Zone Isolation Of Horizontal Wells By Coiled-Tubing-Actuated Tools
Authors: Robison C.E. , Mashaw H.R. , Welch W.R. 
Published: October 2008

Zonal isolation of the producing intervals in highly deviated or horizontal wells is now considered to be one of the most critical areas to address during the design phase of well completion. The likelihood that water coning or gas breakthrough will be a probable determinant for the life expectancy of the well and will most certainly be a factor in expected production cannot be overlooked by the operator when scrutinizing well-management design criteria.

This paper will discuss at length:Completion equipment to manage the various production or injection scenarios.Coiled tubing servicing tools to operate the subsurface flow controls.

INTRODUCTION

In many early horizontal wells, the producing interval was considered as a homogeneous reservoir that needed no zone isolation along the sandface. In many of these openhole wells, the completion equipment consisted of a slotted liner throughout the producing interval, which left little flexibility for isolating the affected zones when premature water coning or gas breakthrough occurred later in the life of the well. Without a means of isolating the undesirable flows of water and gas, some potentially productive horizontal wells were destined to become lower producers than their vertical counterparts.

Completion equipment that can provide zone isolation options and flow regulation is now readily available in a number of configurations for the various producing or injecting conditions that are encountered in a horizontal well. Many of these designs are modified versions of existing equipment that has been used in wells for many years. In addition, coiled tubing offers a proven, cost-effective method for operating the flow controls in the horizontal wells. The new high-strength coiled tubing with 2-inch or larger OD's can reach further into the horizontal sections of the well, and subsequently, can provide enhanced servicing capabilities to operators.

BACKGROUND

Horizontal wells fall in two major categories: open hole and cased hole. In either case, it is desirable to control the flow from the vertical fracture system along the horizontal interval. In open holes, inflatable external casing packers or cementation of short intervals may be used to isolate the fracture systems (Figure 1). Figure 2 shows high pressure packers that are readily available to isolate the perforations in cased holes. Sliding sleeve circulation devices provide a proven method of selectively controlling the flows from the reservoir. The closing sleeves in these flow controls are operated by manipulating a shifting tool.

Conventional slickline operations must rely on gravitational forces to lower the toolstring into the well. In high angle or horizontal wells, the drag on the toolstring can overcome the gravitational forces, rendering the tools inoperable. Initially, this problem was solved by the adaptation of slickline tools to coiled tubing. This enabled the tools to be deployed by coiled tubing into horizontal sections of a well. Further modifications of standard tools to take advantage of the hydraulics inherent with coiledtubing operations have provided a new dimension in the scope of horizontal coiled-tubing technology. Now, deployment of these tools can be accomplished in a cost-efficient manner at speeds unmatched by any other services available.