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Petroleum Reservoir Lifecycle
Published in Ashok K. Pathak, Petroleum Reservoir Management, 2021
Depending on the field’s size, it can last for 10 to 50 years and end up yielding significant profits after the recovery of all the investments made over the reservoir lifecycle. The production rate from a reservoir is the sum of production rates of individual wells. It usually manifests three distinct periods identified as: buildup, plateau, and decline. During the buildup period, oil/gas wells come online, and production builds up progressively. The production buildup depends on the availability and allocation of resources such as drilling rigs and manpower; the higher the resources shorter the buildup period, and vice versa. The plateau period is characterized by a constant rate of production from the reservoir. Production rate is controlled by well-productivity, well-life, infill drilling, well-stimulation, and well-intervention/maintenance activities. A continuous decline in oil rate after the plateau period indicates either the loss of reservoir energy or the waning production potential of oil/gas wells (Figure 1.2). Monitoring the performance of individual wells is, therefore, the key to maintain production from a reservoir. It calls for concerted efforts to measure oil, gas, water production rates of individual wells, bottom-hole pressures, gas oil ratio (GOR), and water cuts to back up well-diagnostics.
Valve and Actuator Technology for the Offshore Industry
Published in Karan Sotoodeh, Coating Application for Piping, Valves and Actuators in Offshore Oil and Gas Industry, 2023
The lateral expansion of the half disks due to stem force is called the wedging effect. The other type of expanding gate valve is a single-expanding gate valve, in which the two half disks only expand due to the wedging effect in the closed position. Single-expanding valves can be used instead of double expanding in order to save cost. TCG valves, whether slab or expanding, are common for wellheads and Christmas trees, as illustrated in Figure 5.33. All the valves shown in the figure on the Christmas tree are TCG valves. The produced fluid from the reservoir passing through the Christmas tree contains a lot of sand; TCG valves are the best choice for such a dirty service. The lower valve, which is not completely shown in the figure, is called a master valve. According to API Spec. 6A, “Wellhead and tree equipment,” identical to ISO 10423, two master valves are typically located at the bottom of the wellhead. The lower master valve, as shown in the API 6A is manual, is normally open, allowing the production fluid to pass through the tree. The upper master valve is called a safety valve in API 6A; it is an actuated valve that closes the production to protect the downstream equipment if something goes wrong in the well. The valve on the right-hand side is called a wing valve, which can be manual or actuated. A wing valve is another valve that can stop the flow production and isolate the downstream facilities and piping. The valve on the left-hand side, which is manually operated, is called a kill wing valve. It is used to inject chemicals into the well. A swab valve is the one on the top, providing vertical access to the well, typically for well intervention. Well intervention, or well work during the well design life, may include maintenance, cleaning or placing equipment such as a pump inside the well to increase production.
Dynamic response of a novel heave-compensated floating platform: design considerations and the effects of mooring
Published in Ships and Offshore Structures, 2023
Marcelo A. Jaculli, Bernt J. Leira, Sigbjørn Sangesland, Celso K. Morooka, Paulo O. Kiryu
The environment can cause excessive loads onto floating vessels, thus limiting operational windows or even rendering operations unfeasible. In the particular cases of the North Sea and the Norwegian Sea, the sea conditions can halt operations completely – this applies especially during the winter season – due to excessive heave and/or pitch motions. Large motions can be experienced due to harsh environmental conditions, with metocean data reported by Offshore Technology Report (2001) for the North Sea and Lønseth (1997) for the Norwegian Sea. Therefore, solutions have been sought to widen the operational window under such extreme environmental conditions, with one of them being the design of a platform capable of decreasing heave motions. A reduced-heave motion platform would be a first step towards improving the platform’s operability under said environmental conditions, with considerations for pitch motion also necessary subsequently. Applications of these floating platforms include extending oil well intervention operations using vessels and increasing the operability of floating wind turbines. The physics behind this concept is similar to passive heave compensation systems (Pomonik and Butler 1973; Niedzwecki and Thampi 1988), in which air chambers are used to dampen the heave motion of attached strings.