The whipstock was the main deflection tool from 1930-1950. A standard whipstock is seldom used nowadays, but it has not disappeared completely. Whipstocks are used in coiled tubing drilling for re-entry work.Â There are 3 types of whipstock used in conventional directional drilling:
Standard removable Whipstock:Â The Standard Removable Whipstock is mainly used to kick off wells, but can also be used for sidetracking. It consists of a long inverted steel wedge which is concave on one side to hold and guide the drilling assembly. It is also provided with a chisel point at the bottom to prevent the tool from turning, and a heavy collar at the top to withdraw the tool from the hole. It will usually be used with a drilling assembly consisting of a bit, a spiral stabilizer, and an orientation sub, rigidly attached to the whipstock by means of a shear pin.Â The whipstock assembly is lowered to the bottom of the hole and orientated. Weight is applied to set the whipstock and shear the pin. The bit is then drilled down and forced to deflect to one side. A 12 to 16 foot â€śrat holeâ€ť is drilled below the toe of the whipstock and the assembly is then pulled out of hole, taking the whipstock with it. A hole opener is run to open the rat hole out to full gauge. The hole opener assembly is then tripped out and a rapid angle build assembly run in hole to â€śfollow upâ€ťthe initial deflection. This whole procedure may have to be repeated several times in the kick-off.
Permanent Casing Whipstock:Â The â€śPermanent Casing Whipstockâ€ť is designed to remain permanently in the well. It is used where a â€świndowâ€ť is to be cut in casing for a sidetrack.A special stinger at the base of the whipstock slips into the packer assembly, and a stainless steel key within the packer locks the whipstock’s anchor-seal and prohibits any circular movement during drilling. The normal procedure is to orientate the system and then set the packer. After this, the starting mill is pinned to the whipstock and the whole assembly run slowly in hole and seated in the packer.Â Although the packer has already been orientated, it is good practice to orientate the whipstock in the same manner as the packer. This will ensure that a faster â€ślatch upâ€ť will take place without endangering the shear pin. After the whipstock has been â€śseatedâ€ť in the packer, the pin is sheared and circulation and rotation started. The starting mill is used to make an initial cut through the casing and mill approximately 2 feet of the window. The lug that held the starting mill to the whipstock must also be milled off. This assembly is tripped out and the mill changed. A tungsten carbide or diamond speed mill is used to cut the rest of the window. Once the window has been cut, approximately 5 feet of formation is cut before pulling out of hole. Next, a taper mill is run with a watermelon mill immediately above it.Â This is done to â€ścleanâ€ť the top and the bottom of the window. Finally, another trip is made to change over to the drilling assembly which is used to drill ahead.Â The advantage of using this system, instead of the normal method of milling a section and sidetracking, is that the operation usually takes less time. The main disadvantage is that it gives a sharp dogleg, and as such the casing whipstock assembly is not recommended if there is a considerable distance to drill below the sidetrack. This is because problems can occur when trying to pull stabilizers, etc back into the casing through the window. On the other hand, if there is only a short distance to be drilled below the sidetrack point, then the casing whipstock is well worth considering.Â In recent years, improvements in the design of the system have eliminated the need for so many trips in and out of the hole.
Sidetracking Whipstocks:Â Sidetrack services for your wellbore requirements.Â For exiting cased or open holes, Schlumberger sidetracking and milling services deliver faster, higher-quality windows and sidetracks to reduce cost and risk. By matching specific technologies to your exact wellbore requirements,Â our sidetrack services can meet your well departure objectives.
Casing Exits:Â Achieve a high-quality window for exiting standard steel casing.
Openhole Sidetracking:Â Sidetrack efficiently in open hole, with maximum probability of success on the first attempt and isolation of lower zones if required.
Thru-Tubing Sidetracking:Â Exit standard steel casing below the production tubing.
Section Milling:Â Single-trip milling to ensure rock-to-rock isolation.
Multilateral Completion Systems:Â Additional laterals for cost-effective increase in reservoir exposure.
Whipback:Â The Whipback tool is a retrievable or non-retrievable, mechanically-set non-hinged whipstock for use in cased holes. It can be oriented and is ideally suited for drilling multiple laterals from a single hole. The most unique feature of the Whipback tool is that in a deviated hole it can be set traditionally to mill up and to the right or it can be set on the low side so that it will mill downward. The top of the tool is concave and locks against the casing bore regardless of orientation.Â The Whipback tool has been designed with a bypass area allowing sidetrack, while producing. It has circulation slots around and ports through the whipstock for more by-pass area.
Packwhip Tool:Â The Packwhip for cased holes is available either as a retrievable or as a non-retrievable, non-hinged type. Both are designed to be set into a permanent packer. If orientation is desired, the Packwhip can use a whipstock packer and stinger with an orienting system. This type of whipstock is easily oriented and ideal for running in deep holes.
Bottom Trip:Â The Bottom Trip for cased holes is a mechanically set, hinged, non- retrievable whipstock that, when set, is highly resistant to rotation. It is specially designed to be set on any plug, cement retainer, liner hanger, junk, or on top of a fish. It is run the same way as the Whipback but is not retrievable.
Cement Type:Â The Cement Type is usually set in an open hole. It is the simplest type designed to accommodate setting and cementing operations. It has a standard thread connection on the bottom to allow the addition of a tail pipe. Once the Cement type is set in the open hole, a drill bit can be used to continue down the concave face of the whipstock.
Stiffback Whipstocks: Based on extensive research and field experience,Â key company has engineered the premier solution in whipstock technology. Keyâ€™s â€śStiffbackâ€ť whipstocks are made of treated 4140 material, which offers greater protection from wear and makes exiting the pipe easy. Threads cut on the concave make the tool easy to retrieve and a bi-directional slip anchors its positioning. The whipstock can be set at any azimuth to cut your window in any direction in your wellbore.
Whipstock Mills: Keyâ€™s whipstock mills are dressed with tungsten carbide for fast cutting of all steel grades of casing. The highly engineered mills create fine particles of cuttings that can be quickly and easily circulated and flowed to the surface. This results in more efficient cleaning of the hole and faster penetration.
Note: The removable whipstock is a reliable deflection tool that is usually used when jetting or when downhole motors cannot be used. It is a cylindrical steel casting, five to thirteen feet long, with a ring at the top, a concave inclined groove formed on one side and a chisel point bottom. The ring at the top is smaller than the bit and provides the means of transporting the whipstock in and out of the hole. The chisel bottom holds the whipstock stationary when it is set, and the indented groove, (usually 3 degrees) guides the bit to a new course.
The circulating whipstock differs from the standard whipstock, in that there is a control sub immediately above the bit that prevents the flow of circulating fluid through the bit and deflects it through a hollow shear pin used to pin the whipstock to the drill pipe assembly. The flow of fluid passes through the shear pin and down to the bottom of the whipstock via a bored circulating channel in the back of the whipstock. The fluid then flows out the bottom of the whipstock. This permits the bridges in the hole to be washed through, and fill up on the bottom of the hole to be circulated clean. Prior to setting the whipstock, a ball is dropped through the drill pipe and seated in the control sub. The drilling fluid is then diverted from the bottom of the whipstock and established through the bit. The whipstock can then be set and drilling commenced. A 15′ – 20′ rat hole is usually drilled below the whipstock setting point. The diameter of this hole is smaller than the open hole, and must be reamed out to the full hole size by means of a hole opener. Therefore, setting a whipstock is slower than other deflection tool methods because more trip time is needed to set and ream the rat hole out to full gauge. A combination universal knuckle joint and short drill collar may be run in conjunction with the whipstock when extreme angles are required to sidetrack an enlarged hole.
Directional Drilling:Â In an operation designed to sidetrack the hole around a non-retrievable fish, such as a broken drill string which has become stuck in the hole, it is necessary to place a cement plug at a specific depth to help support the whipstock for directing the bit into the desired area. Another example of a controlled change in the drilling direction to help reach a specific target area is in shoreline drilling operations for offshore production.
Conventional Re-entry: Deepening and sidetracking wells cover the bulk of the conventional re-entry market, and CTD is suited to a portion of these operations. For sidetracks, a whipstock is set at the kick-off depth, and a window is milled in the casing. In such types of wells CTD has limitations of maximum hole size (6″) and build up rates (>30 degree/100 ft). For horizontal sidetracks the drain hole length is limited by the required WOB. Here too CTD units have to compete with depreciated drilling rigs with low day rate. Here too CTD has the same environmental advantages as for new wells. CTD is also useful for offshore where UBD is required due to depleted reservoir pressures.
Whipstock in Cement (WIC): This technique is slightly more complicated than the CS technique. The casing is filled with cement (preferably to the tailpipe) and a through-tubing directional assembly is used to drill a hole to the inside of the casing at the proper tool face angle. Enough straight hole is drilled adjacent to the casing to make a straight rathole for the whipstock. The procedure described above can be used if the well is theoretically deviated more than 3 degrees at the point where the whipstock is to be set. From a practical stand point, a hole deviation of more than 10 degreesmay be required for stable tool face readings while drilling (this applies to the CS technique also). A bottom trip whipstock is run in with a bottom hole assembly (BHA) of; (a) whipstock, (b) starter mill, (c) steering tool, (d) CT
Through-Tubing whipstock (TTW): Several versions of through-tubing whipstock exist. All consist of an anchor that reacts torsional and axial loads and are designed to allow the small through-tubing diameter to span from the high side to the low side of the much larger casing inside diameter. All TTW are normally used for a near high side exit. This is to allow gravity to force the upper whipstock taper to lay against the low side of the casing.
Look up:Â Whipstock
- Whipstock a long steel casing that uses an inclined plane to cause the bit to deflect from the original borehole at a slight angle.Â Whipstocks are sometimes used in controlled directional drilling, in straightening crooked boreholes, and in sidetracking to avoid unretrieved fish. Found op http://www.encyclo.co.uk/visitor-contributions.php
- Whipstock Whip’stock` nounÂ The rod or handle to which the lash of a whip is fastened. Found op http://www.encyclo.co.uk/webster/W/32
- Whipstock â€˘ (n.) The rod or handle to which the lash of a whip is fastened. Found op http://thinkexist.com/dictionary/meaning/whipstock/
- Whipstock (from the article `petroleum production`) …a number of small deviations must be made. The borehole, in effect, ends up making a large arc to reach its objective. The traditional tool for … Found op http://www.britannica.com/eb/a-z/w/29