Coiled tubing drilling has proven to be a successful technique for rejuvenating mature oil and gas fields. This method has been effectively employed in various fields across the United States, including Alaska, Texas, California, Kansas, and Michigan, among others (Fig. 1). Moreover, the deployment of coiled tubing drilling has experienced significant growth in the Middle East, with the number of CTD rigs doubling in recent years and further expansion anticipated in the future.
WHY UTILIZE CTD?
The utilization of CTD is driven by various factors depending on the specific application. The primary reasons include the need for thru-tubing or slimhole sidetracks, underbalanced drilling, high-pressure wells that require specialized MPD/UBD techniques, and remote operations.
The most commonly employed BHA diameter for CTD is 3⅛ inches, although larger tools with a 5-inch outer diameter and smaller tools with a 2⅜-inch outer diameter are also available (Fig. 2). The size limitations of coiled tubing restrict the BHA sizes to 5 inches and below. This technique is most suitable for smaller hole sizes, typically 8½ inches or below, with the majority of wells drilled using hole sizes less than 4¼ inches. Consequently, the advantages of CTD are most prominent in re-entry drilling operations targeting shallow gas or oil wells. Another perspective to consider is that CTD is a reservoir drilling technology, thus the closer it gets to the reservoir, the more advantageous it becomes.
Coiled tubing is specifically designed for underbalanced operations and continuous circulation, making it ideal for drilling low-pressure mature fields while ensuring the protection of the reservoir rock from damage. This feature is particularly critical when there is limited pressure to drive production. While underbalance can be achieved using a single-phase fluid in high-pressure reservoirs, it becomes even more relevant in fields that require a two-phase drilling fluid, such as water and nitrogen. In such cases, maintaining a stable circulating regime at all times is facilitated. Additionally, in systems where EM telemetry cannot be employed, wired CTD tools become the only viable option in two-phase systems.
Drilling high-pressure wells, whether through managed pressure or underbalanced techniques, is another area where coiled tubing offers significant advantages. The continuous circulation and high-pressure control equipment inherent to coiled tubing drilling enable superior control of downhole pressure through adjustable pumping rates, drilling fluid weight, and choke pressure. Pressure control equipment capable of handling pressures up to 15,000 psi is a standard feature as well.
Offshore projects also benefit from coiled tubing drilling in terms of slot recovery, equipment footprint, and cost reduction. CTD operations can be conducted through tubing, significantly reducing slot recovery operations. Moreover, the compact size of coiled tubing equipment allows it to fit on most platforms, eliminating the need for a jackup rig. This reduces the cost of establishing new wellbores and minimizes the required crew size. The advantages of MPD on coiled tubing further add to its appeal in offshore applications.
The smaller and more mobile nature of coiled tubing equipment provides a clear advantage over conventional rigs in remote locations, such as northwestern Australia. This can be vital for the commercial success of small-scale projects. However, an alternative approach that combines a conventional rig with coiled tubing drilling may be the optimal solution. For instance, a conventional drilling rig can be used to drill the well down to the reservoir, followed by the utilization of a CTD package to drill the reservoir, preferably underbalanced. This approach optimizes the benefits of each technology and allows for the drilling of multiple wells within a specified timeframe or at a lower cost compared to mobilizing two drilling rigs. These advantages are in addition
Do you require further assistance?
We have over 10 years in the Oil & Gas Manpower sector and have an exceptional candidate database to assist with your requirements.
