Abstract
To maximize well productivity, it is essential to maximize fracture cleanup. A field study in the Codell formation of Colorado was conducted to examine the effects of guar removal from hydraulic fractures on gas production.
The conventional method of quantifying cleanup from a hydraulic fracture has been to report load water recovery; however, this value is affected by any formation water that might be produced. A more quantifiable approach to describing fracture cleanup has been performed in this study by determining the amount of guar returned from the fracture during flowback. A 12-well study was performed by sampling flowback fluids during cleanup. The concentration of guar in each sample was determined using a colorimetric technique allowing the total amount of polymer recovered over the flowback period to be calculated.
Under equivalent reservoir conditions (pressure, permeability, etc.) and fracture conditions (width, proppant loading and distribution, etc.), physically, it is reasonable to expect higher production rates from wells which have produced back more guar since a larger volume (porosity) will be available for flow. Under low permeability reservoir conditions such as those in the Codell (−0.01 md), this guar removal will need to provide added length to show an increase in production. This concept is illustrated with field data. For example, wells whose fractures produced 600-700 lb of guar (~180,000 lb proppant) produced gas at rates of 35-40 MSCF/D whereas wells whose fractures produced 1100-1200 lb of guar produced gas at rates of 70-80 MSCF/D, most likely indicating a cleanup over a longer length of the fracture.
In addition, the effects of flowback rate on load water recovery, guar concentration, and guar recovered are illustrated.
