Annular Pressure Losses Research Articles

Effect of viscoelasticity on the filtration loss characteristics of aqueous polymer solutions

Fluid loss control is generally achieved by increasing the shear viscosity of the fluid and developing an internal/external filter cake using fluid loss control additives. If the viscosifiers and fluid loss control additives are not selected properly, both mechanisms may lead to a significant reduction of permeability. Moreover, increasing the fluid shear viscosity may not be desirable all the time due to the high annular pressure losses (i.e., the ECD limit), in particular, when drilling long horizontal and extended reach wells. In this paper, a new methodology is presented to formulate an “ideal well fluid”, which effectively reduces the fluid loss into the formation without causing additional frictional pressure losses in the well. Blends of a water-soluble Polyethylene Oxide (PEO) with different molecular weight distributions and similar average molecular weights (Mw) were prepared. The PEO blends were then used to prepare aqueous polymer solutions, which had similar shear viscosities but significantly different elastic characteristics (i.e., normal stress and relaxation time). Core flow experiments were conducted to investigate the effects of viscoelastic fluid rheology on the formation of “internal cake” (i.e., frictional pressure drop). It was possible to see the effect of fluid elasticity on the frictional pressure losses alone because both fluids had the same shear viscosity but different elastic properties. The resistance of the fluid with higher elasticity to flow through a porous medium was significantly higher than that of the fluid with lower elasticity. The experimental results indicated that the filtration of a polymer-based fluid into a porous medium could be considerably reduced by increasing the elastic properties of the solution through controlling the molecular weight distribution of the polymer, while keeping the shear viscosity and concentration of the polymer constant. Specifically, the formation damage risk of polymer-based drilling fluids could be minimized without inducing additional pressure drop due to fluid flow inside the well.

Fiber Sweeps for Hole Cleaning

Summary Cuttings transport in highly deviated wellbores is more challenging and critical than in vertical wells. In inclined wells, the fluid velocity has a reduced vertical component that may not be sufficient to transport all the cuttings to the surface. When cuttings returns do not appear to be sufficient for the drilling rate, hole-cleaning sweeps are applied to clean the borehole or reduce cuttings-bed thickness. Fiber-containing sweeps have been very effective in cleaning highly deviated and extended-reach wells. In addition, substantial torque and drag reduction has been reported when fiber-containing drilling fluids are used in the field. Although field observations are encouraging, very little is known currently about flow behavior, hydraulics, and cuttings-transport efficiency of fiber sweeps. There is a great need for understanding how fiber particles enhance the cleaning capabilities of fiber-containing sweeps. The interaction between fiber particles and drilling fluid is still not understood fully, although the improvement in cuttings and solids transport is attributed to the formation of a fiber mat network that enhances the carrying capacity of drilling fluids. This article presents results of experimental investigations conducted to study hole-cleaning performance of a fiber sweep. Flow-loop experiments have been carried out to evaluate and compare sweep efficiencies of the fiber sweep [0.47% Xanthan gum (XG) and 0.04% synthetic fiber] and the base fluid (0.47% XG). Equilibrium bed heights were measured at different sweep flow rates in horizontal and inclined configurations. Results from this study indicate that a fiber-containing sweep has better hole-cleaning capabilities than the base fluid, even though these two sweep fluids have very similar rheological properties. Moreover, adding fiber slightly reduces annular pressure loss at the same average bed height.

Development and Evaluation of Various Drilling Fluids for Slim Hole Wells

Abstract Slim hole drilling has gained wide acceptance, however, it presents a new set of challenges and problems. One such challenge is reducing annular pressure losses (APLs). Due to the reduced annular clearance in slim hole wells, the APL is usually high, translating to a high equivalent circulating density which can lead to fracturing the formation and lost circulation. Fifty-three fluids were evaluated for their APLs using three different wellbore configurations under atmospheric conditions and at 150?F. Each fluid was characterized using the Bingham Plastic and Power Law rheological models. It was observed that the partially hydrolyzed polyacrylamide (PHPA) viscosified brines gave the lowest frictional pressure losses of all fluids tested. However, the xanthan viscosified brines exhibited better carrying capacity due to their high viscosities. As expected, APL gradients were reduced at high temperatures due to reduced viscosities which led to reduced carrying capacities of the fluids. Introduction Drilling cost optimization has always been, and will continue to be, the most important issue in the petroleum drilling industry. Using slim hole technology is one of the sure ways to achieve substantial cost savings. The basic difference between conventional wells and slim hole wells is the wellbore geometry. While the hole diameter of the production interval in a conventional well ranges from 6? in to 95/8 in, that of a slim hole well ranges from 3? in to less than 6 in. Recent advances(1–3) in slim hole technology include the development of drilling fluids to reduce the APLs because 60% of the pressure loss occurs in the annulus of slim hole wells(1). Some developments in slim hole drilling fluids design have included the works of Downs et al.(2) They formulated formate brine-based fluid with xanthan gum as a viscosifier. Randolph et al.(3) developed a unique weighting agent for slim hole drilling. In general, low solids-fluids are used to prevent the plating out of solids inside the drill string, and the fluids should have low viscosity to avoid an excessively large equivalent circulating density (ECD). These systems are very costly, thereby reducing the cost savings significantly. The purpose of this study was to develop a low-cost, low viscosity fluid that will reduce the annular pressure loss significantly while maintaining a gauged hole. Study Methodology his study involved the development of several fluids and their rheological characterizations with Bingham Plastic and Power Law models. The data were used for calculating APL gradients for three slim hole geometries and carrying capacities of the fluids. The fluids developed were water-based because they are cheap, environmentally accepted and they require little effort when detecting gas kicks. Two main groups of fluids were tested: bentonite (clay)-based fluids and viscosified brines. Salts were added to the fluids for wellbore stability. The two types of salts used in this study are potassium chloride (KCl) and potassium formate (KF). Xanthan and PHPA (partially hydrolyzed polyacrylamide) polymer were used as viscosifiers in the brines in order to investigate their effects on annular pressure losses.

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.

Rheology and Hydraulics of Polymer (HEC) Based Drilling Foams at Ambient Temperature Conditions

Summary An experimental investigation on polymer-based drilling foams was carried out. Rheology tests were performed with foams that have different concentrations of hydroxylethylcellulose (HEC) and 1% commercial surfactant. Experiments were conducted in a large-scale flow loop that permits foam flow through 2-, 3-, and 4-in. pipe sections, and a 6×3.5-in. annular section. During the experiments, frictional pressure losses across the pipe and annular sections were measured for different gas/liquid flow rates, polymer concentrations (0, 0.25, and 0.5%), and foam qualities (70, 80, and 90%). Significant rheological variations were observed between aqueous foams containing no polymers and polymer-thickened foams. Experimental data show three distinct flow curves for the 2-, 3-, and 4-in. pipe sections, which indicates the presence of wall slip. The Oldroyd-Jastrzebski approach was used to calculate the wall slip velocity and determine the true shear rate. It has been found that wall slip decreases as the foam quality or polymer concentration increases. Two foam hydraulic models, which use slip-corrected and slip-uncorrected rheological parameters, have been proposed. These models are applicable for predicting pressure loss in pipes and annuli. Model predictions for the annular test section are compared with the measured data. A satisfactory agreement between the model predictions and measured data is obtained. This paper will help to better design foam drilling and cleanup operations. Introduction The use of drilling foams is increasing because foams exhibit properties that are desirable in many drilling operations. In practice, aqueous and polymer-based foams have been used with commercial success. However, drilling-foam rheology and hydraulics are still not sufficiently understood to minimize the risk and costs associated with foam drilling. It is generally accepted that the addition of polymers to the liquid phase affects the viscosity and stability of foams. However, the degree to which the bulk properties of drilling foams are enhanced by polymers has not been well understood and is difficult to predict. For safe and economical foam drilling, accurate knowledge of bottomhole pressure is essential. However, foam rheology and pressure drop predictions are not accurate enough to provide adequate hydraulic design information such as equivalent circulation density. This problem is more pronounced when polymers are added, because the apparent foam viscosity of polymer-thickened foams can be significantly higher than aqueous foams. It becomes apparent that there is a need for polymer foam rheological characterization in order to improve the knowledge of foam rheology and hydraulics. Foam rheological characterization was carried out using large-scale, single-pass pipe viscometers (composed of 2-, 3-, and 4-in. pipe sections). Foam qualities were varied from 70 to 90%. Test pressure and temperature were 100 psig and 80°F. Two foam hydraulic models were considered, assuming both no-slip condition at the wall and slip condition at the wall. The first model assumes no-slip boundary conditions in both pipes and annulus. By assuming no slip condition at the wall, slip-uncorrected foam rheological parameters were obtained from the pipe viscometer measurements. It has been found that if we plot friction factors vs. Reynolds numbers for all test data, regardless of pipe diameters, foam qualities, and flow rates, a single curve is obtained. This curve is similar to that obtained for incompressible fluid flow. Pressure drop in the annulus is calculated with the proposed model, and satisfactory predictions are obtained. The second model is based on the assumption that there is wall slip in both pipes and annulus. Rheological parameters and wall-slip coefficient corrections were first obtained using Oldroyd-Jastrzebski approach. The annular pressure losses are predicted based on slip-corrected rheological parameters and wall-slip coefficient correlations.

Effects of High-Speed Pipe Rotation on Pressures in Narrow Annuli

Abstract Variations in annular geometry, eccentricity, and pipe rotational speed strongly affect pressure loss of a fluid flowing in the narrow annulus of a slimhole well. Due to these factors, accurately calculating and controlling pressures in slimhole wellbores are difficult. Accurate pressure calculations are crucial for safely controlling formation pressures and protecting wellbore integrity. Attempts to model non-Newtonian fluid flow in narrow annuli with high-speed pipe rotation have been hampered by the lack of quality data. The results of numerous annular flow experiments presented herein partially correct this deficit. These results supplement annular pressure data from a 2500-ft slimhole test well and standpipe pressure data from a slimhole exploration well. Sensitive pressure measurements were used to characterize fluid flow in concentric narrow annuli created by a 1.25-in. diameter (Dp) steel shaft inside clear acrylic tubes with 1.375-in. to 1.75-in. inside diameter (Dh). Similar tests were conducted in a fully eccentric annulus formed by the steel shaft inside an acrylic tube with Dh = 1.50 in. Maximum shaft rotational speed was 900 rpm and maximum fluid flow rate was 12 gpm. Test fluids included water, glycerin solutions, viscosified clear brines, and several slimhole drilling muds. Models selected from the public domain were used with varying success to calculate results from the hydraulics tests. Simple models typically used by the drilling industry calculated annular pressure loss for non-rotating cases with reasonable accuracy. However, the simple models seldom calculated absolute effects of pipe rotation even though calculated trends correctly match those in measured data. For turbulent flow, annular pressure loss increased with increasing pipe rotation. For laminar flow, annular pressure loss decreased with increasing pipe rotation. In all cases, annular pressure loss increased with increasing mud rheology and decreased with increasing eccentricity.

Well-Control Methods and Practices in Small-Diameter Wellbores

Summary Slim-hole drilling and continuous coring for oil and gas exploration havebetween impeded by lack of documentation of well-control methods forsmall-annulus drilling. Research in annular pressure losses, kickidentification, wireline swab effects, and dynamic-kill well-controleffectiveness helped develop a slim-hole well-control methodology. Introduction Slim-hole drilling is increasingly used as an exploration tool. Thistechnique involves using compact, mobile rigs with drag bits and high rotaryspeeds to drill small-diameter, expendable wellbores. Walker and Millheimdescribed such a system, Stratigraphic High-speed Advanced Drilling System(SHADS), which uses mining exploration rigs for slim-hole oil and gasexploration. Mining rigs are equipped to core 6- to 3-in.-diameter (andsmaller) wells. The rigs have large-diameter (relative to hole size)flush-joint drillstrings that result in annular volumes 1/10 the size ofconventional wells. The concern about well-control capabilities insmall-annulus wells has hindered a greater use of slim-hole drilling. Thisconcern is justified for two reasons. First, the annular volume on a slim-holewell is so small that an influx must be detected more quickly than in aconventional well. Second, well-control practices for small-annulus wells havenot been documented in the literature. System pressure losses. The bestkick-detection methods and most effective kill procedures are unknown to manydrilling procedures are unknown to many drilling personnel. personnel. To solvethe well-control problems, a full-scale slim-hole well was drilled andinstrumented for well control research. Fig. 1 is a cross section of the SHADSwell-control well. The well is cased with 5-in. casing with an ID thatcorresponds to the most commonly drilled slim-hole size (for SHADS) of 4 3/8in. Eight 1/4-in. pressure transmission lines are attached at various depths tothe exterior of the casing. Special ported pup joints, similar to a side-pocketported pup joints, similar to a side-pocket mandrel, allow communication withthe casing ID. Two 1-in. lints are also attached to the exterior andcommunicate with the casing bore near the bottom of the casing. These 1-in. lines allow injection of nitrogen into the bottom of the well for kicksimulation. This well is called SHADS No. 7. Results of tests conducted tomeasure the annular pressure losses were used to develop correlations fordetermining system pressure losses based on hole size, depth, and pressurelosses based on hole size, depth, and fluid properties. Kick-detectiontechniques and kill methods were evaluated at the well. Drilling engineers andrig personnel were with a slim-hole rig over the well. A slim-hole well-controlphilosophy was developed and tested on a full-scale research well before fieldimplementation. This paper describes the techniques necessary to plan safe wellcontrol for a slim-hole well. Throughout the paper. typical 8,000-ftconventional and slim-hole wells are used to compare the two systems. Fig. 2illustrates the casing, hole, and drillstring sizes, along with otherspecifics. System Description. In this paper, the well-control system includes mudpumps, surface kick-detection system (pit volume totalizer, gas detector, pressure recorders, etc.), blowout preventers (BOP's) and choke manifold, drilling fluid, drillstring, and wellbore. The functionality of the system isidentical for conventional and slim-hole wells, although a slim-hole rig oftenuses smaller equipment. To apply the well-control practices of this paper, quantitative flowmeters practices of this paper, quantitative flowmeters arerequired on the mudlines into and out of the well. No additional equipmentshould be needed. The physical differences between slim-hole and conventionalwell control are analyzed first. They include annular volume effects, systempressure losses, and swab pressures. The next sections on kick pressures. Thenext sections on kick detection and the dynamic kill method apply the physicalresults to field operations. Finally, physical results to field operations. Finally, the approach to slim-hole well control is outlined. Physical Differences Physical Differences Annular Volume. A small annularvolume is the most apparent difference between slim-hole and conventionalwells. From a well-control standpoint, the height of an influx when a kick istaken is critical to the severity of a well-control situation. The greater theheight of the influx, the more serious the well-control problem. JPT P. 1380

Field Method of Evaluating Annular Performance of Drilling Fluids

Three criteria are considered here: the transition from laminar to turbulent flow, the annular pressure loss due to circulation, and the average annular viscosity. Field methods of approximating the criteria are presented, as well as a discussion of the accuracy of the field calculations relative to computer-determined values. Introduction A method used successfully to plan drilling hydraulics for various types of mud systems is based on predictions of the ability of a fluid to clean the predictions of the ability of a fluid to clean the hole under conditions that cause neither liquid erosion nor high annular pressure loss. The prediction is based on a mathematical simulation of flow in prediction is based on a mathematical simulation of flow in the annulus between the rotating drillstring and the wall of the hole. The value of the prediction technique is directly related to the inclusion of the pertinent physical forces and laws in the mathematical pertinent physical forces and laws in the mathematical simulation. Savins showed the influence of rotating drillpipe and explained why the simulation must contain the calculation for a helical flow path rather than for simple axial flow. The methods of solving the helical flow equations, which require a computer, are documented, as are the experimental results. Values for annular performance criteria can be calculated using the computer program to determine the capabilities of different types of mud systems as a function of depth and flow rate. Combined with appropriate standards for optimum hydraulics, this method furnishes a sound basis for designing a circulating fluid. However, to extend the technique so that it may be used at the rig site to improve the analysis of hole problems requires methods to approximate the annular criteria calculations and devices to measure the mud's flow properties within the effective range of shear rates. Hole problems are frequently related to cuttings-carrying capacity, annular pressure drop, or liquid erosion. Since remedial action for these situations may be based on changes in mud viscosity of flow rate the expected results of these changes on each of the annular performance criteria should be evaluated. For example, the mud viscosity can be increased at all shear rates or only in some ranges of shear rate. Incorrect viscosity increase can lead to no improvement in hole-cleaning, to a greater loss in flowing pressure, or to a reduction in drilling rate. An pressure, or to a reduction in drilling rate. An increase in flow rate may develop turbulent flow, which increases both the slip velocity of the particles and the tendency towards fluid erosion. The purpose of this paper is to outline methods that can be used in the field to estimate the annular performance criteria and to describe an attachment to performance criteria and to describe an attachment to the Fann Model 34 VG Meter that permits the measurements necessary for the "duo-power" model used to simulate the liquid's stress/rate relation. Estimation of Performance Criteria The three criteria needed to evaluate annular performance are the laminar-turbulent transition, the performance are the laminar-turbulent transition, the annular pressure loss, and the average annular viscosity. A duo-power model is used to simulate the stress/rate relation of the liquid. Laminar helical flow calculations made by the computer were approximated by a combination of equations and graphs suitable for use in the field. Examples for 8 1/2 -in. and 12 1/4-in. holes are presented. JPT P. 167