Specifying suitable materials and seal designs capable of withstanding harsh and caustic environments poses significant challenges.
by James Simpson
September 15, 2015

Artificial lift is used on oil wells to enhance oil recovery rates. Techniques such as gas lift, where expanding gas helps to lift fluids in a well's tubing, lower the density of fluid to decrease the bottom hole flow pressure. These artificial lift pumping systems pose many challenges, particularly in sealing. This is one of the reasons why leading oil and gas field service companies continually evaluate advanced sealing technology. They also encounter constantly evolving operating conditions, such as elevated pressures, extreme temperatures, increased friction and smaller spaces inside the wellbore for upstream pumping. The conditions in these environments are harsh and caustic. Specifying suitable materials and seal designs capable of withstanding these factors poses significant challenges.

Lowering Downtime, Lowering Costs

Careful prior understanding of a well's environment is essential for acquiring long, efficient and substantial yields. The gas lift equipment must be resilient enough to withstand processes and conditions. Using rugged technology proven to endure high pressures and temperatures while reducing friction levels in limited space allows operators to boost production levels in mature fields. Downtime for planned or unplanned maintenance on an artificial lift pump system can be costly for operators. The key to decreasing downtime and extending seal material life is to understand how materials react over time when exposed to severe operating conditions. Matching seals to these arduous and difficult environments is critical and can extend system life, optimize production efficiency and, ultimately, reduce operator costs. In addition, selecting a seal supplier with a broad range of compliant materials has benefits in both vendor reduction and processing performance. Sour gas or hydrogen sulfide (H2S) compatibility is often a sealing requirement for successful artificial lift systems. High levels of H2S may cause severe degradation of polymers typically used in oilfield applications, especially elastomer grades such as hydrogenated nitrile butadiene rubber (HNBR) and fluoroelastomer (FKM). The material selection for such conditions is important to ensure the system's high mechanical integrity and minimize potential seal failure and damaging leakage.

Meeting Seal Standards

Materials are vigorously tested before implementation to ensure they meet required standards such as Norsk Sokkels Konkuranseposisjon (NORSOK) M710, International Organization for Standardization (ISO) 23936-2 and American Petroleum Institute (API)—the minimum now demanded by the industry. Controls such as these ensure safety, and the governing bodies that help to set standards have made a positive impact. In addition, standards provide users with an unbiased, accurate way to assess performance. To meet standards, manufacturers must batch test seal materials. The parts themselves can undergo months or years of testing to ensure that they are able to withstand changing environments and conditions. This often has to be done rapidly. For instance, in just three weeks, one sealing manufacturer was able to deliver a seal developed in a compound to specifically address the impact of sour gas, saving a key project from delay.

Avoiding Catastrophic Failure

Pressure-containing components are vulnerable to sulfide stress cracking (SSC) when exposed to sour environments and can lead to various modes of material failure depending on additional environmental conditions. Material damage can occur in a relatively short time frame and can lead to catastrophic equipment failure. In such scenarios, companies should be aware of this possibility and request specific tests of potential solutions. It may be years before the solution is actually implemented. Choosing a supplier with this level of technical support combined with sealing solutions meeting industry standards ensures a customer receives an effective and reliable product.

Establishing a Supplier Relationship

Long-term relationships are valuable because system operating parameters, such as pressure or temperature levels, change over time in many applications. These changes should be monitored to ensure that the sealing solutions will still operate effectively within amended operational constraints.

Understanding Artificial Lift Environments

Over time, the internal pressure of oil wells drops, and different methods and systems are incorporated to invigorate flow. When reservoir drive does not provide enough pressure to lift fluids to the surface, artificial lift equipment is installed to help lift the fluids. To increase flow rates, the fluid viscosity or density of oil must be decreased. Injecting gas causes this to happen. The gas is introduced through the annulus, the space between the tubing and casing, via gas lift valves. Bubbles form as the gas is introduced at different intervals of depth in the well and lowers the pressure and viscosity within the well. Often, artificial lift uses compressed gas in the wellbore. This method takes full advantage of the gas energy available in the reservoir as it recycles gas from the well and yields high volumes. Gas lift is particularly suited for offshore drilling because of the minimal amount of surface apparatus employed in the process. Gas lift also handles sand and debris better than other methods.