GB2450918A

GB2450918A - Wireline Standoff

Info

Publication number: GB2450918A
Application number: GB0713550A
Authority: GB
Inventors: Guy Wheater
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-07-12
Filing date: 2007-07-12
Publication date: 2009-01-14
Anticipated expiration: 2027-07-12
Also published as: GB0713550D0; GB2450918B

Abstract

The wireline standoff 1 reduces wireline 2 sticking and key-seating. The wireline standoff comprises two finned half shells that clamp on the wireline with an internal safety brake that resists slippage during use. The wireline standoff ameliorates the effects of differential sticking and key-seating of the wireline by eliminating direct contact of the wireline to the borehole wall. In practice, an array of wireline standoffs are clamped onto the wireline to cover the open hole section being logged, resulting in a lower borehole contact area, lower applied pressure against the borehole wall, and lower rolling resistance when conveying the logging tools in or out of the hole. The brake may comprise two opposing cams 14 which grip the wireline 2.

Description

I

Wire].ine Standoff This invention relates to a device that reduces downhole cable sticking during oilfield wireline logging operations.

Wireline]ogging is a common operation in the oil industry whereby downhole electrical tools are conveyed on wireline to evaluate formation lithologies and fluid types in oil, gas, and water wells. In certain wells there is a risk of the wireline becoming stuck in the open hole due to either key-seating or differential sticking, as explained below: * Key-seating happens when the wirelirie cuts a groove into the borehole wall. This can happen in deviated or directional wells where the wireline may exert considerable pressure at the contact point with the borehole, usually on the high side of the hole.

Key-seating can cause problems since the logging tool diameter is generally much bigger than the groove cut by the wireline; it can present a serious obstacle to normal ascent out of the hole and may result in a fishing job or lost tools in hole.

* Differential sticking can occur in a well's permeable zones when the formation pressure is much less than the well bore hydrostatic pressure. The pressure differential induces strong suction forces on the logging tools and wireline against the borehole wall; this commonly occurs if the well is highly overbalanced or if the reservoir is depleted. Additionally, during wireline formation sampling, the wireline may rema1n stationary over such permeable zones for a long period and become differentially stuck. In this case the conventional solution to retrieve the wireline arid logging tools by fishing operation which is expensive and risky.

The invention aims to ameliorate the effects of differential sticking and key-seating of the wireline by eliminating direct contact of the wireline to the borehole wall. This is achieved by clamping an array of wireline standoffs onto the wireline, resulting in lower contact area per unit length of open hole, lower applied pressure of the wireline against the borehole wall, and lower rolling resistance when conveying the wireline in or out of the hole.

Each wireline standoff comprises two half shells that clamp onto the wireline with four M6 bolts. Note that an array of wireline standoffs must be clamped on the wireline to ensure adequate coverage over the open hole section. The standoffs have axial fins cut along their external body to allow easy movement through mud cake and other debris which usually build up at the borehole wall during drilling operations.

The two half shells have a central bore that grips closely around the wireline. The half shells are machined from stainless steel by CNC process and they are vacuum hardened for improved wear resistance during use. Inside the main body of the standoff there is a safety wireline brake comprising of two opposing cams that are held in contact with the wirelirie by twin locating pins and recessed torsional springs. When the logging string is being pulled out of hole there may be considerable axial pressure placed on the standoff, in the event that the bolts cannot hold the standoff in place the cams will rotate a small degree and lock on to the wireline, impeding further movement, and applying a clamping pressure in a proportional fashion.

The standoffs must be clamped on the wirelirie in a specific direction, highlighted by the directional arrows inscribed on both halves of the standoff shells; the arrows will always point uphole.

The invention will now be described in detail with the aid of Figures 1-6, as summarized below: Figure 1 is an isometric view of the wireline standoff before being clamped onto the wireline.

Figure 2 is an isometric view of the wireline standoff clamped onto a short section of wireline.

Figure 3 illustrates an array of wireline standoffs deployed onto the wireline during logging operations.

Figure 3a shows a close up view of the standoff on the wireline in relation to the borehole wall.

Figure 4 is an isometric view of the wireline standoff with the upper half shell removed, to illustrate the internal workings of the standoff.

Figure 5 is an exploded view of the major components of the standoff with the upper half shell removed.

Figure 6 shows the upper half shell of the standoff which clamps Onto the lower half shell, sealing the wireline safety brake assembly.

The wireline standoff [1] as seen in Figure 1 comprises two half shells of external diameter approximately 50mm that are clamped together onto the wireline, of nominal diameter 12mm. The wireline diameter may vary between 10-14mm, depending on the logging company, and the standoff bore is machined to fit the wireline accordingly.

As depicted in Figure 2 the wireline [2] passes through the central bore in the wireline standoff [1) . Four M6 bolts [3j are utilized to clamp the two half shells tightly together. Twelve external fins [4] on the wireline standoff are machined to allow easy passage of the wireline standoff through mud cake and other debris which may be present in the open hole.

Figure 3 shows a generic wireline operation and standoff deployment.

An array of wireline standoffs [1 is clamped onto the wireline [2] which is stored on the wireline drum [7J and spooled into the well by a winch driver and logging engineer in the logging unit [6). The logging unit is fixed firmly to the drilling rig or platform (5] and the wireline is deployed through the derrick via two or three sheaves [8] and [9] to the maximum depth of the well. The logging tool connected to the end of the wireline (12] takes the petro-physical measurements or fluid samples in the open hole section. The number of standoffs and their positions on the wireline are determined by the length of the open hole section, the position of permeable tones, and the overall trajectory of the well, which may be deviated or directional in nature. As per the close up illustration in Figure 3a the wireline standoff [1] can be seen in relation to the wireline [2] and the borehole wall (11] and the borehole (10) Figure 4 shows the wireline standoff with the upper half shell removed such that the internal components can be viewed. Two opposing cams (14] sit in a machined recess in the central cavity of the bottom half of the wireline standoff [15] and are held in position by two locating pins (13). In the event the four M6 clamping bolts (3] allow wireline slippage during large overpulls the cams will immediately rotate and clamp the wireline, impeding any further movement and gripping the wireline proportionally. The cam profile has been evaluated such as to clamp the wireline effectively but not damage the line permanently; they are machined to a precise design from soft alloys for this purpose.

Figure 5 shows an exploded view of the wireline standoff with the upper half shell removed to provide further detail and explanation.

Additional to Figure 4 two torsional springs [16] are employed to apply counter-rotating contact torque of the cams onto the wireline, such that the braking will always be effective, even if the standoff and cams have suffered from vibration and movement when running in hole. The torsional springs [16] are positioned over the locating pins [13) and are hidden from view inside the cams (14]. The axial spring legs are designed to fit into opposing holes drilled into the cam body [14] and the bottom half of the standoff (15]. The heads of the locating pins [13] have flat head screwdriver slots cut into them and they are located with M4 threads, to allow potive location but free rotation of the cams [14] in the bottom half of the standoff body [15).

Figure 6 shows the upper half shell of the standoff body 118) with the two circular recesses (l7J for the upper heads of the locating pins [13]. When the standoff is clamped together the heads of the locating pins sit neatly inside the recesses [17) in the upper half of the standoff (18) providing rigidity for the locating pins (13) and the cams [14) . When the standoff is firmly clamped together with the four M6 bolts (3) the clearance between the two half shells (15], (18) is less than 1mm along the length of the standoff [1], thus applying a minimal bending moment on the half shells.

Claims

Claims: 1. A wireline standoff comprising two half shells that are

clamped onto the wireline during well logging operations. An array of wireline standoffs is deployed on the wireline to ameliorate the effects of differential sticking and key-seating of the wireline. The standoffs eliminate direct contact of the wireline to the borehole wall.

resulting in a smaller contact area to the borehole wall during logging; a lower applied pressure of the wireline against the borehole wall; a lower rolling resistance when conveying the wireline in or out of the hole. The wireline standoff has an internal safety brake that resists slippage during ascent out of the hole, when overpulls may be experienced due to hole conditions.
2. The wireline standoff according to claim 1 in which the safety brake comprises two opposing cams that grip proportionaliy onto the wireline in the event of standoff slippage during overpulls.
3. The wireline standoff according to c'aim 1 in which the half shells have external fins arranged in an axial direction that aid easy passage of the wireline standoff through mudcake and other debris against the borehole wall.
4. The wireline standoff according to claim 1 in which the internal safety brake comprises custom made cams manufactured from soft alloy material, permanently held in place against the wirelirie by torsional springs that are recessed under the cams.
5. The wireline standoff according to claim 1 in which the internal safety brake applies a proportional braking force on the wireline in relatiun to the tension over-pull on Lhe wireline.
6. The wireline standoff according to claim 1 in which the maximum external diameter of the standoff is less than the standard size overshot for retrieving wireline logging tools through fishing on drill pipe. In the event of a fishing job the array of standoffs will fit inside the fishing assembly provided by the client, enabling the logging tools or wireline cable head to be successfully latched by the fishing overshot.