RIASSUNTO
Abstract
This paper displays a new approach in downhole workover operations. Environmental pollution was resulted from downhole workover operations, such as spills of crude oil and produced water. These accidents can pose safety risks to operations, and has direct adverse impact on local people daily lives, public health, and agriculture etc. Workover operations are strictly regulated by HSE Management Standards.
After many years of practices, a series of multi-purpose clean downhole workover technologies have been developed and many types of equipment have been created, such as movable produced water treatment technology, to prevent spills of oil and produced water. These technologies and equipments have guaranteed green downhole workover in Daqing Oilfield.
Green downhole workover operation technology
In order to prevent the occurrence of gas blowout accidents, improve the downhole operation quality, and realize the green environmental operation, studies and related applications about well control and environmental protection technologies were carried out by each unit in all aspects, from underground, wellbore to the ground, which acquired obvious effects in Daqing Oilfield.
To implement formation control technology by enhancing well control risk analysis
Based on the well control characteristics of Daqing Oilfield, combined oilfield development data, well control risk analysis was carried out last year in Daqing Oilfield. The abnormal high pressure wells, gas wells such as deep gas well, periphery gas-field, gas-cap gas well and shallow gas well, and wells that had experienced kick and blowout were plotted on the well location map of oilfield development and thus formed the well control high risk zone diagram. The diagram had been gradually applied widely in each unit, which not only was helpful to well control graded management and to take emphasized precautions against those high risk zones, but also provided scientific references for compiling well control design, selecting well control equipment and implementing well control measure. For water injection well, the formation pressure in high risk zone could be adjusted through reducing and controlling the water injection rate, or even ceasing water injection, and for production well, the abnormal high pressure could be reduced effectively through fracture or re-perforation to release the high pressure.
To conduct well bore control technique by optimizing the string design
In order to control downhole string, the right pipe string should be selected in accordance with different well condition, mechanical production type and different pump type to avoid dirty oil and sewage spraying on the ground. The mature technique includes self-sealing device of oil pump, pen-type sliding sleeve switch, retrievable hollow bridge plug for no-killing well, mechanical tubing anchor for screw pump, tubing drain device, etc.
(1)Self-sealing device in oil pump
Self-sealing device is mainly suitable for pump wells with disjunctive device. The structure is shown as figure 1.
The operational principle is described as follows. The self-sealing device is connected at the lower of pump barrel. The piston with tub rod is inserted in the main body of self-sealing device. When running the string, the oil channels are closed, and when pulling up the tub rod during oil production, oil channels are open. In secondary operation work, released from disjunctive device, the piston with tub rod will run down into the main body of self-sealing device and prevent the occurrence of blowout following the fluid channels closed.