DRILLING ENGINEERING PACKAGE USED FOR EXTENDED REACH PROJECT

Feb. 20, 1995
Paul Chapman BP Exploration Sunbury, U.K. Alan Good Baker Hughes Inteq Houston Extended reach drilling can improve the economics, of some field developments by minimizing the number of facilities required to access remote reserves. The technique requires detailed engineering design and monitoring, however, to minimize the risk of operating at the limits of drilling equipment.

Paul Chapman
BP Exploration
Sunbury, U.K.

Alan Good
Baker Hughes Inteq
Houston

Extended reach drilling can improve the economics, of some field developments by minimizing the number of facilities required to access remote reserves. The technique requires detailed engineering design and monitoring, however, to minimize the risk of operating at the limits of drilling equipment.

The extended reach program has had a profound impact on the commercial success of BP Exploration's Wytch Farm field. Several wells have been drilled and completed with world record step-outs., With completion of five extended reach wells to date, Wytch Farm production has increased from its previous 68,000 bo/d to current production in the range of 100,000 bo/d.

Working as a team over the past 4 years, BP Exploration (BPX) and Baker Hughes Inteq have developed an integrated drilling engineering package for the planning, monitoring, and review of well construction data. The drilling engineering application platform (DEAP) is now used by BP Exploration worldwide for the integrated engineering design, monitoring, and review of its wells.' The platform consists of a suite of engineering applications developed by BP Exploration and validated by field experience over several years.

These engineering applications are linked together via a data base and drilling reporting system. Integration between rig site reporting and the engineering applications allows the current drilling operation to be analyzed at the touch of a single computer button. DEAP also provides links to commercially available software packages. This facility, along with its graphical user interface, encourages and simplifies the use of engineering tools at the rig site.

The full capabilities of DEAP can perhaps be seen as four key functions necessary for successful well bore construction management:

  • Well profile planning

  • Operations planning

  • Operations monitoring

  • Performance review.

WELL PROFILE PLANNING

The DEAP system was designed by drilling engineers to be used by drilling engineers as an aid in running daily drilling activities, with the following specific functions inherent:

  • The transparent software platform automatically manages the interface between the engineer, the DEAP data base, and the applications.

  • The system's relational data base contains information about the rig, inventory, the well under development, offset wells, and other wells in the same geographic area or similar wells worldwide.

  • As an interactive well planning tool, the system automatically generates documentation needed to proceed from the initial planning phases through each successive phase of well bore construction.

Several of the system's modules have particularly powerful attributes in well bore planning, modeling, and monitoring.

WELL PLANNING

The well planning module has four major components, including well activity and cost planning for both drilling and completions. To ensure continuity of planning and performance monitoring, DEAP has a simple data base extraction tool and a trouble time reporting tool.

The latter is a performance analysis application having predefined queries that are closely linked to the conventional morning report/activity progress log. A performance inquiry tool enables data extraction and comparison and statistical analysis of reported activities ranging from single well programs to all wells within a country. Additional planning functionality is continually being added to DEAP.

DIRECTIONAL DRILLING

The directional drilling support system module has been in a process of continual development. The directional drilling support system is designed to perform full directional well planning that is intrinsically linked to all aspects of well bore construction and engineering applications. A checklist of procedures complements the software:

  • Directional well planning

  • Survey program design

  • Well target analysis

  • Survey uncertainty calculations

  • Vertical section definition

  • Directional and survey data plotting

  • Directional survey calculator

  • Survey data (multishot)

  • Survey instrument performance analysis

  • Well definition generation

  • Coordinate conversion

  • Global geomagnetic model

  • Multiple survey interpolation.

ANTICOLLISION PROCEDURES

Each time a plan is altered, collision scans can be performed automatically on all wells.' Adjacent wells are viewed on a traveling cylinder in the same scan. Separation rules are enforced by "do not cross" tolerance lines drawn on the cylinder. This procedure simplifies the directional driller's job at the well site by ensuring that the initial well plan adheres to the conventional best practice for controlling well bore placement.

SURVEYS

Since 1987, BPX has used particular survey error models and propagation calculations. Incorporated into DEAP, the models consist of independently validated, vendor-survey, instrument - specific models that have been "black boxed" to prevent tampering. Error propagation calculations produced by the models contain significant differences from those by Wolff and de Waardt in respect to their treatment of random errors, depth measurement errors, and inclination bias.'

These models are currently used in survey program design, determining well separation rules, and quantitative screening of redundant survey data.

SURVEY PROGRAM DESIGN

The directional drilling support system enables the engineer to design a custom survey rather than assemble a similar well survey. In this module, DEAP automatically composes the survey filing structure based on the logic of the user's design.

The constituent parts of a definitive survey may be implicitly defined at any point in the well. A major cause of practical problems is thereby eliminated because the concept of tie-in points is transparent to the user, having been defined in the planning stage.

A practical result of this design is that multishot surveys are treated differently than single shots. A number of features (such as measurement while drilling) may be associated with surveys:

  • Enhanced magnetic survey accuracy through in-hole referencing

  • Look ahead predictions

  • Calculation of traveling cylinder coordinates.

Additional features include the following:

  • Sidetrack well planning/footprint analysis

  • Gyro/magnetic changeover decisions

  • Unique data reduction methods

  • Bottom hole assembly performance/selection data base plus a 2D simulator

  • Menu structure designed to reflect the needs of different users.

This software was used exclusively at Wytch Farm for well plan trajectory design and survey programming. The extreme step-out of the Wytch Farm wells meant that survey uncertainty calculations were critical for realistic target sizing.

During drilling of the early wells, the directional drilling support system module was used to benchmark the performance of downhole tools that were operating at their limit under the high angles. The collision avoidance software maximized the number of wells that could be drilled through the existing well structure and still reach a number of targets that were all east of the surface location.

CEMENT VOLUME CALCULATOR

Every primary cement job is different. Both the well conditions (size, deviation, equivalent circulating density limitations) and the job objectives (successful shoe leak-off test, zonal isolation across multiple zones, protection of casing from corrosion) will vary dramatically from one job to the next.

The planning module calculates the volumes of cement slurries, spacers, and displacing fluids, given the required top depth. Alternatively, top depths can be calculated from input volumes. A user-specified excess in included in the open hole volumes calculation. Open hole caliper data can be entered to obtain open hole volume. Additionally, the system will calculate the mix water and total cement additives required.

Equivalent circulating densities (ECDS) were a problem in the reservoir section at Wytch Farm because of the length of the section and associated annular pressure drops. One of the key aspects of the cement design was to ensure that the reservoir fracture pressure was not exceeded. The cement volume calculator was used to analyze different cement and slurry rheologies to maximize the pump rate, optimizing the displacement without exceeding the fracture pressure.

Mud displacements were also analyzed using the cement volume calculator, which can be used for any displacement operation.

OPERATIONS PLANNING

Once initial feasibility had been determined, the next step was to select an appropriate rig. The drillstring simulator was again used to calculate rig mechanical requirements, including maximum hook load, maximum drilling torque, and total rig power requirements for top drive, mud pumps, and draw works.

For the Wytch Farm extended-reach wells, the required rig was the largest onshore rig in Europe, the Deutag T47. Even this rig required upgrading to a high-torque top drive, three 1,600-hp pumps, and an additional generator to yield 5,440 hp.

INITIALIZATION MODULE

Program initialization is the tool for following a program through five stages of development: initialized, planned, started, completed, and closed.

First, rig initialization supplies data to planning, daily operations, and post well review. Then well initialization provides the foundation upon which most of the DEAP applications rest. The initialization module thus allows the user to define relationships between fields, targets, facilities, slots, wells, rigs, and drilling programs. The module can also generate and link a sidetrack.

HYDRAULICS MODULE

Hole cleaning in large-diameter holes has historically accounted for a large proportion of an operator's stuck pipe costs. The vast majority of problems occur in sections deviated greater than 30, where cuttings beds form on the low side of the hole. Depending on the angle, these cuttings beds can cause high torque and drag or may even slide back down the annulus, resulting in packing off or stuck pipe.

This module incorporates sophisticated mathematical models of hydraulics and hole cleaning for open hole sections up to 24-in. in diameter. This module was part of the initiative undertaken on extended-reach drilling between 1986 and 1992, and initially involved experimental tests at the BPX Sunbury Research Centre flow loop.

These tests systematically investigated all of the key variables. The models were then field validated using information from more than 100 wells in the Gulf of Mexico, North Sea, and Alaska. The hole sizes ranged from 8 1/2 in. to 24 in., and both oil-based and water-based muds were included.5

The DEAP hydraulics program integrates pressure drop calculations for given mud rheologies with hole cleaning requirements for a given hole size and well geometry. The program emphasizes the minimum flow rate to clean a hole section and the pump pressure required. Hydraulics and hole cleaning are critical in high-angle, extended-reach wells, especially in the Wytch Farm wells with such long reaches. The high flow rates needed to clean high-angle holes result in high pump pressures.

The DEAP hydraulics model was initially used to predict the flow rates and pressures required to clean each hole section. As the wells increased in length, it became necessary to introduce and extend the use of 6 5/8-in. and 5 1/2-in. drill pipe to minimize pressure drop. The use of larger drill pipe creates a conflict in extended-reach drilling; the larger pipe is beneficial because it reduces pressure drop but detrimental because it increases torque requirements.

SWAB/SURGE CALCULATOR

The swab/surge model performs an array of calculations for varying running speeds at each depth while running casing in a given mud rheology. The results indicate the maximum running speeds without swabbing or surging the formation. This model has been validated with data from the Rogalands research test well in Stavanger, Norway.

A combination of the shallow true vertical depth of the Wytch Farm reservoir and the long reservoir section indicated that swab/surge pressures would be critical during running of the production liner. The selection of a 5!4-in. production liner inside an 8%-in. hole resolved these concerns.

MUD CALCULATIONS

Mud data stored in the DEAP data base have been used to perform mud calculations for costs and consumption. These calculations have been conducted manually at Wytch Farm but are being incorporated as an application in the DEAP system. As the DEAP data base grows, similar performance calculations will be used to compare different wells and different operating procedures (Fig. 1) (66614 bytes).

OPERATIONS MONITORING

To aid in monitoring the drilling/completion operation, the system has an integrated drilling, completion, and production reporting tool:

  • Documentation of quality control checks provides traceable and fully auditable project management reports.

  • A flexible data base querying tool enables ad-hoc queries on reported activities as an aid to efficiency, performance, safety, and management and local government reporting.

  • Stock control and inventory functions maintain accurate records of rig site materials usage.

COMPANY MAN MODULE

This module is essentially a driller's tool kit; it includes a directional survey calculator, vertical section definition, hole cleaning and hydraulics calculator, swab/surge calculator, a cement volume/plug-back calculator, and a bottom hole assembly (BHA) performance selector. All of these applications allow the user to make rapid I what if" investigations, which are particularly valuable in critical well operations and planning.

DAILY OPERATIONS MODULE

The daily operations module includes routines that provide daily cost tracking, a fluids report, and a morning report. Certain items are automatically transferred from the morning report to specific applications. Additionally, other information is stored, including formation integrity test data, actual cement data, actual casing data, bit and BHA records, and inventory stock control.

HOLE CLEANING

Difficulties were experienced in cleaning the 8 1/2-in. hole in the reservoir section when the high flow rates required to clean the high angle hole led to losses because of high ECDS. The problems were ultimately attributed to the high density sands not normally associated with such a shallow vertical depth. When the cuttings density was corrected, the model again correlated with field experience.

The DEAP hydraulics model was used on all five wells to optimize the mud rheology, pump pressure and ECD, and hydraulics with respect to hole cleaning. On the first well, the mud rheology was not fully optimized as indicated by operational evidence of poor hole cleaning. When the DEAP model was run to simulate the field case, two possible solutions were highlighted:

  • Reduce the yield point with turbulent flow to clean the annulus.

  • Increase the yield point to clean the annulus by using the resulting laminar flow.

Either option had the benefits of reducing the flow rate and reducing the pump pressure requirement. The first option, however, significantly reduced the ECD because the pressure drop in the annulus was minimized when thinner mud was used (Fig. 2) (44933 bytes) and (Fig. 3) (43187 bytes).

DRILLSTRING SIMULATOR

An analysis of torque and drag proved accurate for all but the 8 1/2-in. section where torque for all Wytch Farm extended reach wells has consistently been some 30% greater than that predicted. Detailed observation of the torque for the 8 1/2-in. section has shown that torque increases from default values immediately when the section is drilled and cuttings are produced and that there is an unusually strong correlation between torque and hole cleaning. This high torque has been attributed to the combination of low mud weight, very high angles, high cuttings density, and abrasive reservoir sands.

Although cuttings are being transported out of the hole, the drill pipe is rotating in a bed of cuttings on the low side of the hole. This effect could not be avoided, and subsequent torque and drag calculations have been compensated to account for the higher friction.

One of the most critical operations at Wytch Farm was the running of the 9 5/8-in. casing. Some 5,700 m of 9 5/8-in., 40-lb/ft casing had to slide into 12 1/4-in. hole at a tangent angle of 83. The shallow depth of the Wytch Farm reservoir meant that gravity provided very little assistance to sliding operations, and hook load rapidly dropped off. Because running casing was the most critical operation, the drillstring simulator module was used to optimize the well bore trajectory for running the 9 5/8-in. casing.

The drillstring simulator was also used during the 9 5/8-in. casing running operation. Prior to the running of the 9 5/8-in. casing, the latest well data were transferred into the drillstring simulator from the DEAP data base, and the surface hook loads were predicted. During the casing run, any divergence from prediction was used as an indicator of downhole problems. Corrective action, such as reciprocation and circulation, was conducted prior to continuing to run in hole. Reciprocation and circulation were critical to the successful running of the casing (Fig. 4) (61467 bytes).

Rotation of the 5 1/2-in. production liner was considered critical to get a good cement bond through the long reservoir section. The drillstring simulator module was used to calculate the maximum torque applied downhole to the liner. The model indicated that torque would vary through the cement displacement, as the differing densities of mud, cement, and spacers would have a significant effect on the buoyancy of the string. This effect correlated well with actual operations.

Divergence of predicted and actual torque when cement rounded the casing shoe indicated that the liner was subjected to significantly higher torque during rotation in cement. This observation prompted the upgrading of liner coupling to ensure integrity was not compromised (Fig. 5) (58336 bytes).

DIRECTIONAL DRILLING

The directional drilling support system program was constructed by BPX operations staff in an operational drilling department. Thus, the software very closely matches the requirements of the operator for managing routine operations.

A truly multidisciplinary approach to the design of directional survey programs can be taken because of the rigorous modeling of survey errors inherent in the software. Once a survey program has been designed, survey execution can be carried out to required accuracy. The target size may be set to accommodate survey errors. Subsurface separation between wells can be visualized using the traveling cylinder, with separation rules based on the quantitative risk assessment method.

CEMENT

The cement volume calculator predicts pump pressure during slurry and displacement fluid pumping and the U-tubing effect on flow out of the well. ECD and hydrostatic head are predicted at up to five points in the annulus and compared with pore and fracture pressure limits. A plot of predicted pump pressure vs. number of pump strokes is provided for the displacement. Hydraulics during mud circulation are modeled for a range of mud flow rates. Checks are made for potential problems such as casing float out and casing collapse. The user is warned when limits such as fracture pressure and cement thickening time are exceeded.

PERFORMANCE REVIEW

Although the drillstring simulator was initially designed for drilling operations, it has become clear that completion and workover operations are often limiting factors in extended reach wells. An analysis of completion running data from the first Wytch Farm extended reach wells indicated that the coefficient of friction (0.17) of the completion in brine was lower than expected (Fig. 6) (56170 bytes). The low friction factor gave confidence that mechanical setting of packers and retrieval of completion strings would not pose a problem for even greater step-outs.

A high level of professionalism and project execution by the entire Wytch Farm team has achieved notable success in constructing record-setting extended reach wells. The use of current technology, such as the drilling engineering applications platform, has contributed to the drilling and completion process.

ACKNOWLEDGMENT

The authors thank BP Exploration and Baker Hughes Inteq for permission to publish this article. The authors also thank the Wytch Farm project team and drilling and completions group at BP Technology Centre for their contributions and Frank A. Radez with Baker Hughes Inteq for his editorial assistance.

REFERENCES

  1. Payne, M.L., Cocking, D.A., and Hatch, A.J., "Critical Technologies for Success in Extended Reach Drilling," Society of Petroleum Engineers paper No. 28293, presented at the SPE 69th Annual Technical Conference and Exhibition, New Orleans, Sept. 25-28,1994.

  2. Sawaryn, S.J., and Grayson, H.L., "Industry Participation in the Development of an Integrated Drilling Engineering Applications Platform," SPE paper No. 23892, presented at the IADC/SPE Drilling Conference in New Orleans, Feb. 18-21,1991.

  3. Thorogood, J.L., "Instrument Performance Models and their Application to Directional Survey Operations," SPE paper No. 18051, presented at the SPE Technical Conference & Exhibition, Houston, Oct. 2-5,1988.

  4. Wolff, C.J.M, and de Wardt, J.P., "Borehole Position Uncertainty - Analysis of Measuring Methods and Derivation of Systematic Error Model," journal of Petroleum Technology, December 1981, pp. 2339-50.

  5. Swanson, B.W., Thorogood, J.L., and Gardner, A., 'The Design and Field Implementation of a Drilling Hydraulics Application for Drilling Optimization," SPE paper No. 27548, presented at the SPE European Petroleum Computer Conference, Aberdeen, Mar. 15-17,1994.

THE AUTHOR

Paul Chapman is a drilling engineer for BP Exploration Technology Ltd. in Sunbury, U.K. He specializes in drill-string mechanics and has been instrumental in the development of the DEAP system during his work on the Wytch Farm project over the past 4 years. Chapman holds a BS from Imperial College, London University.
Alan Good is a product specialist for Baker Hughes Inteq in Houston. He has 15 years' experience in operations and technical support for the petroleum industry. Good holds a BS from the University of Aston, Birmingham, U.K.

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