Interest in fracturing high-permeability formations to control sand production and bypass formation damage has recently increased. These treatments typically require a "tip screenout" design, followed by efficient proppant packing, to achieve the high conductivities required to achieve optimum results. The need for a tip screenout and the relatively short treatment pumping times require that fluid loss characteristics of the formation must be very well defined before job execution.
Borate-crosslinked fluids and linear HEC gels are by far the most commonly used fluids for high-permeability fracture treatments. Extensive laboratory testing has shown that the fluid loss behavior of these fluids can be very different from that described by conventional fluid loss models. Traditional minifrac analysis techniques fail to account for the correct fluid loss behavior of these gels. As a result, use of these techniques can lead to severe errors in the estimation of the leakoff parameters, resulting in over- or under-designed jobs. This paper presents a novel minifrac analysis technique that more accurately accounts for the fluid loss characteristics of the fracturing fluid, allowing for better design.
This analysis has been verified against actual treatments and shows excellent agreement with the observed 'net' pressure response for the rninifrac and the actual treatments. Several case histories are provided to illustrate the method. This technique has broad applications to low and intermediate-permeability fracturing applications as well.
Minifrac analysis has been commonly used to help optimize hydraulic fracture treatment design, since the analysis provides critical information pertaining to the well to be treated. Many of the minifrac analysis practices commonly used, however, consider only relatively simple cases, and include making several assumptions that are not necessarily valid in all situations. As a result, minifrac procedures have not performed as well as expected in a number of cases, e.g., high-permeability or naturally fractured reservoirs. These inadequate performances have prompted some new research and development to determine minifrac procedures that could be successfully applied to any well.