Novel Method and Apparatus for Sticking Fluid Performance ...€¦ · recovery of stuck pipe from a particular mud cake matrix. The method and apparatus promises to play an important

SUMMER 2017 SAUDI ARAMCO JOURNAL OF TECHNOLOGY

ABSTRACT

Drilling fluid is the lifeline of safe and economic drilling oper-ations that explore for oil and gas resources. It is also the root cause of various mud-related drilling problems, such as shale and drilling fluid interactions, borehole instability, loss of cir-culation, differential pipe sticking, etc. Differential sticking is a major drilling problem, and it is particularly common when drillpipe is passing through a high permeability zone. It is one of the primary causes of nonproductive time, which dramati-cally increases the total drilling cost, especially if there is a de-lay in recovering the stuck pipe. Delay in recovering a stuck pipe or the inability to do so may lead to other drilling prob-lems, which then can lead to abandonment or sidetracking of a well. Therefore, every effort should be made to recover a stuck pipe as soon as possible.

One of the most effective strategies for quick recovery of a stuck pipe is the use of a highly efficient and rapidly acting spotting fluid, which works to damage, degrade and destroy the mud cake that bonds with the pipe. Spotting fluid must be placed as quickly as possible to release the stuck pipe from the mud cake matrix. This dictates quick laboratory evaluation of the various spotting fluids that are available to identify the best one for a particular mud and mud cake composition. Because the chemistry of the mud additives and the deposited mud cake materials influences the performance of a spotting fluid, it is highly recommended that the debonding, degrading and de-structive potential of a spotting fluid be evaluated for a partic-ular mud cake composition before making a selection. There is no API method or any other method available to the indus-try that can be used for the quick screening of spotting fluids to find the most efficient one for a particular stuck pipe rescue operation. This article describes a novel, dedicated operating software-driven laboratory method for the quick screening and reliable prediction of the performance of various spotting flu-ids. The article demonstrates the suitability of this method and its test apparatus for oil and gas field applications.

Experimental results indicate that the newly developed method and test apparatus can consistently and precisely pre-dict the performance of various spotting fluids when applied to specific mud cake compositions. It provides useful guide-lines and a practical decision making tool for use by drilling

and mud engineers or consultants seeking the quick and easy recovery of stuck pipe from a particular mud cake matrix. The method and apparatus promises to play an important role as well in the development of a new generation of high per-formance spotting fluids able to overcome current and future challenges associated with differential pipe sticking.

INTRODUCTION

Several challenges and operational problems are frequently encountered while drilling wells for the exploration and ex-ploitation of oil and gas resources. Mitigation of the critical factors associated with these drilling challenges is very import-ant for safe and economic drilling operations in both onshore and offshore drilling environments. Pipe sticking is one of the challenges most often faced in drilling operations. Some of the critical factors that can lead to pipe sticking are the use of im-proper drilling practices, inadequate hole cleaning, wellbore instability, excessive reaming or back reaming, poor mud rhe-ology, deposition of thick mud cake, and the sticky quality of the mud and the deposited mud cakes, among others1-4.

Based on which factor triggers a pipe sticking event, it can be classified as mechanical or differential. An analysis of all the pipe sticking events occurring in 2009 in Saudi Aramco’s fields5 indicated that 69.5% of stuck pipes were related to mechani-cal factors and 30.5% were associated with high permeability zones. A worldwide survey conducted by a major drilling con-tractor in 1992 estimated that about 36% of all reported drill-ing problems were related to pipe sticking6. The nonproductive time (NPT) associated with pipe sticking could be from several hours to several days, depending on the complexity of the prob-lem and the difficulty in completing the recovery operation. In some cases, where it is impossible to free a stuck pipe, side-tracking may be required. In other cases, differential pipe stick-ing may interrupt the drilling operation for weeks, with a dras-tic increase in total drilling cost. In extreme cases, pipe sticking may force operators to abandon a well and start a new one. Even just a few hours of NPT, along with the cost of recov-ery operations, can significantly increase the total drilling cost. Therefore, mitigation of the causes of pipe sticking problems and actions to ensure rapid recovery in the event of a stuck pipe are very important for reducing the total drilling cost.

Novel Method and Apparatus for Sticking Fluid Performance Evaluation

Dr. Md. Amanullah and Mohammed K. Al-Arfaj

SAUDI ARAMCO JOURNAL OF TECHNOLOGY SUMMER 2017

Differential pipe sticking occurs when the drillstring comes into intimate contact with the mud cake. The close proximity of the drillstring to the mud cake surfaces allows the formation of sticking bonds in the interface both via the action of phys-io-chemical forces, such as van der Waals, adhesive, cohesive, intermolecular, intramolecular, capillary, etc., forces, and also via the action of mechanical interlocking forces. The strength of the sticking bonds that result from the combined action of physio-chemical and mechanical interlocking forces plays an important role in recovering a stuck pipe. The mud cake prop-erties, based on the physics and chemistry of the mud addi-tives, significantly affects the strength of sticking bonds.

Several authors have highlighted the effect of the mud cake composition in causing pipe sticking1, 7. Haden and Welch (1961)8 reported experimental results that show how the forces necessary to move a steel pipe on the mud cake vary with the different mud cake compositions. Annis and Monaghan (1962)7 studied the friction between a steel plate and a mud cake under the action of differential pressure, testing different mud cake compositions to demonstrate the varying frictional resistance that occurred. Helmic and Longley (1957)9 experi-mentally demonstrated that 45% of the pipe holding force is associated with mud cake/pipe interfacial friction forces, i.e., the sticking forces associated with the bonds that form be-tween the mud cake and the contacting pipe surface. Reid et al. (2000)10 highlighted the effect of mud composition on those sticking forces at the mud cake/pipe interface. According to the authors, oil-based mud has the lowest sticking value, gel-based mud has the highest, and polymer-based mud has intermediate sticking values. Isambourg et al. (1999)11 investigated the ef-fect that the types and amount of solids in the mud cake have on its sticking characteristics as well as their effect on the pull-out force required to free a stuck pipe. Bushnell-Watson and Panesar (1991)12 also observed the importance of drill solids and their effect on the mud cake behavior during pipe stick-ing events. All of these reports suggest that laboratory evalu-ation of the sticking bond strength formed by a mud cake in the mud cake/pipe interface is very important to predict the tearing, shearing and/or pulling forces needed to improve the chances of recovery of a stuck pipe.

If a pipe is stuck, initially pulling, slacking off, jarring and/or torqueing the pipe can sometimes free it. If these mechanical methods of recovering the pipe are unsuccessful, a combina-tion of chemical and mechanical methods is tried. The chem-ical part of the recovery process consists of placing a suitable spotting fluid in the vicinity of the sticking zone. These spe-cially designed fluids attack the mud cake to break it down or weaken the sticking bonds holding the pipe to the mud cake matrix. They do this by causing damage and degradation of the cohesive and adhesive forces or by weakening the intermo-lecular, intramolecular, van der Waals and other physio-chem-ical forces. They also reduce the mechanical interlocking forces by lubricating the interface surface with a thin film to increase the separation between the mud cake and the pipe. Various

spotting fluids will perform differently even in the presence of a mud cake of the same composition. Therefore, not only the mud cake composition, but also the composition of a spotting fluid — along with the base fluids used to formulate a spotting fluid — can significantly affect the ease of recovery of a stuck pipe. Randomly selecting a spotting fluid without any prior laboratory evaluation reduces the probability of a successful rescue operation, and therefore, reduces the likelihood of miti-gation of the related NPT.

The varied performance of different spotting fluids is due to the variation in their composition and in the carrier fluids used in their formulation. This is well-known to the industry and is reflected in Adams (1977)13, a review of case studies conducted using field data. The review of 310 case studies related to the recovery of differentially stuck pipes found that only 44% of rescue operations were successful. Two factors in the poor suc-cess rate were improper mud displacement due to channeling of the spotting fluid and the use of inadequate volumes of the spotting fluid. These are in addition to the effect of the spot-ting fluid composition.

Krol (1981)14 demonstrated how the performance of differ-ent spotting fluids varied due to their composition and base fluids using a specially designed test simulator. He highlighted the various working mechanisms associated with spotting fluid components and their capacity to cause damage or degradation of mud cake pipe interface bonds. His simulation explained why some chemicals and surfactant-based spotting fluids work better than others. Haden and Welch (1961)8 noted the easy recovery of a stuck pipe in the presence of certain surfactants in addition to the effect of mud and mud cake composition in recovering a stuck pipe. According to the authors, some drill-ing muds and their deposited mud cakes require greater force to dislodge a stuck pipe. As the strength of spotting fluid in-teractions varies significantly depending on the nature and chemistry of the components used in their formulations, they showed variable performance in the presence of this partic-ularly sticky mud cake. In general, glycol-based spotting flu-ids showed superior performance and greater ease of recovery than oil-based spotting fluids. Ayers Jr. et al. (1989)15 con-ducted a survey to compare diesel-based and mineral oil-based spotting fluids for effectiveness in freeing stuck pipes in the Gulf of Mexico between 1983 and 1986. According to the au-thors, the success rate was about 51% when a diesel pill was applied and 33% when mineral oil pills were used. Most op-erators consider diesel superior for freeing stuck pipes. As pre-viously noted, the mud cake composition and the chemistry of the mud additives influence the performance of a spotting fluid, which can show superior performance in the presence of one mud cake but not show the same performance in the presence of another mud cake with a different chemical composition.

Differential pressure sticking is a nightmare for rig crews, which always try to avoid it in the first place, and if a pipe is stuck, make every effort to recover it as quickly as possi-ble. Delay in recovering a stuck pipe progressively increases


the contact between the mud cake and pipe interface as the mud cake matrix fluid is expelled under the overbalance pressure effect. In addition, delay may lead to further com-plications by triggering other drilling problems. Outmans (1974)16 highlighted the importance of placing the spotting fluid immediately after a pipe sticking event. Clark and Alm-quist (1992)17 used a full-scale differential pressure simulator to evaluate the performance of various spotting fluids. Based on the test results, the authors concluded that the time taken to place a spotting fluid in the stuck zone has an effect on the time required to release a stuck pipe. This dictates that a spot-ting fluid be placed in the vicinity of a stuck zone as soon as possible. Ayers Jr. et al (1989)15 also noted the need for quick placement of spotting fluid, especially diesel pills. But it needs to be a highly compatible and high performance spotting fluid that is suitable for the particular mud cake. There are no tech-nical benefits from using an incompatible and low perform-ing spotting fluid even if it is placed quickly to recover a stuck pipe. This dictates first conducting a laboratory evaluation of the various spotting fluids supplied by different vendors to make the correct selection for a stuck pipe recovery job.

In addition to the quick placement of a suitable spotting fluid in the stuck zone, the allowance of an appropriate soak-ing time is very important for effective infiltration of the spot-ting fluids into both the mud cake matrix and the mud cake/pipe interface. Outmans (1974)16 highlighted the need for ade-quate soaking time. This again dictates the quick screening and evaluation of various spotting fluids available from various vendors and service companies, in this case to identify the opti-mum soaking time.

This article describes a simple and easy test method and the apparatus it uses to make a reliable prediction of the per-formance of various spotting fluids on a particular mud cake, along with the soaking time required.

MUD CAKE SPOTTING FLUID INTERACTION MECHANISMS

Figure 1 shows the formation of numerous sticking bonds at the mud cake/metal ball interface. Some mud cakes form weaker interfacial and matrix bonds and so are easier to break during a rescue job, and some mud cakes produce stronger sticking bonds.

Figure 2 shows the infiltration of a spotting fluid into the mud cake matrix and the metal ball/mud cake interface. Infil-tration of a spotting fluid into the mud cake matrix reduces the differential pressure acting in the direction of the high permea-bility formation and so reduces the mechanical push of the for-mation pressure and the bending force of the metal ball (pipe). The entry of the fluid also causes weakening, degradation and damage to the cohesive and adhesive bonds within the matrix. Fluid infiltration into the mud cake/metal ball (pipe) interface increases the separation distance between the two, has a loos-ening effect and produces a lubricating action. The shrinkage,

dehydration and cracking of the mud cake matrix due to the action of the spotting fluid also reduces the contact area and the number of effective sticking bonds. The cracking of the mud cake in addition makes it more permeable to the spotting fluid, leading to further damaging and weakening of the stick-ing bonds. All these factors help in reducing the pulling force required to unstick the pipe.

DEVELOPMENT OF TEST APPARATUS

For quantitative evaluation of the effectiveness of various con-ventional and newly developed spotting fluids, a novel test setup and laboratory method have been developed. Figure 3 shows a schematic diagram of the test setup.

The test apparatus includes a load cell that is coupled to communicate with a control system to control the loading and unloading at a constant displacement rate during the test-ing. The load cell can measure up to 50 kilograms-force (kgf) during the pulling and embedment stages of testing. It includes a carrier arm mounted on a stand for communication with the control panel. The stand can lower and raise the carrier arm to place the spherical foot at the desired location relative to the mud cake.

There are upper and lower position limiters mounted adja-

Fig. 1 Fig. 2

Matrix Material Bonds

Mud Cake

Loading and Unloading Arm

Stuck Spherical

Ball

Interfacial Bonds


Mud Cake


Stuck Spherical

Ball

Interfacial Bonds

Spotting Fluid

Fig. 1. Diagram showing interfacial and matrix bonds at the spherical ball/mud cake contact region before spotting.

Fig. 2. Diagram showing interfacial and matrix bonds at the spherical ball/mud cake contact region after spotting.

Fig. 1 Fig. 2


Mud Cake


Stuck Spherical

Ball

Interfacial Bonds


Mud Cake


Stuck Spherical

Ball

Interfacial Bonds

Spotting Fluid


cent to the load stand to set the upper and lower movement

limits of the carrier arm during the test. The setup includes a

PC and a PC-based data acquisition system to record and dis-

play the test data while running the test. The control panel

for the test frame allows the setting of desired test parame-

ters, which are controlled using a dedicated operating software

module. It also has an emergency stop button to terminate the

test if the load exceeds the capacity of the load cell. The mud

cake, prepared by using the API filter press and API filtration

test, is transferred to a modified API test cell that has an inlet

and an outlet port. Then the modified API test cell is fixed on

the mounting table of the test frame. The mud cake in the cell

is assumed to be representative of the mud cake present in the

wellbore, and the spherical ball is assumed to simulate the area

of mud cake/pipe contact.

Method Development

The fully automated test method uses a PC-based operating

and data logging software module to control the test parame-

ters and record the experimental data. The data logger also in-

cludes an output device to display the test data on-screen. The

graphically displayed data allows for the termination of the

test after recording the peak pulling force. The test procedure

developed for the evaluation of the performance of various

spotting fluids is as follows:

• Prepare the mud cakes using the API filter press or an-

other high-pressure, high temperature test apparatus.

Run the API filtration test for enough time to produce a

mud cake of more than 10 mm thickness to avoid any

artifacts associated with thinner mud cakes.

• After the preparation of the mud cake, transfer it from

the API test cell to the spotting fluid evaluation test cell

equipped with an inlet and outlet port to circulate a

spotting fluid.

• Position the modified API test cell containing the mud

cake in the load frame using a special positioning device.

Set it properly to prevent any movement while testing.

• Set the test parameters using the dedicated operating

software module, which ensures the same test condi-

tions apply for all the tests as well as before and after

the mud cake and spotting fluid interactions.

• Embed the spherical foot into the mud cake matrix at a

fixed rate of downward displacement until a 5 mm em-

bedment depth is reached.

Fig. 3

Fig. 5

Forc

e (k

g)

Distance (mm)

— Test 1 — Test 2 — Test 3

Fig. 3. Test apparatus for spotting fluid performance evaluation.


• Allow some time for stabilization of the embedded foot/mud cake interface.

• Measure the initial pull resistance at a constant rate of upward displacement in the absence of any spotting fluid.

• Perform analyses of the test curves to determine the sticking bond modulus (SBM) and the ultimate sticking bond strength (USBS) for the original mud cake. Repeat the tests three times to get a reliable average value.

• Prepare another mud cake, using the same mud com-position and preparation method, and transfer the mud cake to the spotting fluid evaluation test cell.

• Set the test cell in the test frame as before and embed the spherical foot up to 5 mm depth.

• Place the spotting fluid in the test cell through the inlet port up to the outlet port level. Allow for the optimum soaking time.

• After the soaking period, measure the pull resistance at the same constant rate of upward displacement that was used in the absence of any spotting fluid.

• Analyze the test curve to determine the SBM and the USBS after the spotting fluid and mud cake interactions. Repeat the tests three times to get a reliable average value.

MUD SELECTION

To evaluate the suitability of the test apparatus and method outlined above, a weighted potassium chloride (KCl) polymer mud was used to prepare the mud cake. Table 1 shows the composition of the weighted KCl polymer mud.

SPOTTING FLUIDS EVALUATED

Three commercial spotting fluids were used for evaluating the suitability of the newly developed test apparatus and labora-tory method for screening spotting fluids. Tables 2 and 3 show the formulations of two commercial non-aqueous spotting flu-ids, and Table 4 shows the formulation of a glycol-based spot-ting fluid, all of which were used for this evaluation.

EXPERIMENTAL PROCEDURE

The comprehensive experimental procedure is composed of several distinct steps to accurately simulate the various ele-ments associated with a pipe sticking event and a stuck pipe recovery operation. A detailed description of all steps is pro-vided next.

Mud Cake Preparation

The first step of the test is the preparation of a mud cake to simulate the deposition of mud cake on the borehole wall. An

KCl Polymer Mud

Make up water bbl 0.784

XC polymer ppb 0.75 – 1.0

Starch ppb 4.0 – 6.0

PAC-L ppb 0.5 – 1.0

KCl ppb 37

KOH ppb 0.25

Lime ppb 0.25

Barite ppb 257

Sodium Sulfite ppb 0.25 – 0.30

Soltex ppb 2.0 – 4.0

CaCO3 medium ppb 20

Table 1. Weighted KCl polymer mud used for mud cake preparation

EZ SPOT® Spotting Fluid

Components Field

Formulation (bbl)

Concentration (%)

Lab Formulation

(ml)

Diesel 64 0.64 224.34

EZ SPOT® 7.85 0.08 27.52

Water 28 0.28 98.15

Total Volume

99.85 — 350.00

Table 2. Field and lab formulations of EZ SPOT® spotting fluid

Pipe-Lax Spotting Fluid

Components Field

Formulation (bbl)

Concentration (%)

Lab Formulation

(ml)

Diesel 64 0.64 224.34

Pipe-Lax 7.85 0.08 27.52

Water 28 0.28 98.15

Total Volume

99.85 — 350.00

Table 3. Field and lab formulations of Pipe-Lax spotting fluid

Glycol-Based Spotting Fluid

Components Field

Formulation (bbl)

Concentration (%)

Lab Formulation

(ml)

Glycol 85.1 0.80 281

Lubricant 15.7 0.15 52

Pipe-Lax 5.23 0.05 17

Total Volume

99.85 — 350.00

Table 4. Field and lab formulations of a glycol-based spotting fluid


API filter press, Fig. 4, is used to prepare the mud cake using a modified filtration procedure. The result is a mud cake of 10 mm or more thickness, the minimum thickness needed to avoid any artifacts while testing and also to improve data reliability and accuracy. In the modified filtration procedure, instead of the 30-minute filtration time recommended by API, a filtration time period that is sufficient to prepare a mud cake thickness of 10 mm or more is used.

Embedment of the Spherical Foot

After preparation of the mud cake in the API test cell, the mud cake is removed carefully and washed gently to remove the soft, gel-like mud material from the top of the mud cake. Then the mud cake is transferred to the spotting fluid test cell, which has the same inner diameter as the API test cell but is lower in height. In addition, the spotting fluid test cell has an inlet through which to place the spotting fluid and an outlet to re-move the spotting fluid after it circulates; the goal is to main-tain a constant level of spotting fluid in the test cell during the soaking and interaction period. After transferring the mud cake to it, the spotting fluid test cell is tightly fixed on a metallic bench to keep the setup stable during the testing and evalua-tion process. A spherical foot, used to simulate a tiny section of pipe, is embedded into the mud cake matrix using controlled downward displacement of the spherical foot at a rate of 0.5 mm/sec until an embedment depth of 5 mm is reached. After the embedment of the foot, 2 minutes are allowed to stabilize the foot position, the mud cake/foot interface and the mud cake matrix material. At this point, the initial starting readout is set at zero for the pulling test using the operating software.

Placement of the Spotting Fluid

After the embedment and stabilization, a spotting fluid is placed in the spotting fluid test cell and circulated until the top of the spotting fluid reaches 10 mm to 15 mm above the top of the mud cake or exits through the spotting fluid outlet to be collected in a collection tank.

Soaking Time for Spotting Fluid Mud Cake Interactions

Usually 12 to 16 hours soaking time is used in the field to complete the spotting fluid and mud cake interactions, which include dehydration, degradation, infiltration and lubrication. Because this is too long for quick screening of a large num-ber of spotting fluids, two soaking times are used to evaluate the debonding, degrading and damaging effects of the spotting fluid on the adhesive and cohesive forces causing the foot to stick to the mud cake matrix. A 6-hour soaking time deter-mines short-term effects, and a 16-hour soaking times estab-lishes long-term effects.

Application of Pulling Force

After the soaking/interaction time is over, a pulling force is applied using the apparatus previously shown in Fig. 3. This is done under the same test conditions used before to test the mud cake without any spotting fluid. During the pulling test, the force vs. the displacement curve is recorded automatically by the dedicated software, which also ensures the same test conditions apply across all the tests. The software also pro-vides an on-screen display of the test data so the test can be terminated after recording the maximum pulling force.

EXPERIMENTAL RESULTS

Figure 5 shows the pulling force vs. the displacement curve of the KCl polymer mud cake in the absence of any spotting fluid. The slope of the initial linear part of the curve was used to de-termine the SBM of the mud cake. The peak force of the curve indicates the USBS of the original mud cake. The tests were repeated three times to get an average value of the SBM and USBS of the original KCl polymer mud cake.

Table 5 shows the individual and averaged SBM and USBS values for the KCl polymer mud cake in the absence of any spotting fluid. The table also shows the correlation coefficient

Fig. 4. API filter press and the filtration test apparatus used for mud cake preparation.

Fig. 5. Pulling force vs. the displacement curve of mud cake without any spotting fluid interactions. Table 5. The SBM and USBM of KCl polymer mud cake with no spotting fluid interactions

Test No. Correlation Coefficient

SBM (Slope) USBS (Max Pulling Force)

kgf/mm kgf Test 1 (No Spotting Fluid) 0.999 40.73 6.35 Test 2 (No Spotting Fluid) 0.997 36.93 5.93 Test 3 (No Spotting Fluid) 0.997 37.07 5.76 Average ---- 38.24 6.01 S.D. ---- 2.16 0.30 Coef. of Variation ---- 5.64 5.00

Fig. 4. API filter press and the filtration test apparatus used for mud cake preparation.

Fig. 5

0

1

2

3

4

5

6

7

0 2 4 6 8 10 12 14 16

Forc

e (k

g)

Distance (mm)

Test 1

Test 2

Test 3

Fig. 5. Pulling force vs. the displacement curve of mud cake without any spotting fluid interactions.


of the fitted curve used to determine the SBM, along with the coefficient of variation in the experimental data to demonstrate the statistical significance of the test results. These characteris-tic values of the untreated KCl polymer mud cake will be used to compare the performance of various spotting fluids by de-termining the percent reduction in the SBM and the USBS in the presence of the spotting fluids. The capacity of a spotting fluid to reduce these values is directly related to the dehydrat-ing, damaging and lubricating properties of the spotting fluid, and so can provide a relative ranking of the performance of various spotting fluids to enable engineers to select the most suitable fluid for a stuck pipe recovery operation.

Figures 6 to 8 show the pulling force vs. the displacement curves of the KCl polymer mud cake in the presence of three different spotting fluids after 6 hours of soaking time. These curves were used to determine the average SBM and USBS val-ues of the KCl polymer mud cake after its interaction with the spotting fluids for comparison with the original mud cake val-ues to evaluate the short-term effect. Tables 6 to 8 show the SBM and USBS values of the KCl polymer mud cakes after 6 hours of mud cake interactions with the three spotting fluids. Figures 9 to 11 show the pulling force vs. the displacement curves of the three spotting fluids after 16 hours of soaking time. As before, these curves were used to determine the aver-age SBM and USBS values of the KCl polymer mud cake after these interactions with the spotting fluids for comparison with original mud cake values, in this case to evaluate the long-term effect. Tables 9 to 11 show the SBM and USBS values of the KCl polymer mud cakes after 16 hours mud cake interactions with the three spotting fluids.

DISCUSSION

The load displacement curves of the pulling force needed for

recovering the spherical foot from the original mud cake ma-trix with no spotting fluid — Fig. 5 — shows a much higher pulling force compared to that required for the same mud cake in the presence of the spotting fluids, Figs. 6 to 11. The orig-inal mud cake has a USBS of 6 kgf and a SBM of 38.24 kgf/

Test No.Correlation Coefficient

SBM (Slope)USBS (Max

Pulling Force)

kgf/mm kgf

Test 1 (No Spotting Fluid)

0.999 40.73 6.35


0.997 36.93 5.93


0.997 37.07 5.76

Average — 38.24 6.01

S.D. — 2.16 0.30

Coef. of Variation

— 5.64 5.00

Table 5. The SBM and USBM of KCl polymer mud cake with no spotting fluid interactions

Fig. 8

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 2 4 6 8 10 12 14 16

Forc

e (k

g)

Distance (mm)

Test 1Test 2Test 3

Fig. 8. Pulling force vs. the displacement curve of mud cake after 6 hours of soaking with a glycol-based fluid.

Fig. 7. Pulling force vs. the displacement curve of mud cake after 6 hours of soaking with Pipe-Lax spotting fluid.

Fig. 6

0

0.5

1

1.5

2

2.5

3

3.5

0 2 4 6 8 10 12 14 16

Forc

e (k

g)

Distance (mm)

Test 1Test 2Test 3

Fig. 6. Pulling force vs. the displacement curve of mud cake after 6 hours of soaking with EZ SPOT® spotting fluid.

Fig. 7

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 2 4 6 8 10 12 14 16

Forc

e (k

g)

Distance (mm)

Test 1Test 2Test 3


mm — Table 5.

The test curves generated after 6 hours of soaking time in

the presence of EZ SPOT® spotting fluid gave an average SBM

value of 33.92 kgf/mm and an average USBS value of 2.81

kgf — Table 6. The curves generated after 16 hours of soak-

ing time gave an average SBM value of 22.28 kgf/mm and

an average USBS value of 1.5 kgf — Table 9. Calculation of

the percent reduction in the SBM and the USBS after 6 hours



Pulling Force)

kgf/mm kgf

EZ SPOT® 6 hr (Test 1)

0.991 33.349 3.11


0.992 33.186 2.87


0.974 35.213 2.46

Average — 33.92 2.81

S.D. — 1.13 0.33

Coef. of Variation

— 3.33 11.74

Table 6. The SBM and USBM of KCl polymer mud cake after 6 hours of interaction with EZ SPOT® spotting fluid



Pulling Force)

kgf/mm kgf

Pipe-Lax 6 hr (Test 1)

0.983 22.35 1.26


0.984 21.08 1.23


0.989 24.61 1.32

Average — 22.68 1.27

S.D. — 1.79 0.047

Coef. of Variation

— 7.89 3.69

Table 7. The SBM and USBM of KCl polymer mud cake after 6 hours of interaction with Pipe-Lax spotting fluid



Pulling Force)

kgf/mm kgf

Glycol 6 hr (Test 1)

0.990 20.120 0.583


0.972 21.204 0.636


0.983 23.634 0.578

Average — 21.653 0.599

S.D. — 1.799 0.032

Coef. of Variation

— 8.31 5.34

Table 8. The SBM and USBM of KCl polymer mud cake after 6 hours of interaction with a glycol-based spotting fluid

Fig. 11. Pulling force vs. the displacement curve of mud cake after 16 hours of soaking with a glycol-based spotting fluid.

Fig. 10

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

0 2 4 6 8 10 12 14 16

Forc

e (k

g)

Distance (mm)

Test 1Test 2Test 3

Fig. 10. Pulling force vs. the displacement curve of mud cake after 16 hours of soaking with Pipe-Lax spotting fluid.

Fig. 9. Pulling force vs. the displacement curve of mud cake after 16 hours of soaking with EZ SPOT® spotting fluid.

Fig. 9

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

0 2 4 6 8 10 12 14 16

Forc

e (k

g)

Distance (mm)

Test 1Test 2Test 3

Fig. 11

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 2 4 6 8 10 12 14 16

Forc

e (k

g)

Distance (mm)

Test 1Test 2Test 3


soaking time indicates more than 11% and 53% reduction of the SBM and USBS, respectively, Table 12. Calculation of the percent reduction in the SBM and USBS after 16 hours of

soaking time indicates about 42% and 75% reduction of SBM and the USBS, respectively, Table 12. The data clearly indi-cates that the EZ SPOT® fluid is able to reduce the SBM and USBS of the mud cakes significantly after 6 and 16 hours of soaking time. As the tests indicate a significantly higher reduc-tion of the SBM and the USBS after 16 hours of soaking time compared to 6 hours of soaking time, the 6 hours of soaking time is clearly not sufficient to complete the mud cake’s com-prehensive interaction in the presence of the EZ SPOT® spot-ting fluid. Therefore, a longer soaking time is needed for the EZ SPOT® spotting fluid to damage and degrade the sticking bonds formed by the mud cake in the interface.

The test curves generated after 6 hours of soaking time in the presence of the Pipe-Lax spotting fluid gave an average SBM value of 22.68 kgf/mm and an average USBS value of 1.27 kgf — Table 7. The curves generated after 16 hours of soaking time gave an average SBM value of 30.43 kgf/mm and an average USBS value of 1.75 kgf — Table 10. Calculation of the percent reduction in the SBM and the USBS after 6 hours of soaking time indicates more than a 40% and 78% reduc-tion of the SBM and USBS, respectively, Table 12. Calculation of the percent reduction in the SBM and USBS after 16 hours of soaking time indicates more than a 20% and 71% reduc-tion of the SBM and the USBS, respectively, Table 12. The data clearly indicates that the Pipe-Lax spotting fluid is able to reduce the SBM and USBS values of the mud cakes signifi-cantly after 6 and 16 hours of soaking time. The tests indicate a somewhat lower reduction of the SBM and USBS values af-ter 16 hours of soaking time compared to 6 hours of soaking time, which suggests that a hardening effect on the sticking bonds in the presence of the Pipe-Lax spotting fluid was revers-ing the original degradation effect. The results further suggest that extending the soaking time above an optimum period for a spotting fluid has little benefit and may lead, in fact, to the need for a higher pulling force to unstick the pipe.

These results show why it is advisable to evaluate the per-formance of various spotting fluids in the lab to identify the optimum soaking time for maximum ease of recovery of a stuck pipe. Based on this observation, it can be concluded that the newly developed test apparatus and method may play a pivotal role in determining the optimum soaking and interac-tion times for various conventional and new spotting fluids, which can serve to guide the rig crews in their selection and application of a spotting fluid.

The test curves generated after 6 hours of soaking time in the presence of a glycol-based spotting fluid gave an average SBM value of about 22 kgf/mm and an average USBS value of 0.6 kgf — Table 8. The curves generated after 16 hours of soak-ing time gave an average SBM value of about 23 kgf/mm and an average USBS value of about 0.6 kgf — Table 11. Calcula-tion of the percent reduction in the SBM and the USBS after 6 hours of soaking time indicates about a 43% and 90% reduc-tion of the SBM and USBS, respectively, Table 12. Calculation of the percent reduction in the SBM and USBS after 16 hours of



Pulling Force)

kgf/mm kgf


0.992 17.11 1.49


0.985 24.65 1.43


0.990 25.07 1.57

Average — 22.28 1.5

S.D. — 4.48 0.069

Coef. of Variation

— 20.12 4.61

Table 9. The SBM and USBM of KCl polymer mud cake after 16 hours of interactions with EZ SPOT® spotting fluid



Pulling Force)

kgf/mm kgf


0.993 28.835 1.825


0.993 30.706 1.758


0.994 31.739 1.653

Average — 30.427 1.745

S.D. — 1.472 0.087

Coef. of Variation

— 4.84 4.98

Table 10. The SBM and USBM of KCl polymer mud cake after 16 hours of interactions with Pipe-Lax spotting fluid



Pulling Force)

kgf/mm kgf


0.988 23.765 0.560


0.982 25.346 0.727


0.970 20.113 0.500

Average — 23.075 0.596

S.D. — 2.684 0.118

Coef. of Variation

— 11.63 19.80

Table 11. The SBM and USBM of KCl polymer mud cake after 16 hours of interactions with a glycol-based spotting fluid


soaking time indicates about a 40% and 90% reduction of the SBM and the USBS, respectively, Table 12. This result indicates no/negligible reduction in the SBM and USBS after 6 hours of soaking time. The data clearly indicates that the glycol-based spotting fluid is able to reduce the SBM and USBS of the mud cakes significantly within a short time interval. The data further indicates that the longer soaking time has no significant benefit for this spotting fluid, which achieves a full and complete inter-action within an optimum time of short duration.

Evaluation of the performance of the three spotting fluids used in this study indicates that the glycol-based fluid is very effective in causing damage and degradation of the sticking bonds formed between the mud cake and the spherical metal-lic ball. The Pipe-Lax spotting fluid test result provides two valuable pieces of information. First, it indicates that a shorter time is needed for interactions to cause damage, degradation and weakening of the sticking bonds of the mud cake/metal interface in the presence of this fluid. This is reflected in the dramatic drop of SBM and USBS values after 6 hours of soak-ing time. Second, the data indicates that long-term interaction has a hardening effect on the sticking bonds in the presence of the Pipe-Lax spotting fluid. This is reflected in the higher SBM and USBS values after 16 hours of soaking time compared to 6 hours of soaking time.

Results for the glycol-based spotting fluid also provides two valuable pieces of information. First, it indicates that a shorter time is needed for interactions to cause damage, degradation and weakening of the sticking bonds of the mud cake/metal in-terface. The data further indicates that 6 hours or less of soak-ing time is enough for the glycol-based spotting fluid to achieve sufficient degradation of the sticking bonds. Second, the data indicates the absence of any long-term hardening effect in the presence of this spotting fluid. This is reflected by negligible changes in the SBM and USBS values after 16 hours of soaking time compared to 6 hours of soaking time.

Comparative analyses of the results for all the spotting flu-ids used in this study indicate that the glycol-based spotting fluid has the best performance in reducing the sticking bond strength, and therefore, is the most suitable one for recover-ing a stuck pipe from a similar mud cake matrix. The Pipe-Lax spotting fluid has a lower performance compared to the gly-

col-based spotting fluid, but better performance in weakening the sticking bonds and releasing the embedded spherical ball from the mud cake matrix compared to the EZ SPOT® spot-ting fluid. Therefore, the test provides valuable technical guide-lines and a decision making tool for mud and drilling engineers to use in selecting the most suitable spotting fluid to unstick a stuck pipe.

CONCLUSIONS

1. The method and apparatus described in this article allows quick screening and evaluation of the performance of various spotting fluids to select the best one for speedy recovery of a stuck pipe.

2. As the delay in recovery of a differentially stuck pipe is one of the major cost items that significantly increase total drilling cost, the proposed method will help reduce the NPT and significantly reduce the drilling cost.

3. The pulling force vs. the upward displacement curve allows the determination of two quantitative index parameters, defined as the SBM and the USBS, which can be used to evaluate the performance of various spotting fluids.

4. The slope of the initial linear part of the pulling force vs. the upward displacement curve defines the SBM, and the peak value of the curve indicates the USBS.

5. Comparative evaluation of these two index parameters derived from tests of mud cake in the presence of various spotting fluids can provide technical guidelines to mud engineers to select the best spotting fluid for improving the probability and likelihood of the success of a rescue operation.

6. Spotting fluids that damage, degrade and weaken the sticking bonds can improve the success rate of a recovery job significantly.

7. Some spotting fluids need more soaking time than others to be effective in causing adequate damage and degradation of mud cakes and the sticking bonds acting at the mud cake/metal interface.

8. Due to the variation in the composition, chemistry and physics of various spotting fluids, they may show

Mud Cake — Spotting Fluid CombinationAverage SBM

(kgf/mm)Average USBS

(kgf)SBM Reduction

(%)USBS Reduction

(%)

Mud Cake — No Spotting Fluid 38.24 6.01 — —

Mud Cake EZ SPOT® 6 hr 33.92 2.81 11.30 53.24

Mud Cake Pipe-Lax 6 hr 22.68 1.27 40.69 78.87

Mud Cake Glycol 6 hr 21.65 0.6 43.38 90.02

Mud Cake EZ SPOT® 16 hr 22.28 1.5 41.74 75.04

Mud Cake Pipe-Lax 16 hr 30.43 1.75 20.42 70.88

Mud Cake Glycol 16 hr 23.08 0.596 39.64 90.08

Table 12. Average SBM and USBS values and percent reduction of KCl polymer mud cake after interactions with three spotting fluids


significantly different performance in recovering a stuck pipe.

9. Experimental results indicate that some spotting fluids may have poor short-term performance but excellent long-term performance after an optimum soaking time. Therefore, identification of the optimum soaking time for each type of spotting fluid is very important.

10. Some spotting fluids may show excellent short-term performance but poor long-term performance due to some hardening of the sticking bonds linking the metal surface to the mud cake matrix. It again demonstrates the importance of the determination of optimum soaking time to improve the ease of recovery of a stuck pipe.

11. The experimental results presented in this article indicate the best performance was achieved by the glycol-based spotting fluid compared to the oil-based spotting fluids used for comparative evaluation.

12. The spotting fluid that requires the least force to recover the stuck metallic object should be selected to recover a stuck pipe in a borehole environment.

13. The newly developed test apparatus and method provide a useful tool to the industry to provide judicial guidelines in selecting the superior spotting fluid for a stuck pipe rescue operation instead of relying on random selection.

14. Routine application of the method in evaluating various spotting fluids will improve the success rate of a stuck pipe recovery job.

ACKNOWLEDGMENTS

The authors would like to thank the management of Saudi Aramco for their support and permission to publish this arti-cle. The authors also cordially acknowledge the support and encouragement from EXPEC ARC management for this pi-oneering research. Our sincere thanks to Eric Moellendick, DTT Chief Technologist, for his support for this innovative re-search. Special thanks to Omar Fuwaires, Turkie Alsubaie and Ali Radwan for testing and commissioning of the newly devel-oped method and apparatus.

This article was presented at the SPE Kingdom of Saudi Arabia Annual Technical Symposium and Exhibition, Dam-mam, Saudi Arabia, April 24-27, 2017.

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BIOGRAPHIES

Dr. Md. Amanullah is a Petroleum Engineering Consultant working at Saudi Aramco’s Exploration and Petroleum Engineering Center – Advanced Research Center (EXPEC ARC). Prior to joining Saudi Aramco, he worked as a Principal Research Sci-

entist at CSIRO in Australia. Aman is the lead inventor of a vegetable oil-based

dielectric fluid (patented) that led to the formation of a spinoff company in Australia for commercialization of the product.

He has published more than 80 technical papers and filed 40 patents, with nine already granted. Two of Aman’s patents were highlighted in scholarly editions of two books published in the U.S. He is one of the recipients of the 2005 Green Chemistry Challenge Award from the Royal Australian Chemical Institute. Aman also received the CSIRO Performance Cash Reward in 2006, the Saudi Aramco Mentorship Award in 2008 and the World Oil Certificate Award for nano-based drilling fluid development in 2009. He is a member of the Society of Petroleum Engineers (SPE). Aman received the 2014 SPE Regional Service Award for his contribution to the industry.

He received his M.S. degree (First Class) in Mechanical Engineering from the Moscow Oil and Gas Institute, Moscow, Russia, and his Ph.D. degree in Petroleum Engineering from Imperial College, London, U.K.

Mohammed K. Al-Arfaj joined Saudi Aramco in 2006 as a Petroleum Engineer, working with the Drilling Technology Team in the Exploration and Petroleum Engineering Center – Advanced Research Center (EXPEC ARC). He works in the area of drilling

and completion, and has conducted several projects in the areas of shale inhibition, drilling nano-fluids, loss circulation materials, spotting fluids, swellable packers, completion fluids and oil well cementing.

Mohammed received his B.S. degree in Chemical Engineering from King Fahd University of Petroleum and Minerals (KFUPM), Dhahran, Saudi Arabia, in 2006. In 2009, he received his M.S. degree in Petroleum Engineering from Heriot-Watt University, Edinburgh, Scotland. Mohammed is currently finalizing his Ph.D. study in Petroleum Engineering from KFUPM.

Novel Method and Apparatus for Sticking Fluid Performance ...€¦ · recovery of stuck pipe from a particular mud cake matrix. The method and apparatus promises to play an important

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