讲稿幻灯片-yl6 Chapter 6 petroleum application

Clearly, the greater the standoff distance,
the smaller the jet pressure exerted on the
bottom of hole.
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Jet Centerline Pressure Attenuation Experimental Result
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1. Effective Use of Jet Energy at Bottom-Hole



In jet bit drilling application, the main measure to enhance bit hydraulic power was by the increase of the surface pump ratings. However the increase of pump pressure would increase not only pump initial expense but operating costs and hazards as well. Then there is a need to make effective use of energy at Bottomhole
Chapter 6
Applications of WJT in Assisted Mechanical Drilling
1
Road map
Back ground and introduction 1. Effective Use of Jet Energy 2. Ultra-High-Pressure Jet Assisted Mechanical Drilling 3. Negative pressure pulsed jet
It is just the first two functions that made the rotary drilling possible.
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Back Ground
Progress in Jet-Bit Drilling:

Rock breaking effect of jet had not been universally recognized until the beginning of 1950’s. Bit hydraulic power was limited to 3-5 hp per inch of bottomhole diameter. It is from 1950’s to 70’s that the bit horse power was gradually increased to obtain higher drilling speed. Jet-bit drilling in China petroleum industry experienced three stages characterized by pump pressure levels. With the changes in hydraulic parameters, the drilling speed increased amazingly.
2
Back Ground
In 1980’s, America launched a large research
program funded by DOE to look for rock drilling or
breaking methods better than conventional. Through
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Actually in the bit hydraulics, there are several key factors to indicate and show whether the flow around the bit and across the bottom of hole is good or bad. These are:

cleaning, lubricating and cooling bit cutters-primary function cleaning the bottom and carrying particles or cuttings into the annulus –after 1900


impacting and breaking the bottom rock--after1950
PL Po p L 1 0.5 L LI po L0.5 LI pL L LI 0.5 L0.5 LI po for L LI for LI L L0.5 for L L0.5
PL = jet centerline dynamic pressure in MPa; Po = jet dynamic pressure at nozzle exit in MPa; L = jet standoff distance in mm; LI = the length of potential core in mm; L0.5 = pressure half-decay distance in mm.
Other special hydraulic factors to affect bit
Through improvement in any of these factors, higher drilling speed can be acquired.
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1.1 Extended Nozzle Tri-cone Bit
be possibly put into use in short future.
3
Back Ground
Bit hydraulics (钻头水力学)plays multiple roles in rotary drilling. The beneficial functions of the jets include:
1) The standoff distance, from the nozzle exit to the hole bottom is fairly large. 2) About 90% of the bits used in oil well drilling are roller bits. Fixing method:
1) welded on
2) with circlip/o-ring
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Foundation -- Pressure attenuation of submerged non-free jet

For a tri-cone bit of 215.9 mm in diameter, this SOD is about 140 mm, more than 10do. And the distance is bigger for bigger bits.
extensive & long term studies in many Labs, 25
types of rock breaking methods including laser, plasm, HPWJ, explosion, etc. have been experimented with in rock drilling. It is concluded that the HPWJ is the most promising Design Criterion


Jet pressure at the bottomhole is 35%-50% of that at nozzle exit for 8.5〞bit. Based on the above studies, the hydraulic horsepower design was improved, and a new optimal design method was derived which is referred to as the maximum bottom-hole hydraulic power design, in which Bottomhole Maximum Horsepower is calculated according to the true value arrived at bottom surface rather than previously at the bit.


bottom-hole hydraulic power: by 30 - 40%
dynamic pressure: by 90 - 110% pressure gradient by more than 1.5 times.

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Field Application Results

Utilization of the extended nozzle bits in 13 oil fields has resulted in the improvement of :
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Performance of Extended Nozzle
When L is shortened from original 140 mm to
40 mm for 8.5 inch bit, without changing the surface pump ratings, the extended nozzle can increase:

1. Effective Use of Jet Energy at Bottom-Hole
Hydraulic power , impact force to the bottom
Pressure and pressure gradient over the bottom rock