The US Department of Energy (DOE) has announced the selection of six projects to receive approximately $30 million in federal funding for cost-shared research and development in unconventional oil and natural gas recovery. The projects, selected under the Office of Fossil Energy's Advanced Technology Solutions for Unconventional Oil and Gas Development funding opportunity, will address critical gaps in the understanding of reservoir behavior and optimal well-completion strategies, next-generation subsurface diagnostic technologies, and advanced offshore technologies. As part of the funding opportunity announcement and at the direction of Congress, DOE solicited field projects in emerging unconventional plays with less than 50,000 B/D of current production, such as the Tuscaloosa Marine Shale and the Huron Shale. The newly selected projects will help master oil and gas development in these types of rising shales. This cement will prevent offshore spills and leakages at extreme high-temperature, high-pressure, and corrosive conditions.
Following the significant reservoir depletion on Elgin / Franklin fields since 2007, drilling infill wells was considered to not only be high cost but also carry a high probability of failure to reach the well objective. The recent campaign on the Elgin field, one of the most heavily depleted reservoirs worldwide, demonstrated that infill drilling can be achieved safely while improving performance.
Drilling of HPHT infill wells on the Elgin field faced increasing challenges arising from the reduction of reservoir pressure that changed the stresses in the formations above and influenced the overall pressure regime. This stress reorganization in the overburden has affected the fracture network in these formations resulting in reduction in Fracture Initiation Pressure (FIP) and increase of gas levels.
Challenges were faced during the drilling of three wells in the 2015-2017 campaign. Loss events in Chalk formations in the intermediate sections significantly decreased the already Narrow Mud Weight Window (NMWW). A strategy to define and validate the minimum required MWW in 12-1/2" and 8-1/2" sections was developed following a complex subsurface well control event. Managed Pressure Drilling (MPD) technique was extensively used to safely manage gas levels and assess pore pressure.
Reservoir entry with more than 850 bar of overbalance remains the main challenge in infill drilling. A total loss event during first reservoir entry in the latest campaign confirmed the limitations of wellbore strengthening mud and stress caging materials available today.
Lessons learned from each well in this campaign were implemented to address these challenges and improve performance. This paper describes the Elgin HP/HT infill drilling experience and the specific techniques and practices that were developed to address these challenges and improve performance. The importance of Equivalent Circulating Density (ECD) management with very narrow MWW, successful high gas level management with MPD and depleted reservoir entry, shows that even in a highly complex environment, drilling performance can be improved allowing for further economical development drilling. The successful and safe delivery of the Elgin 2015-2017 infill drilling campaign demonstrates this at a time the industry moves toward unlocking the reserves of more challenging HPHT fields.
The North Sea Oil and Gas industry counts over 7,800 wells drilled. The industry is now entering an era of well abandonment and decommissioning. Current barrier verification for P&A requires appropriate pressure testing and includes surface and downhole monitoring.
Globally, Spectral Noise Logging (SNL) has been utilized in many thousands of cases to detect fluid movement behind completion tubulars and/or across a cement barriers.
In Nov 2017, full-scale verification tests were conducted at the International Research Institute of Stavanger (IRIS). These tests were conducted in a controlled environment to verify current technology thresholds. These showed the technique validated the cement barrier integrity during pressure tests and can diagnose channeling as low as 9 ml/min behind the casing. The threshold matrix for different cement defect versus pressure and flow rates allowed the usage of the technology to support the positive qualification of the barrier elements (
Utilizing a purpose-built test assembly of standard oilfield tubular and cement with fitted end caps, a series of pressure tests operations were conducted to identify the pressure and associate leak rates in conjunction with the SNL. The results clearly demonstrated that the logging tool can provide evidence of barrier verification over a wide range of well applications. Barrier qualification requires that three conditions are met; firstly, cement behind casing is in place and not displaying a micro-annulus or any form of fluid movement behind pipe. Secondly, that a cement plug holds pressure and there is also no fluid leak and finally natural shale barriers are active and create a sufficient barrier. Currently, technology is in its 10th generation, and since the IRIS tests have been used in many wells, covering both onshore and offshore oil and gas wells and wells in highly sensitive environmental areas. On each case the logging operations were used to verify well status before and after the barrier establishment via cement squeeze or section milling and, in several cases, clearly, demonstrate that the barrier status remained ineffective, hidden and further remedial work was required.
This paper discusses the downhole passive noise listening and its spectral analysis technique to prove the effective cement barriers are in place. The concept, methodology and its application which have been successfully tested via yard and field tests are presented in this paper.
I am encouraged that we, as an industy, continue to refine and tweak our practices to solve zonal-isolation and cementing challenges in every well environment in which we work. As cementing techniques are improved, so, too, are the cement-evaluation methods and work flows. This paper demonstrates a new way to create gas-tight seals during well abandonment, overcoming the limitations of traditional methods and reducing the operator’s liability and potential environmental impact after decommissioning has been completed. This paper discusses shale creep and other shale-deformation mechanisms and how an understanding of these can be used to activate shale that has not contacted the casing yet to form a well barrier. Well RXY is located in Cairn’s Ravva offshore field in the Krishna-Godavari Basin in India.
Content of PetroWiki is intended for personal use only and to supplement, not replace, engineering judgment. SPE disclaims any and all liability for your use of such content. In the context of cement, a channel is a flow area in the cement from inefficient cementing displacement of the drilling mud. In the context of rock formations, a channel is an interconnected pathway through the matrix of the rock or an open fracture or other feature that connects a reservoir and the wellbore.
Content of PetroWiki is intended for personal use only and to supplement, not replace, engineering judgment. SPE disclaims any and all liability for your use of such content. In the context of formation, cement is a formation binding agent (calcite, clay, silica overgrowth, heavy oil, etc.) that hold the formation grains together. In the context of completions, cement is typically the Portland, silicate, and/or pozzilin, etc., mixtures used to form a stone-like permanent seal between the pipe and the formation.
There are different definitions of what is Well Integrity. The most widely accepted definition is given by NORSOK D-010: "Application of technical, operational and organizational solutions to reduce risk of uncontrolled release of formation fluids throughout the life cycle of a well." Other accepted definition is given by ISO TS 16530-2 "Containment and the prevention of the escape of fluids (i.e. Well Integrity is a multidisciplinary approach. Therefore, well integrity engineers need to interact constantly with different disciplines to assess the status of well barriers and well barrier envelopes at all times.
The table also includes an indication of the primary uses and benefits, along with the cements that they can be used with. The primary effects of the cement admixtures on the physical properties of the cement, either as a slurry or set, are presented in Table 2. This is a quick reference, and individual additives in a given category may not agree in total with the effects as given. It is also typically defined for individual additives, the properties and effects of which can be modified when additive combinations are used.