TX 75083-3836 U.S.A., fax 01-972-952-9435. AbstractThe popularity of water fracs has increased in recent years. The reduction in fluid cost and overall fracture stimulation cost has in some cases revived exploration in low-permeability reservoirs like the Barnett shale in north central Texas. Water fracs have also been used effectively in reservoirs with low permeability and large net pays, which require large volumes of fluid to attain adequate fracture half-lengths to achieve commercial production.In the past, the design of water fracs has been more of an art than a science. While the term "water frac" implies that the fluid is proppant-free, in most cases some proppant is usually pumped. The amount and concentration is usually low when compared to conventional fracture treatments. Water-frac designs are further complicated by the fact that fracture geometry, conductivity, and proppant transport are not easily modeled.Despite these difficulties, the attractiveness of water fracs requires the implementation of a design methodology. This paper discusses a design procedure for water fracs from a field operation/design standpoint. Volume and rate requirements are discussed for a specific zone height, desired fracture length, and aerial width. A fracture width vs. proppant size requirement is applied, and a simple material balance calculation is performed to generate a fracture volume taking fluid leakoff into account. Fracture conductivity of a low proppant-concentration, high fluid-volume fracture is estimated to optimize proppant length and fracture conductivity ratio (C fd ). A pump schedule is generated based on the results of the previous calculations. All design calculations are simple and require only a handheld calculator or simple spreadsheet.The design model was calibrated to a microseism-mapped Cotton Valley Lime test well. A leakoff coefficient multiplier was used to calibrate the model. The model-predicted volume was then compared to actual volume on a second Cotton Valley Sand test well and on a 10-well average Barnett shale microseism fracture-mapping data set. The overall modelpredicted volume for the mapped microseism geometry is compared to actual volume pumped.

The aim of this paper is to trace the evolution of the flight documentation of Concorde, with special emphasis on crew operating procedure, and to make some generalised predictions of the impact of recent technology on the methods of operating aircraft in the future. The overall process of Concorde certification has been described elsewhere, the aspect with which we are concerned here being the approval of the aircraft’s operating procedures. The generation of these procedures is an involved process, one which started for Concorde in December 1967, with many possible difficulties foreseen in the aircraft operational sphere and neither of the prototypes having flown.