused by pad/fluid depletion. A very high percentage of screenouts occur in the near-wellbore region due to a restriction caused by a tortuous path connecting the wellbore with the main body of the fracture, and/or insufficient fluid viscosity to transport proppant through this region.

-The interpretation that a screenout occurred due to insufficient far-field fracture width (with a distinction made between the near-wellbore and the far-field fracture widths) and that such screenouts can be avoided by pumping additional pad fluid in order to develop more far-field width. While larger fluid volumes do increase the far-field fracture width to some extent, such increased volumes almost always have detrimental effects on the far-field proppant placement. Also, there is some evidence that larger fluid volumes improve the near-wellbore fracture connection, but the resulting negative affect on farfield proppant placement still applies. Fortunately, other methods can be used to improve the near-wellbore fracture connection without jeopardizing the far-field proppant placement.

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