Oil and gas production process starts from exploration, to appraisal, to development, and finally to abandonment. Exploration is done on the prospective field to determine presence of hydrocarbon (HC) and if present, an appraisal of the extent and volume of the HC is done. If the quantity of HC is found to be enough, it is developed and produced and after production of the HC reserve, abandonment is done. For the exploratory, appraisal and development processes, wells are drilled, and this drilling involves making holes thousands of feet into the sub soil and the installation of tubulars and other completion accessories to ensure that the hydrocarbon comes to surface with ease and in a safe manner. Wells are abandoned either because it has produced its potential and cannot be used for production anymore, or due to some integrity issues that could only be prevented by abandonment. To abandon a well, the produced/open HC reservoirs are properly isolated to prevent flow into other HC reservoirs or water bearing sands. The installed tubulars and accessories are then retrieved to surface. After abandonment, to further reduce the environmental impact of the oil development, the sites are recommended to be fully restored to the pre-development state as much as possible. This paper details the technical abandonment activities carried out for five wells that have produced for several years in onshore Nigeria. The paper also explains the site restoration activities and shows the various well site restoration stages including the re-vegetation of some of the well sites.
Well integrity is a key focus area in any oil and gas development. There have been several cases of well integrity issues which have resulted in scenarios of blowout, loss of lives, assets, and reputation, including costs spent for clean-up and environmental remediation, amongst others. These and more have made the energy industry put a keen focus to making sure all hydrocarbon production and processing facilities are integral, with newer technologies still being developed to aid the diagnosis of well integrity problems. Well integrity considerations cut across the entire life cycle of the well, from well conceptualization/planning through to drilling, completion, production and abandonment. This case study presents a high-pressure, high temperature gas well with sustained annulus pressure in the early production phase of the well. Well X is a gas well completed in an elevated pressure and temperature reservoir on a land terrain. The reservoir is about 13000ftss deep, with a temperature of 219°F and a reservoir pressure of 9300psi. The well was completed, cleaned up and brought to production about a year ago and annular pressures were observed. This paper details the different approaches used in diagnosing the sustained annular pressures – separating thermal effect from sustained pressure due to leak. It shows the different scenarios of leak paths identified and how these were streamlined. The paper also highlights the integration of data acquired during the investigation. Some of the data acquired include well annuli pressures, high precision temperature logs, spectral noise logs and electromagnetic corrosion logs.
Clearly delineating contacts are usually aimed at before development, but what happens when later data indicates contacts different from what have been interpreted? How do we ‘work back in time’ to re-estimate the original contacts? Our case study documents a reservoir which due to the poor well coverage, paucity of log data, side wall sample and pressure data, was initially interpreted as an oil bearing reservoir, however, a new well drilled post production of over 20 years indicated the presence of a huge gas cap, the size of which could not have been due to the formation of a secondary gas cap. This necessitated the determination of the original contacts in order to properly define the reservoir volumes which will impact on its future development. This paper presents the use of an integrated thinking approach which makes use of all the available geological, petrophysical and dynamic data in determining the original fluid contacts in a post production scenario. Reservoir simulation using simple tools as material balance combined with petrophysical and geological concepts were applied in this paper. The results obtained shows that the use of static data alone such as petrophysical logs in determining the original contacts for post production reservoirs can be greatly misleading as the results obtained may conflict with dynamic data available for the reservoir and therefore not fully representative of the reservoir and its history.
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