New Hydrajet Tool Offers Better Horizontal Well Fracturing
Authors: Surjaatmadja J.B. 
Published: March 2010

A new hydrajet tool initiates horizontal well fractures more successfully by creating directional cuts in formations that cause fractures to be precisely aligned with perforations for better production fluid flow. Tortuous fracture paths to the wellbore are eliminated or reduced because the tool creates radial, fan-shaped slots behind the casing, and the tool produces small enough slots in the casing that casing integrity is maintained. Stimulation, damage-bypass treatments, and treatment of separate zones will be improved by the new tool.

Introduction

Horizontal wells are attractive to the industry because of their potential to improve oil production rates in many reservoirs. Advanced technology for drilling and completing horizontal wells makes horizontal wells economically feasible, and field experience demonstrates that re-entering an existing vertical wellbore to drill a horizontal segment is economically advantageous(l,2,3).

Although many technologies designed for use in vertical wells can be used in horizontal wells, special problems arise in adapting them to the different characteristics of horizontal wells. Many of the differences between vertical and horizontal well treatment results are caused by the borehole position relative to the gravitational force. For example, correct placement of cement or stimulation fluids can be much more difficult in horizontal wells than in vertical wells. Hydrated cement particles tend to settle to the bottom "side" of the borehole annulus. Overburden forces act vertically, and thus are perpendicular to the axis of the horizontal wellbore. Reservoirs are positioned horizontally, and fractures, both pressure-induced and naturally occurring, are usually vertical, especially in the deeper wells.

Horizontal Well Fracturing Problems

Horizontal well fracturing is affected by the method of well completion. The method of completion used on the well determines the fracturing characteristics that influence injection rates. Three types of completions are described below.

Open-hole Completions

If borehole stability is not a problem, open-hole completions are often selected because of their low cost. However, open-hole completions provide few options for future remedial work, and they do not allow for abandoning the well effectively. These wells may be costly to manage during the later stages of well life.

Slotted-liner Completions

These completions offer better protection against wellbore collapse than open-hole completions, and they are relatively inexpensive. However, slotted-liner completions, like open-hole completions, provide few options for remedial procedures.

Cemented-casing Completions

Although cemented-casing completions are more expensive than the other completions, they offer the most options for remedial treatments, such as effective stimulation treatments and isolation of zones. They also allow for effective well abandonment. Cemented-casing completions, while initially more expensive, are cost effective throughout the life of the well.

The best completion to use when fracture stimulations are required is a cemented-casing completion. In open-hole and slotted- casing completions, it is difficult to avoid creating multiple parallel fractures without using tools to isolate areas within the length of the well. With too many fractures opening, the injection rate into each one is insufficient to create a fracture of adequate width and length.

Other complications are caused by the well fracture geometries of horizontal wells.