3、Common problems during casing operation

(1). Unclear make-up torque of casing entering the well

At present, the casing update of casing manufacturers is too fast, the makeup torque is higher and higher, the database update of casing team is not timely, and the management of the current casing team is disordered, which often results in inadequate casing makeup torque. The engineer must verify the performance data after the casing arrives at the well, ask the manufacturer to provide the make-up torque, and strengthen the supervision of the casing running process.

(2). Adding casing centralizer is required for uneasiness

Casing centralizer plays an important role in improving displacement efficiency and ensuring cementingquality. If the adding method is unreasonable or the risk is too high, the modification opinions will be put forward during the review of cementingconstruction design. Mark the casing with centralizer at the male buckle.

(3). The formulation of anti jamming measures during casing running is unreasonable or not implemented

It is very important to prevent jamming and leakage during casing running, especially for large size casing. However, at present, some drilling teams reduce the grouting times in order to seize the time, which leads to a long time for light filling when the casing is finally run down or the casing is blocked to connect the circulation cap for circulation, which affects the construction safety. When casing running is suspended due to circulation and other reasons, the casing is not moved according to the requirements. If it is water-based mud or there is a large section of mudstone, the risk of sticking is increased. Casing sticking can be generally divided into the following three categories: first, casing sticking, second, wellbore shrinkage, third, wellbore collapse or sand bridge. Causes and influencing factors of casing jamming:

(a) Casing sticking is due to the large contact area between casing and well wall, the long time of making up and the inability to rotate, so the probability of casing sticking is high.

(b) It is caused by borehole instability, especially when drilling in peristaltic salt rock or formation of thick mud cake due to poor drilling performance, which leads to borehole shrinkage and casing sticking accident.

(c) Borehole collapse or sand bridge casing sticking is a casing sticking accident caused by borehole collapse or sand bridge during or after casing running.

Technical measures:

(a) Before running the casing, the well shall be shut in carefully and the reduced section shall be reamed repeatedly.

(b) Adjust the performance of drilling fluid, ensure the formation is stabilized, prevent wellbore collapse, and reduce the creep speed and wellbore shrinkage of the creep formation.

(c) Before casing running, the casing can be run only after the drilling fluid performance is carefully handled, the viscosity, shear force and water loss of the drilling fluid are reduced, and the drilling fluid is fully recycled.

(d) For deep well, long open hole well, directional well and horizontal well, it is necessary to add plastic or glass ball with liquid lubricant before running casing to reduce wellbore friction coefficient.

(e) The casing operation shall be carefully prepared (including personnel organization, tools, etc.), which can only reduce the casing running time and intermediate stop.

(f) Before running the casing, it is required to plug the lost formation well, control the running speed of casing and prevent the formation from fracturing.

(g) Before running casing in high pressure formation, it is required to keep pressure stable to prevent overflow during running casing and maintain pressure balance in well.

(h) In case of any obstruction during casing running, the casing shall be moved repeatedly, and Kelly or circulating head shall be connected for circulation treatment of drilling fluid. Blind down pressure shall not be allowed to prevent casing from being stuck.

(i) Before running the casing, the wellhead shall be corrected to prevent the wrong connection when running the casing. If necessary, the casing stabbing Board shall be used, and the casing shall be stabbed manually or mechanically, so as to prevent the wrong connection and speed up the casing running.

(j) Grouting and filling frequently to reduce the stopping time of running casing caused by grouting.

(k) After running the casing, it is required to fill the drilling fluid first, and then slowly start the pump for circulation. After the circulation is smooth, slowly increase the circulation flow rate, so as to prevent the difficulty of starting the pump and the formation leakage caused by air mixing.

(l) The distance between the upper and lower movable casings shall not be less than 2m.

(4). The formulation of leakage prevention measures for running casing is unreasonable or not implemented

Lost circulation is one of the most important factors affecting cementingquality. Engineers must realize this and do their work carefully and solidly. For specific measures, please refer to the section of wiper trip and leakage prevention.

(5). Complexity caused by casing accessories

The common ones are sealing ball blocked or damaged, insufficient pressure bearing capacity, not using strong closed accessories, debris falling into the casing to block the water hole, etc. The engineer must carefully check the implementation as required and strengthen the supervision of the cementingteam.

(6). Joint calculation error

The calculation accuracy of the coupling joint is very high when using the mandrel for cementing. Once the mandrel fails to be set, the engineer should take it seriously. If not, re measure the void height from the drilling platform to the upper end of the casing head. The first spud in must be calibrated and the position of casing head shall be determined. The later spud in can be calculated according to the corresponding height of casing head. Then according to the calculated data and the actual measurement data, the above errors can be effectively avoided. Attention shall be paid to the details of several joint jacking joints. The upper and lower end faces of the mandrel shall not be reversed. The upper neck part of the mandrel shall be equipped with seals and must be protected. The joint jacking joint must be loosened properly after reaching the torque.

(7). The wellhead is not normal or the inner diameter of the bell mouth is small, so it is difficult to seat the mandrel

This is a common problem. Before running the casing, the engineer should check the centering condition and the inner diameter of the bell mouth in advance, and make preparations in advance, so as to align the mandrel in time. The maximum outer diameter of the mandrel and the maximum outer diameter of the pressure test plug are basically the same. As long as the pressure test is carried out after the bell mouth is installed, there is no problem for the mandrel to pass.

(8). The key nodes are not fixed tightly during casing running

Items to be monitored mainly include: lower accessories, conversion nipple, positioning short sleeve shall be in place by side, the number and arrangement order of centralizer running in shall be explained clearly and marked at the casing buckle.

(9). Error in basic data of cementingdesign

In general, the following points are most likely to make mistakes: no well temperature data is collected during electric logging, the calculation of well diameter expansion rate is wrong, the mud performance data is incomplete or not updated, and the track data unit is wrong.

4、Common problems during cementingoperation

(1). Inadequate preparation for well cementation

Many preparations are involved in casing and cementingoperations, such as clear water storage and supply, pilot slurry preparation and mud recovery, cement preparation, cementingtool preparation, blowdown, packer flushing, back extrusion and back pressure construction.

Technical measures:

(a) The drilling crew shall divide the work of preparation according to the requirements of the meeting, and the Engineer shall personally check and accept the work after preparation.

(b) Before cementingconstruction, the drilling crew must store sufficient clean water and implement the supply according to the requirements of the pre casing meeting.

(c) The mud team leader shall prepare the pilot slurry with the performance meeting the design as required, and the engineer must accept it. Set up the recovery mud pump in advance, and make sure its working capacity can meet the requirements of recovery drilling fluid.

(d) Before running the casing, the construction scheme of flushing, back extrusion and back pressure of the well packer shall be prepared at the meeting, and the tools such as transfer joint shall be prepared in advance.

(2). Key points control in cementingprocess

The items to be noted include the performance of rubber plug, pilot slurry, flushing fluid, isolation fluid and cement slurry as well as the actual well inflow, and whether the displacement of injection meets the design requirements.

5、Common problems in liner cementing

The requirements for liner hanger in liner cementingprocess are "down going, hanging, tight sealing, inverted opening and lifting out". Its complexity mainly includes the following:

(1). Inaccurate weighing of tailpipe and casing

Technical measures:

Before the casing operation, the engineer must determine the feeding drilling tools and arrange them in a good order, and weigh the feeding drilling tools in advance in the process of wiper trip, so as to check the error later. When the well is fully filled with mud (before the pump is turned on), record the total suspended weight of the drilling tool entering the well 1 (remove the traveling block, hook and faucet). After all the drilling tools are lifted out (the annulus is filled with mud), record the hanging weight of drilling tools 2 (remove the traveling block, hook and faucet), and then reduce it to the hanging weight of the drilling tools. The weighing operation shall also be carried out during tailpipe lowering. After the tail pipe is all put into the well, it shall be filled with mud, weighed into the well tail pipe suspension weight (excluding traveling block, hook and faucet), and the total suspension weight (excluding traveling block, hook and faucet) shall be recorded after the tail pipe is put into place, and then the drilling tool suspension weight (excluding traveling block, hook and faucet) shall be fed. If the drilling fluid performance does not change much during the wiper trip and casing running, and the suspension deviation of the drilling tool is not large, if the drilling fluid performance is greatly adjusted, the weighing data of the following liner shall prevail.

(2). Tailpipe hanger seat cannot be hung
The reasons for the failure to seal the liner hanger seat include: (a) the copper ball does not reach the ball seat position; (b) the inner wall of the upper casing is not scratched cleanly, the inner wall of the casing is seriously worn, or the wall thickness of the casing is small and the strength is low, or the seat hanging position is just in the coupling, and other reasons, which may cause the failure to hang; (c) the design defects of the hanger itself, such as: the taper design of the seat hanging slip is improper, self-locking can not be realized, and the liner is suspended The design clearance of the hanger seat seal hydraulic cylinder is not appropriate, which causes the piston not to move up effectively. (d) the liner hanger seat slip is damaged in the process of lower liner. (e) the suspension weight is large, the hanger body is deformed, the piston upward resistance is large. (f) the solid content of the drilling fluid is high, and the performance is unstable, which causes the block of the seat hang hydraulic cylinder.

Technical measures:

(a) The diameter of the drilling tools to be fed shall be in accordance with the technical requirements, and the outer diameter of the drift diameter gauge shall meet the requirements of the manufacturer.

(b) Scrape the inner wall of the upper casing before running the liner, especially for the wells with long drilling period. In the well section with wall hanging, the case of unsuccessful cementingat the bottom of the well should be considered;

(c) The reasonable location of the seat should avoid the serious abrasion of the inner wall of the casing and the coupling of the casing;

(d) Control the speed of tailpipe lowering to prevent the liner hanger seat slip from being damaged in the process of tailpipe lowering;

(e) Reasonable design clearance of hydraulic cylinder for liner hanger seat, and tension test seat hanging test on the ground;

(f) Improve the stability of drilling fluid, and design a reasonable hydraulic cylinder anti blocking structure;

(g) The float shoe at the lower part of the hydraulic liner hanger shall be designed with a bypass hole. If there is no one or three holes above the float shoe that can be screwed, in case the seat cannot be hung, the bottom of the well can be reversed to complete the cementingconstruction.

(3). Obstruction in the middle of lower tail pipe

There are two kinds of situations in the middle of the lower tail pipe, one is in the upper casing, the other is in the open hole section. If there is resistance in the upper casing, it is generally caused by the early setting of the liner hanger's slips. In addition to the hanger, the resistance in the open hole section may also be caused by the formation. The reasons for the advance seating of the slips of the liner hanger (hydraulic type) include: (1) the pressure of the circulating pump when the pump is turned on exceeds the shear pressure of the pins of the hanger's seating, which causes the slips of the liner hanger to seat in advance; (2) the speed of running the liner is too fast, which may also cause the slips to seat in advance and get stuck; (3) the design of the outer diameter of the cone standard of the liner hanger body is too large, such as the inner wall of the upper casing is not clean If there is a little deformation or wellbore shrinkage, it may cause obstruction in the middle of the lower liner.

Technical measures:

a. If the lower tail pipe is blocked, it is necessary to circulate the drilling fluid, and control the circulating pump pressure of the start-up pump not to exceed the shear pressure of the hanging pin of the hanger seat;

b. Control the speed of running the tail pipe. Generally, the running time of a casing shall not be less than 30s, subject to the requirements of the manufacturer;

c. A rigid centralizer with an outer diameter larger than the cone is added to the upper and lower cones of the liner hanger body;

d. Properly increase the shear pin pressure of hanger seat.

(4). Tail pipe hanger cannot be opened or lifted out

If the liner hanger fails to open or lift out, it means that after the liner is lowered to the bottom of the well, the back buckle part of the hanger's back buckle device and the liner can't be opened, or the delivery and release tools can't be raised after the back buckle, resulting in the hanger unable to release.

The reasons why the liner hanger can not be opened are as follows:

a. in case of back fastening, the force on the back fastening nut causes difficulty in back fastening;

b. there is dirt at the screw down nut, causing sticking;

c. the design strength of the back-up nut is low, and it has been deformed when running the tail pipe;

d. the well angle is large, and the dogleg degree of the well is large, so the reverse torque can not be transmitted to the bottom of the well normally during the reversal.

Technical measures:

The liner hanger shall be strictly and carefully inspected before entering the well. If the reversal is serious, the neutralization point shall be calculated carefully to ensure that the nut of the reversal is not stressed and the friction of the reversal is less; when increasing the reversal torque, the number of turns of one reversal shall not exceed the allowable torsional strength of the drill pipe to prevent the drill pipe from twisting off; if it is judged that the buckle has been turned off, the hanger shall be lifted up and down quickly to release the hanger.