BASIC COMPLETION METHODS
1. Abandonment: Plugging the well with cement, recovering any casing or other tangible equipment that can be economically removed and, on land, restoring the surface location to its original condition.
2. Completion: Installing the tools and equipment needed to safely produce hydrocarbons from the well. Completion may also involve stimulating the well to improve its productivity, either by pumping an acid mixture into the productive formation or fracturing the rock.

In some cases—most notably offshore exploration wells—abandonment is a foregone conclusion. In offshore projects, exploratory wells are usually abandoned after extensive evaluation and testing; producing wells are drilled and completed later, as part of the overall development plan. In onshore projects, on the other hand, the decision to abandon or complete is generally based on the results of the well evaluation.

Each drilled wellbore awaiting completion is unique. Even nearby wells drilled to the same reservoir can have different depths, formation characteristics, and hole sizes. It follows, then, that a wide variety of equipment designs and procedures have been developed to provide safe, efficient conduits from subsurface reservoirs to the surface in different situations. In each case, the ideal completion design minimizes initial completion and operating costs, while providing for the most profitable operation of an oil or gas well over its entire life.

The basic completion design may follow one of several configurations:

* open hole completion, where casing extends only to the top of the producing interval ( Figure 1 (a))


Figure 1

* uncemented liner completion ( Figure 1 (b)), where a slotted liner is set across the producing interval
* cemented and perforated completion ( Figure 2 (c) and (d)), where casing or a liner is cemented across the productive interval and then perforated to establish a conduit between the formation and the wellbore.


Figure 2

One of these configurations will be the basis for the completion design, which may incorporate one or multiple strings of tubing and tubing accessories to facilitate production from one or multiple zones.