Abstract

Because horizontal technology is being applied to more and different types of reservoirs, it's becoming apparent that better completion designs are required to optimize production rates, long-term economics, and ultimate producible reserves.

In Mexico, early horizontal completions in compact sandstones reservoirs consisted mainly of open hole and slotted-liner completions. An optimum completion design requires preplanning by geoscientists and reservoir, production, and drilling personnel.

In addition to the required hardware, the completion design considerations include such items as wellbore location within the reservoir, drive mechanism, future remedial and stimulation requirements, dogleg severity, and horizontal length.

Increased emphasis is being placed on effective and economical zone isolation techniques, especially those which minimize the cost of workover requirements.

No standard or special completion design exists for horizontal wells, just as there is no standard completion design for conventional wells. Horizontal wells, at least until they become far more routine, will require extensive preplanning and more team-work between all the disciplines involved.

There is a considerable amount of completion technology available today which can applied to horizontal completion problems, and this technology will undoubtedly be expanded and refined over the coming years. Not only will this new technology be useful in horizontal wells, but also in highly deviated long-reach wells and, in some cases, conventional vertical wells.

Slotted (or preperforated) liner completions are by far the most common completion run in horizontal wells. The primary purpose of the slotted-liner is preventing hole collapse in formations that may tend to cave in after being drilled, or as the formation pressure depletes.

This paper discusses particular aspects critical to designing a successful slotted-liner completion for compact sandstone reservoirs in Mexico. Three examples are given of applications of these special completions in these horizontal wells.

Introduction

Oil and gas wells are drilled horizontally for a variety of reasons, chiefly to improve production without drilling multiple vertical wells and to prevent water or gas coning at specific conditions. Benefits of horizontal drilling are well documented and without exaggeration, horizontal hole technology can be classified as the hottest technical issue of today.

As discussed in previous literature, two basic types of horizontal completions exist: the continuos entry and the discreet flow entry. Open hole and slotted-liner completions fall into the category of continuos flow entry completions and are characterized by the fact that they offer little or no provisions for zone isolation.

An open hole completion is the most basic and is the simplest completion method. Open hole (Fig. 1) completions can be effective only where reservoir rock has enough integrity to prevent wall collapse or sloughing from blocking product flow to the wellhead. Success of this completion style depends also on existence of natural fractures and permeability in the reservoir, since stimulation of drain holes is not particularly effective because isolation of intervals for treatment is unlikely to be feasible.

These wells are cemented through the vertical portion of the hole and just into the producing interval. Production may be from natural forces in the reservoir, or tubing may be run through the vertical portion and into the pay zone to allow for removal by pump.

The open hole may be cleaned up by circulating fluids via conventional tubing or coiled tubing. Some operators have acidized wells completed open hole; however, some of these treatments have brought on caving and sloughing of wellbore walls. Slotted liners may be hung from liner hangers or production packers. (Fig. 2) shows a horizontal completion using a centralized slotted liner. P. 613

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