Oil and gas companies drilling in demanding offshore environment have to face a variety of challenges, such as High pressure/High temperature reservoirs, Geological uncertainties, Waves and unexpected sea movements, etc. Therefore special equipment, and technologies are required for overcoming these challenges. In this essay, I will present an introduction on different kinds of Risers, which are widely used in offshore drilling.
Marine risers are used to provide a return flow path between the wellbore and the drill vessel and to guide the drill string or casing to the BOP stack on the ocean floor. Riser must withstand the lateral forces of waves, currents, and movements of vessel from directly over the well. They also have to withstand the axial i.e. lengthwise loads imposed by the weight of the drilling mud and, conversely, the buoyancy of riser itself in seawater.
There are two kinds of drilling risers. A tie-back riser is a rigid pipe with little give used with fixed platforms and stable floating platforms. A tie-back riser is a smaller, thicker-walled pipe used with surface BOPs. Because the BOP is at surface, the tie-back riser must contain full well pressure. A marine drilling riser is used with floating rigs that have very little stability or mooring. This uses a BOP on the seafloor. Since the BOP is below it, marine risers do not need to contain full well pressure.
Whether you use a marine riser or tie-back riser depends on the type of vessel doing the drilling. A permanent production platform with an onboard drilling rig will usually use a tieback riser, because the platform is reliably fixed in place with a 1000-year storm rated anchor spread. So there's no reason to expect the rig to need to disconnect from the sea floor and the pressure control equipment can be on surface. But a temporary drilling vessel (like a dynamically-positioned drill ship) may periodically lose position and have to disconnect from the sea floor. In this case, you want a subsea BOP to secure the well, and a marine riser will be used. A production riser is the permanent pipe used to flow oil to surface. It may be a single pipe, or concentric pipe, or a bundle of multiple flowlines.
As drilling has progressed to deeper waters, rises assemblies have become heavier. The point has been reached where it is not feasible to employ more tensioning to support riser weight. Therefore, various types of floating devices have been tried experimentally. Foam matrix material clamped on a riser length can effectively reduce the apparent weight when submerged, but the material is easily damaged in handling and absorbs water when submerged for a long period. Synthetic buoyancy material made of hollow bubbles of synthetic resin anchored in a hard plastic material molded to fit the riser provides desired buoyancy. in figures below you see buoyancy module.
Shadizadeh Seyyed Reza, Offshore Drilling Engineering, Course Note
Carlyle Ryan, Research Scientist at SINTEF Petroleum Research, www.quora.com/What-is-the-difference-between-a-marine-riser-drilling-riser-and-production-riser
Atencia Vincent, Riser basics, oilpro.com
References for images:
**This article was first published on 6 December 2016 by Ali Seyedalangi, MSc in Drilling Engineering and is reprinted here with full permission.
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Headline crude prices for the week beginning 11 February 2019 – Brent: US$61/b; WTI: US$52/b
Headlines of the week
Midstream & Downstream
Global liquid fuels
Electricity, coal, renewables, and emissions
2018 was a year that started with crude prices at US$62/b and ended at US$46/b. In between those two points, prices had gently risen up to peak of US$80/b as the oil world worried about the impact of new American sanctions on Iran in September before crashing down in the last two months on a rising tide of American production. What did that mean for the financial health of the industry over the last quarter and last year?
Nothing negative, it appears. With the last of the financial results from supermajors released, the world’s largest oil firms reported strong profits for Q418 and blockbuster profits for the full year 2018. Despite the blip in prices, the efforts of the supermajors – along with the rest of the industry – to keep costs in check after being burnt by the 2015 crash has paid off.
ExxonMobil, for example, may have missed analyst expectations for 4Q18 revenue at US$71.9 billion, but reported a better-than-expected net profit of US$6 billion. The latter was down 28% y-o-y, but the Q417 figure included a one-off benefit related to then-implemented US tax reform. Full year net profit was even better – up 5.7% to US$20.8 billion as upstream production rose to 4.01 mmboe/d – allowing ExxonMobil to come close to reclaiming its title of the world’s most profitable oil company.
But for now, that title is still held by Shell, which managed to eclipse ExxonMobil with full year net profits of US$21.4 billion. That’s the best annual results for the Anglo-Dutch firm since 2014; product of the deep and painful cost-cutting measures implemented after. Shell’s gamble in purchasing the BG Group for US$53 billion – which sparked a spat of asset sales to pare down debt – has paid off, with contributions from LNG trading named as a strong contributor to financial performance. Shell’s upstream output for 2018 came in at 3.78 mmb/d and the company is also looking to follow in the footsteps of ExxonMobil, Chevron and BP in the Permian, where it admits its footprint is currently ‘a bit small’.
Shell’s fellow British firm BP also reported its highest profits since 2014, doubling its net profits for the full year 2018 on a 65% jump in 4Q18 profits. It completes a long recovery for the firm, which has struggled since the Deepwater Horizon disaster in 2010, allowing it to focus on the future – specifically US shale through the recent US$10.5 billion purchase of BHP’s Permian assets. Chevron, too, is focusing on onshore shale, as surging Permian output drove full year net profit up by 60.8% and 4Q18 net profit up by 19.9%. Chevron is also increasingly focusing on vertical integration again – to capture the full value of surging Texas crude by expanding its refining facilities in Texas, just as ExxonMobil is doing in Beaumont. French major Total’s figures may have been less impressive in percentage terms – but that it is coming from a higher 2017 base, when it outperformed its bigger supermajor cousins.
So, despite the year ending with crude prices in the doldrums, 2018 seems to be proof of Big Oil’s ability to better weather price downturns after years of discipline. Some of the control is loosening – major upstream investments have either been sanctioned or planned since 2018 – but there is still enough restraint left over to keep the oil industry in the black when trends turn sour.
Supermajor Net Profits for 4Q18 and 2018
- 4Q18 – Net profit US$6 billion (-28%);
- 2018 – Net profit US$20.8 (+5.7%)
- 4Q18 – Net profit US$5.69 billion (+32.3%);
- 2018 – Net profit US$21.4 billion (+36%)
- 4Q18 – Net profit US$3.73 billion (+19.9%);
- 2018 – Net profit US$14.8 billion (+60.8%)
- 4Q18 – Net profit US$3.48 billion (+65%);
- 2018 - Net profit US$12.7 billion (+105%)
- 4Q18 – Net profit US$3.88 billion (+16%);
- 2018 - Net profit US$13.6 billion (+28%)