Copyright 1998, Society of Petroleum Engineers, Inc.

This paper was prepared for presentation at the 1998 SPE International Conference andExhibition in China held in Beijing, China, 2-6 November 1998.

This paper was selected for presentation by an SPE Program Committee following review ofinformation contained in an abstract submitted by the author(s). Contents of the paper, aspresented, have not been reviewed by the Society of Petroleum Engineers and are subject tocorrection by the author(s). The material, as presented, does not necessarily reflect anyposition of the Society of Petroleum Engineers, its officers, or members. Papers presented atSPE meetings are subject to publication review by Editorial Committees of the Society ofPetroleum Engineers. Electronic reproduction, distribution, or storage of any part of this paperfor commercial purposes without the written consent of the Society of Petroleum Engineers isprohibited. Permission to reproduce in print is restricted to an abstract of not more than 300words; illustrations may not be copied. The abstract must contain conspicuousacknowledgment 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

A 3.5in. O.D. MWD system has been developed which iscapable of providing Directional and Gamma Ray services inshort radius wells at build rates up to 3.3°/meter, a build ratethat had not previously been available through conventionalMWD technology. Specially selected materials, innovativetool joint design and an integral MWD Transmitter/Drillingsub-assembly have been utilised in order to withstand thestresses associated with high build rates while maintaining fullfunctionality in small diameter drill collars. Innovative testingmethods were required to qualify the system for short radiusapplications, resulting in the implementation of significantdesign improvements.

Utilising the new MWD system with short radius drillingtechnology has opened up the possibility of horizontal re-entry of existing wells completed with small diameter casing.Three case histories in the Shengli Oilfield are presented. Thethree re-entry wells, Y-CP1, X-CP1 and L-CP1 had originallybeen completed in 139.7mm casing. Two of the re-entry wellswere kicked off through 2.1meter casing windows usingoriented whipstocks with 118mm and 121mm bits at 3235 and2109 meters respectively. Well L-CP1 section milled 18meters of casing then side-tracked and built angle, reaching aTD of 2906 meters measured depth. Build rates for the wellsaveraged 2.0°/meter with a maximum of 3.3°/meter.Maximum horizontal reach was 151 meters from landingpoint.

Performance of the drilling and MWD systems wasexcellent during the drilling phase of the wells. Using theknowledge and experience gained it will be possible to utilisethe equipment to re-complete and extend the life of thenumerous wells that have been completed in small diametertubing in the Shengli area. Well designs can be planned thatcould not have been considered using conventionaltechnology. Significant production gains will be made as aresult.

Introduction

Many existing oil and gas wells in China (and world-wide)have been completed in small diameter casing. A significantproportion of these wells are candidates for re-drilling and re-completion to tap remaining reserves that have not beenreached by the existing well pattern. Until recently it had beennecessary to pull the small diameter casing in order to re-drillthese wells. It was recognised that a slim-hole MWD systemcombined with similar size steerable mud motor assembliescould not only successfully drill sidetracks out of such casingbut could also drill significant horizontal sections in order tomaximise production from the new hole. In addition, it wouldbe advantageous if the MWD system was capable of operationin short radius drilling operations in order to minimise the holelength required to land the well. In developing the new MWDsystem the following criteria were set:

1. The MWD tool should have full functionality,including directional and gamma ray measurements.

2. It should be capable of operating in hole sizes down to114mm. and at build rates of up to 3.3°/meter.

3. It should be functional in all mud types with sandcontent up to 0.5% (higher for short periods) and atflow rates up to 570 liters/minute.

4. With the exception of the mud pulse transmitter, theMWD probe should be compatible with standardlarger MWD collar sizes (Ref.1) in order to maximiseutilisation.

5. MWD signal size should be equivalent to or biggerthan that produced by the conventional tool.

SPE 48862

Flexible 3.5in. O.D. MWD System Enhances Short Radius, Horizontal DrillingApplications in Shengli Oilfield, ChinaLi Hongwei, SPE, Shengli Petroleum Administrative Bureau SINOPEC, S.C.Page, SPE, Geolink (UK) Ltd., WangZhenghu, SPE, Shengli Petroleum Administrative Bureau SINOPEC and Dr. J.H.Knight, Geolink (UK) Ltd.

2 LI HONGWEI, S.C.PAGE, WANG ZHENGHU, J.H.KNIGHT SPE 48862

Development Programme

The 3.5in. MWD development program commenced in 1991and was completed in 1992. On commencement of the designprogramme, it was immediately apparent that the reduceddiameter of the MWD collars and subs would requireengineering innovations in order to maintain full functionalitywhile meeting industry criteria for strength in a drill stringcomponent (API Spec. 7 and API RP7G). The two maindesign innovations were:

1. The MWD mud pulse transmitter (Fig. 1) wasdesigned as an integral part of a drilling sub ratherthan being a bolt in device as in previous designs. TheTransmitter Sub is fitted with a semi-permanentreceptacle for the electrical actuation assembly andhydraulic wear parts that generate the negative mudpulse. Three orifices are inserted through the wall ofthe sub at 120° intervals, allowing mud to pass fromthe inside of the drill string into the annulus at timedintervals according to the data being transmitted.Despite the innovative design, the Transmitterdevelopment used many common wear parts from thelarger conventional design.

2. A special thread (Fig. 2) had to be designed so that theinternal diameter of the pin was capable of acceptingthe MWD probe while maintaining both strength andsufficient clearance to keep mud velocities withinacceptable limits in a 2.5in. bore.

Fig. 1 – The 3.5in. MWD Transmitter showing the new threaddesign, the exit orifice for mud bypass and the tail piece carryingthe electrical connections.

Transmitter Design

In order to maintain compatibility with existing surfaceequipment and signal detection algorithms it was decided thatthe Transmitter should utilise negative mud pulse telemetry. Itwas realised that the reduced pipe diameter to surface wouldhave an attenuating effect on the signal which initially causedconcern that it may not be detectable above system noise.

A computer model of the circulating system was generatedwhich included the fluid bypass characteristics of the MWDTransmitter. The model predicted that, due to the increasedratio between flow diverted and normal flow in the pipe, thepulse size at source would be larger than normal and that thiswould overcome the attenuating effect of the pipe diameter. Inthe final design it was necessary to add additional metering tothe flow bypass in order to control the pulse size and this hadthe additional benefit of reducing flow related wear and tearon the internal parts of the Transmitter. The computer modelwas used to predict the pulse size that would be seen onsurface during first field tests of the system and was found tobe accurate within an error limit of +/-5%.

Space constraints within the 3.5in. O.D. sub defied aconventional approach to transmitter installation. Previousnegative pulse designs had been based on a transmitterassembly bolted into a separate sub. In this case, thetransmitter housing was designed as an integral part of the subwith the actuating device and wear components replaceablethrough the box connection at the up-hole end. At the down-hole pin end, a tail piece carrying electrical connections passesthrough the connection, projecting so that it can be made up tothe conventional MWD probe. Machining the transmitterhousing in situ and leaving sufficient area for mud flow wasconsidered to be an impractical solution so the housing wasdesigned to be machined separately to a British Standardinterference fit and then placed into the main sub body using afreezing process to allow installation.

Thread Design

The original design criterion for the new proprietary threadwas that it should emulate or exceed the performance of anAPI 2-3/8in. IF thread form in a similar drill collar size. Table1 shows a comparison of performance between the proprietaryand API threads.

Drill Collar SizeThread

O.D. I.D.

TorsionalStrength

Nm

TensileStrength N

Proprietary 3.5in. 2.5in. 15,592 1,401,189API 2-3/8 in. IF 3.375in. 1.75in. 9,219 1,395,318

Table 1 – Comparison of Thread Specifications

The improved performance of the Geolink thread wasachieved by a combination of design and material, allowing alarger than normal I.D. to allow the MWD probe to passthrough the connection whilst maintaining mud velocities at anacceptable level.

The thread design (Fig. 2) called for a 2 stage squarethread with 3 sealing/torquing faces. When fully made up, all3 faces provide a seal against a potential wash-out.

SPE 48862 FLEXIBLE 3.5" OD MWD SYSTEM ENHANCES SHORT RADIUS, HORIZONTAL DRILLING APPLICATIONS IN SHENGLI OILFIELD,CHINA 3

Fig. 2 – Cross section of the MWD thread design (pin end)showing the 3 sealing/torquing faces and the 2 stage thread.

API Spec. 7 Copper/Beryllium was chosen for the MWDTransmitter sub, drill collar and cross-overs for three reasons:

1. It has excellent anti-galling properties that are criticalfor the make-up and break-out performance of the newconnection.

2. The tensile strength is greater than the standard gradesof austenitic steel normally used for MWD drill stringcomponents.

3. It is more easily machined than the high strengthgrades of austentic steel now available.

Laboratory Testing

Prior to field testing, an intensive programme of workshoptests was carried out to qualify the new design. Two of themost important tests concerned the strength of the newconnection and the ability of the system to function at extremerates of dog-leg severity during drilling (up to 3.3°/metersliding and up to 1.65°/meter rotating).

The new thread design was manufactured in prototypeform and placed on a break-out machine to test for torque toyield. The connection was made up to torque values in excessof 16,270Nm without yield but with some deformation. Thisvalue was well beyond expected exposure during drillingoperations. Despite the deformation, it was still possible tobreak out the connection normally.

The ability of the tool to function in short radius drillingenvironments was tested by a novel use of water weights. Thetool was made up in its drill collar and subs and thensuspended at each end from an overhead crane and a fork lift.A water weight suspended from the middle of the MWD string(Fig. 3) was filled with variable amounts of water in order toinduce varying degrees of bend in the tool to a maximumexceeding the specification of 3.3°/meter. The MWD tool wasset working during the test and the output monitored remotely.

Fig. 3 – FunctionTest on bent MWDstring

During initial tests it was noted that Transmitter functionbecame erratic at extreme bends (4.95°/meter) due to themechanical binding of internal moving parts. A design reviewwas able to increase clearances and flexibility between theseparts sufficiently to allow operation at turn rates in excess ofthe tool specification of 3.3°/meter.

Field Testing

Field tests were carried out on a commercial drilling operationin Texas, USA with the operator’s consent. A re-entry wellwas built to horizontal at a rate of 2.5°/meter during 7 tripsinto the hole. The MWD system performed according tospecification during the test although several failures of otherdrill string component connections occurred. MWD signal sizewas within 5% of the predicted pulse size from the computermodel.

Case Studies - Introduction

Shengli Oilfield is the second largest oil producing area inChina, located onshore in and around the Yellow River deltaand in the adjacent shallow water area (5m or less) offshore inBohai Bay. Re-entry drilling and completion technologieshave been the subject of important research by the ShengliPetroleum Administrative Bureau in order to increaseproduction and reduce development costs. There are over 2000abandoned wells in the field due to casing damage, down-holeengineering problems and water invasion of producing zonesand it was recognised that short radius horizontal welltechnology is one of the potential routes to restore production.

Once this concept had been accepted, proposals were put

© Geolink (UK) Ltd

4 LI HONGWEI, S.C.PAGE, WANG ZHENGHU, J.H.KNIGHT SPE 48862

forward to sidetrack existing wells from windows in 139.7mm(5-1/2in.) O.D. casing and then drill short radius horizontalextensions at build rates in excess of 1.5°/meter. Key to thesuccess of the proposed project was the correct choice of bothdrilling and surveying equipment. After comprehensiveperformance comparisons, the flexible 3.5in. MWD systemdescribed earlier was chosen as the main orientation andsurvey instrument. In addition, it was decided to run MWDgamma ray measurements in two wells (both during drillingand tripping operations) in order to correlate geological wellposition and recognise entry into reservoir zones.

Case Histories – Drilling Assembly Specification

The most important consideration for the MWD system fromthe drilling engineering design standpoint was the capability topass through and survive the proposed short radius build rates.The recommended minimum allowable radius for the systemis 17 meters (or 3.33°/meter build rate) while slide drilling andthe maximum planned radius for the project was 28.65 meters(or 2°/meter) for the three wells.

Wells Y-CP1 and X-CP1 were kicked off from whipstockswhich were set in the direction specified by the reservoirengineers. Each whipstock was oriented using a surface readout gyro and then set using a hydraulically actuated packer andshear pin. Once the whipstock had been set, a window wasmilled in the casing on the oriented side of the whipstock,approximately 2.1 meters from top to bottom. Well L-CP1 waskicked off from a cement plug in an 18 meter casing window.

The planned bottom hole assembly for the build section(Fig. 4) was a 118mm or 121mm PDC or tri-cone bit, 3-3/4in.Articulated Positive Displacement Motor with bent housing, 3-1/2in. MWD Cross-over/Restrictor sub, 3-1/2in. BerylliumCopper non-magnetic Drill Collar, 3-1/2in. MWD TransmitterSub, 3-1/2in. Beryllium Copper non-magnetic Drill Collar,Cross-Over Sub and 2-7/8in. Drill Pipe to surface. In order toavoid damage to the Motor and MWD assemblies it wasnecessary to restrict drilling and tripping to sliding mode onlywhile in the curve. A combination of a 19mm Restrictor jetand a flow rate of 9 liters/sec was chosen in order to optimiseMWD signal transmission and detection.

Once the well had been landed, drilling the horizontalsection was carried out using both articulated and non-articulated bent housing positive displacement motors. Drillingalternated between sliding and rotary mode.

Case Histories – Well Descriptions, MWD Use andPerformance

Since January 1997, three short radius horizontal wells havebeen drilled and completed using the flexible 3.5in. MWDsystem for orienting and surveying the drilling phases out ofold 139.7mm casing completions. The Gamma Ray tool was

used on two out of the three wells. Throughout the project theMWD system provided all required information without anysurface or down-hole failures. The Gamma Ray measurementplayed a key role in determining position in the reservoir, thusplacing the second and third wells more accurately. Actualmaximum build rate achieved with the system was 3.6°/meter.

Case History 1 – Well Y-CP1 – January 1997

Location : Onshore, Shengli OilfieldWell Type: Re-entry of old oil

producerReservoir Formation/Lithology: Sharsan SandDrilling Fluid: MMHOriginal Casing Size: 139.7mmRig Type: Daqing II/Diesel Engine

DriveWindow Cutting Method: Permanent WhipstockK.O.P. Depth: 3225.33 metersFinal Measured Depth: 3337.42 metersCurve Radius: 24 – 41 metersLateral Hole Size: 118mmLateral Hole Length: 51 meters

Completion Description

The well was completed (Fig. 5) with 73mm O.D. slottedliner hanging on the original 139.7mm casing. The slottedliner section was set in the known reservoir section withnormal tubing placed above to isolate the hydrated Shaleimmediately above the reservoir from entering the liner andplugging off production.

Project Results

All test aims were achieved. The window was cutsuccessfully and no problems were encountered with the deepkick off. Drilling by sliding and rotating proceeded smoothlyto the planned TD. Production was recovered from thepreviously abandoned well.

Case History 2 – Well X-CP1 – October 1997

Location : Onshore, Shengli Oilfield

Well Type: Re-entry of old oil producer

Reservoir Formation/Lithology: Sharer SandDrilling Fluid: MMHOriginal Casing Size: 139.7mmRig Type: XZJ162/Electric driveWindow Cutting Method: Permanent WhipstockK.O.P. Depth: 2106.80 metersFinal Measured Depth: 2224.53 metersCurve Radius: 16 – 42 metersLateral Hole Size: 121mm

SPE 48862 FLEXIBLE 3.5" OD MWD SYSTEM ENHANCES SHORT RADIUS, HORIZONTAL DRILLING APPLICATIONS IN SHENGLI OILFIELD,CHINA 5

Lateral Hole Length: 31.52 meters

Completion Description

The well was completed (Fig. 6) with 73mm O.D. slottedliner hanging on the old 139.7mm O.D. casing. External andinternal casing packers had to be used to ensure isolationbetween oil and water zones because a water aquifer existed inthe bore-hole.

Project Results

All test aims were achieved. Window cutting, drilling andcompletion proceeded smoothly. The MWD Gamma raysystem was used to place the well in the reservoir. The well isnow undergoing stimulation treatments.

Case History 3 – Well L-CP1 – January 1998

Location : Onshore, Shengli Oilfield

Well Type: Re-entry of old oil producer

Reservoir Formation/Lithology: Sharsan SandDrilling Fluid: MMHOriginal Casing Size: 139.7mmRig Type: XZJ162/Electric driveWindow Cutting Method: Section MilledK.O.P. Depth: 2661 metersFinal Measured Depth: 2906 metersCurve Radius: 35-51 metersLateral Hole Size: 121mmLateral Hole Length: 151 meters

Completion Description

The well was completed (Fig. 7) with 73mm O.D. slottedliner hanging on the old 139.7mm O.D. casing. External andinternal casing packers had to be used to ensure isolationbetween oil and water zones because a water aquifer existed inthe bore-hole.

Project Results

All test aims were achieved. Window cutting by sectionmill, drilling and completion proceeded smoothly. The MWDGamma ray system was used to place the well in the reservoir.The well has been recovered and production has reached morethan 30 tons/day which is about 3 times the amount fromconventionally completed offset wells.

Conclusions

The 3-1/2in. MWD system design has proved to be effectiveand reliable in short radius drilling applications.

The new thread design provides an effective alternativewhere drill collar I.D. prohibits the use of conventionaldesigns.

Re-entry and re-completion of wells completed in smalldiameter casing using short radius drilling techniques has beenshown to be an effective way of rejuvenating mature fields inthe Shengli Field. This technology will have widerapplications both in and outside China.

Acknowledgements

The authors would like to acknowledge the encouragementand permission to write this paper of the Shengli PetroleumAdministrative Bureau of SINOPEC and Geolink (UK) Ltd.

Thanks are due to all of the personnel in Shengli who gavetheir efforts to planning and carrying out the Shengli ShortRadius Horizontal Drilling Project.

Last, but not least, thanks are also due to Graham Miller ofGeolink who was present as MWD Technical Advisor duringthe drilling of Y-CP1 and gave his time and efforts to illustratethis paper.

References

1. Moorley, A., Prain, K.A.R. and Dickinson, R.T.: “System DesignFactors Impact the Cost of MWD Service Provision inDirectional and Horizontal Wells”, presented at the ColombianEnergy Seminar, Cartagena, Colombia, September 1993.

SI Metric Conversion Factors

In. x 2.54* E + 00 = cm

*Conversion factor is exact

6 LI HONGWEI, S.C.PAGE, WANG ZHENGHU, J.H.KNIGHT SPE 48862

Fig. 4 – Typical Kick-Off Bottom Hole Assembly used for theShengli Short Radius Drilling Project.

MWD Ultra-Slim (3.5”) Transmitter

BeCu Drill Collar w/. MWD tool

BeCu Drill Collar

Articulated PDM with Articulated Centralisers

BeCu crossover (MWD)

BeCu Restrictor/ crossover (MWD)

118 mm PDC Bit

Deflecting Pad

SPE 48862 FLEXIBLE 3.5" OD MWD SYSTEM ENHANCES SHORT RADIUS, HORIZONTAL DRILLING APPLICATIONS IN SHENGLI OILFIELD,CHINA 7

Fig. 5 – Completion Schematic of Well Y-CP1

Fig. 6 – Completion Schematic of Well X-CP1

137.5mm casing

73mm liner

Kick-off point at 3225.33m

2.1m window

Oriented Whipstock

Curve radius: 24m /41m

Well: Y-CP1

51m lateral section .

Circulating cross-over

Not drawn to scale

3337.42m MD

73mm slotted liner

137.5mm casing

73mm liner

Kick-off point at 2106.80m

2.1m window

Oriented Whipstock

Curve radius: 15.91m /42m

Well: X-CP1

31.52m lateral section .

2224.53m MD

Circulating cross-over

Not drawn to scale

73mm slotted liner

8 LI HONGWEI, S.C.PAGE, WANG ZHENGHU, J.H.KNIGHT SPE 48862

Fig. 7 – Completion Schematic of Well L-CP1

137.5mm casing

73mm liner

Kick-off point at 2661m

Section mill - 18m

Curve radius: 35m /51m

Well: L-CP1

151m lateral section .

3337.42m MD

Circulating cross-over

Not drawn to scale

73mm slotted liner