Field Validation of Transient Swab-Surge Response With Real-Time Downhole Pressure Data
- G. Robello Samuel (Landmark-Halliburton) | Ashwin Sunthankar (Landmark-Halliburton) | Glen McColpin (Landmark-Halliburton) | Peter Bern (BP plc) | Tim Flynn (Halliburton)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- December 2003
- Document Type
- Journal Paper
- 280 - 283
- 2003. Society of Petroleum Engineers
- 1.11 Drilling Fluids and Materials, 1.11.2 Drilling Fluid Selection and Formulation (Chemistry, Properties), 1.14 Casing and Cementing, 1.6.10 Running and Setting Casing, 1.7.1 Underbalanced Drilling, 1.12.6 Drilling Data Management and Standards, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 3 Production and Well Operations, 1.10 Drilling Equipment, 1.7.6 Wellbore Pressure Management, 6.3.3 Operational Safety, 1.6 Drilling Operations, 2 Well Completion, 1.1 Well Planning, 5.3.2 Multiphase Flow
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This paper describes the field validation results of the transient swab-surge model with real-time downhole annular pressure data. The maximum pressures encountered during tripping or reciprocation are indispensible for making appropriate well-completion decisions. The prediction of swab and surge pressures is of critical importance in wells in which the pressure must be maintained within narrow limits of the pore and fracture pressures. It also plays a major role in running casing, particularly with narrow annular clearances. For these critical cases, a fully dynamic model is required to better estimate the maximum pressures encountered.
This paper presents actual surge-and-swab field data collected with downhole-drilling-data measuring tools during tripping and circulating operations. These data were obtained from Alaska and North Sea wells with a range of hole diameters and different base-fluid muds. The data were compared and interpreted with steady-state calculations as well as a dynamic surge model, which includes the effects of fluid inertia and compressibility, wellbore elasticity, pipe axial elasticity, and temperature-dependent fluid properties.
The sampling rate was specifically increased to 2 seconds and, in some cases, 1 second. This prevents downhole data attenuations and captures the full waveforms more accurately. Different operations were included in the downhole-drilling-data measuring tool runs to cover swabbing, surging, reciprocation, and simultaneous pumping operations during tripping. Model predictions for downhole pressure behavior were in excellent agreement with the measured real-time downhole pressure data.
Qualitative assessment and quantitative characterization of well pressures are of critical importance to many phases of well construction. They allow not only subsequent adjustments to the well plan when combined with payzone geo-steering tools but also successful completion of extended-reach and complex wells.
Increasingly, more difficult wells are being drilled with a narrow margin between pore and fracture pressures. This requires that swab-surge pressures be maintained within narrow limits while tripping drillpipe, running casing, and cementing. Working outside this safe-operating window for even short durations has historically led to costly well complications. Monitoring the actual downhole pressure in real time with a downhole-drilling-data measuring tool is a reliable method; however, real-time data are generally confined to periods of continuous circulation. In addition, it is not possible to run conventional downhole-drilling-data measuring submarine with casing strings. If a reliable, predictive, validated model with the real-time data is available, it will help accurately evaluate transient wellbore pressures early in the well planning phase. It also offers a viable tool not only for providing accurate data in the planning phase but also for better defining the operating limits for both drilling and casing operations.
Developing confidence in computational predictions requires establishing a rigorous procedure to ensure that the trends and magnitudes of the results match reality. This paper focuses on the validation process.
Pressure surges in critical wells are commonly determined with steady-flow surge models. In these models, the drilling mud is perfectly displaced by the pipe motion. These models neglect fluid inertia, the compressibility of the fluid and the wellbore, and the axial elasticity of the pipe. The first fully dynamic surge-pressure model was developed by Lubinski.1 This model emphasized the importance of compressibility in pressure calculations. He also concluded, on the basis of steady-state flow, that the actual surge and swab pressures are inadequate and could differ considerably from those predicted. Lal2 corrected a number of deficiencies in the Lubinski model and presented the influence of various parameters affecting surge pressures. Both Lubinski and Lal assumed rigid pipe displacement. Mitchell3 added the effect of pipe axial elasticity to the dynamic surge analysis. The Mitchell model is used in this paper for validation. Engineering detail needs to be sufficient to accurately predict swab and surge pressures; more importantly, issues involving the validity, accuracy, and lack of data confirmation need to be addressed before deciding whether the model predicts reasonably well. This also allows the model to be verified, which ensures that the computer simulation mimics the designed conceptual model and accurately represents the actual systems considered. Even though the model has been extensively field-validated4 with an earlier generation of downhole and surface data, the advent of highly accurate downhole tools has provided an opportunity to revalidate it.
The real-time downhole drilling data are compared with the dynamic surge/swab model, which includes directional wells, circulation while tripping, and dynamic pipe behavior. The enhanced dynamic model3 includes fluid inertia, fluid compressibility, wellbore elasticity, axial elasticity of moving pipe, temperature-dependent fluid rheology for both water- and oil-based muds, simultaneous circulation, pipe movement, well deviation, and eccentricity.
The data capture rates at the surface and downhole were a major concern because full dynamic response to swabs and surges are being studied. The measurement's sampling rate was adjusted to every 2 seconds and, in certain cases, 1 second. Simulation indicated that this rate was fast enough to adequately characterize any transient response. The method and details of the model involved are beyond the scope of this paper and are explained elsewhere.3
The following case studies are from the data file of Well A from North Slope. The well schematic is presented in Fig. 1. Conductor casing of 16 in. was landed at 110 ft followed by 7 5/8-in. surface casing to a depth of 4,286 ft. Further, 6 3/4-in. drilling was in progress.
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