Lateral-Jet Hydraulics and Oval-Cutter Technology Combine To Improve PDC Performance, North Sea Scott Field
- J.R Lewis (BBL) | R. Begbie (Amerada Hess) | Neil Simpson (BBL)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- June 1997
- Document Type
- Journal Paper
- 137 - 143
- 1997. Society of Petroleum Engineers
- 4.3.4 Scale, 2 Well Completion, 4.1.5 Processing Equipment, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 4.1.2 Separation and Treating, 1.6 Drilling Operations, 1.5.1 Bit Design, 4.5 Offshore Facilities and Subsea Systems, 1.5 Drill Bits, 1.5.4 Bit hydraulics, 6.5.2 Water use, produced water discharge and disposal, 1.11 Drilling Fluids and Materials
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The successful implementation of Lateral Jet PDC hydraulics has emerged over the last few years with quantifiable results. Lateral Jets set into the blades of the bit improve the cutter cleaning efficiency thereby increasing ROP. In addition to cleaning the plenum in front of the jet, fluid entrainment creates a venturi effect drawing the fluid across the blades serviced by the downward jets. This flow is then ejected at high speed to the junk slots.
The operators of the North Sea Scott Field took a major initiative in this development, and in conjunction with the Lateral Jet company, expanded the technology to initiate a new cutter design and the second general of Lateral Jet type bits, the Fully Lateral Jet.
This paper will track the development of the technology from the initial trials of Lateral Jets in the Scott Field, the rationale and design criteria that initiated oval PDC cutters and most recently the Fully Lateral Jet PDC drill bit.
Introduction to Scott Field
The Scott Field straddles Blocks 15/21 and 15/22 and is one of the largest fields to come onstream in the UKCS in the past few years (Fig 1).
The first well drilled on the crest of the Scott structure was 15/22-3, drilled in 1977 This well encountered no sands of reservoir quality and it was not until 1983 that well 15/22-4 encountered oil bearing sands in what are now known as the Scott (C) sands of Block 1a. A follow-up down-dip appraisal well, 15/22-5, was a dry hole and estimates of the size of the accumulation were downgraded.
It was not until the drilling of well 15/21a-15 in 1987 that the potential size of the accumulation became apparent. Rapid appraisal of the Waverly prospect as it was know by the 15/21 group, and the Brunei prospect as it was known by the 15/22 group, continued through to 1989 leading to Annex B approval in 1990 for the newly named Scott Field.
In order to achieve a rapid build up to plateau production, seven sub sea production wells and seven associated water injection wells were drilling and completed prior to first oil. Drilling has continued with a programm of production wells being drilled from the production platform. The sub sea wells have been drilled from four different locations which in conjunction with the platform gives five separate surface clusters of wells (Fig 2).
Lithology and Typical Well Design
The lithology is similar to many neighbouring fields with oil being produced from Jurassic Sands. All directional work is completed in the 16" hole section before setting 13 3/8" casing in Paleocene shales. A 12 1/4" tangent section is then drilled through the lower Paleocene and Cretaceous, with 9 5/8" casing being set before the top of the Kimmeridge clay formation. An 81/2" section is then drilled to TD. Less toxic oil based mud is used from below the 20" casing shoe until TD (Fig 3).
Established Drilling Practice in 12 1/4" Hole
Considerable drilling has taken place in the immediate vicinity of Scott. Block 15/21 contains the producing Ivanhoe, Rob Roy and Hamish fields and had seen some forty wells drilled before the commencement of development drilling on Scott. A large amount of offset information was therefore available and considerable work had already been done to optimise bit selection and establish the suitability of PDC bits for the various formations.
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