00079918

Copyright 2003, SPE/IADC Drilling Conference This paper was prepared for presentation at the SPE/IADC Drilling Conference held in Am-sterdam, The Netherlands, 19–21 February 2003. This paper was selected for presentation by an SPE/IADC Program Committee following review of information contained in an abstract submitted by the author(s). Contents of the paper, as presented, have not been reviewed by the Society of Petroleum Engineers or the International Association of Drilling Contractors and are subject to correction by the author(s). The material, as presented, does not necessarily reflect any position of the SPE, IADC, their officers, or members. Electronic reproduction, distribution, or storage of any part of this paper for commercial purposes without the written consent of the Society of Petroleum Engineers or the International Association of Drilling Contractors is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of where and by whom the paper was presented. Write Librarian, SPE, P.O. Box 833836, Richardson, TX 75083-3836, U.S.A., fax 01-972-952-9435.

Abstract Exploiting the Troll reservoir in the Norwegian North Sea requires horizontal drilling through relatively loose sandstone and local hard calcite-cemented zones. Depending on the orientation of the calcite interval, and the drilling parameters when entering or exiting the calcite interval, the bit can be forced aside to create a potentially severe local dogleg. High local doglegs introduce significant stresses into the drilling system that can rapidly accelerate fatigue of the BHA components and connections. Until recently, the driller could only identify local doglegs in the vertical plane when a rapid change of a near-bit inclination measurement was reported to the surface. No means were available for detecting azimuthal doglegs in the horizontal plane.

A new downhole dynamics tool, positioned above the rotary steerable system, is capable of measuring the bending moments in the BHA generated by side forces at the bit. If transmitted to the surface while drilling, the BHA bending information allows early detection and quantification of local doglegs independent of their orientation.

The paper explains the details of the bending moment measurement and the bending response of the BHA to local doglegs. Several field examples demonstrate the sensitivity of the measurement and the remedial actions initiated in response to the downhole BHA bending information. In one case drilling was stopped earlier than planned due to the detection of an extremely severe local dogleg, and a potentially catastrophic failure close to TD was avoided. Introduction The Troll field is one of the largest offshore gas fields in the world, extending into four blocks in the Norwegian North Sea over an area of about 770 square kilometers. It consists of two main structures, Troll East which is essentially a dry gas

structure, and Troll West which contains a thin but exploitable oil column (12-26m) below a thick gas column. The Troll West reservoir consists of the Upper Jurassic Sognefjord formation, a stacked series of sandstone units lying at a depth of approximately 1500 m below sea level. These sandstone units were formed by shoreline development on the northwestern edge of the Horda Platform during the Upper Jurassic. Clean medium to coarse-grained target sandstones alternate with finer, poorer quality non-target intervals. The shallow depth of burial has preserved good to excellent reservoir properties that are only locally reduced by calcite cementation. Calcite nodules and stringers up to several meters thick, derived from shell material within the sands, occur throughout the reservoir and can create difficulties for drilling. Many of the stringers have stratigraphic significance, but predicting their distribution is difficult as they are only locally developed. Other calcites are randomly scattered throughout the reservoir. The photograph of the Bridport Sands on the Dorset Coast of the UK shown in Figure 1 provides a good impression of the structure of the calcites in the Troll reservoir.

The oil reservoir is exploited through long horizontal sections of up to 3,200 m in length. Within the limitations posed by the thin nature of the oil column, these wells are geosteered through the reservoir to avoid non-productive zones and to keep the well path closely (+/- 0.5 m TVD) above the oil water contact. Fiksdal et al.1 have described in an earlier paper the work that has led to a better understanding of the drilling challenges posed by the calcite cemented intervals. The paper also describes the step change in drilling performance realized by introducing rotary steerable systems2 (RSS) with PDC bits.

Depending on the dip angle and the orientation of the calcite stringer surfaces, the condition of the bit and the drilling parameters when entering or exiting the calcite stringer, the bit can be forced aside into the more drillable loose sand. This behaviour can potentially result in high local doglegs (HLD) as exaggeratedly illustrated in Figure 2. The figure also shows the well path correction back to the original vertical depth in order to keep the required distance to the oil water contact. Depending on their severity, the doglegs in the well path introduce significant stresses into the BHA that can rapidly accelerate fatigue of the BHA components and connections. Several catastrophic downhole BHA failures, cracked component and mud intrusion events were clearly

SPE/IADC 79918

Real-Time BHA Bending Information Reduces Risk when Drilling Hard Interbedded Formations J. Hood, SPE, Baker Hughes INTEQ, J. Hovden, Norsk Hydro, G. Heisig, SPE, K.D. Ernesti, SPE, Baker Hughes INTEQ, and A. Knipper, SPE, Baker Hughes OASIS

2 SPE/IADC 79918

traced back to high local doglegs, as indicated by the near-bit inclination measurement of the RSS shown in figure 3. However, there were also cases with similar problems with no indication of a local dogleg in the vertical plane.

Driven by an initiative to further improve drilling performance and to better understand the downhole environment in Troll reservoir drilling, it was decided to deploy a new drilling dynamics tool along with the RSS. The concept, functionality and capability of this system have been described in detail in ref. 3. The downhole tool simultaneously processes high rate (1000 Hz) measurements from a total of 14 drilling process sensors and further diagnoses the occurrence and severity of various drilling dynamics phenomena. For the scope of this paper it is important to mention the capability of the tool to measure the bending moment in the BHA generated by side forces at the bit and at other wall contact points of the BHA. Figure 3 shows the position of the downhole dynamics tool with the bending moment measurement point in the bottom hole assembly.

Downhole bending moment data have been published in the literature earlier by Wolf et al.5 in 1985. However, the focus of their study as well as of the analysis later presented by Vandiver et al.6 was on drilling dynamics and the frequency content of the bending moment signal. Cook et al.7 presented in 1989, for the first time, bending moment data recorded during directional drilling operations with steerable motor systems.

This paper presents and discusses application of the downhole bending moment information with rotary steerable systems and formation induced well path changes. As the measurement of bending moment is not yet very common in the drilling industry, the paper starts with a brief review of bending moment theory and measurement.

Bending Moment – Theory and Measurement Any bottom hole assembly deviated from vertical is subjected to bending moments due to side forces acting on the BHA. Side forces are introduced by gravity, by dynamic effects or at wall contacts of the BHA in borehole sections with planned or unplanned doglegs. Figure 4 illustrates the bending moment distribution along the BHA presented in figure 3. The bending moment distribution was calculated with a proprietary finite-element model of the BHA assuming a perfectly straight, in-gauge horizontal wellbore. In this case, the side forces in the lower part of the picture are the wall contact forces calculated to balance the weight of the BHA and the steering force at the steerable stabilizer of the RSS. In general, the location of the BHA wall contact points, the magnitude of the resulting contact forces as well as distribution and magnitude of the bending moment, all depend strongly on the geometry of the wellbore section, i.e. well path, local curvatures, over-gauged section etc.

Figure 5 schematically shows the bending stress distribution σ(y) in a cross section of the BHA introduced by the bending moment M at that position. The stress in a “fiber” with distance y from the center axis is

( ) yI

My =σ , …………………………..(1)

where M is the bending moment and I is the moment of inertia of the BHA cross section. The bending stresses σ(y) act in the axial direction and can significantly exceed the stresses introduced by the weight-on-bit (WOB). As shown in figure 5, the fibers on the outside diameter are subjected to the highest stresses. Rotation of the BHA leads to cyclic loading of the material between tension and compression. Depending on the magnitude of the bending moment, this can rapidly accelerate fatigue of the material and ultimately introduce cracks into the BHA components.

The bending stresses in figure 5 shorten the fibers on the side of the BHA in compression and extend the fibers on the side of the BHA in tension. As a result, the BHA elastically deforms – it bends. The relationship between the resulting curvature of the deformed BHA and the bending moment at any given point in the BHA is

EIM

=κ , ……………………………..(2)

where κ denotes the curvature and E is the modulus of elasticity. The term EI is very often referred to as bending stiffness. Eq. (1) and (2) represent the basic relationships between bending moment, bending stress and the resulting elastic deformation in the string. The equations for the full three-dimensional case are beyond the scope of this paper and can be found in ref. 8 or in other mechanical engineering textbooks. The relationships introduced above are not valid for areas in the BHA with discontinuities in the bending moment or the bending stiffness. In particular, abrupt changes in BHA diameter and local features such as pockets or cut-outs in the BHA lead to local stress concentrations that are more difficult to analyze.

The bending moment in the BHA can be measured by applying two strain gauges each on opposite sides of the BHA and connecting them to a measurement bridge. Strain gauges change their resistance by a small amount when subjected to an elastic deformation, resulting in a small output signal from the measurement bridge. After analog-to-digital conversion the signal is multiplied by a scale factor determined in expensive calibration procedures in which each tool is subjected to pre-defined bending moment cycles. The downhole tool utilized for the measurements presented in this paper features two measurement bridges perpendicularly arranged to measure the bending moment in the rotating BHA. The total bending moment is then determined as the vector sum of the individual signals of the two axes,

22yxtotal MMM += …………………………..(3)

The measurement in the downhole tool is updated every 5 seconds and recorded in the on-board memory. The interval between MWD transmissions to the surface typically varies between 90 and 180 seconds depending on selected transmission format and speed. It is worthwhile mentioning that the tool also utilizes the individual bending signals to diagnose detrimental downhole BHA whirl. This application has shown to be extremely valuable in field applications4.

SPE/IADC 79918 3

Field Examples The data presented in Figures 6-9 were recorded on different wells on Troll West in 2001 and 2002. Figures 6-8 are depth-based log excerpts of drilling process data recorded at surface and downhole, along with formation data. Figure 9 is a time-based log excerpt of drilling process data. For the interpretation of the depth-based logs it is important to keep in mind that the gamma and density data, the hole caliper and the bending moment data are plotted at sensor depth while all other data are plotted at bit depth. This is illustrated in Figure 6 in which the black dots mark a set of data recorded at the same point in time. While the bending moment sensors are located 13.9 m behind the bit, it will be demonstrated in the examples below that the sensors respond to doglegs in the well path between bit and sensor position due to the “transmission” of the bending signal along the BHA.

The logs presented are based on memory data for maximum log quality. The equivalent logs available while drilling, and based on transmitted data, have a data density which is generally lower and depends on the rate of penetration (ROP) and the selected data transmission interval. Example 1: The log excerpt in Figure 6 shows data from the last 75 m of the reservoir section of well 31/2-N-23A Y1H. The interval was drilled with an 8 ½” Tungsten Carbide Insert (TCI) roller cone bit at rotary speeds of 50–100 RPM. From 4325 m onwards, the lithology was mostly calcite-cemented sandstone with short intervals of looser sandstone, as indicated by the variation in the density data and the corresponding washouts in the borehole caliper. The ROP varied between 1-2 m/hr in the calcite intervals and about 6-8 m/hr in the sand. The inclination angle measured in the RSS 1.1 m behind the bit stayed close at 90°; the bending moment varied between 8-12 kNm in this interval.

At 4345 m the near bit inclination angle started to increase slightly. In response, an attempt was made to steer the bit downwards. The WOB was reduced to control the ROP and to give the bit time to cut into the rock on the low side of the hole. However, the near bit inclination continued increasing and finally rose dramatically by 4° over a distance of less than five meters. The inclination stabilized at 95° and then decreased slightly while drilling with high WOB and low ROP. About 8 m after the start of the steep increase of the near bit inclination the bending moment started to increase significantly and reached a maximum value of 67 kNm. In the same interval the gamma ray and resistivity measurements failed. Alerted by the high bending moment and the sensor failures, the drilling crew tried for two hours to reduce the dogleg by reaming the last 20 m of the hole several times. However, the near bit inclination and bending moment transmitted to the surface showed that the remedial action had little effect in this case. Since similar high local doglegs had earlier led to two catastrophic failures in the Troll field, it was decided to stop drilling this reservoir section, which was originally planned to be 300 m longer.

It is assumed that this severe dogleg was created when the bit hit a calcite nodule at a low dip angle and followed the path of least resistance into the loose sand. The bit had accumulated about 25 drilling hours before the high local dogleg occurred.

At the surface, the bit showed severe wear with almost no teeth left on the heel rows. It is not known whether this damage occurred prior to drilling the high dogleg, or while drilling it, or afterwards during the extensive reaming period. Severe wear at the heel row is known to reduce the side cutting capability of the bit. As a result, it increases the bits tendency to be forced aside when encountering a hard stringer at a low dip angle, and it limits the bits ability to ream off the high local dogleg.

Example 2: The log excerpt in figure 7 recorded on well 31/2-X-14A Y2H shows the transition from a lower quality sandstone with a higher shale content to the coarsely grained target sandstone at about 3660 m. Compared to example 1 a different RSS configuration has been used as sketched in figure 7. While drilling this reservoir section the rig instrumentation failed and was not available for two days. During this period, the drilling process was controlled solely based on transmitted WOB, torque and RPM. The interval shown in figure 7 was drilled with a TCI bit at rotary speeds of 120–140 RPM. The caliper data, as well as the extremely small variation in the near bit inclination, demonstrate the excellent quality of the hole, which was drilled at an instantaneous ROP of 40-60 m/hr.

The log shows an increase in the bending moment from 4 kNm at 3640 m to a maximum of 30 kNm at 3650 m sensor depth. As the near bit inclination remained constant during this depth interval, the increase in bending moment had to be caused by a curvature of the hole in the horizontal plane. A survey taken at 3652 m showed a decrease in azimuth by 3.3° and confirmed the existence of a moderate dogleg in the horizontal plane. At 3672 m a loss in downhole WOB and a reduction in ROP were observed, most likely due to a stabilizer above the downhole diagnosis tool passing the local dogleg. In this case a short trip to ream the hole was successful in overcoming this weight transfer problem.

It is assumed that the dogleg was introduced in the transition from the finer sand with the higher shale content to the less dense production sand.

Example 3: The log excerpt in Figure 8 shows data from a hole interval on well 31/2-N-21 Y1H drilled with a PDC bit. The start of the log illustrates the optimization of drilling performance using the downhole stick-slip analysis. At 2088 m an increase in WOB to about 5 tonnes led to drilling rates of up to 120 m/hr. However, the increase in WOB also led to an increase in stick-slip vibrations as indicated by the wider spread between minimum and maximum RPM on the log. Over the next 20 meters both WOB and rotary speed are finetuned in response to the downhole stick-slip diagnostic to keep the stick-slip vibrations at an acceptable level, while maintaining an optimum ROP.

At 2107 m the ROP slowed down significantly and the stick-slip severity also decreased. At 2112 m the rotary speed was reduced to 100 RPM and the WOB was increased as it was assumed that a calcite nodule had been encountered. When the drilling rate picked up again at 2115 m, the near bit inclination started to decrease from 90° to almost 88°. At the same time an increase in bending moment up to 55 kNm was measured. At 2121 m a new steering command were sent to

4 SPE/IADC 79918

the RSS to steer the bit upward. The rotary speed was kept at 100 RPM until the complete BHA had passed the local dogleg and the bending moment had decreased to a level of 20 kNm. After an RPM increase at 2140 m, and a WOB increase at 2143 m, drilling continued with a high instantaneous ROP of 90–120 m/hr.

The higher density between 2110 m and 2120 m indicates that the dogleg was caused by a calcite-cemented zone. While drilling this interval the transmitted bending moment data was the only information indicating the severity of the dogleg. Compared to the example in figure 6 the changes in near bit inclination were relatively small. The survey data at 2133 m, however, showed an azimuthal change of 5° in the horizontal plane, revealing the severity of the dogleg at this depth.

Example 4: The time-based log in figure 9 shows a three hour period of slow drilling through a calcite stringer on well 31/2-N-21 Y1H. Over the two meters drilled during the first hour on the log excerpt, the bending moment increased from 24 kNm to 36 kNm. In response, the rotary speed was reduced to minimize the fatigue rate of the BHA components. At 21.25 hours, an attempt was made to remedy the local dogleg by reaming the last 15 m of the hole. A reduction in the bending moment by about 2.5 kNm could be achieved.

Discussion The examples above have demonstrated that several actions can be taken once a high local dogleg has been detected from the near bit inclination or the bending moment measurement.

In some cases repeated reaming was successful in decreasing the bending moment in the BHA. In other cases, however, reaming made the problem worse by enlarging the hole in the looser sand in front of a stringer, and ultimately led to an increase in the bending moment when drilling ahead. All available information needs to be carefully reviewed prior to deciding to ream a hole section with a high dogleg.

Reducing the rotary speed helps to minimize the fatigue rates in the BHA when drilling through a high dogleg. On the Troll drilling rigs both occurrence and severity of the doglegs are now recorded on so-called “Hole Restriction Forms”. During tripping in and out of the hole, rotation of the BHA is avoided in the critical sections.

As shown in the first example, the most dramatic action that might have to be taken in response to an extreme dogleg is to simply stop drilling.

While the real-time BHA bending information helps to reduce the risk while drilling, it became obvious in the course of the problem analysis that doglegs cannot be cured but need to be prevented. It was decided to investigate changes in the design of the BHA and drilling program that would eliminate or at least reduce the occurrence of high local doglegs.

The unique downhole closed-loop mode of the RSS is designed to actively resist propagation of local doglegs in the vertical plane. To cope with the extreme contrasts in rock hardness on Troll, the steering parameters of the closed-loop mode were altered to react faster and more aggressively to unwanted direction changes. However, once a dogleg in the well path has been detected, the RSS is steered less aggressively back to the target vertical depth.

Special considerations have been given to bit design and selection. Historically, medium to heavy set PDC bits with a short gauge have been used to drill the reservoir sections on Troll. While these bits provide optimal lateral steering capability, they are also sensitive to unwanted directional changes when hitting a calcite-cemented nodule. After the downhole bending moment measurement had pointed to the negative impact of the local doglegs on the stresses in the BHA, it was decided to reduce the side cutting efficiency of the PDC bits by increasing the gauge length. In order to compare the directional performance of the short vs. the long gauge bit, the drilling and formation data over a total distance of 16,000 m were analyzed to determine the likelihood of creating a high dogleg when entering or exiting a calcite-cemented stringer. For the purpose of this study a high local dogleg was defined as a change in near bit inclination exceeding 5°/30 m in one direction followed by a similar change in the opposite direction over a distance of less than 20 m. Figure 10 demonstrates that the longer gauge length on the PDC bit significantly reduces the risk of creating a high local dogleg when drilling through the calcite-cemented zones.

Experience has also shown that, as long as their side cutting capability is not detrimentally influenced by wear, TCI roller cone bits create less unwanted doglegs due to their better drilling efficiency in the calcites. Recent improvements of the TCI bit drilling performance in the clean sandstone have resulted in an increased utilization of TCI bits in the Troll field. The decision of TCI vs. PDC bit is now typically based on the calcite prognosis for the upcoming run.

The improved understanding of the downhole environment based on the downhole bending moment measurement, the subsequent implementation of the changes described above and the ongoing real-time monitoring of near bit inclination and bending moment while drilling have successfully eliminated high dogleg related failures as shown in figure 11. As a result, the average number of runs required to drill the reservoir sections on Troll has been reduced substantially. The reduction of high local doglegs has also improved overall hole quality providing additional benefits such as less torque losses, reduced drill string wear and less problems during completion. However, additional studies are required to quantify these benefits.

Conclusions 1. The downhole bending moment information complements

the near-bit inclination data in detecting high local doglegs in the well path. In particular, the bending moment information helps identify the occurrence and severity of unwanted well path changes in the horizontal plane.

2. Several field examples have been presented to illustrate how timely reaction to high local doglegs reduces the risk of drilling in the difficult environment on Troll.

3. The downhole bending moment information was instrumental to understand the importance of poor hole quality as the key limiting factor in system reliability and drilling performance. Based on this lesson, changes in drilling practices, bit selection and system design have been implemented to control the occurrence of high local doglegs.

SPE/IADC 79918 5

Acknowledgments The authors would like to thank Norsk Hydro and Baker Hughes INTEQ for the support and the permission to publish this paper. They would also like to thank all individuals from both Norsk Hydro and INTEQ who were involved in the successful introduction of the downhole diagnosis system on the Troll field. In particular, the authors would like to thank John Dexter with Norsk Hydro and Marianne Stavland, Harald Fiksdal and Geir Johnson with INTEQ for their contributions to this paper. Thanks are extended to John Macpherson and Ed Robnett with INTEQ for the critical review of the paper.

References 1. Fiksdal, H., Rayton, C. and Djerfi, Z.: ”Application of Rotary

Steerable System/PDC Bits in Hard Interbedded Formations: A Multidisciplinary Team Approach to Performance Improvement”, paper IADC/SPE 59110 presented at the 2000 IADC/SPE Drilling Conference held in New Orleans, Louisiana, 23-25 February 2000.

2. Johnstone, J.A. and Allan, D.: “Realizing True Value From Rotary Steerable Drilling Systems”, paper SPE 56958, presented at the 1999 Offshore Europe Conference held in Aberdeen, Scotland, 7-9 September 1999.

3. Heisig, G., Sancho, J., Macpherson, J.D.: “Downhole Diagnosis of Drilling Dynamics Data Provides New Level Drilling Process Control to Driller”, paper SPE 49206 prepared for presentation at the 1998 SPE Annual Technical Conference and Exhibition in New Orleans, planned for Sept 27-30, 1998.

4. Hood, J.A., Leidland, B.T., Haldorsen, H., Heisig, G.: „Aggressive Drilling Parameter Management Based on Downhole Vibration Diagnostics Boosts Drilling Performance in Difficult Formation”, paper SPE 71391, presented at the 2001 Annual Technical Conference and Exhibition held in New Orleans, Louisiana, 30 September – 3 October 2001.

5. Wolf, S.F., Zacksenhouse, M., and Arian, A.: “Field Measurements of Downhole Drillstring Vibrations”, paper SPE 14330, presented at the 1985 SPE Annual Technical Conference, Las Vegas, Nevada, September 22-25, 1985.

6. Vandiver, J.K., Nicholson, J.W., Shyu, R.-J.: “Case Studies of the Bending Vibration and Whirling Motion of Drill Collars”, paper IADC/SPE 18652, presented at the 1989 IADC/SPE Drilling Conference held in New Orleans, Louisiana, February 28 – March 3, 1989.

7. Cook, R.L., Nicholson, J.W., Sheppard, M.C. and Westlake, W.: “First Real Time Measurements of Downhole Vibrations, Forces and Pressures Used to Monitor Directional Drilling Operations”, paper SPE/IADC 18651 presented at the 1989 SPE/IADC Drilling Conference in New Orleans, Louisiana, February 28 - March 3, 1989.

8. Timoshenko, S.P., Goodier, J.N.: Theory of Elasticity; 3rd edition, McGraw-Hill, New York, Toronto, London, 1970.

SI Metric Conversion Factors m x 3.280840 E+00 = ft mm x 3.937008 E-02 = in. N x 2.224808 E-01 = lbf Nm x 7.375620 E-01 = ft-lbf

6 SPE/IADC 79918

Fig. 1 – Calcite stringers and nodules observed in the Bridport Sands at the Dorset Coast in the UK

Fig. 2 – Artistic illustration of a high local dogleg (HLD) developed at the surface of a calcite cemented stringer

Major calcitestringers

Local calcites

SPE/IADC 79918 7

Fig. 3 – Bottom Hole Assembly (BHA) including Rotary Steerable System (RSS), downhole dynamics tool and LWD tool suite

Fig. 4 – Calculated bending moment and side force distribution in the BHA in Fig 3 assuming a perfectly straight, in-gage horizontal hole

Fig. 5 – Schematic representation of the bending stress distribution in a BHA cross-section

Near BitInclination

InclinationAzimuth

Bending Moment Measurement Point

1.1 m

10.2 m

13.9 m

20.9 m

Rotary Steerable System (RSS) Downhole Dynamics Diagnosis Tool LWD tool suite

15,8 m

Gamma Resistivity Density Porosity

Near BitInclination

InclinationAzimuth

Bending Moment Measurement Point

1.1 m

10.2 m

13.9 m

20.9 m

Rotary Steerable System (RSS) Downhole Dynamics Diagnosis Tool LWD tool suite

15,8 m

Gamma Resistivity Density Porosity

gravity

bending moment maxima

Bending Moment Color ScaleBending Moment Color Scale

MinimumMinimum MaximumMaximum

gravitygravity

bending moment maxima

Bending Moment Color ScaleBending Moment Color Scale

MinimumMinimum MaximumMaximum

x

y y

z

Tension

Compression

σ(y)

M

Material “Fiber”

x

y y

z

Tension

Compression

σ(y)

M

Material “Fiber”

8 SPE/IADC 79918

Fig. 6 – Example 1: Depth-based log excerpt with drilling and formation data showing high local dogleg in vertical plane

4350

4300

Steep rise in bending moment after RSS steering unit has entered high local dogleg

First slight increase in Near Bit Incl., then dramatic rise

150.0 0.0 0.0 5.0 0.0 25.0 50.00.0 450.0-50.0 10.00.0

Rate of Penetration( m/hr)

1.00 m Average

Axial Vibration(g_RMS )

Surface WOB( tonnes)

Surface Torque( kN-m)

Min DH RPM( rpm)

Lateral Vibration I

( g_RMS)

Density( g/cc)

1.80 2.80

Near Bit Inc.( degrees)

85.0 95.0

Downhole WOB( tonnes)

0.0 25.0

Downhole Torque( kN-m)

25.00.0

Avg. DH RPM( rpm)

450.0-50.00

Lateral Vibration II

( g_RMS) 10.00.0

Gamma Ray( MWD – API)

0.0 150.0

Bending Moment( kN-m)

0.0 60.0

Max DH RPM( rpm)

450.0-50.0

Caliper( inch)

9.507.50

Bending RPM( rpm) 450.0-50.0

DEPTH

METERS

1:500

DEPTH

METERS

1:500

Reduced WOB to control ROP and dogleg

4350

4300

Steep rise in bending moment after RSS steering unit has entered high local dogleg

First slight increase in Near Bit Incl., then dramatic rise

150.0 0.0 0.0 5.0 0.0 25.0 50.00.0 450.0-50.0 10.00.0


1.00 m Average




Min DH RPM( rpm)

Lateral Vibration I

( g_RMS)

Density( g/cc)

1.80 2.80


85.0 95.0


0.0 25.0


25.00.0

Avg. DH RPM( rpm)

450.0-50.00


( g_RMS) 10.00.0


0.0 150.0


0.0 60.0

Max DH RPM( rpm)

450.0-50.0

Caliper( inch)

9.507.50


DEPTH

METERS

1:500

DEPTH

METERS

1:500

150.0 0.0 0.0 5.0 0.0 25.0 50.00.0 450.0-50.0 10.00.0


1.00 m Average




Min DH RPM( rpm)

Lateral Vibration I

( g_RMS)

Density( g/cc)

1.80 2.80


85.0 95.0


0.0 25.0


25.00.0

Avg. DH RPM( rpm)

450.0-50.00


( g_RMS) 10.00.0


0.0 150.0


0.0 60.0

Max DH RPM( rpm)

450.0-50.0

Caliper( inch)

9.507.50


DEPTH

METERS

1:500

150.0 0.0 0.0 5.0 0.0 25.0 50.00.0 450.0-50.0 10.00.0


1.00 m Average




Min DH RPM( rpm)

Lateral Vibration I

( g_RMS)

Density( g/cc)

1.80 2.80


85.0 95.0


0.0 25.0


25.00.0

Avg. DH RPM( rpm)

450.0-50.00


( g_RMS) 10.00.0


0.0 150.0


0.0 60.0

Max DH RPM( rpm)

450.0-50.0

Caliper( inch)

9.507.50


DEPTH

METERS

1:500

DEPTH

METERS

1:500

Reduced WOB to control ROP and dogleg

SPE/IADC 79918 9

Fig. 7 – Example 2: Depth-based log with drilling and formation data showing a local dogleg in the horizontal plane

3650

150.0 0.0 0.0 5.0 0.0 25.0 50.00.0 450.0-50.0 10.00.0


1.00 m Average




Min DH RPM( rpm)

Lateral Vibration I

( g_RMS)

Density( g/cc)

1.80 2.80


85.0 95.0


0.0 25.0


25.00.0

Avg. DH RPM( rpm)

450.0-50.00


( g_RMS) 10.00.0


0.0 150.0


0.0 60.0

Max DH RPM( rpm)

450.0-50.0

Caliper( inch)

9.507.50


DEPTH

METERS

1:500

DEPTH

METERS

1:500

3600

Survey at 3625 mInclination 90.2°Azimuth 137.8°


Transition from low quality finer sand to production sand

Surface instrumentation failed, drilling operation was controlled w/ transmitted downhole data only

Weight transfer problem due to stabilizer passing local dogleg

3650

150.0 0.0 0.0 5.0 0.0 25.0 50.00.0 450.0-50.0 10.00.0


1.00 m Average




Min DH RPM( rpm)

Lateral Vibration I

( g_RMS)

Density( g/cc)

1.80 2.80


85.0 95.0


0.0 25.0


25.00.0

Avg. DH RPM( rpm)

450.0-50.00


( g_RMS) 10.00.0


0.0 150.0


0.0 60.0

Max DH RPM( rpm)

450.0-50.0

Caliper( inch)

9.507.50


DEPTH

METERS

1:500

DEPTH

METERS

1:500

150.0 0.0 0.0 5.0 0.0 25.0 50.00.0 450.0-50.0 10.00.0


1.00 m Average




Min DH RPM( rpm)

Lateral Vibration I

( g_RMS)

Density( g/cc)

1.80 2.80


85.0 95.0


0.0 25.0


25.00.0

Avg. DH RPM( rpm)

450.0-50.00


( g_RMS) 10.00.0


0.0 150.0


0.0 60.0

Max DH RPM( rpm)

450.0-50.0

Caliper( inch)

9.507.50


DEPTH

METERS

1:500

150.0 0.0 0.0 5.0 0.0 25.0 50.00.0 450.0-50.0 10.00.0


1.00 m Average




Min DH RPM( rpm)

Lateral Vibration I

( g_RMS)

Density( g/cc)

1.80 2.80


85.0 95.0


0.0 25.0


25.00.0

Avg. DH RPM( rpm)

450.0-50.00


( g_RMS) 10.00.0


0.0 150.0


0.0 60.0

Max DH RPM( rpm)

450.0-50.0

Caliper( inch)

9.507.50


DEPTH

METERS

1:500

DEPTH

METERS

1:500

3600



Transition from low quality finer sand to production sand

Surface instrumentation failed, drilling operation was controlled w/ transmitted downhole data only

Weight transfer problem due to stabilizer passing local dogleg

10 SPE/IADC 79918

Fig. 8 – Example 3: Depth-based log with drilling and formation data showing the bending moment response to a high local dogleg

2100Survey at 2105 mInclination 90.49°Azimuth 171.12°


Bending Moment

Near-bit Inclination

2150

150.0 0.0 0.0 5.0 0.0 25.0 50.00.0 450.0-50.0 10.00.0


1.00 m Average




Min DH RPM( rpm)

Lateral Vibration I

( g_RMS)

Density( g/cc)

1.80 2.80


85.0 95.0


0.0 25.0


25.00.0

Avg. DH RPM( rpm)

450.0-50.00


( g_RMS) 10.00.0


0.0 150.0


0.0 60.0

Max DH RPM( rpm)

450.0-50.0

Caliper( inch)

9.507.50


DEPTH

METERS

1:500

DEPTH

METERS

1:500

RPM reduction to drill local calcite zone

RPM increase after passing local dogleg

ROP Improvement after RPM increase

Higher density indicates calcite cemented zone 2100



Bending Moment

Near-bit Inclination

2150

150.0 0.0 0.0 5.0 0.0 25.0 50.00.0 450.0-50.0 10.00.0


1.00 m Average




Min DH RPM( rpm)

Lateral Vibration I

( g_RMS)

Density( g/cc)

1.80 2.80


85.0 95.0


0.0 25.0


25.00.0

Avg. DH RPM( rpm)

450.0-50.00


( g_RMS) 10.00.0


0.0 150.0


0.0 60.0

Max DH RPM( rpm)

450.0-50.0

Caliper( inch)

9.507.50


DEPTH

METERS

1:500

DEPTH

METERS

1:500

150.0 0.0 0.0 5.0 0.0 25.0 50.00.0 450.0-50.0 10.00.0


1.00 m Average




Min DH RPM( rpm)

Lateral Vibration I

( g_RMS)

Density( g/cc)

1.80 2.80


85.0 95.0


0.0 25.0


25.00.0

Avg. DH RPM( rpm)

450.0-50.00


( g_RMS) 10.00.0


0.0 150.0


0.0 60.0

Max DH RPM( rpm)

450.0-50.0

Caliper( inch)

9.507.50


DEPTH

METERS

1:500

150.0 0.0 0.0 5.0 0.0 25.0 50.00.0 450.0-50.0 10.00.0


1.00 m Average




Min DH RPM( rpm)

Lateral Vibration I

( g_RMS)

Density( g/cc)

1.80 2.80


85.0 95.0


0.0 25.0


25.00.0

Avg. DH RPM( rpm)

450.0-50.00


( g_RMS) 10.00.0


0.0 150.0


0.0 60.0

Max DH RPM( rpm)

450.0-50.0

Caliper( inch)

9.507.50


DEPTH

METERS

1:500

DEPTH

METERS

1:500

RPM reduction to drill local calcite zone

RPM increase after passing local dogleg

ROP Improvement after RPM increase

Higher density indicates calcite cemented zone

SPE/IADC 79918 11

Fig. 9 – Example 4: Time-based log with drilling process data showing small effect of reaming on measured bending moment

Time

hh:mm

0.0 5.0

Axial Acceleration( g_RMS)

Block Position( m)

-5.0 30.0Near Bit Inc.

( degrees)

85.0 95.0


0.0 60.0

0.0 25.0 50.00.0 450.0-50.0 10.00.0



Min DH RPM( rpm)

Lateral Vibration I

( g_RMS)


0.0 25.0


25.00.0

Avg. DH RPM( rpm)

450.0-50.00


( g_RMS) 10.00.0

Max DH RPM( rpm)

450.0-50.0


3598 m

3599 m

3600 m

3601 m

3602 m

21:00

22:00

23:00



RPM decreases in response to high bending moment

Reaming of last 15 mto reduce bending moment

Time

hh:mm

0.0 5.0

Axial Acceleration( g_RMS)

Block Position( m)

-5.0 30.0Near Bit Inc.

( degrees)

85.0 95.0


0.0 60.0Near Bit Inc.

( degrees)

85.0 95.0


0.0 60.0

0.0 25.0 50.00.0 450.0-50.0 10.00.0



Min DH RPM( rpm)

Lateral Vibration I

( g_RMS)


0.0 25.0


25.00.0

Avg. DH RPM( rpm)

450.0-50.00


( g_RMS) 10.00.0

Max DH RPM( rpm)

450.0-50.0


3598 m

3599 m

3600 m

3601 m

3602 m

21:00

22:00

23:00



RPM decreases in response to high bending moment

Reaming of last 15 mto reduce bending moment

12 SPE/IADC 79918

33.0%

17.5%

0%

5%

10%

15%

20%

25%

30%

35%

Short Gauge RSS PDC Bit Longer Gauge PDC Bit

Perc

enta

ge o

f Str

inge

rs D

rille

d C

ausi

ng a

Hig

h Lo

cal D

ogle

g

Fig. 10 – Effect of bit gauge length on the occurrence of high local doglegs (HLD)

0

5,000

10,000

15,000

20,000

25,000

Q1 '01 Q2 '01 Q3 '01 Q4 '01 Q1 '02 Q2 '02 Q3 '02

Aver

age

Dist

ance

Dril

led

Betw

een

HLD

Failu

res

per Q

uarte

r [m

]

0

1

2

3

4

5

HLD

Rela

ted

Failu

res

per Q

uarte

r

Fig. 11 – Reliability and performance improvements on Troll West drilling operation after introducing changes and procedures to control high local doglegs (HLD)

Documents

00079918