GB2482542A - Wireline standoff with inserts - Google Patents

Abstract

Wireline standoff 1 reduces wireline 8 sticking and key-seating. The wireline standoff comprises two half shells with inserts 3 that clamp on the wireline. The cable standoff reduces the 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 shells may have external fins 6 distributed radially to aid the passage of the centralizer through mudcake and other borehole wall debris. The cable inserts 3 may be formed from aluminum and allowed to deform around a slickline without damaging the cable.

Description

Low Area Wireline Standoff This invention relates to a device that improves wireline cable performance during logging operations in a variety of boreholes. The use of low area wireline standoffs ameliorates the effects of wireline cable differential sticking, wireline cable key-seating and high cable drags by reducing or eliminating the contact of the wireline cable with the borehole wall during the logging operation.

Wireline logging is a common operation in the oil industry whereby down-hole electrical tools are conveyed on wireline (also known as "e-line' in industry parlance) to evaluate formation lithologies and fluid types in a variety of boreholes. In certain wells there is a risk of the wireline cable and/or logging tools becoming stuck in the open hole due to differential sticking or key-seating, as explained below: * Key-seating happens when the wireline cable cuts a groove into the borehole wall. This can happen in deviated or directional wells where the wireline cable may exert considerable sideways pressure at the contact points with the borehole. Since the logging tool diameter is generally much bigger than the groove cut by the wireline cable a keyseat can terminate normal ascent out of the borehole and result in a fishing job or lost tools in hole.

* Differential sticking can occur when there is an overbalance between hydrostatic and formation pressures in the borehole; the severity of differential sticking is related to: o The degree of overbalance and the presence of any depleted zones in the borehole.

o The character and permeability of the formations bisected by the borehole.

o The deviation of the borehole, since the sideways component of the tool weight adds to the sticking forces.

o The drilling mud properties in the borehole, since the rapid formation of thick mud cakes can trap logging tools and the wireline cable against the borehole wall.

o The geometry of toolstring being logged on wireline. A long and large toolstring presents a larger cross sectional area and results in proportionally larger sticking forces.

Additionally, during wireline formation sampling, the logging tools and wireline may remain stationary over permeable zones for a long period of time which also increases the likelihood of differential sticking.

This invention ameliorates the effects of differential sticking and key-seating of the wireline cable by reducing or eliminating direct contact of the cable to the borehole wall. This is achieved by clamping an array of low area wireline standoff s onto the wireline cable, resulting in a lower contact area per unit length of open hole, lower applied sideways pressure of the wireline against the borehole wall, and lower cable drag when conveying the wireline in or out of the hole. The use of low area standoffs will also enable more efficient use of wireline jars in the logging string since they reduce the cable friction above the jars, allowing firing at lower surface tensions and easier re-rocking of the jars in boreholes where high cable drag is a problem (absorbing the applied surface tension before it can reach the wireline cable head and jars).

An array of low area wireline standoffs can be installed on the wireline cable to minimize the wireline cable contact over a selected zone(s) of the open hole section. The low area wireline standoffs may be installed on the wireline cable to either straddle known permeable zones where differential sticking is a risk (eliminating cable contact 100%) or they can be placed at regular intervals along the wireline cable to minimize keyseating, taking into account the dog leg severity of the borehole. The higher the dogleg severity the shorter the recommended spacing between wireline standoffs installed on the wireline cable.

The spacing of wireline standoff s on the cable may be from 1 Os of feet to 1 DOs of feet, depending on the requirements for the particular borehole being logged.

Each low area wireline standoff comprises two opposing assemblies which accurately mate together onto the wireline cable with four cap head bolts. The assemblies comprise stainless steel half shells which contain disposable cable inserts made from aluminum. Contact with the wireline cable exterior is solely with the aluminum cable inserts and not the stainless steel half shells. The cable inserts, being machined from aluminum, are designed to slightly deform around the outer wireline cable armour during installation without physically damaging the wireline cable. There are a large range of cable inserts available to fit the wireline cable, taking into account any manufacturing tolerances and varying degrees of wear or distortion along the length of the wireline cable. Therefore, for an array of low area standoffs installed on the wireline cable a range of different cable inserts may be employed to ensure a fit which does not allow slippage along the wireline cable or damage to the wfteline cable when clamped. The four cap head bolts that clamp the two assemblies together are torqued to a consistently safe limit with a calibrated torque wrench.

The stainless steel half shells are vacuum hardened for improved wear resistance during use and a range of shell sizes are available for installation on the wirelne, from 50 mm O.D. upwards. The aluminum cable inserts are positively secured into each stainless half shell by small cap head bolts that pass through the outside of each half shell into tapped holes in the cable insert bodies. The cable inserts have zero freedom of movement inside the half shells because: a) a central spigot eliminates rotation of the cable inserts in the half shells.

b) a central flange on the cable inserts ensures no axial movement in the half shells.

The low area wireline standoffs have 12 polished low area fins cut along their length to allow easy movement along the borehole and through mud cake and other debris which may have accumulated in the borehole during drilling. Furthermore, each fin has a smooth radial cross section profile which reduces the f in contact area against the borehole wall. This reduces the differential sticking force acted upon each fin at the contact points with the borehole wall and also allows for easy rotation of the standoffs if the wireline cable rotates when it is deployed and retrieved from the borehole. Note that it is the general nature of wireline logging cable to rotate during logging operations due to the opposing lay angles of the inner and outer armours which can induce unequal torsional forces when tensions are applied. The design of the wireline standoffs allows easy rotation of the wireline cable during the logging operation, avoiding the potential for damage if excessive torque was allowed to build up.

Finally, four holes in the Standoff half shells are used to connect a lanyard during installation, to avoid dropped objects on the drill floor during installation on the wireline cable.

The invention will now be described in detail with the aid of Figures 1-7, as summarized below. Note that low area wireline standoff' implies the full assembly of aforementioned components i.e. the stainless steel half shells, the aluminum cable inserts, and the associated cap head bolts.

Figure 1 is an isometric view of the wireline standoff before being clamped onto the wireline.

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

Figure 3 illustrates an array of low area wireline standoffs installed on a wireline cable in the borehole during logging operations.

Figure 3a shows an example close up view of the low area wireline standoff on the wireline cable in relation to the borehole wall.

Figure 4 is an isometric view of the low area wireline standoff with one half shell removed, to illustrate the fitting of the aluminum cable insert.

Figure 5 is an exploded view of the half shells and cable inserts that make up each low area wireline standoff assembly.

Figure 6 illustrates the use of small cap head screws to hold the cable inserts inside the half shells.

Figure 7 illustrates a cross section of the half shell, cable inserts, cap head fixing screws and wireline cable.

The low area wireline standoff [1] as seen in Figure 1 comprises two stainless steel half shells [2] (75 mm external diameter in this example) which contain two aluminum cable inserts [3] that clamp directly onto the wireline cable using four cap head bolts [4]. The cable inserts are secured in their half shells by two fully recessed small cap head bolts [5]. Twelve external fins [6] on the low area wireline standoff are profiled to allow easy passage along the borehole and through mud cake and any other debris which may be present in the borehole. The fins [6] have a smooth radial cross section to minimize the contact area with the borehole wall and allow for standoff rotation under the action of cable torque. The empty space between the fins allow for circulation of drilling mud inside drill pipe if the wireline cable and standoff assembly are fished using drill pipe. Holes across the two half shells [7] permit the fitting of a lanyard to avoid dropping them during their installation onto the wireline cable on the drill floor.

As depicted in Figure 2 a short section of the wireline cable [8] passes through the central bore of the cable inserts [3] in the low area wireline standoff [1]. The wireline cable diameter may vary between 10 -mm, depending on the logging vendor. The cable inserts are carefully matched to the diameter of the wireline cable regardless of any variations in size or profile that might occur along the length of the wireline cable. The cable inserts are made from aluminum which is considerably softer than the armour material of the wireline cable. An accurate fit of the cable inserts on the wireline cable and the controlled torque of the four cap head bolts [4] during installation ensures that the cable inserts cannot damage the wireline cable when the bolts are tightened, pulling the two half shells [2] together.

Figure 3 shows a generic logging operation and low area wireline standoff deployment. An array of low area wireline standoffs [1] is damped onto the wireline cable [8] which is stored on the wireline drum [9] and spooled into the well by a winch driver and logging engineer in the logging unit [10). The logging unit is fixed firmly to the drilling rig or platform [11] and the wireline is deployed through the derrick via two or three sheaves [12] and [13] to the maximum depth of the well. The logging tool connected to the end of the wireline cable [8] takes the petro-physical measurements or fluid or rock 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 location of sticky, permeable, or depleted zones, 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 low area wireline standoff [1 can be seen in relation to the wireline cable [8] and the borehole wall [14] and the borehole [15].

Figure 4 shows half the low area wireline standoff with one half shell [2] removed such that the other half shell [2] with cable insert in-situ [3] can be viewed.

Figure 5 shows an exploded view of the low area wireline standoff with the main components exposed: half shells [2] and cable inserts [3]. The cable insert flange [16] and anti-rotation spigot [17] lock the half shells and inserts together.

Figure 6 shows an exploded view of the cable inserts [3] with small cap head screws that retain them in the half shells. The cable insert flange [16] and anti-rotation spigot [17] are clearly visible.

Figure 7 shows a cross section of the standoff installed on the wireline cable [8]. It includes a cable insert [3] with small cap head screws that retain them in the half shells [2].

Claims (7)

1. Claims: 1. A low area wireline standoff comprising two half shells and cable inserts that are clamped onto the wireline during well logging operations. An array of low area wireline standoffs is deployed on the wireline cable to ameliorate the effects of differential sticking, borehole key-seating, and high drags on the wireline cable. The standoff s reduce or 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 from the wireline against the borehole wall, and a lower dynamic friction factor when conveying the wireline into or out of the borehole.
2. 2. The low area wireline standoff according to claim 1 in is profiled along its axis with an angle of attack that supports smooth movement along the borehole and past any obstructions when running the wireline cable in or out of the borehole.
3. 3. The low area wireline standoff according to claim 1 in which the half shells have external fins distributed radially which aid the passage of the low area wireline standoff through mudcake and other debris against the borehole wall.
4. 4. The low area wireline standoff according to claim 1 in which the external fins have a smooth radial cross sectional area to minimize the fin contact with the borehole wall and allow easy rotation as the wireline is deployed and retrieved from the borehole.
5. 5. The low area wireline standoff according to claim 1 in which the external fins allow the easy circulation of drilling mud past the standoff assembly during a fishing operation.
6. 6. The low area wireline standoff according to claim 1 in which cable inserts are available for installation onto a wide range of different wireline logging cables. The cable inserts accurately fit the wireline cable taking into account any manufacturing tolerances and varying degrees of wear or distortion along the length of the wireline cable. The cable inserts, being machined from aluminum, are allowed to deform slightly on the outer wireline cable armour during installation without physically damaging the wireline cable. The cable inserts do not allow slippage along the wireline cable during logging operations or damage to the wireline cable when the half shells are clamped together.
7. 7. The low area wireline standoff according to claim 1 in which the maximum external diameter of the standoff is less than the size of overshot and drill pipe i.d. during fishing operations. In the event of a fishing job the array of low area standoffs will safely fit inside the fishing assembly provided by the Operator, enabling the wireline cable head or tool body to be successfully engaged by the fishing overshot. The wireline cable and low area wireline standoff array may then be safely pulled through the drill pipe all the way to surface when the cable head is released from the logging string.