Investigation of Height Growth In Frac Pack Completions
Authors: Mullen M.E. , Norman W.D. , Wine J.D. , Stewart B.R. 
Published: December 2007

This is a study of height growth in nine (9) wells encompassing thirteen (13) productive intervals that were completed as frac packs. The data used to evaluate these completions include bottom hole pressure recordings during treatment placement, multiple radioactive tracer logs, production spinner surveys, pulse neutron logs, and production history profiles. This study addresses concerns about fracture containment near water and barrier integrity. The study also involves limited aspects of fracture completions in laminated reservoirs. The completions studied include high pressured formations, depleted low pressured situations, as well as normal pressure zones.

Introduction

There are copious publications discussing the issue of height growth in conventional hard rock formations. This work was initiated due to the perceived lack of available published data regarding height growth of fractures in soft formations requiring sand control. This data is presented to provide supporting evidence for addressing the following concerns:What can constitute a barrier in soft formations?How close to water can you place a fracture?Will fractures in soft formations connect laminated pays sections?

During the review process, pad volumes, pump rates, and formation log character were related to the bottom hole pressures encountered during the placement of the fractures. Summaries of some of the zone statistics (Table 1), treatment parameters (Table 2), and the treatment results (Table 3) are provided. Production histories were compared to the placement pressures and production logs (pulse neutron, spinner surveys, and tracer logs).

The soft formations referenced in this study are characterized as unconsolidated to friable, moderate to high permeability, and require sand control. Also low Young's modulus and high Poissonws#x0027;s ratio are common characteristics of these soft sediments.

Hard rock fracturing requires significant propagation pressures which in turn requires higher stress contrast between layers to confine the fracture. If a sufficient stress contrast is not present, then the layer thickness must be great enough to avoid communication with undesirable formations to be considered a barrier. Conversely, the relatively low propagation pressures of soft formations coupled with only a small contrast in formation stress can result in fracture height confinement. The short fracture half length, relative to the perforated height, usually generated with frac packs also limit the height growth. Therefore, variations in formation character as well as small shale streaks, may constitute a barrier.

Fracturing near water in hard rock formations is normally considered hazardous. Because high net pressures are required to overcome the tensile strength of the rock to propagate the fracture. The stress contrast required for containment is often exceeded, especially at the end of the fracture treatment. On the other hand, in soft formations there is very little, if any tensile strength, and the net pressures required to propagate and contain the fracture are very low. When low pump rates are observed, in conjunction with thin fracturing fluids, obtaining a fracture and controlling height growth is possible.

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