Drilling Fluid Flow Research Articles

Application of the New Drilling Technology for Increasing Penetration Rate in Deep and Ultra-Deep Wells

The rotary percussion drilling technology can greatly increase the penetration rate of deep and ultra-deep wells; however, the short service life of the impactor limits its wide application. Therefore, the turbine type hydraulic impactor developed by the China University of Petroleum (Beijing) for the deep and ultra-deep wells was used to extend life of impactor. Based on the analysis of pressure field and velocity field under different flow conditions, the drilling fluid flow range of rotary percussion drilling was optimized to be 32-41 L/s. In this range, it can ensure that the wearing parts of the turbine hydraulic impactor can fully exert the impact of the impactor and high rock breaking efficiency without serious erosion. Application of deep well sections in ultra-deep wells in Tarim Oilfield achieved that the penetration rate of the rotary percussion drilling increased by more than 60% compared with the composite drilling technology. At the same time, the normal working life of the turbine hydraulic impactor was more than 140 hours, which is more than 2 times of the life of the screw drill. The results of field application show that the turbine hydraulic impactor has a wide application prospect in deep and ultra-deep wells drilling.

A Comprehensive Prediction Model of Hydraulic Extended-Reach Limit Considering the Allowable Range of Drilling Fluid Flow Rate in Horizontal Drilling

Hydraulic extended-reach limit (HERL) model of horizontal extended-reach well (ERW) can predict the maximum measured depth (MMD) of the horizontal ERW. The HERL refers to the well’s MMD when drilling fluid cannot be normally circulated by drilling pump. Previous model analyzed the following two constraint conditions, drilling pump rated pressure and rated power. However, effects of the allowable range of drilling fluid flow rate (Qmin ≤ Q ≤ Qmax) were not considered. In this study, three cases of HERL model are proposed according to the relationship between allowable range of drilling fluid flow rate and rated flow rate of drilling pump (Qr). A horizontal ERW is analyzed to predict its HERL, especially its horizontal-section limit (Lh). Results show that when Qmin ≤ Qr ≤ Qmax (Case I), Lh depends both on horizontal-section limit based on rated pump pressure (Lh1) and horizontal-section limit based on rated pump power (Lh2); when Qmin < Qmax < Qr (Case II), Lh is exclusively controlled by Lh1; while Lh is only determined by Lh2 when Qr < Qmin < Qmax (Case III). Furthermore, Lh1 first increases and then decreases with the increase in drilling fluid flow rate, while Lh2 keeps decreasing as the drilling fluid flow rate increases. The comprehensive model provides a more accurate prediction on HERL.

Performance study of erosion resistance on throttle valve of managed pressure drilling

The throttle valve designed for managed pressure drilling (MPD) is a core equipment of MPD technology. Due to the direct contact with drilling fluid at well site, the throttle valve's internal flow passage will be eroded and worn by the drilling fluid with high mobility, which would negatively affect the working performance and service life of the throttle valve. Therefore, based on the working principle and geometric structure of throttle valve, the computational fluid dynamics (CFD) technique is used to establish the three-dimensional fluid numerical model, and the renormalization group k-epsilon (RNG k-ε) model is selected for the turbulence model of liquid-solid two-phase flow in throttle valve of MPD. At the same time, the fluid flow in the wall region is solved by wall function which allows the physical quantity near the wall surface to connect with it in the core turbulence region. In addition, the discrete phase model (DPM) model is selected for the discrete phase model, and the Ahlert erosion model is selected for the erosion model. The finite volume method is used in discrete calculation, and the SIMPLE algorithm is applied in continuity equation, momentum equation, energy equation and turbulent kinetic energy equation when solving the control. The influences of drilling parameters (such as throttle valve opening, drilling fluid flow rate, drilling fluid density, mass flow rate of solid particle) on the erosion characteristics of throttle valve of managed pressure drilling are studied by CFD. The results show that the erosion of the solid particles on the wall of MPD throttle valve mainly occurs at the end of the valve spool. Meanwhile, the drilling fluid flow rate has the greatest impact on the erosion rate of solid particles, which is followed by the solid mass flow. Compared with the above two, the erosion rate of solid particles is less influenced by the throttle pressure difference between inlet and outlet which is caused by the change of throttle opening and drilling fluid density. In addition, the simulation result reaches a good agreement with the laboratory data of throttle valve erosion experiment. This study could give several advices for relevant throttle valve investigation work and operators who attempts to decrease the erosion in valves.

Study on the prediction model of the open-hole extended-reach limit in horizontal drilling considering the effects of cuttings

An open-hole extended-reach limit model was established and published by the authors to determine how far a horizontal extended-reach well (ERW) can extend. The published model shows that the open-hole extended-reach limit (the maximum measured depth of the horizontal ERW) is mainly dependent on the annular pressure drop and the fracture pressure of drilled formation. Moreover, some optimal control methods, such as lowering drilling fluid density, reducing drilling fluid flow rate and optimizing drill pipe eccentricity, were also presented to obtain greater open-hole extended-reach limit. However, the published model was established based on the assumption that the annular fluid is ideal single-phase flow. Failing to consider the effects of cuttings may lead to an inaccurate prediction of the open-hole extended-reach limit and even drilling safety hazards. In this paper, in order to overcome the shortcomings of the published model, a prediction model of the open-hole extended-reach limit in horizontal drilling considering the effects of cuttings is established and analyzed. The study shows that due to an increase of annular pressure drop, the horizontal-section limit (the maximum measured depth of horizontal-section for the horizontal ERW) is relatively smaller when considering the effects of cuttings. Meanwhile, a case study is carried out, and the results show that the horizontal-section limit is 1610 m when the cuttings are considered. In contrast, when the cuttings are ignored, the limit is 1941 m based on the published model. Furthermore, since several main parameters of the established model may greatly affect the annular pressure drop and the horizontal-section limit, parameters sensitivity analysis are also performed and some conclusions are drawn. First, the horizontal-section limit first increases and subsequently decreases with the increase in drilling fluid density. Second, there is an increase in horizontal-section limit when the drilling fluid flow rate increases. Third, the horizontal-section limit gradually increases with the increase in the drill string rotation speed. Finally, there is also a decrease in the horizontal-section limit when the rate of penetration (ROP) and the consistency coefficient increase. In sum, the simulated condition in this paper is more consistent with the situation of field drilling practice than that of the published model. This study will also provide a more accurate result of the open-hole extended-reach limit, which is of great significance to the drilling design and drilling safety.

Mechanisms and Application for Hydraulic Pulsed Cavitating Jet Generator

To improve the rate of penetration (ROP) further, based on analysis of the jet modulating mechanism, a new drilling tool is designed which couples the advantages of both pulsed jet and cavitating jet. When drilling fluid flows through the tool in drilling process, the fluid is modulated to pulsed and cavitating jet by impellers and in self-resonant chamber. Thus, pulsed cavitating jet is formed at the outlet of the bit nozzle. Because of jet pulsation, cavitating erosion and local negative pressure effect, bottom cuttings cleaning efficiency is enhanced and the ROP is improved. The hydraulic pulsed cavitating jet generator has been applied in 8 oil fields and more than 100 wells in China. The results indicated that the maximum density of test drilling fluid was 1.70 g/cm 3 , the maximum test well depth was 6,162 m. The generator could work over 230 h, and the maximum operation time was above 520 h. As the result, the average ROP had been increased by 10.1% to 104.4%. The generator has the characteristics of simple structure and long operation time, and has a well adaptability to the existing drilling equipments, technological parameters, which provides a safe and efficient new drilling technology for deep well.

A Wellbore/Formation-Coupled Heat-Transfer Model in Deepwater Drilling and Its Application in the Prediction of Hydrate-Reservoir Dissociation

Summary On the basis of the wellbore and reservoir heat-transfer process during deepwater drilling, a heat-transfer model between wellbore and formation is built up for two different conditions: without riser and with riser. Wellbore and formation temperature distributions under different drilling-fluid-injection temperatures, flow rates, circulating times, and drilling depths are simulated by use of this model. Taking the hydrate-phase equilibrium into consideration, a possible region of hydrate-formation dissociation is analyzed, and effective methods are proposed to control the hydrate dissociation. The results indicate that, during shallow formation drilling, the increase of drilling-fluid flow rate will cause the wellbore temperature to rise, but below the hydrate-dissociation temperature in the whole process; during deep-formation drilling, drilling fluid is heated, and the heat is transferred from the deeper formation to the shallower formation through fluid circulation. Thus, the hydrate-reservoir temperature increases gradually along the wellbore radial direction. Hydrates will dissociate after the hydrate equilibrium temperature is reached; this may cause wellbore collapse or methane leak from the reservoir and result in disaster. To control hydrate dissociation during deepwater drilling, attention should be paid to the period of deep-formation drilling. Sensitivity studies indicate that the risk of hydrate dissociation rises as the drilling-fluid-injection temperature, flow rate, and circulating time increase.

Prediction of frictional pressure loss for multiphase flow in inclined annuli during Underbalanced Drilling operations

In Underbalanced Drilling (UBD) method, it is difficult to predict the equivalent circulation density due to co-existence of three phases which are air, cuttings and drilling fluid. This study presents the application of a developed model inspired from a novel intelligent algorithm namely radial basis function optimized by genetic algorithm (GA-RBF) algorithm to calculate frictional pressure loss of two-phase gasified drilling fluid flow along with cutting as the third phase in inclined wellbore portions. The suggested approach was conducted to extensive data reported in literature and was based on Rate of Penetration (ROP), wellbore inclination, pipe rotation and in situ flow rate of each phase. The results of this study show that the proposed model could reproduce the experimental frictional pressure loss data to an acceptable accuracy due to high correlation coefficient (R2 > 0.99) and very small values of average absolute relative deviation (AARD) (2.166726), standard deviation (STD) (0.038222) and root mean square error (RMSE) (0.008783). Results of this study could couple with commercial drilling simulators to accurately predict the frictional pressure loss of three phase flow.

Integrated Use of Geological, Geophysical, Radiocarbon and Stable Isotopes Data for Tracing the Conduit Flow Paths in a Small Karstic Aquifer: Poocher Swamp Freshwater Lens, South Australia

&lt;p class="1Body"&gt;An integrated approach combining lithological logs, downhole geophysics, electromagnetic survey and the distribution of radiocarbon (&lt;sup&gt;14&lt;/sup&gt;C) and the stable isotopes of water molecules (&lt;sup&gt;18&lt;/sup&gt;O) were used to identify the conduit flow paths of a small freshwater lens. Lost circulation zones, where drilling fluid flows into geological formation instead returning up the annulus recorded during water well drilling, were considered as the major fracture zones. The presence of high porosity zones within boreholes were identified using caliper, gamma and neutron logs. These methods were used to identify the depth intervals at which cavities and the existence of conduit porosity within the boreholes. Transient electromagnetic (TEM) method was used to investigate resistivity anomalies in the profiles along nine pre-determined lines across the freshwater lens. Resistivity anomalies were related to borehole information and other surface features such as sinkholes. Low resistivity zones of the TEM tomography sections had excellent correlation to fracture zones identified during well drilling, and downhole geophysical logs. Similarly, high resistivity zones in the profiles correlate well with the zones of cemented or recrystallized limestone identified from the lithological logs. The interpreted resistivity anomaly accurately depicts depth to watertable at 15-18 m, presence of main fracture zone at 20-25 m, presence of possible conduits flow paths and the cemented or recrystallized limestone below 35 m depth. The &lt;sup&gt;14&lt;/sup&gt;C, &lt;sup&gt;13&lt;/sup&gt;C and &lt;sup&gt;18&lt;/sup&gt;O signatures of the groundwater confirm the presence of conduits and potential pathways of preferential flows. This investigation illustrates the effectiveness using an integrated approach to trace the conduit flow paths in karst aquifers. The information gained from the study is currently being used for the management of the freshwater lens.&lt;/p&gt;

Experimental investigation of solids transport in horizontal concentric annuli using water and drag reducing polymer-based fluids

When drilling long horizontal wells, drilled solids tend to settle down on the low side of the wellbore and form a stationary bed. Presence of stationary cuttings bed causes operational difficulties such as pack-off, excessive torque and drag, slow drilling rate, and in severe cases, stuck pipe, lost circulation, and even loss of the well control. Despite significant progress made in drilling fluids, tools, and field practices, along with more than 50 years of university and industry research, field experience indicates that cuttings transport is still a major problem in most horizontal wells.There are many variables affecting the efficiency of cuttings transport (e.g. drilling fluid type, density, flow rate and rheological properties, hole inclination angle, drill pipe rotation speed and eccentricity). Among these variables, the drilling fluid flow rate and rheological properties are the most critical ones as they have strong influence on cuttings transport while at the same time, field control of these variables can be managed conveniently. An experimental study was, therefore, designed and conducted to simulate solids transport in the horizontal annuli under controlled conditions of solids feed rate, fluid flow rate and fluid rheological properties.Cuttings transport experiments were carried out using a 6.5 m long horizontal flow loop with concentric annular geometry (Outer Pipe ID = 0.074 m, Inner Pipe OD = 0.047 m).Water and high molecular weight partially-hydrolyzed polyacrylamide (PHPA) polymer solutions with various degrees of drag reduction capability were used as carrier fluids. Solids were made out of industrial sand with median (D50) diameter of 0.00275 m.Effects of drilling rate (i.e. solids feed rate), drilling fluid flow rate and polymer concentration (i.e. drag reduction effect) on the cuttings transport efficiency and pressure losses were investigated.Maximum drag reduction was observed (i.e., 38% reduction in frictional pressure drop) when optimum polymer concentration of 0.07% W/W was used. The polymer fluid yielding the maximum drag reduction also resulted in the most efficient cuttings transport, which was observed as the lowest cuttings bed deposit height in the annulus.

Curve-fitting equation for prediction of the start-up stress overshoot of an oil-based drilling fluid

Drilling fluids usually gel at rest in order to avoid cuttings to precipitate over the drill bit when circulation is interrupted. At flow start-ups, pumping pressures higher than the steady-state circulation pressure are usually required to surpass the gel strength. The gel-liquid transition may have significant importance, especially in ultra-deep waters where high pressures and low temperatures take place. In the current work, controlled shear rate rheometric tests were conducted to investigate the yielding of an oil based drilling fluid. An algebraic equation, that accounts for both shear rate and shear history, is proposed to predict the gel breaking. This equation requires less fitting parameters than the current structural kinetic models available in literature, and is quite useful to represent the pressure peaks that take place during drilling fluid flow start-ups. The equation fit to rheometric data and is able to predict satisfactorily the start-up shear stress of a gelled drilling fluid at different shear rates.

A multibody dynamic model of the drilling system with drilling fluid

This article is intended to present a multibody dynamic model of the drilling system, consisting of drillstring and drilling fluid. The drillstring is a complex rigid–flexible coupling system, including rigid bodies, Euler–Bernoulli beam elements, constraints and dynamic loads, and its dynamic model is established using the absolute nodal coordinate formulation. The drilling fluid, composed of internal, annulus, and under-bit fluids, is modeled as one-dimensional compressible fluid; the relative flow of the drilling fluid is modeled using the Arbitrary Lagrangian–Eulerian description; the force of the drillstring acting on the drilling fluid is introduced through the drilling fluid transport motion; meanwhile, the reaction force acting on the drillstring is taken as an external load. The contact between the drillstring and drilling fluid is simulated based on Hertz contact theory, and the rock penetration model is built based on the rock-breaking velocity equation. Based on this model, the coupled vibration of the drillstring and the effects of the drilling fluid flow rate and density on the drilling process are investigated through several examples.

A novel tool to improve the rate of penetration by transferring drilling string vibration energy to hydraulic energy

The ultra-high pressure water jet assisted mechanical drilling technology is an effective approach to improve the rate of penetration (ROP), however, due to unreasonable design ideas and low reliability of the existing down-hole supercharger, this technology is not applied widely. To make breakthrough of this technology, a new idea of utilizing the drill string vibration energy to modulate ultra-high pressure jet is first proposed, and a novel down-hole supercharger, down-hole drill string absorption & hydraulic supercharging device (DSAHSD), is developed. The DSAHSD combines the advantages of reducing the axial drill string vibration and generating ultra-high pressure jet to effectively assist rock breaking. When the drilling fluid flows through this tool, part of the drilling fluid will be modulated to the ultra-high pressure jet by periodic compression of piston drove by drill string vibration. Because of hydraulic auxiliary rock breaking of the ultra-high pressure jet, the drillability of rock and the ROP will be enhanced. To analyse the feasibility and influence factors of the tool, mathematical model were established, the results show that the tool could produce more than 140MPa pressure and the outer pressure increases with the increase of weight on bit and rotary speed. Moreover, there is an optimal diameter of ultra-high pressure nozzle to optimal performance of the tool. This tool has been applied to more than 60 wells in four oil fields throughout China. The results indicate that the maximum density of the test drilling fluid is 1.9g/cm3, the single maximum footage is 1480m, and the operation time of the tool is more than 200h. Furthermore, the average ROP was increased by approximately 11–831%. In conclusion, the DSAHSD has the characteristics of a simple structure, has a long lifetime, is able to adapt well with existing drilling equipment, and can provide guarantee for wide application of the ultra-high pressure jet technology in oil fields.

Impact of drilling fluid rheology and wellbore pressure on rock cuttings removal performance: numerical investigation

AbstractDrilling fluids exhibits non‐Newtonian behavior that is generally described in the literature by two rheological models: Power Law and Herschel–Bulkley models. We have used Eulerian–Eulerian multiphase flow model to evaluate the drilling fluid flow patterns and filter cake formation patterns for both models for ultra‐deep drilling conditions. Simulated drilling fluid flow patterns clearly show that the Herschel–Bulkley model exhibits fewer vortices around the drilling pipe, indicating better rock cuttings removal performance. In addition to mud rheology, we have analyzed the pressure drop variation with the filter cake formation on the wellbore during ultra‐deep drilling process. We have shown that filter cake thickness at the wall linearly increases with differential pressure between the well and formation. This implies that the differential pressure needs to be optimized. Very thin filter cake may lead to excessive fluid seepage into the permeable subterranean vertical zone resulting in a loss of fluid circulation and hence in a loss of rock cuttings removal. Yet, very thick filter cake reduces the effective diameter of the hole, which may lead to a poor rock cuttings removal performance and stuck pipe. The mathematical model presented here needs to be experimentally validated when filter cake thickness data in deep drilling conditions become available. The model could be useful to provide drilling engineers insight on the filter cake formation and drilling fluid flow pattern and give guidelines to optimize the filter cake as field experimental data are scarce. © 2015 Curtin University of Technology and John Wiley &amp; Sons, Ltd.

Comparative Analysis of the Pressure Loss from the Circulation of Drilling Fluid During Microhole Drilling with the Use of Coiled Tubing

The choice of fluid-circulation conditions is of great importance in microhole drilling (MHD) conducted with coiled tubing (CT) as the drill string because of the long length and small bending radius of the tubing coiled on the reel, which result in high circulation friction pressure loss (CFPL). A model for calculating CFPL in flexible CT has been constructed by combining a power-law fluid flow equation and the Dean Number. The calculations have revealed patterns of change in the CFPL during MHD. The CFPL in CT, whether reeled or in downhole, increases steeply with an increase of drilling fluid flow rate, decreases slowly with increasing CT inner diameter, and rises linearly with an increase in CT length. The total CFPL over the entire CT decreases slowly with decreasing CT length when the CT is run downhole from the reel. Deep MHD is suitable only for low drilling-fluid flow rates when the inner diameter of CT is large. Suitable ranges of drilling-fluid flow rate and CT inner diameter have been determined for various drilling depths. The research will provide a basis for selecting CT and drilling-fluid circulation parameters for MHD.

Polymer Drilling Fluid with Micron-Grade Cenosphere for Deep Coal Seam

Traditional shallow coal seam uses clean water, solid-free system, and foam system as drilling fluid, while they are not suitable for deep coal seam drilling due to mismatching density, insufficient bearing capacity, and poor reservoir protection effect. According to the existing problems of drilling fluid, micron-grade cenosphere with high bearing capacity and ultralow true density is selected as density regulator; it, together with polymer “XC + CMC” and some other auxiliary agents, is jointly used to build micron-grade polymer drilling fluid with cenosphere which is suitable for deep coal seam. Basic performance test shows that the drilling fluid has good rheological property, low filtration loss, good density adjustability, shear thinning, and thixotropy; besides, drilling fluid flow is in line with the power law rheological model. Compared with traditional drilling fluid, dispersion stability basically does not change within 26 h; settlement stability evaluated with two methods only shows a small amount of change; permeability recovery rate evaluated with Qinshui Basin deep coal seam core exceeds 80%. Polymer drilling fluid with cenosphere provides a new thought to solve the problem of drilling fluid density and pressure for deep coal seam drilling and also effectively improves the performance of reservoir protection ability.

Model-based drilling fluid flow rate estimation using Venturi flume

Monitoring the flow rate out of the well is critical for good control of the downhole pressure in drilling operations. In this feasibility study, we explore the possibility of using a Venturi flume to provide a cost-effective measurement of the flow rate, with improved accuracy compared to conventional methods. A Venturi flume has been simulated both using CFD and a simplified 1D model. By proper design of the Venturi flume, a jump in the fluid level in the throat section of the flume can be injected. Four methods of using this jump information are discussed, each with their own advantages and disadvantages, such as dependence on fluid properties, length of the flume, computation time, etc. Further work is necessary to improve sensor set-up and numeric methods, as well as testing out the concepts on a Venturi rig.

Numerical simulation of drilling fluid flow in annular the space of the borehole

Numerical simulation of drilling fluid flow in annular the space of the borehole

Flow Field Analysis on the Erosion Prone Parts of the Drilling Equipment

The erosion and wear mechanism for drilling equipment is studied in this paper, which is for the problem of unstable performance of drilling system and short lifetime caused by the erosion of drilling equipment by drilling fluid. The flow field, surface pressure of the erosion prone parts and drilling fluid flow rate are calculated by the finite element method. The results demonstrate the parts eroded seriously by drilling fluid appear in where the curvature of the curve of the wall changes suddenly and where the rate of change in the stress field is greater, which provide a theoretical basis on design, optimize, repair of drilling equipment.

Hydraulic Circulation Test and CFD Analysis of Prestressed Cementing Unit Earth Anchor

In the process of thickened oil thermal recovery, the pre-stress cementing needs to be anchored at the bottom of the casing pipe. And the reliable opening and closing of anchor flukes directly influence the anchoring. In allusion to the problems of how to get the critical value of drilling fluid flow rate of when the anchor flukes begin to open, completely open, begin to close and completely close, whether different nozzles can open or close reliably, getting the corresponding differential pressure and discharge coefficient of the different nozzles, this paper conducts a study from both theory and experiment to obtain the relevant parameters. By simulating the anchor in actual work and dealing with the data, we conclude that: (1) The fluke can open smoothly when the flow rate reaches a certain flow and it can also close smoothly when the flow rate declines. (2) The critical flow rate of the flukes, when two kinds of anchors are with different nozzles, has been acquired. (3) Corresponding differential pressure and discharge coefficient of the different nozzles in different flow rate have been ascertained.

Study of the Effect of Borehole Size on Wellbore Stability

Based on the size effect of rock strength, the borehole stability analysis model is established, which the borehole size is taken into consideration. Through this model, the relation between borehole size and collapse pressure under borehole pressure, ground stress and drilling fluid flow function is analyzed. The analysis shows that with the increase of borehole diameter, collapse pressure increases significantly, and borehole stability becomes poor, but the variation of borehole size is not proportional to collapse pressure: the bigger the borehole, the smaller the variation. When borehole diameter increases from 152.4 mm to 444.5 mm, wellbore collapse pressure increases from 1.18g/cm3 to 1.315g/cm3 and the rate of the increase is 11.44%. When slimhole drilling technology is applied, the density of minimum fluid that maintains wellbore stability is lower than the one used in conventional wellbore drilling.