Drilling is becoming increasingly difficult as companies are reaching further into deeper reservoirs. Drilling deeper poses a challenge to engineers as wells become ever more complex. One issue is the narrow pressure window, or fracture gradient, that must be navigated to reach certain reservoirs.
The fracture gradient is the pressure range between the pore pressure and fracture pressure that exists for a particular formation. The driller will typically aim to keep the annular hydrostatic pressure above the pore pressure, to prevent a kick, and below the fracture pressure, to prevent formation damage, which may result in fluid loss. Such obstacles may prevent wells from being drilled using conventional techniques.
In the last decade, however, drillers have utilized managed pressure drilling (MPD) to address this. MPD involves using lower density mud, a surface choke manifold and surface back pressure to dynamically control the annular pressure profile. By adjusting the surface backpressure with the choke, proper equivalent circulating density (ECD) can be maintained to stay within the fracture gradient. MPD allows the driller to quickly respond to and control wellbore conditions, while having the added benefit of extending the casing setting point or removing the need for a section of casing.
As wells targeting deeper, more challenging reservoirs become common place, MPD is used more frequently. This technique, originally used onshore, is becoming a viable option offshore, thus changing the initial environment for which the MPD systems and the associated equipment were developed.
Recognizing this trend and the need to ensure operations are performed in a safe environment, DNV GL, the American Bureau of Shipping (ABS) and the American Petroleum Institute (API) are releasing their own set of MPD class rules and recommended practices at the end of 2H 2015.
“API standards are recommended practices for conducting managed pressure drilling operations that apply across the board,” says CJ Bernard, global business development manager at Halliburton’s Sperry Drilling GeoBalance group. “Everything from the planning aspects, to well control event identification, response and management, to equipment design, selection and testing, to equipment requirements, so they have to do more specifically with MPD operations.
“Whereas classification societies (ABS, DNV & Lloyds) speak to requirements of the equipment as it relates to interactions with the other ‘classed’ drilling equipment on the rig,” says Bernard, who also serves as class society task force chair on the International Association of Drilling Contractors (IADC) MPD committee.
In 2011, DNV became the first classification society to have general rules for MPD systems on board DNV-classes drilling units with the class notation Drill(N). A more detailed set of requirements were released in the update of DNV-OS-E101 in 2013. This revision is currently being used to classify and certified MPD system, says DNV GL’s Arne Handal, Ph.D, principal engineer for drilling and well intervention, in a comment to OE.
“The new standard includes requirements for managed pressure drilling systems, definitions of associated safety systems and requirements for well barriers and drawworks,” said Kenneth Vareide, executive vice president of offshore class at DNV GL, upon release of the 2013 revision. “Our aim has been to take class a new step forward by focusing on control, transparency and efficiency. In addition, the intention has been to ensure that the latest best practices and innovations are rapidly implemented by the industry. The end result will be improved safety.”
However, as with any pioneering works, there are kinks to work out.
“There are issues within the original rules that industry is currently working through with the class societies that hinged more so on a misunderstanding of MPD operations and intent,” Bernard says.
In response to this, DNV GL spokesman Kristian Lindøe said in a statement to OE that the company works with the industry to update their rules on a continual basis.
Handal furthers this point saying: “Our updates build on experience from the application of these standards, so reviewing and addressing industry concerns are considered as part of the updating process along with safety and technology developments.”
As a classification society, ABS is an independent, externally audited body that reviews plans, operational maintenance, and surveys construction processes for its clients. Currently, ABS plans to publish the ABS Guide for Classification of Drilling Systems (CDS Guide) with an appendix for MPD rules, Appendix 7.
Following ABS’ own discussion with 50 industry companies, including a mix of both operators and drilling contractors, the CDS Guide will be updated with the appendix available in early 2015. The document will include requirements for the design, construction, and commissioning of MPD systems, subsystems, and components onboard mobile offshore drilling units (MODUs).
“ABS sees MPD as a growing trend in offshore drilling and is currently working on several MPD projects. MPD is now being used offshore to facilitate drilling of previously un-drillable wells and to enhance a well’s primary well barrier,” says Harish Patel, director of offshore technology at ABS. “In addition to defining a new technology qualification standards approach to high-pressure, high-temperature drilling, ABS is finalizing requirements that specify certification for MPD systems, including (dual gradient drilling) DGD systems, and associated subsea components.”
With the upward trend of MPD use and the ever present concern for safety, Appendix 7 will provide ABS’ clients with guidelines to plan future operations. Appendix 7 will focus on offshore MPD applications, and address needs unique to offshore drilling operations. The guidelines aim to help operators comply with the rules and requirements associated with drilling in the US offshore, as well as provide greater reliability and consistency to lower potential risks during offshore operations. Because the MPD system and all of its subsystems will be considered a part of the primary well barrier system, all associated components used in MPD operations will require ABS design approval and an ABS survey for installation, to be classed by ABS.
In the case of DGD systems, a type of MPD, no specific US requirements existed prior to the application of the first DGD system on a MODU. ABS worked with US supermajor Chevron to class the Pacific Santa Ana, which has a DGD installation onboard. The ship, owned by Pacific Drilling, began a five-year contract with Chevron in 2012, and was used to successfully drill its Anchor prospect in the US Gulf of Mexico in 2014.
“The DGD system’s major subsea components reviewed by ABS were the mud lift pump, subsea rotating device, and solids processing unit. The DGD project resulted in establishing a minimum standard for CVAs (the independent certified verification agents performing the safety reviews and working with regulatory bodies such as the US Coast Guard and Bureau of Safety and Environmental Enforcement) while certifying offshore MPD technology. ABS also used this experience to develop new classification requirements for MPD systems as part of the CDS Guide,” Patel says.
With demand for certification involving DGD installations confined to a single vessel, plans for more extensive discussion on DGD systems will occur at a later date following the release of Appendix 7.
“As with any new technology application, applying MPD systems offshore requires careful consideration with regard to equipment and system design as well as any operational, maintenance, and safety issues – the risks – associated with offshore drilling practices and ultra-deepwater rig configuration and system integration,” Patel says.
While ABS has been developing its MPD appendix, API has similarly forecasted the need to standardize MPD systems. In contemporaneous development with the CDS Guide, API’s Recommended Practice 92M, Managed Pressure Drilling Operations with surface back pressure (92M), is set to come out by the end of 2H 2015. 92M is being developed with support from the IADC UBO-MPD Committee.
In regards to drilling rigs with surface BOPs, 92M will provide information for planning, installation, testing, and operations for wells drilled within the surface pressure category. This will allow everyone in the industry that is drilling with these techniques to have a standard practice that they can reference to as they approach complex wells and bring additional consistency, safety, and environmental awareness to offshore operations, says David Miller, director of standards at API. The main difference between the two lies in the process and company objective.
“[API’s] standard development process is accredited by the American National Standards Institute, which is the body in the US that accredits standards developing organizations,” Miller explains. “As an accredited standards developing organization, we are responsible for a process that, by design, is open and transparent.”
And proving that point further, while the standards were under ballot from late November to 23 January 2015, they were available on the API website for review.
When the guidelines and 92M are available, companies will be able to look at their operation, and see which document suits the company’s project.
When these guides and standards are issued later this year, some will have to make changes to their MPD operations.
“[Most MPD service providers are] not used to having that amount of scrutiny on MPD systems, fail-safes, and procedures,” says Earl Dietrich, global director of deepwater systems at Weatherford. “However, it is making us, our suppliers, and all competitive vendors, improve their game.
“Now you will be required to demonstrate how the systems work; how you’re going to test it; how the fail-safe systems work; what kind of redundancy there is.”
When it comes to safety and efficiency, consistency will play an important role.
“Hopefully, some standardization will make it easier for us to specify proper equipment and have consistent installations, whether they be temporary or permanent, that are not specific to the rig contractor, operator, or country of operation,” Dietrich says.
“More stringent standardization of systems, installations, capacities, and characteristics will allow personnel to more readily move between various rigs and systems.”
The industry will also benefit by having more fit-to-purpose guidelines. “For example, in reference to our hoses, the highest standard is called 17K, but that standard is for continuous production of hydrocarbons to flexible hoses. We don’t do that,” Dietrich explains. “We may have a gas cut mud event with hydrocarbons that we deal with, but it’s not continuous. However, for right now, we don’t have a fit-for-purpose document or hose specification for our installations.
“We are continually involved with IADC, API, ABS, DNV, NORSOK, BSEE, and other groups advocating the improvement of personnel and rig safety, operations, and system standardization and requirements by providing enhanced MPD, early kick detection, and pressurized mud-cap drilling services,” Dietrich says.
ABS, DNV, and API have worked with industry members to address concerns regarding the original and the newly developed MPD requirements. Halliburton’s Bernard says, all organizations must come together to discuss equipment design and operational intent so that together, we can provide proper guidance and requirements to help industry meet the public’s safety expectations of the industry.
With MPD technology being deployed in new inherently risker areas, it is crucial to ensure that all interactions have been reviewed and that hazards and risks are managed to acceptable levels.
“That’s one of the things ABS and DNV look at, to ensure that all of the interactions between rig and MPD equipment don’t create unsafe conditions,” Bernard says. “In order to be class approved, you have to prove to ABS and DNV that you’ve done all the hazard analysis necessary to ensure that the controls and barriers are in place to manage the different hazards from these operations and equipment interactions.”
As a benefit, the classification applies equally to all service providers, so it creates a level playing field and once certified it’s not necessary to go through the process again for every customer’s project. Most importantly, by having a set of standards that must be met and adhered to it shows the public that the intent is to provide industry rules and guidance to conduct MPD operations in the safe manner.
The original written by Jerry Lee