Swab Pressures Research Articles

A numerical model to predict surge and swab pressures for yield power law fluid in concentric annuli with open-ended pipe

Excessive surge pressure can cause many downhole problems such as loss circulation, leakage, fracture formation, and blowout. Accurately predicting surge and swab pressures can provide a guarantee of safety in a downhole. Multiple research endeavors have been conducted based on close-ended pipes (CEP); however, no exact or approximate models to predict surge and swab pressures have been reported for yield power law (YPL) fluid in an open-ended pipe (OEP). In this paper, an exact numerical model was established to predict surge and swab pressures for YPL fluid in concentric annuli with OEP. Additionally, existing regression models for Bingham plastic (BP) and power law (PL) fluids were modified based on the exact numerical solutions in concentric annuli with OEP. The accuracy of the modified regression model is ±5% and ±15% for BP and PL fluids, respectively. In addition, an accurate (to within 5% error) new regression model was developed to predict surge and swab pressures for YPL fluid in a concentric annulus with OEP on the basis of exact numerical solutions. The effects of fluid properties, annular geometries and drilling parameters on surge and swab pressures in OEP were investigated using an exact numerical model.

Simplified surge pressure model for yield power law fluid in eccentric annuli

Axial movement of drillstring during drilling operations causes downhole pressure variations, which are commonly known as surge and swab pressures. This paper presents a new eccentric annulus surge pressure (EASP) model for yield power law (YPL) fluid. To develop the model, flow in eccentric annulus was investigated using computational fluid dynamics (CFD) technique (ANSYS Fluent). CFD simulations were conducted varying fluid rheological parameters, tripping speed and annular geometry. Simulation results are analyzed considering surge pressure ratio (i.e. ratio of surge pressure in eccentric annulus to that of concentric annulus) as a parameter for quantifying effect of eccentricity on surge pressure. Surge pressure ratio (SPR) is found to be very sensitive to fluid behavior index and annular eccentricity and diameter ratio. In addition to the CFD studies, small-scale laboratory experiments were conducted to validate accuracy of the EASP model. Results show that the model accurately (i.e. maximum error of ±5%) and conveniently predicts surge and swab pressures for YPL (Herschel Buckley) fluid in eccentric annulus without requiring complex numerical procedures. The model is valid for wide ranges of diameter ratio (0.2≤Kd≤ 0.8), eccentricity (0≤ ε≤0.9) and fluid behavior index (0.2≤n≤ 1).

Abnormal down hole pressure variation by axial stick-slip of drillstring

Downhole pressure variation is generally believed to be a kind of surge and swab pressure due to the axial movement of drillstring during the tripping in/out operation, and even wave loading induced heave motion. In order to predict downhole pressure variation, the Stribeck friction model has been used to analyze the friction-induced self-excitation vibration (stick-slip). This model describes the axial stick-slip motion of the drill pipe through four regimes of contact: sticking, boundary lubrication, partial fluid lubrication, and full lubrication. The results indicate a significant increase in the peak velocity of the drillstring compared to the velocity at the surface point. In addition, axial tension induced geometrical stiffness has been taken into account, which results in a time dependent normal force between the drillstring and the borehole in the curved section of borehole. Simulations show that the wave form of the downhole drillstring motion is different from the surface motion.

Risk-based safety analysis of well integrity operations

Assurance of well integrity is critical and important in all stages of operation of oil and gas reservoirs. In this study, well integrity is modeled during casing and cementing operations. Two different approaches are adapted to model potential failure scenarios. The first approach analyzes failure scenarios using bow-tie model which offers a better visual representation of the logical relationships among the contributing factors through Boolean gates. The second approach takes advantage of Bayesian network, both to model conditional dependencies and to perform probability updating. The analysis identified managed pressure drilling system, logging tool, slurry formulation, casing design, casing handling and running method, surge and swab pressures as critical elements of the well integrity model. A diagnostic analysis on the slurry formulation further identified pilot test(s) and the interpretation of the test(s) as key elements to ensuring integrity of cementing operation. Relevant safety functions and inherent safety principles to improve well integrity operations are also explored.

A new simplified surge and swab pressure model for yield-power-law drilling fluids

Surge and swab pressures have been known as common phenomena to cause wellbore pressure control problems such as lost circulation, formation fracture, fluid influx, kicks, and even blowouts. Accurate prediction of these pressures is very important to avoid associated drilling problems. To date, there is no exact analytical model to predict surge pressure developed in concentric annulus with yield-power-law (YPL) fluids. Most of the available models (analytical and regression models) are developed based on narrow-slot approximation of the annular flow. The models provide prediction for diameter ratio ranging from 0.4 to 0.85 with discrepancy of up to 20%. This paper presents a new regression-based surge-pressure model, which makes accurate predictions (maximum error of ±3%) for wide range of diameter ratios (0.4–0.85). To develop the regression model, an exact numerical model was formulated and extensive numerical simulations were performed. The results were analyzed to formulate a simplified regression model that predicts surge and swab pressures conveniently for YPL fluids without requiring iterative calculation procedures. To verify model predictions, laboratory experiments were conducted in small scale setup (50.8 × 33.5 mm annulus). Model predictions demonstrated reasonable agreement with experimental measurements and exact numerical solutions.

Elastic Pipe Control and Compensation for Managed Pressure Drilling Under Sea Wave Heave Conditions

Managed pressure drilling (MPD) was developed as a group of technologies to more precisely control the annular pressure profile for which accuracy of the estimation of the bottomhole pressure is important. Particularly, under severe wave heaves in deepwater environments, the estimation based on static state pipe movement models can result in underestimation/overestimation of bottomhole pressures. The purpose of this study is to investigate the dynamic axial response of the drillstring with friction to applied heaving velocity, with particular interest to the effect at the bottomhole pressure. The paper presents an efficient and accurate method for solving the dynamic axial drillstring with friction and it allows it to be applied to heave velocity at the surface. The model that couples the pipe motion solves the full balance of mass and balance of momentum for pipe and annulus flow, considering the compressibility of the fluids, the elasticity of the system, and the dynamic motions of pipes and fluids. Also considered are surge pressures related to fluid column length below the moving pipe, compressibility of the formation, and axial elasticity of the moving string. Fluid properties are adjusted to reflect the effects of pressure and temperature on the fluids. The modeling takes into account the pipe elasticity under different combinations of heave and pipe velocities. Furthermore, the real-time torque and drag models are calibrated to actual hole conditions in real-time using survey, temperature, pressure, and downhole tool data to calculate friction factors in a wellbore. It has been observed that different conditions exist, some resulting in velocity reversal; thus causing surge or swab pressures. It has also been observed that heave amplitude has significant influence on bottomhole pressure. The different conditions observed for periodic or time function of displacements include (1) surface pipe velocity attributed to wave heave is in phase with the bottom movement of the string; (2) surface velocity of the pipe is out of phase with the bottom velocity of the pipe; (3) wave velocity and surface pipe velocity can be out of sync, and the bottom pipe velocity can be in phase with the surface velocity; and (4) wave velocity and surface pipe velocity can be out of sync, and the bottom pipe velocity can be out of phase with the surface velocity. The results of these calculations can be coupled to a real-time hydraulics model to determine a setpoint pressure for the MPD choke system. (SPE 173|005)

Numerical model for predicting the surge and swab pressures for yield-power-law fluids in an eccentric annulus

Of all of the rheological parameter models for drilling fluids, the yield-power-law (YPL) model is the best one for performing actual calculations. However, no exact general analytical solution has been found for YPL fluids in both concentric and eccentric annuli because currently, all of the published methods for predicting the surge and swab pressures for YPL fluids apply the narrow-slot approximation technique.To analyze the actual flow characteristics of YPL fluids in an eccentric annulus, this paper introduces an exact model for predicting the surge and swab pressures based on fluid mechanics and the properties of YPL fluids. This model fully analyzes the effects of the rheological parameters of drilling fluids, of the geometric parameters of the annulus and of the pipe velocity on the surge and swab pressures. The results show that the maximum velocity weakens with an increased clearance (θ) when the main flow path is in the range of θ = 0 ∼ 120 deg, that the surge and swab pressures decrease with an increase in the eccentricity of the annulus but increase rapidly with an increase in the diameter ratio, and that the surge and swab pressures are most sensitive to changes in the fluid behavior index (n) when 0.7 < n < 1.When the results of this model are also used to evaluate the validity of the narrow-slot model, it is found that the accuracy of the narrow-slot model, which is slightly affected by the rheological parameters (τ0, K and n), is high when the diameter ratio is larger than 0.8 (i.e., the accuracy is within 2% error). However, when the diameter ratio is less than 0.6, the accuracy is influenced by only a few factors, among which Bingham plastic fluids (n = 1) has the most effect, followed by power-laws fluid (τ0 = 0).

Suppressing Pressure Oscillations in Offshore Drilling: Control Design and Experimental Results

As oil exploration and development costs rise, the oil industry increases its efforts to improve oil recovery (IOR) from existing fields. IOR is achieved mainly by drilling more wells, but drilling in partially depleted reservoirs is challenging due to narrow pressure margins. Offshore drilling in harsh environments, such as the North Sea, presents additional challenges, since the heaving motion from a floating rig induces large surge and swab pressures in the well. This brief suggests a remedy for this problem using automatic control of well pressure. Taking advantage of an experimental lab facility recently completed at NTNU, a model of the drilling system is developed using subspace identification methods. The model serves as a basis for state estimation and controller design using model predictive control. Applying the controller to the lab facility, pressure oscillations are suppressed by 70%-90% compared with the open-loop case, depending on the period of the heave motion.

A steady-state approach for evaluation of surge and swab pressures in flows with free surface boundary conditions

A new approach for predicting surge and swab pressures in open-ended pipes running in steady-state is proposed. In addition to the fluid flow through the annulus and drill pipe, the upper ends of drill pipe and annular space are assumed to be opened to the atmosphere, creating two free surfaces. The approach is based on the modified Bernoulli׳s equation applied to Bingham fluid flows. The pressure differences are not only due to viscous losses but also to fluid velocity differences, and to the fluid column weight differences. The model results are compared with measured data for a Newtonian fluid and the differences lie within an error range of 0% to +10%. A sensitivity analysis is conducted, depicting that the model depends on the Reynolds, Bingham and Froude numbers, and also on the pipe geometry (diameter ratios). • A new approach for evaluation of surge and swab pressures is proposed. • The pressure gradient is as a function of the Reynolds, Bingham and Froude numbers. • The differences between measured and computed values lie within a 10% error band.

A new model for computing surge/swab pressure in horizontal wells and analysis of influencing factors

In the drilling of horizontal wells in complex formations such as subsalt fractural formation, factors such as high drilling liquid density, rheological uncontrollability, and narrow safety density window of drilling fluid may lead to downhole pressure fluctuation, which, however slightly gives rise to complex downhole problems. In order to accurately calculate the surge/swab pressure of horizontal wells in such formations, this paper, based on hydromechanics and a width-variable flat-plate flow model, introduce a new model for computing surge/swab pressure in horizontal wells. This model takes the effects of velocity drilling string on the boundary conditions of surge/swab pressure into consideration, as no previous model has. With the tripping of drilling string under consideration, and when the annular flow remains the same, we find that, in the computation of swab pressure, the velocity in the inside and outside velocity zones are both larger than those produced by previous ones, and that in the computation of surge pressure, while the velocity in the inside velocity zone is first smaller and then turns greater, the velocity in the outside velocity zone is always larger. A comparison with previous models also reveals larger surge pressure, larger swab pressure at low rate and smaller swab pressure when annular flow rate reaches a certain level.An analysis of major factors that influence surge/swab pressure in this model shows that pressure drop is at the mercy of a number of factors; the surge pressure drop decreases with the increased eccentricity whereas the swab pressure drop increases with the rising eccentricity at low annular flow rate; the surge pressure drop decreases with the rising yield point whereas the swab pressure drop increases with the rising yield point; the surge pressure drop increases largely with the increase of plastic viscosity whereas the swab pressure drop largely decreases with the dropping plastic viscosity; the surge pressure drop increases with run in hole (RIH)speed; the swab pressure drop increases with pull out of hole (POOH) speed at small annular flow rate whereas the swab pressure drop decreases with the POOH speed when the annular flow rate reaches a certain level.The analysis also indicates that the surge/swab pressure is most sensitive to the plastic viscosity of drilling fluid. Then, it is of great significance to monitor the plastic viscosity during the drilling process when other factors are well controlled.

Disturbance Rejection by Feedback Control in Offshore Drilling: Experimental Results

As oil exploration and development costs rise, the oil industry increases its efforts to improve oil recovery (IOR) from existing fields. IOR is achieved mainly by drilling more wells, but drilling in partially depleted reservoirs is challenging due to narrow pressure margins. Offshore drilling in harsh environments, such as the North Sea, presents additional challenges, since the heaving motion from a floating rig induces large surge and swab pressures in the well. The paper suggests a remedy for this problem using automatic control of well pressure. Taking advantage of an experimental lab facility recently completed at NTNU, a model of the drilling system is developed using subspace identification methods. The model serves as a basis for state estimation and controller design using model predictive control. Applying the controller to the lab facility, pressure oscillations are suppressed by 70-90% compared to the open-loop case, depending on the period of the heave motion.

P2.034 Sampling Technique is Important For Optimal Isolation of Pharyngeal Gonorrhoea

<h3>Background</h3> Culture is insensitive for the detection of pharyngeal gonorrhoea but isolation is pivotal to antimicrobial resistance surveillance. The aim of this study was to ascertain whether recommendations provided to clinicians on pharyngeal swabbing technique could improve gonorrhoea detection rates and to determine which aspects of swabbing technique are important for optimal isolation. <h3>Methods</h3> <b></b>This study was undertaken at the Melbourne Sexual Health Centre, Australia. Detection rates for pharyngeal gonorrhoea among clinicians were compared before (June 2006–May 2009) and after (June 2009 - June 2012) recommendations on swabbing technique were provided. Associations between detection rates and reported swabbing technique obtained via a clinician questionnaire were examined. <h3>Results</h3> The overall yield from testing before and after provision of the recommendations among 28 clinicians was 1.6% (134/8586) and 1.8% (264/15,046) respectively (p = 0.17). Significantly higher detection rates were seen following the recommendations among clinicians who reported: a change in their swabbing technique in response to the recommendations (2.1% versus 1.5%; p = 0.004); swabbing a larger surface area (2.0% versus 1.5%;p = 0.02); applying more swab pressure (2.5% versus 1.5%; p &lt; 0.001); and a change in the anatomical sites they swabbed (2.2% versus 1.5%; p = 0.002). The predominant change in sites swabbed was an increase in swabbing of the oropharynx - from a median of 0% to 80% of the time. <h3>Conclusion</h3> <b></b>More thorough swabbing improves isolation of pharyngeal gonorrhoea using culture. Clinicians should receive training to ensure swabbing is performed with sufficient pressure and that it covers an adequate area that includes the oropharynx.

Sampling technique is important for optimal isolation of pharyngeal gonorrhoea

BackgroundCulture is insensitive for the detection of pharyngeal gonorrhoea but isolation is pivotal to antimicrobial resistance surveillance. The aim of this study was to ascertain whether recommendations provided to clinicians...

Surge-and-Swab Pressure Predictions for Yield-Power-Law Drilling Fluids

Summary Surge and swab pressures have been known to cause formation fracture, lost circulation, and well-control problems. Accurate prediction of these pressures is crucially important in estimating the maximum tripping speeds to keep the wellbore pressure within specified limits of the pore and fracture pressures. It also plays a major role in running casings, particularly with narrow annular clearances. Existing surge/swab models are based on Bingham plastic (BP) and power-law (PL) fluid rheology models. However, in most cases, these models cannot adequately describe the flow behavior of drilling fluids. This paper presents a new steady-state model that can account for fluid and formation compressibility and pipe elasticity. For the closed-ended pipe, the model is cast into a simplified model to predict pressure surge in a more convenient way. The steady-state laminar-flow equation is solved for narrow slot geometry to approximate the flow in a concentric annulus with inner-pipe axial movement considering yield-PL (YPL) fluid. The YPL rheology model is usually preferred because it provides a better description of the flow behavior of most drilling fluids. The analytical solution yields accurate predictions, though not in convenient forms. Thus, a numerical scheme has been developed to obtain the solutions. After conducting an extensive parametric study, regression techniques were applied primarily to develop a simplified model (i.e., dimensionless correlation). The performance of the correlation has been tested by use of field and laboratory measurements. Comparisons of the model predictions with the measurements showed a satisfactory agreement. In most cases, the model makes better predictions in terms of closeness to the measurements because of the application of a more realistic rheology model. The correlation and model are useful for slimhole, deepwater, and extended-reach drilling applications.

A simplified surge and swab pressure model for yield power law fluids

Abstract Surge and swab pressures can be generated in different stages of well construction including tripping operations and reciprocation of drillstring in the wellbore. Significant surge and swab pressures can lead to a number of costly drilling problems such as lost circulation, formation fracture, fluid influx, kicks, and blowouts. This phenomenon is of economic importance for the oil industry. Theoretical and field studies indicate that pressure surges strongly depend on drillpipe tripping speeds, wellbore geometry, flow regime, fluid rheology, and whether the pipe is open or closed. Although a large number of studies were conducted in the past to investigate surge and swab pressures, experiments under controlled laboratory conditions have never been reported. This paper presents results of an experimental study aimed at investigating the effects of pipe speed (i.e., tripping speed), fluid properties and borehole geometry on surge and swab pressures under laboratory conditions. Other phenomena such as fluid gelling and pipe eccentricity effects were also examined. Experiments were performed in a test setup that has the capability of varying the tripping speed and accurately measure the surge or swab pressures. The setup consists of fully transparent polycarbonate tubing and inner steel pipe, which moves axially using a speed-controlled hoisting system. Experiments were conducted using mineral oil and polymeric fluids. A new regression model has been developed to calculate surge and swab pressures under steady-state flow conditions. The model is based on the results of approximate numerical solutions obtained by considering the annulus as a narrow slot. Model predictions were compared with experimental measurements and predictions of existing models. A satisfactory agreement has been obtained. Experimental results and model predictions confirm that the trip speed, fluid rheology, annular clearance and pipe eccentricity significantly affect the surge and swab pressures.

The Prediction of Surge and Swab Pressures and Critical Pipe Running Speed While Tripping in a 12 1/4-in. Hole (Gachsaran Formation) of Maroun Field in Iran

Maroun field is a large oil field located in southern Iran. The producing formations in this field are deposited under the Gachsaran formation, which has an extremely high value of pore pressure. The mud density through the Gachsaran formation usually exceeds 20 ppg. In this situation the pipe running velocity is a critical issue and careless moving of the drill string may cause the risk of kick or formation breakdown. The purpose of this study is to develop a model for prediction of critical pipe running speed. The method of study is the basis of simple fluid flow equations and computer programming is used to simplify primary data analyzing. New correlations are developed using multiple regression method and SPSS software for predicting critical pipe running speed using only simple input data such as well geometry and drilling fluid properties, which can be measured using American Petroleum Institute testing methods.

Hydraulic Fracturing: Compensation of Surge and Swab Pressures in Floating Drilling Operations

This article, written by Technology Editor Dennis Denney, contains highlights of paper SPE 110562, "Contacting More of the Barnett Shale Through an Integration of Real-Time-Microseismic Monitoring, Petrophysics, and Hydraulic-Fracture Design," by J. Daniels, SPE, G. Waters, SPE, J. LeCalvez, SPE, J. Lassek, SPE, and D. Bentley, Schlumberger, prepared for the 2007 SPE Annual Technical Conference and Exhibition, Anaheim, California, 11-14 November. The paper has not been peer reviewed. With effective stimulation techniques, economics for horizontal wells in shale-gas reservoirs are favorable compared to vertical wells. Real-time fracture mapping enables on-the-fly changes in fracture design to maximize the effective stimulation volume (ESV). ESV is defined as the reservoir volume effectively contacted by the stimulation treatment as determined by microseismic (MS) event locations and density. Correlation of MS activity with log data enables estimating fracture geometry. These data then are used to design a fit-for-purpose stimulation that has the greatest chance of maximizing the ESV and production. Introduction The Barnett shale is a Mississippian marine-shelf deposit that lies unconformably on the Ordovician Viola limestone/Ellenberger group and is conformably overlain by the Pennsylvanian Marble Falls limestone. The Barnett shale, within the Fort Worth basin, was the focus of this study, concentrating on wells in Denton, Wise, and Tarrant counties of Texas: the "core area." The Barnett in the core area ranges from 300 to 500 ft thick. Matrix permeabilities range from 0.00007 to 0.0005 md, with porosities ranging from 3 to 5%. The Barnett is its own source rock and is abnormally pressured in this area, with a pore-pressure gradient of approximately 0.5 psi/ft. Hydraulic-fracture stimulation is required to obtain commercial production. Before 1997, Barnett wells were completed with massive hydraulic-fracture treatments of crosslinked gelled fluids and large amounts of proppant. Difficulties in cleaning up fracture damage from the crosslinked gel and the high cost of these massive stimulation treatments led to marginally economical wells. In 1997, large-volume high-rate slick-water fracture-stimulation treatments were tested. While well performance was not increased significantly, completion costs were reduced by approximately 65%. In 2002, horizontal wells were drilled to increase wellbore exposure to the reservoir. The first horizontal wells increased the estimated ultimate recovery by 300% at double the well cost relative to vertical wells. Horizontal wells offer an economic solution outside the core area because fracture-height growth can be reduced while creating a large fracture-surface area. This solution is critical for regions in which the shale is bounded by potentially water-producing formations. Horizontal wells reduce the number of surface locations needed near populated areas and have been used in various infill-drilling programs. Gas-recovery factors can be improved by focusing the stimulation treatments on zones in the lateral section that have not been contacted by offset wells.

Compensation of Surge and Swab Pressures in Floating Drilling Operations

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 108346, "Evaluation of MPD Methods for Compensation of Surge and Swab Pressures in Floating Drilling Operations," by Olve Sunde Rasmussen, SPE, and Sigbjorn Sangesland, SPE, Norwegian U. of Science and Technology, prepared for the 2007 IADC/SPE Managed Pressure Drilling and Underbalanced Operations Conference and Exhibition, Galveston, Texas, 28–29 March. One of the main concerns in deepwater drilling and drilling in depleted reservoirs is the low margin between fracture- and pore-pressure gradients. Drillstring tripping causes pressure variations in the borehole. Use of a mobile offshore drilling unit (MODU) in deep water results in even more-severe surge and swab pressures that are more difficult to control because of MODU heave motion. The full-length paper details the magnitude of surge and swab pressures that can occur in typical drilling operations, but focuses on through-tubing rotary-drilling (TTRD) operations. Introduction Through-tubing drilling using coiled tubing has gained acceptance as a cost-effective method for short-drainhole drilling. TTRD is more expensive but allows longer sections to be drilled, primarily because of drillstring rotation that reduces drillstring drag forces and improves hole cleaning. TTRD has been performed from fixed platforms, but rarely from MODUs. Only a few of these operations have been conducted in the North Sea. The first TTRD well drilled from a floating platform in the North Sea was drilled by Norsk Hydro in 2005. The limitation of TTRD in most wells is the small clearance between the borehole and drillstring, which causes high annular-pressure losses during drilling. Maintaining the bottomhole pressure (BHP) within acceptable limits when drilling from a MODU is more complicated because of the motion of the MODU. The heave compensator on the MODU controls the position of the drillstring in drilling and tripping modes. However, during makeup and breakout of the connections, the drillstring is suspended in slips in the rotary table and the entire drillstring moves up and down with the heave of the MODU. This can cause high surge and swab pressures that may lead to lost circulation or influx of formation fluid, respectively. These consequences may limit the drilling length of the borehole section and may result in well-control challenges. Surge and Swab Pressures Surge and swab pressures take place as a result of fluid displacement caused by drillstring movement in a fluid-filled borehole. In long low-annular-clearance directional wells, mechanical friction and fluid drag will reduce and slow the motion of the lower end of the drillstring; as a result, the surge and swab pressures will be smaller than in shorter vertical wells. Calculations in the full-length paper are conservative because a closed-pipe model was used and drillpipe stretch is not considered. In a low-clearance wellbore, tripping speeds must be monitored and con-trolled to ensure that excessive surge or swab pressures are not generated. Pressure Fluctuation in a Closed-Hole Volume Caused By Drillstring Displacement Some managed-pressure-drilling (MPD) methods can be considered closed-loop systems. A rotating control head (RCH) allows the annulus to be pressurized while the returning fluid volume from the borehole is bled off through a choke manifold.

Field Validation of Transient Swab-Surge Response With Real-Time Downhole Pressure Data

Summary 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.

The Benefits of Real-Time Downhole Pressure and Tension Data With Wired Composite Tubing

Abstract Continuous composite coiled tubing with embedded electric conductors can provide uninterrupted flow of data from downhole tools. This capability makes monitoring borehole stability throughout the entire drilling process possible, even when conventional mud-pulse telemetry tools are not operating and cannot provide information in real-time. An operator faces many borehole stability problems: stuck pipe, pack-off events, lost circulation, kicks, leak-off tests, and formation integrity tests, all of which can result in periods of non-circulation. However, an operator no longer has to rely solely on surface gauges to provide downhole information to deal with these problems because downhole readings are now available. The benefits of downhole pressure and tension data throughout these problematic and routine activities provide valuable information on events during the most critical operating procedures. Consequently, corrective actions can be taken to prevent or cure borehole stability problems almost as soon as they develop. In addition, downhole data can help reduce drilling time. The borehole is under constant scrutiny. Drilling, tripping, non-circulating, and circulating operations can be optimized while avoiding other potential problems. For example:Swab and surge pressures can be monitored constantly while tripping without circulating;Ledges and tight spots can be identified before they cause severe damage;Time for leak-off tests (LOT) and formation integrity tests (FIT) can be minimized;Early indications of borehole ballooning can be identified before ballooning becomes a major borehole stability issue; and,Hole cleaning intervals can be optimized, reducing drilling time. This paper covers a series of examples where continuous, uninterrupted data transmission was used to anticipate and prevent borehole stability problems and optimize the drilling procedure. Introduction The embedding of copper electrical conductors in Advanced Composite Coil Tubing (ACCT) allows a stream of high speed, high density data to be transmitted in real-time between the downhole components and the surface system. This uninterrupted communication enables the operator to receive all of the data, all of the time, regardless of the operating activities underway. In pipe-conveyed drilling, the real-time application of the "pressure while drilling" (PWD) data has been well documented. It is a very useful tool when used in conjunction with all the other drilling parameters to measure and anticipate drilling problems(1- 3). However, the extent to which mud-pulse telemetry data can be used during all operating activities is limited. The real-time application of PWD data has been hindered because of the constraints placed on the amount of data that can be pulsed to the surface. Ironically, one of the times when PWD data is most useful occurs when it cannot be pulsed up. This could be due to low flow rates or the pumps having to be switched off to avoid damaging the borehole or getting stuck. Surface gauges then have to be relied upon for downhole measurements. With the ability to have "real-time data all the time," pump-off data that could not be seen until the end of the run can now be seen immediately.