The Application of Limited-Entry Techniques in Massive Hydraulic Fracturing Treatments

Abstract

SPE Member Abstract Application of the limited entry technique has been extended to massive hydraulic fracturing (MHF) of low permeability formations, such as the Niobrara and Codell intervals of the DJ Basin. Analysis of the bottomhole pressure data of these treatments indicates that proppant alters the mechanical configuration of the perforations, as evidenced by a change in the magnitude of perforation friction in opposition to the Bernoulli constant energy equation. The practical significance of changing pressure drop across perforations in limited entry stimulation treatments is that it alters treatment fluid distribution and injection rate profiles among the multiple intervals. This can result in zonal shut-off due to insufficient pressure drop (i.e., zone fracture pressure) wellbore pressure) or zonal sand-out due to inadequate pad volumes and/or treating rate. This paper investigates the mechanisms involved in fluid and slurry flow through perforations. Fluid mechanics research and experimental laboratory and field testing are referenced. The effect of proppant on perforation friction is calibrated. Limited entry design and procedural guidelines for large scale fracturing treatments are presented to assist in achieving the desired placement of fluid and proppant into individual zones. Fundamental limitations of the limited entry technique in MHF applications are also discussed. Introduction " Limited entry" is a term for the practice of limiting the number of perforations in a completion interval to promote the development of perforation friction pressure during a stimulation treatment. The resulting "choking" effect creates excess pressure in the casing, allowing the simultaneous entry of fracturing fluid into multiple zones of varying in-situ stress states. Once limited to acid fracturing and small scale proppant fracturing treatments, limited entry techniques have recently been applied in massive hydraulic fracturing (MHF) treatments. There are two situations in which large scale, limited entry fracturing is particularly useful. Begnaud and Claiborne described a fracturing environment in which two porosity zones are separated by a non-porous "partial" barrier. Hydraulic communication between the pay intervals occurs routinely, yet due to an apparent width reduction in the portion of the fracture penetrating the bounding zone, proppant remains isolated in the perforated interval. When these zones are treated separately, the adjacent unperforated pay zone acts as a permeable fluid sink and proppant concentrating, with associated screenout risks, will occur. However, if the zones are simultaneously stimulated with a limited entry treatment, this leak-off source will be eliminated and less total fracturing fluid will be needed to displace a given volume of proppant. P. 29^