Why are so many wells drilled?

When producing oil, only part of the oil flows naturally to the surface due to the reservoir pressure. Over time, the pressure declines, leaving significant volumes of oil behind. To recover more, methods known as Improved Oil Recovery (IOR) or Enhanced Oil Recovery (EOR) are used.

IOR includes measures such as better well placement, water injection, and horizontal drilling, while EOR is a more advanced form that involves gas injection, chemicals, and heat to make the oil more mobile and easier to produce. Such methods can increase recovery rates from roughly 30 to over 60 percent. The introduction of horizontal and multilateral wells (wells with several branches) has made it possible to reach previously inaccessible parts of the reservoir, thereby improving recovery potential.

Complex geology

The reservoir at Gullfaks is geologically complex and consists of several sandstone formations—such as the Brent, Statfjord, Cook, and Lunde formations—which vary in thickness, porosity, and permeability.[REMOVE]Fotnote: Field: Gullfaks Norwegian Petroleum

In addition, the reservoirs are segmented by faults that create separate pressure zones. This means that the oil and gas are not contained within a single structure but are distributed across many sub-reservoirs with limited communication between them.[REMOVE]Fotnote: https://equinor.industriminne.no/en/gullfaks-the-big-qualifying-test/ To produce efficiently from the entire reservoir, a large number of wells with different angles and lengths must therefore be drilled to reach the various zones. Vertical, horizontal, and multilateral wells are used to access “pockets” of oil and gas that would otherwise be difficult to exploit.

Pressure support

Another key factor is the need for pressure support. As oil and gas are produced, reservoir pressure decreases, which can lead to declining production. At Gullfaks, extensive water and gas injection is used to replace the lost pressure and drive more oil toward the production wells. This requires a large number of injection wells working in parallel with production wells. A balanced distribution between producers and injectors is essential for maintaining stable production and achieving high recovery rates.

Other wells

The field’s long lifetime has also made it necessary to drill new wells to replace older ones. As some wells mature or produce little, some must be plugged and abandoned, while others are rehabilitated or re-drilled. In this way, the field is continuously renewed to secure future production. In addition, Gullfaks has several satellite fields—Gullfaks South, Skinfaks, and Rimfaks—which are tied back to the main platforms via pipelines and control systems. Each of these fields requires its own production and injection wells, further contributing to the total number of wells in the Gullfaks area.

Different rig types for different tasks

Drilling at Gullfaks also involves various rig types depending on the tasks to be performed. The three main platforms—Gullfaks A, B, and C—are integrated production, drilling, and accommodation installations with concrete gravity-based structures (GBS). The fixed drilling rigs on the platforms are used for drilling new production and injection wells as well as sidetracks, meaning a new well path is drilled from an existing wellbore instead of drilling a completely new well from the surface, providing a stable and safe drilling operation. For drilling on satellite fields and subsea installations, mobile rigs—often with dynamic positioning—are used and can be mobilized to different locations. Lighter rig types or specialized rigs are used for well intervention, sidetrack drilling, plugging, and maintenance.

The choice between fixed platform rigs and mobile rigs reflects a strategic balance between cost, flexibility, and operational efficiency. While platforms are best suited for long-term production drilling, mobile units offer greater mobility and the ability to service multiple fields in the region.

In summary, the large number of wells at the Gullfaks field is the result of geological complexity, the need for pressure support, the ambition for high recovery rates, the field’s long history, and the integration of nearby fields. Drilling many technologically advanced wells has been essential to maintaining production.

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