I had an eye appointment recently. Not much is as valuable to us as our eyesight, so it is very important to have eyes and vision checked regularly. My eyes felt fine, vision was good, and things looked fine to the doctor, too. No damage. But eye pressure had gotten a bit too high, so a preemptive eye drop treatment to reduce pressure was prescribed. If eye pressure increases beyond a certain level, it can lead to the need for a much more costly and risky procedure, and one that would very likely only provide partial restoration, at best.
Increased pressure in wells. So, too, it is with oil and gas wells that develop increasing pressure—at the formation face or across the completion. All can seem fine with a well, even as pressure (and skin damage) is increasing. A well with increasing pressure and skin may be producing at a perfectly acceptable level, at or above its projected (and budget) performance. Increasing drawdown (via choke opening, increasing pump rate, or increasing gas lift volume) can maintain sufficient rate and mask the damaging effects.
In time, if pressure and skin continue to increase unchecked and untreated, severe damage to productivity, and even to the integrity of the well, can occur. Such a situation would require a very, if not prohibitively, expensive procedure, especially with high-value offshore wells. And there is no guarantee that a damaged well could even be restored to its prior, healthier state.
Wells are, of course, getting older every day. While most wells continue to perform at or above expectations, beneath the surface they are declining, due to increasing near-wellbore pressure (drawdown) and skin, and becoming more at-risk. With respect to offshore wells, in particular, and corrective measures to reduce skin, well intervention is nothing new—for example, for reperforating or chemical production enhancement treatments. But what would be “new,” in too many cases, would be conducting relatively low-cost, preemptive well interventions.
Holding off intervention. Some operators will investigate any offshore well for potential stimulation, once the well reaches a certain skin level, say,15 or 20, or when drawdown at the wellbore exceeds a certain pressure limit. That is a sensible practice. But in the majority of cases, as long as the well is performing adequately, regardless of skin, drawdown is periodically increased to maintain production, but while skin continues to rise. At a certain point, a very high skin can exert enough stress on the completion to blow an opening in a sand screen, resulting in sand (formation) and proppant production (if a propped fracture completion).
At the very least, prior to such a failure, formation fines can mobilize with increasing drawdown, causing severe plugging at, and near, the wellbore that is difficult to fully remove. Proppant embedment or even crushing can occur, if drawdown pressure is excessive, reducing fracture conductivity and well productivity. Higher drawdown levels can increase the potential for downhole inorganic scale and organic deposition. Effective intervention must take place before such severe consequences of increasing pressure, skin, and drawdown occur.
A hindrance to early or preemptive action in subsea wells, especially those completed in deepwater environments, has always been the high costs associated with intervention. Rig-based interventions, and just vessel deployment alone, are very expensive. While well intervention is perhaps ultimately anticipated, it is too often delayed or avoided as long as possible. But what should be understood is that even what is deemed a very high cost may encourage an unwise avoidance of addressing a well problem, resulting in a substantially greater cost down the road, or even the loss of a well altogether.
What should also be understood is that the cost of offshore well intervention is being driven down. It can now be accomplished at lower costs than what most professionals realize—with advancements to riser-less light well intervention (RLWI) systems that provide significantly lower cost and safe operation alternatives to rig-based intervention operations.
RLWI systems. RLWI refers to any intervention performed without high-pressure tubulars (risers) during interventions on subsea wells. RLWI systems do not require rig mobilization. Special light well intervention systems (equipment) are installed on, and deployed from, dynamically positioned, fit-for-purpose, intervention vessels. RLWI systems include equipment supporting applications such as running slickline, e-line, milling, setting and pulling tubing and trees, removal of plugs, pumping cement plugs, actuating sliding sleeves, perforating, well plugging and abandonment, fishing operations, and remedial stimulation, including acidizing, scale removal, and organic deposit removal, optionally utilizing coiled tubing. Top of Form
Bottom of Form
Light well intervention is not so new, with the first application back in the 1970s in 20 m of water, offshore Abu Dabi, in which a Flopetrol-designed subsea well intervention lubricator was used. Since then, tremendous advances have been made in light well intervention equipment and applications, and in vessel technology. Technology breakthroughs continue to be made, driven by the need for lower costs, to encourage greater and more frequent implementation, as is very much needed, as wells mature.
Regarding remedial well stimulation, which is the prescription remedy for decreasing formation face/near-wellbore pressure and damage skin, again, RLWI systems and vessels offer a significantly lower-cost alternative to rig-based intervention. Costs can be roughly 50% to 60% less, at least. Efforts continue to be made to further reduce costs by RLWI system technology developers, such as TechnipFMC, Expro, AKOFS Offshore, C-Innovation, Baker Hughes, and Halliburton, along with light well intervention vessel providers, such as Helix Energy Solutions and Oceaneering.
Also, remedial stimulation treatments are often over-designed, that is, with larger-than-necessary treatment fluid volumes and steps. Smaller, more simplified treatments will allow for greater use of smaller light well intervention vessels, shorter pumping times, with greater cost-savings as a result.
Be informed. There is considerable information available online for those wanting to learn more about RLWI technologies, vessels and applications. In addition to new technology development, greater understanding and expertise is necessary in the engineering and technical communities to take advantage of RLWI opportunities, especially in remedial well stimulation offshore, to preemptively address increasing well skin/pressure before it’s too late for a relatively low-cost operation. Wells are too valuable, and production is too important, to wait too long, and then having no choice but to conduct more complex, much more costly, and much-higher-risk corrective procedures that will likely only provide partial restoration, at best.
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