Superior dependability of the drill string plays an important role in drilling deep and especially ultra-deep, highly inclined and long departure horizontal wells, where it is often exposed to extreme loading conditions in a high pressure and high temperature environment. This need has resulted in the technological development of high strength Aluminum Drill Pipe (ADP) for use in deep and ultra-deep wells, where its' properties and the advantages that it offers can make a significant contribution to reaching the most challenging of drilling targets. Drilling intervention operations such as milling and fishing are also a major challenge in such extreme environments and have led to the development of new tools and techniques to address them. This paper will review the use of ADP in comparison to steel drill pipe and discuss the milling scenarios of cemented and un-cemented drill pipe as well as fishing operations using external and internal engagements. The intent of this paper is to disseminate technical knowledge in this new area of drilling technology.
Both above and under the ground, hydocarbon storage is subject to many stringent compliance standards regarding health, environment, and ground water safety. Various issues—such as zoning regulations, future expansion needs, secondary and tertiary containments, design efficiency for storage and transfer, and financial viability of projects—determine the storage installation method. Underground storage maximizes real estate usage, reduces fire hazards, protects against weather events, and enables storing large amounts of hydrocarbons. The principal methods for underground storage include salt caverns, depleted reservoirs, and acquifers. Each method has its own application advantages and physical properties, such as retention capability and permeability. These factors, along with the economics of site establishment and maintenance as well as deliverability rates, regulate the suitability of that method for particular applications. For example, salt caverns provide very high withdrawal and injection rates relative to their working gas capacity. When the operator locates a suitable salt dome or salt bed, the site is excavated to form a cavern. This excavation process is usually accomplished by pumping or injecting highly pressurized water into the salt layer to dissolve the salt and create a cavern cavity; this method is referred to as cavern leaching or solution mining. After this process, the operator can remove the brine and commence operations. However, if this leaching phenomenon occurs in existing natural gas storage caverns, the leached area behind the intermediate casing becomes an inaccessible part of the reservoir. To access this area, the lower section of this casing must be removed. Traditional section milling can achieve this; but if the inside diameter (ID) of the inner string is smaller than the outside diameter (OD) of the servicing tool, existing technology cannot be used. Situations such as this require new technology to pass through the restricted ID and open a section in the next-larger-size string.
In recent years plug and abandonment (P&A) technologies are receiving greater attention around the world as more and more fields reach the end of their productive life. Permanent P&A is done with the objective of the well being sealed and isolated forever. Over the years the market for permanent P&A has grown into estimates of several billions of dollars. There are thousands of wells world wide, both onshore and offshore, that require P&A operations to safely abandon the erstwhile producing asset while maintaining environmental regulations and standards. Since the P&A operations do not result in increase in revenue or any asset value, the attitude of almost all operators is that the least amount be allocated towards this operation in the well life cycle plan. This means that newer technologies must be developed in order to increase efficiencies and reduce the overall costs and foot prints for P&A operations. Many times existing conventional technologies do not fill in these requirements, and thus there is a need to develop and deploy newer downhole technologies. This paper will discuss well abandonment P&A introduction, methods for preparing a well before setting cement plugs, a brief comparison between different methods, development of section milling technology to dual string, field application on an offshore gas field abandonment campaign, and finally conclusions regarding this new and emerging dual string milling technology.
In recent years, plug and abandonment (P&A) technologies have been receiving greater global attention as more and more fields reach the end of their productive life. The objective of permanent P&A is permanent isolation. Several operators have requested the development of a section mill capable of milling two adjacent casing strings. Removing two adjacent casing strings enables a permanent, solid-cement "rock-to-rock" barrier across the formation in open hole. Various methods have been used to section mill dual casing strings with results ranging from costly multiple trips to total failures. The scope of the project was to develop a milling system that permits the removal of both 9 5/8-in. and 13 3/8-in. (or 13 5/8-in.) casing in either one trip or multiple trips into and out of the well. The new milling system should be capable of handling different flow rates for successful tool operation and efficient hole cleaning. The focus of the new milling system also was to minimize trips and bottomhole assembly handling to reduce operational cost. The new technology enables the removal of more than 100-ft (30-m) section of inner and outer casings in multiple trips. In this work, we conducted extensive numerical simulations using computational fluid dynamics to achieve the best possible milling system configuration.
At some point, an oil or gas well inevitably shifts from asset to liability, whether the result of reaching its economic limit, sustaining irreparable damage or being a disposable exploratory well. At the end of its life cycle, a well must be plugged and abandoned (P&A); while adhering to regulatory and environmental standards, its supporting infrastructure must be carefully dismantled to ensure that it poses no safety or environmental threats and any useable components salvaged to help defray costs. In addition to creating significant safety and environmental hazards, failure to properly abandon a well can lead to a noncompliant status with regulatory agencies and undermine an operator's image. Despite its multiple liabilities, abandonment offers no real return on investment (ROI), underscoring the importance of minimizing cost while still ensuring a safe and regulatory compliant operation. One of the main challenges is to retrieve the wellhead without damage so that it can be used again. Clearly wells in onshore or shallow water offshore environments present little difficulty in accessing the wellhead and carrying out the required P&A operations. However the most challenging wells to P&A are deepwater wells where the wellhead is located on the ocean floor often at considerable depth so that physical access to it is infinitely more challenging. In this subsea environment there exist two different approaches to the problems associated with well abandoned and wellhead recovery. These involve internal cutting of the surface and conductor casings combined with either internal or external latching of the wellhead. In this paper the authors will review these two different approaches, comparing their viability and describe in detail the external latching system which offers some distinct advantages in the P&A process. They will go on to provide some detailed case studies which illustrate its’ successful use in various deepwater offshore operations.
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