30-01-2013, 04:35 PM
[size=medium]Laser Drilling in Oil Rigs [/align]
1Laser Drilling.pdf (Size: 364.56 KB / Downloads: 69)
INTRODUCTION
Rock disintegration and removal is a significant issue in the process of oil and gas well drilling and completion. Millions of cubic meters of rock have been removed, with tremendous capital investment, over the years as a result of drilling of oil and gas wells. Approximately 20000 wells of oil, gas and dry wells were drilled onshore in the United States of America in 1999, with an average depth of 1830 m. This is equivalent to approximately 37014 km or approximately three times the diameter of the earth (12712 km). Nearly half of the time was spent on drilling, a quarter of the time on moving tools in and out of wells and the remaining quarter on casing and cementing activities. Major potential cost reductions related to well drilling were likely to come from increasing the rate of penetration of the drill bit into the earth, and reducing the time involved with moving tools, such as bits and pipes, in and out of holes, in general Other than the reservoir rock, a quantitative amount of time can be spent on drilling through rock strata. Drilling in hard rocks such as granite is extremely difficult and can expend a great amount of resources with little penetration resulting. Stuck pipes, fishing operations for lost tools down holes, and side tracking procedures, all of which are time and money consuming processes, are other costly problems associated with drilling process. Reduction of costs associated with these drilling operations would have significant and qualitative economic impacts for exploration and production operations.
Potentials of LASER drilling and conventional drilling
The potential use of LASER is broad and with a diverse range of control mechanisms. Using both the parameters of the LASER and the properties of the rock, the rock can be chipped, melted or even vaporized. Making a more direct comparison of the potential of LASERs and the conventional drilling techniques, the apparent difference is in the equipment used which is smaller and requires fewer moving parts, but the mechanical differences between a drill and a LASER are easily seen. The implications of these are the persuasive aspect of the use of LASERs and may be the most valuable area of comparison. Laser drilling not only allows continuous information to be gathered over a subsurface profile but also allows for a continuous understanding of the subsurface distribution of contamination.
In conventional drilling, the process is slow and much of the time used is with support services to help and facilitate the drilling rather than the actual drilling .it is found out that only 50% of the time spent on drilling actually saw the drill used to make the hole, 25% of the time was spent on tripping and the remaining 25% of the time was spent on casing and cementing. The use of lasers offers the potential to reduce much of this non productive time and processes and as well reduces costs, for example, with a laser, there is no need for bit replacement, drill string removal and setting casings. It is also estimated that the use of LASERs will increase drilling speed at anywhere between 10 and 100 times the current rates of using the boring technology. Part of the increased speed is due to the lack of additional processes required, however, the use of LASERs is also potentially much faster than the drilling process itself. Considering that a typical oil or gas well on land will cost in excess of $400000 to build and a gas or oil well that is offshore can cost $4.5 million, a system that operates between 10 and 100 times faster will offer significant savings.
LASER effect on rock phase behavior
When LASER power is applied, the melting temperature determines any phase change observed in rock samples. Recent research showed that the melting temperature of the rock samples increased as the percentage of quartz increased. Rock destruction decresed as the melting temperature of rock increased. Putting SE into consideration, in this concept, the greater the percentage of quartz in the rock sample, the higher the energy consumed in secondary mechanisms, including melting and vaporization. This concept applies more when making deep holes, however, it could be minimized with shallower holes. Other parameters, such as physical characteristics surface may play an important role in LASER/rock interaction, roughness, color, grain cementation, unconformities in the matrix such as vugs and fractures; and thermal properties like conductivity, heat capacity and diffusivity. Two techniques are used in conjunction to accomplish thermal analysis; Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC). TGA examines thermal stability while DSC maps the material transitions. These endothermic and exothermic transitions indicate structural and chemical changes in material. These methods are used to determine when melting, disassociation, dehydration and degasification take place.
LASER effects on well drilling/spalling
The removal of rock with LASER spallation is the use of LASER induced thermal stress that fractures the rock which is then broken into small pieces prior to melting. High intensity LASER energy is targeted at the rock which will have only a very low level of thermal conductivity, and is focused on a local area of rock. This focusing causes a sharp local temperature rise. The temperature can be maintained at a emperature
just below the melting point of the rocks melting point. This level of temperature can then be maintained and is the right level for the rock to be spalled. This reveals new rock surfaces and can continue with the aid of high pressure gas purging so that the rock fragment are blown out of the way.
High-power lasers in the energy industry
Foro Energy is commercializing high-power lasers in the oil, gas, geothermal, and mining industries with a unique capability and hardware platform that uses field-packaged high-power fiber lasers and fiber-optic cables to transmit the laser power over long distances. This laser power is then combined with mechanical tools to provide enhanced and potentially breakthrough performance and capabilities. These energy industries spend in excess of $100 billion per year to extract the natural resources that power the economy, employing a conventional technology toolkit of mechanical cutters, explosives, chemicals, and high pressures. Foro Energy's mission is to drill and perform a variety of other operations faster, safer, cheaper, and more effectively than today's tools. Upon reaching technology critical mass, high-power lasers potentially will have the same type of impact on the oil, gas, geothermal, and mining industries that is occurring in the automotive, manufacturing, defense, and medical industries The company has discovered how to combine the long-distance and high-efficiency capabilities of telecommunication fibers with the high-power capabilities of shorter automotive and manufacturing fibers. Many experts thought that this was impossible due to the nonlinear effect of stimulated brillouin scattering (SBS) prevalent in optical fibers. When working with power levels of 20 kW, SBS can cause a significant portion of the laser power to be transmitted backwards through the fiber, resulting in catastrophic damage to optical components as well as the laser itself. This problem was compounded because the onset of SBS has an exponential relationship with power and length