Case History: 180 Degree Phasing Used in Fracturing of Low Resistivity Zones in Gulf of Mexico Wells
Authors: Soliman Mohamed , Dupont Richard , Chapman Bobby , Folse Kent 
Published: October 2008

Fracturing highly permeable, unconsolidated sands and gravel packing has become common practice in the Gulf of Mexico. While underbalanced tubing-conveyed perforating using largehole guns with spiral phasings has traditionally been the method of choice for sand control completions, this method is most efficient when radial flow is present and flow is uniform around the perforations. However, when a hydraulic fracture is created in formations less than 500 md, the majority of the flow into the wellbore is delivered through the perforations connected to the fracture. For this reason and because spiral phasings offer limited bi-directional flow area, 180-degree phasing, when applied correctly. can provide maximum flow area to the fracture and assist in the placement of a single highly conductive fracture into the formation.. Also, because offfracture perforations are eliminated, the chance of creating multiple fractures, a common problem in soft rock fracturing, is reduced. This paper will discuss the methods employed by an operator in offshore Louisiana in perforating shallow, unconsolidated formations to obtain highly conductive gravel pack fractures. In this case history, 180 degree phasing was used by the operator. and excellent completion efficiency resulted. Significant in the success of the completion was the use of a new perforating system that offered 8 spf shot density, 180- degree phasing. A mechanical orienting tool developed for this work allowed for gun centralization, which maximized flow area and uniform hole distribution, thus enhancing flow into the well bore and assisting in better sand control.

Introduction

The hydraulic fracturing of high permeability and/or poorly consolidated (generally &gt; 10 md) formations to increase well productivity and control sand production is usually referred to as FracPac. Fracturing aspects of the FracPac process have been discussed recently in the literature (Mathur, et al., 1995, Meese, et al., 1994, and Roodhart, et al., 1994),123 The reservoir engineering aspects of FracPac were discussed by Hunt and Soliman and Chen and Raghavan.4 Operationally, fracturing high permeability formations must be addressed differently from fracturing low permeability formations due to the expected high leak-off rate that influences fracturing pressure as a function of time. In addition, because of the desired high fracture conductivity, the concept of tip screen-out is applied. In tip screen-out, (Smith et al., 1987)5 the fracture is designed in such a way that by the time the fracture reaches the desired length, the leading pad volume has leaked off into the formation. After the pad volume has leaked off, the presence of the proppant-Laden-fluid at the leading edge of the fracture initiates the screen-out process. Continued injection of the proppant-Iaden fluid causes the fracture to widen or balloon, reaching a greater than average width and high proppant concentration (a packed fracture). During the packing period, the fracturing pressure is expected to sharply increase. The tip-screenout fracturing technique has been successfully applied in the field. Martins and Stewart, 1992, reported that tip-screenout succeeded in more than doubling productivity of treated wells in the Ravenspurn field.6 Other authors, Abass, et aI., 1993, Dusterhoft and Chapman, 1994, and Roodhart, et al., 1994, have reported equally impressive results.7.8 Another factor that affects fracturing candidates of FracPac is the poor consolidation of many of these high permeability formations.