Logging Through Casing Drill Pipe: Pumpdown Techniques 51

1.9 Wireline Logging Operations in Deviated Holes 50

1.9.3 Logging Through Casing Drill Pipe: Pumpdown Techniques 51

Another method of lowering tools past difficult hole sections is to install open ended casing, tubing or drill pipe over these sections and to log the open hole section below it. Pumping down of the tools is required where friction is too high.

When the complete open hole section cannot be logged in one run, it is necessary to lower the pipe over parts of the objective section as well and to log the remaining open hole. This procedure may have to be repeated several times to obtain logs over the complete sequence. It is advisable to install a tool re-entry guide on the bottom of the pipe to facilitate re-entry of pad type tools and to avoid cable damage.

The internal diameter of the casing, tubing or drill pipe used may be too small for standard tools and slim hole tools have to be used. Allow 13 mm diameter clearance in the drill string.

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Confidential-Property and Copyright: SIPM, 1991 Wireline Logging: General

The following tools are available:

The procedure for logging through drill pipe is as follows:

(a) Run in hole with open ended drill pipe. Collars and Heviwate should only be used when essential (check clearance required for tools with the minimum ID string). Fit a guide shoe or skirt to the bottom of the string to permit easy re-entry of the logging tool. The pipe should be moved up and down slowly with the blocks to prevent sticking.

(b) Attach mud pumps via Chicksan line to a circulating head installed at the top of the drill string.

(d) Thread logging cable over sheave wheels and through the pressure control equipment and connect tool.

(e) Set pipe in slips. Pick up pressure control equipment with tugger line;

pick up tool with cable winch and run tool to 30 m below the drill floor.

Slack off on tugger and connect pressure control equipment to circulating head.

(f) Reciprocate pipe and begin circulation with the mud pumps. The mud pumps should be started with caution and only 10 – 15 bar pressure is normally required to circulate the mud.

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(g) Run logging tool down inside the drill pipe as fast as possible without causing any drop in cable tension. The pipe should not be reciprocated as the tool approaches the guide shoe.

(h) As soon as the tool is descending in open hole, move the pipe again if there is any risk of sticking.

(i) Log from the lowest depth reached. Continue circulating mud until tool is inside drill pipe.

(j) Stop moving pipe when tool approaches the guide shoe.

(k) Depending on the maximum depth reached, it may be necessary to add some more stands to the drill string and set the guide shoe about one hundred metres deeper before the next attempt is made to get the tool down to total depth.

If difficulty is encountered when re-entering the drill pipe after logging, very slow rotation of the pipe should allow re-entry.

A disadvantage of slim hole tools is the reduced accuracy of the porosity measurement (by 2–3%) and resistivity measurement due to the larger borehole effects.

1.9.4 Logging of Near-Horizontal Holes

To overcome the problems with slim hole tools and to be able to log near-horizontal holes, two systems have been developed as described below:

(a) Logging Horizontal Wells by the SIMPHOR System

The Institut Français du Pétrole and Elf Aquitaine have developed and used this method to log horizontal boreholes.

Standard open and cased hole Schlumberger logging and perforating (4" carrier) tools have been lowered into the hole inside a protective housing on the bottom of the drill-pipe string. When this string reaches the shoe of the last casing, a 7 conductor electric transmission cable connected to a sinkerbar and female electrical connector system is lowered inside the drill pipe, until it locks mechanically into the logging sonde and makes the electrical connection. The logging cable is brought outside the drill string via a side entry sub. Further adding of drill pipe brings the logging tool in the open hole and logging can commence after power is applied to the cable.

Some 500 m of near-horizontal 8¹/2" hole have been logged in this manner with standard 3 to 4” OD tools using the 5" OD SIMPHOR system.

A 3" SIMPHOR is available for running tools without a protective housing.

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Confidential-Property and Copyright: SIPM, 1991 Wireline Logging: General

Logs recorded to-date using this method are: induction, spherically focussed, dual laterolog, gamma ray, neutron, BHC sonic, 4 arm-caliper, CBL, CCL and 4"

perforating gun for perforating 7" liner (9 m length).

(b) Logging Deviated Holes over 65º

A prototype has been built by Schlumberger of a tool system to lower standard size logging tools in a steel envelope with a stinger on the bottom of the drill pipe.

A locomotive brings an 8-conductor cable down through the drill pipe and first connects the stinger and then makes the electrical connection with the tool.

Further pumping brings the tool out of the steel envelope into the open hole, and logging can commence.

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1.10 Sticking of Wireline Logging Equipment

Most Frequent Causes of Stuck Tools

(a) Differential sticking. Cable or logging tools can be stuck to the wall of the hole by differential pressure if the tools are not moved or moved at a very low speed.

(b) Key seating. Cable or logging tools can be pulled into a slot (key seat) which is sometimes cut in the (high) side of the hole by the cable during a series of logging operations, particularly so in deviated wells.

Prevention of Differential Sticking

(a) Move the logging cable continuously when running tools in open hole.

(b) Calibration of certain tools which may be carried out in a 150 m open-hole section immediately below the casing shoe should take the shortest possible time.

(c) During WLFT, after setting the tool, the cable should be slackened off and moved ('yo-yoing') throughout the test period.

(d) Limit the number of logging runs in between bit trips in the hole particularly when heavy mud is used or frequent drag is experienced.

This limit may be relaxed if the hole is in excellent condition and no drag is experienced. It is at the discretion of the Toolpusher advised by the WSPE and the Logging Engineer to decide if and when a checktrip will be made.

(e) During sidewall sampling, the samples should be taken while moving the tool very slowly upwards (‘sampling on the run’).

(f) Should the Logging Unit break down whilst running tools in the open hole, the following emergency procedures should be followed:

Move the traveling block over a 3–5 m interval to move the cable, taking care that the cable does not jump out of the groove of the top sheave.

Check the weight on the Martin Decker gauge.

Before starting this operation, ensure that the Logging Contractor’s weight indicator cable is not fastened to the derrick floor and can move freely. The operation should always be supervised by the Logging Engineer.

If possible there should be inter-communication between the Logging Unit and the Driller so that the operation can be controlled by the more sensitive wireline logging tension meter.

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Confidential-Property and Copyright: SIPM, 1991 Wireline Logging: General

1.10.1 General Guidelines on Stuck Tool, Weak Point and Fishing Kit (a) If tool is stuck on bottom, pull to maximum safe tension and hold it.

(b) If tool is stuck during logging, try to go down. If tool is free to descend, attempt to pass bridge. If tool is not free to descend, tool or cable is stuck. Pull to maximum safe tension and hold it.

(c) If the tool fails to come free after working the cable for 30-40 min, the ‘cut-and-thread’ technique should normally be attempted. The cable will hold the tool in a centralised position and serve as a guide for the overshot.

(d) On no account should an attempt be made to break the weak point unless clear instructions have been given from base to do so.

(e) Sharp edges and abrasive formations will cause wear during working the stuck cable. The weak point above the tool is therefore no longer the weakest point necessarily. Even if successful, breaking the weak point considerably reduces the chance of recovering the tool.

(f) In a vertical hole of good condition with no sign of cable key-seating, or when inside casing, a tool can be fished with good probability, using the technique of breaking the weak point and fishing with an overshot with OD slightly smaller than bit size.

(g) NEVER break the weak point when a radioactive tool is stuck. Cutting and threading is obligatory.

(h) Never SUDDENLY release tension on a cable. This causes 'bird cages' and broken cables. Tension should be released slowly and should not drop below half the 'normal’ logging tension.

(i) Know the cable weight, the allowed overpull and hence the maximum safe pull which can be applied at all times.

(m) Never pull more than 4,500 lb on the standard weak point unless breaking is intended (and only on clear instructions from Base).

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(n) Never pull more than 1,500 lb on the weak point of a small cable

unless breaking it is intended. Safe pull is 1,125 + (0.08 x depth in feet) lb.

Schlumberger Fishing Kit

The fishing kit is designed to fit 4 / " IF tool joint. It includes: ¹2

1. A complete overshot assembly. Four guides are available: 3 / ", 4'/ ", 5 / " ¹2 2 3

and 7" OD. The grapples fit the different cable heads. 4

2. A spear rope socket with matching overshot rope socket assembly.

3. A circulating sub.

4. A cable hanger.

Note: The WSPE should check with the Logging Engineer the correct size of grapple to use for the logging head in use before to RIH. The size of the grapple should be measured as a double check.

1.10.2 Fishing for Stuck Tool 1.10.2.1 Open Hole

When a tool becomes stuck in open hole and all attempts to free it have failed, the decision must be made at Base whether to fish the tool or cement it in place.

This is particularly important in the case of tools containing radioactive sources, to which special regulations apply (see 8.1).

In the unlikely event that the decision is made to cement the tool in place, specific instructions for the procedure to be followed will be telexed from Base.

In general, the Wireline Company Engineer will probably have more experience at fishing for wireline equipment than the Oil Company Engineer. Nevertheless the responsibility for the fishing operation rests with the WSPE and the Toolpusher who should familiarise themselves with the equipment and technique to be used before the operation commences. The wireline company engineer will supply the required fishing tools and advise if requested, but once the tool is stuck his assistance is advisory only.

The following procedure is to be adopted when fishing with the ‘cut and thread technique' (stripping over cable):

Preparing the Cable:

(a) Set cable tension at 2,000 lb above normal hanging weight.

(b) Clamp the T-bar on the cable just above the rotary table, and lower the cable until the T-bar is supported by the rotary table. Continue lowering cable until there are several feet of slack cable on the drill floor.

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Confidential-Property and Copyright: SIPM, 1991 Wireline Logging: General

(c) Cut the cable a few metres (1.5-2 m) from the T-bar and make up the Bowen spear to the logging unit end and socket to the tool end.

(d) Rig down Wave Compensator (floating rigs). Attach upper wireline sheave to main cross-member of derrick with special chain to leave blocks free to run pipe. Ensure that the wireline tension device cable is carefully trained around the outside of the derrick to avoid damage during drill floor operations.

Threading Cable Through Drill Pipe:

(e) Make up correct fishing guide and grapple assembly for fishing neck of stuck tool. Use correct skirt for hole size. Feed socket on cable end through fishing assembly.

(f) Thread overshot spear through first stand of pipe and stab into socket.

(g) Take tension on wireline, check overshot assembly. Remove T-bar.

Make up first stand to fishing assembly.

(h) Run first stand into hole, set slips.

(i) Place C-clamp over top of drill pipe, lower cable assembly to catch lower rope socket on C-clamp, disconnect spear.

(j) Pick up next stand of drill pipe, thread overshot spear through pipe, stab into rope socket, take cable tension with winch, remove C-clamp.

(k) Lower stand, watching cable tension carefully, and stopping if cable tension increases. DO NOT ROTATE PIPE while lowering, to avoid possibility of cutting cable.

Approaching and Engaging the Fish:

(I) When the grapple is one joint above the tool, install circulating sub, circulate slowly to clean top of tool. Continue circulation while lowering pipe and engaging fish in overshot. Note increase in pumping pressure and cable tension as tool head enters overshot. Stop circulation. (While circulating, the

cable is held onto the circulating sub by a special bushing.) Breaking the Weak Point:

(m) Ensure that fishing head is engaged in grapple, set pipe in slips. Attach T-bar to cable (below socket), pick up T-bar with travelling blocks.

(n) Pull up slowly on cable and break weak point. DO NOT SNATCH.

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(a) Remove Bowen spear overshot and rope socket, knot logging cable, take cable tension with logging unit winch, remove T-bar.

(p) Spool cable on logging unit.

(q) Pull pipe out of hole slowly. DO NOT ROTATE. Close BOPs as soon as tool is safely through.

(r) Ensure that complete tool has been recovered.

Grapples, guides, skirts and circulating sub are supplied by the Wireline Logging Contractor.

In deviated wells ( > 25º) it is almost invariably safer to strip over the cable to recover both tool and cable. If the cable breaks at a dogleg, it will still be retained inside the drill pipe.

The procedure to be followed in this case is given above.

1.10.2.2 Cased Hole

It should not normally be necessary to strip over the cable to recover a tool stuck inside a vertical casing. In this case it is far quicker, easier and cheaper to break the weak point and fish for the tool with the cable removed from the hole.

Nevertheless, the decision to follow this course must be made by Base.

Procedure in vertical casing when strip over is NOT required is as follows:

(a) Clamp the T-bar to the cable above the rotary table.

(b) Rig down Wave Compensator (floating rigs). Attach upper wire line sheave to main cross-member of derrick with special chain to leave blocks free.

(d) Lower blocks, take cable tension with logging unit, remove T-bar, spool cable on logging unit,

(e) Rig down wire line.

(f) Make up fishing assembly with correct fishing guide, skirt and grapple for casing size and tool fishing neck.

(g) Run in to top fish, carefully engage fish.

(h) When fish is securely engaged, pull out slowly. DO NOT ROTATE.

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(i) Close BOPs as soon as tool is safely through.

(j) Ensure that complete tool has been recovered.

Grapples, guides, skirts and circulating sub are supplied by the Wireline Logging Contractor.

1.10.2.3 Fishing through Tubing

1. When a tool gets stuck either in or below tubing, the only remedy in most cases is to pull tubing to recover the fish. It is not unknown for a fish to be retrieved by pumping it out, using reverse circulation (down the tubing/ casing annulus, up the tubing).

2. Fishing can be attempted on piano wire. The technique can only be successful if the tool is free, e.g. it has dropped off the end of the logging cable.

Fishing for a stuck tool using piano wire will almost invariably aggravate the problem.

3. Equipment required for fishing on piano wire is supplied and maintained by the piano wireline contractor.

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1.11 Detection of Stuck Point/Back-Off Equipment

Detection of the stuck point in order to find the lowest possible back-off can be established by stretching the string and using stretch charts for drill pipe. A more accurate method of free point detection is using the Stuck Pipe Indicator Tool (SIT) (see Figure 1.11-1).

1.11.1 Stuck Pipe Indicator Tool

In order to back-off the string at the deepest possible point a Stuck Pipe Indicator Tool (SIT) can be run on electrical wireline to determine the deepest free point of the string.

By applying stretch and torque on the pipe the SIT can determine elongation or rotation at any depth by use of a strain sensor placed between two spring- loaded or hydraulic centralisers.

The operation is monitored at the surface and depth control is provided by a CCL.

A plot of depth versus the percentage of surface torque and pull transmitted downhole will show the deepest point at which the string is free (see Figure 1.11-2).

Procedure for Running the SIT

(a) Before running the tool the spring centraliser pads should be checked by the WSPE both for wear and for the correct pressure for the particular size of drill pipe. All IDs of the string should be checked to ensure the tool can pass through.

(b) Determine approximately where the pipe is stuck by measuring the stretch of the pipe.

(d) Pull up to the neutral weight of the pipe above the stuck point. Mark the pipe at this point. Label this Mark No. 1.

(e) Pull up to the neutral weight of the pipe plus the stretch required. Label this Mark No. 2.

(f) After this the Martin-Decker gauge is not used but still observed. All tensions are referred to by the marks on the DP.

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Write out for the Driller the four instructions for the measurements viz:

(i) Pull pipe up to Mark No. 2. Take reading.

(ii) Release tension in pipe, go down below Mark No. 1 and pull back up to Mark No. 1.

(iii) Drop in the slips without moving the pipe if possible. (If not using a kelly).

Apply the required torque. Work down the torque using tongs pref- erably on a convenient tool joint to prevent the pipe from rotating.

Pull up to Mark No. 1 before taking the measurement. Keep all non- essential personnel off the drill floor during this operation.

(iv) Release the torque. Report the number of turns that come out of the pipe. Work the pipe to remove all torque. Pull back up to Mark No. 1.

Notes:

1. It is essential that the pipe is pulled up to the marks to avoid problems due to pipe friction in the hole.

2. It is essential when measuring stretch that there is no torque in the drill pipe, and vice versa.

3. When taking the readings the Logging Engineer should refer to each instruction by

In document Petrophysical Engineering (Page 58-90)