Consistent Entrance Hole Size Initiation Changes Economics of Horizontal Completions
Authors: Smith Charlie H. , Smith Jonathan 
Published: May 2016

Horizontal completions can present different challenges for developing consistent completion designs. Achieving an efficient completion design can be complicated by alterations to the completion process along the horizontal length of the well. A variable that can be a contributor to these alterations is the difference in hole sizes from perforating charges, which can vary according to their clearance from the casing. These alterations can result in inconsistent breakdown and extension pressures in stimulation treatments used to achieve commercial rates of production.

An innovative perforation charge was introduced that is designed to provide a consistent perforation diameter, regardless of the clearance from the casing. Variations in perforation diameter were up to 75% when premium perforating charges were tested. This variation was reduced to 28% through innovative designs that attempted to minimize this perforating artifact. This standardization was expected to result in reductions in treating and extension pressures, as well as better exposure to the reservoir by the stimulation.

This concept was tested in two offset horizontal wells in the same reservoir. One was perforated with a premium charge, and the other was perforated with the charge designed to provide a consistent perforation diameter. Fracture treatment designs were identical for both wells.

A comparison of pump pressures in the two wells showed that the desired results were achieved. Average breakdown pressure was decreased by 1,100 psi and average extension pressure was reduced by 500 psi for the well in which a consistent perforation diameter was established in the casing.

Introduction

Many variables can affect the financial success of horizontal well projects. The trend in many horizontal productive intervals is to increase the length of the horizontal well. Some of these have extended to 2 miles, or 10,000 m, in length. This increased length adds many complicating factors to the completion, many of which can change the economic value of the asset.

Nothing affects this value more than the cost of the fracturing treatment. The completion scheme of these extended laterals maintains the same characteristics in terms of spacing, density, and fracture treatment size. The implication is that, with double the well length, the number of treatments will be doubled. In addition, the friction caused by moving the treating fluid the additional distance increases the pressure required to establish effective treatments and proppant placement. This means that if nothing else changes, the cost of the completion could more than double.

An additional trend in horizontal wells is to establish closer spacing of the perforation clusters. The idea is that the closer spacing allows greater coverage of the reservoir by exposing more surface area to the flow highways created by the fracturing treatments. This increased density could add 40 to 50% additional stages in the horizontal well.

Both of these methods are designed to ensure effective and better coverage of the reservoir by the completion design. Both also involve an increase in the number fracturing treatments necessary and sometimes the horsepower required to establish effective fracturing treatments in the reservoir.

Fracturing treatment costs already comprise a significant portion of total well costs in current engineering applications. In most horizontal wells, the treatment costs are one-third to one-half of the total well costs. Increasing the amount of treatment costs also increases the percentage of total well cost. Increased costs can result in a decline of project economics.