By Akpelu Paul Kelechi
“Many wells today where you have well integrity and zonal isolation issues are a result of a failure of the cement”
It is practically impossible to discuss well completions without a nod to the cementing process: the standard procedure that isolates the various down-hole formation zones.
Prior to 1921, one of the greatest obstacles to successful development of oil bearing sands was the encountering of liquid mud, water and other sediments during and after the process of drilling a well; this was before the art of well cementing was “perfected.” It is easy to assume that almost a century later in 2019, well cementing would have advanced so much technologically that no undesirable basic, sediment and water (BS&W) would be produced from oil wells due to the failure of the cement to seal. Unfortunately, we still have frequent challenges mainly due to the hole geometry, formation types, pore pressure, differential pressure, etc. The production from typical oil wells which are hampered by BS&W intrusion require time, energy and expense to correct and has led to the abandonment of many wells which would otherwise have developed more profitable results for operators.
In July 2019, the French major Total announced that it successfully deployed a new breed of cementless completion called the Welltec Annular Isolation (WAI) in the Moho North Albian field. According to Ronan Bouget, the Drilling and Completions manager of Total E&P Congo, the technology was jointly developed with Welltec. Gbenga Onadeko, Senior Vice President, Welltec Africa, tells Africa Oil+Gas Report that the “Welltec Annular Barrier (WAB) provides effective zonal isolation at discrete points within the well, whereas, the WAI provides zonal isolation across the length of the reservoir replacing the cement.”
“Many wells today where you have well integrity and zonal isolation issues are because of failures of cement. Attempting to place cement and achieve full circumferential coverage around a piece of pipe that is over three kilometres downhole in a well could be challenging due to gravitational effects especially if the well has some deviation, Gbenga explains. “The cement will tend to go to the lower side of the liner / casing while the upper side of the liner / casing may be left without cement, creating what is called a channel. The cement could also be contaminated due to interactions with mud and formation cuttings. The channels and micro annulus may lead to a loss of integrity or isolation between zones which could accelerate the production of water or gas break through.”
Squeeze cementing is a remedial cementing technique deployed when challenges occur during the primary cementing process. Gbenga continues. However, “this has a relatively low success rate with high cost. This is often the reason why wells produce 60% to 70% water cut from day one and is a contributor to cost overrun. In addition, depending on the age of the well, for example in the case of a relatively old well, cracks could develop in the cement due to thermal expansion and contraction, which can then lead to the leakage of gas or water.”.
The WAI technology can be deployed in various and even hostile well environments, adds Joseph Bagal, who is the Director of Well Completions for Welltec Africa. Joseph is a sand control expert with global experience and gained significant knowledge of the Niger Delta from various assignments living and working in Nigeria. He is familiar with the challenges associated with clastic depositional environments of the Niger Delta and he says that “although the first deployment of the WAI was in the Moho North which is a carbonate field, the WAB and the WAI technologies are also applicable in clastic environments.
The materials used to manufacture the WAI are the same as used for very hostile environments including within Geothermal wells. They are highly resistant to corrosion and specifically selected for their life of well properties. Today, the industry continues to use cement because that is historically the solution utilized (even though as mentioned many well integrity issues arise from cement failure). The technical qualification performed on the Welltec Annular Sealing Products (WAB, WLP, WAI) are more stringent than the qualification tests on cement, when used for isolation – particularly their sealing capabilities” he claims.
The application of the WAI on the Moho North field dates back to 2016, when TOTAL E & P Congo selected the WAB in the development of the Moho North Albian field “this initial application was in conjunction with cement (assurance to provide a seal to isolate the zones)”, comments Joseph. “Total initially selected a cemented and perforated liner solution, the liner length was short and deep, implying the volume of cement was relatively small, which increases the operational risk of cementing the reservoir section. Because of the potential of cement contamination and also to increase the success rate of placing it behind the liner, the volume of cement pumped was increased by enlarging the hole (under-reaming) and drilling deeper i.e. a longer rat hole section, which placed the toe of the well within less preferential sections of the formation increasing the drilling and production risks.
With the liner deployed and cement in place, the WAB is expanded quickly under full surface control sealing against the formation rock, displacing the cement, providing a high integrity pressure isolation between zones. This in turn ensures that even if channels or micro-annulus are present in the cemented interval, effective isolation is still achieved within the annulus.
Following this initial success with the WAB and the efficiency drive by TOTAL E & P Congo to further reduce drilling expenditure (partially driven by the low commodity prices), this presented an opportunity to extend the scope of the utilization of the WAB to make the project more economical. This provided the impetus for the joint development of the WAI between Welltec and Total E & P Congo.
The WAI technology is based on the WAB platform, with the packers extending over the complete length of the liner (the joints are not covered). The WAI effectively replaced the cement within the annulus across the reservoir interval. A large quantity of Welltec Proprietary seals are installed along the length of the WAI, providing zonal isolation down to each 20 cm, with each seal qualified for 4,500 PSI of differential pressure. By eliminating the cement completely from the reservoir section of the wells, the drilled interval is shortened (i.e. no rat hole), the need to under-ream for hole enlargement is removed along with the need to perform extensive wellbore cleanout. This reduction in work scope delivered significant savings in the number of days predicted to complete the well compared to the best composite result achieved in the field. Non-Productive Time (NPT) from the wells where the WAI were deployed was reduced. The use of the WAI led to a reduction in rig time and saved a huge amount of cost for our client.”
Returning to the WAB technology, which has been deployed all over the world including clastic environments in the North Sea and as well as in the Benin Basin Offshore Lagos, Nigeria. “If you have a clastic reservoir, cement is pumped all the way to the cap rock to achieve isolation and well integrity. We successfully used the WAB product to assist a minor deepwater operator in Nigeria to achieve approximately 3,000 barrels per day of oil production. Two WABs were installed in the side-tracked section of their last well which successfully eliminated the water cut, but more importantly eliminated the gas flowing from the gas gap and the associated sustained casing pressure as monitored at the well head. It is understood that the well has kept this state since 2017 when it was put on production.”
The catch with the oil and gas industry however, is the conservative nature of the industry in adopting new and improved technology. As an innovative company with pioneering technologies, Welltec often experiences this challenge. Gbenga sums it up with these words: “We develop cutting edge technologies and work extremely hard to convince our clients to deploy the value adding solutions. One of values we add to the industry is to assist our clients in overcoming their initial reluctance. We want to ensure that these technologies are included in their field development plans to avoid paying premiums later due to rush mobilizations. Including the technologies in their initial plans reduces the risk of budget variation. With the WAI, we predict that cost savings of up to $75Million to $100Million over a 15 to 20 wells deepwater field development plan can be achieved (including reduced NPT). Proportional savings can also be achieved in onshore and shallow offshore markets. Approaching it from a larger scale makes the value proposition more obvious. We like to think that we work on solutions that are best for the well and the overall project. In most cases, our industry is integral to the economies of the oil and gas producing countries. We therefore believe that we are having a positive impact on the overall wealth of the nations we operate in.”