4.- DRILLING RIGS

DRILLING BARGES : A drilling barge consists of a barge with a complete drilling rig and ancillary equipment constructed on it. Drilling barges are suitable for calm shallow waters (mostly inland applications) and are not able to withstand the water movement experienced in deeper, open water situations. When a drilling barge is moved from one location to another, the barge floats on the water and is pulled by tugs. When a drilling barge is stationed on the drill site, the barge can be anchored in the floating mode or in some way supported on the bottom. The bottom-support barges may be submerged to rest on the bottom or they may be raised on posts or jacked-up on legs above the water. The most common drilling barges are inland water barge drilling rigs that are used to drill wells in lakes, rivers, canals, swamps, marshes, shallow inland bays, and areas where the water covering the drill site in not too deep.

SUBMERSIBLES RIGS: Submersible drilling rigs are similar to barge rigs but suitable for open ocean waters of relative shallow depth. The drilling structure is supported by large submerged pontoons that are flooded and rest on the seafloor when drilling. After the well is completed, the water is

pumped out of the tanks to restore buoyancy and the vessel is towed to the next location. 

JACK - UP RIGS: 

Jack-up drilling rigs are similar to a drilling barge because the complete drilling rig is built on a floating hull that must be moved between locations with tug boats. Jack-ups are the most common offshore bottom-supported type of drilling rig. Once on location, a jack-up rig is raised above the water on legs that extend to the seafloor for support. Jack-ups can operate in open water or can be designed to move over and drill through conductor pipes in a production platform. Jack-up rigs come with various leg lengths and depth capabilities (based on load capacity and power ratings). They can be operated in shallow waters and moderate water depths up to about 450 ft.

SEMI - SUBMERSIBLE RIG: Semi-submersible drilling rigs are the most common type of offshore floating drilling rigs and can operate in deep water and usually move from location to location under their own power. They partially flood their pontoons for achieving the desired height above the water and to establish stability. “Semis” as they are called may be held in place over the location by mooring lines attached to seafloor anchors or may be held in place by adjustable thrusters (propellers) which are rotated to hold the vessel over the desired location (called dynamically positioned).

DRILLSHIP:   Drillships are large ships designed for offshore drilling operations and can operate in deepwater. They are built on traditional ship hulls such as used for supertankers and cargo ships and move from location to location under their own power. Drillships can be quite large with many being 800 ft in length and over 100 ft in width. Drillships are not as stable in rough seas as semi-submersibles but have the advantage of having significantly more storage capacity. Modern deepwater drillships use the dynamic positioning system (as mentioned above for semisubmersibles) for maintaining their position over the drilling location. Because of their large sizes, drillships can work for extended periods without the need for constant resupply. Drillships operate at higher cruising speeds (between drillsite locations) than semi-submersibles.

WELL SERVICES ENGINES

Drilling rigs use direct current generators and motors that have an approximate efficiency of 68%. Actual efficiency in conjunction with drilling machinery is 87.5% due to additional losses in the power requirements of field induction generators, cooling blower, commutator temperature, brushes, and feeder cable length. In this system, the available energy is limited for the reason that only one DC generator. can be electrically linked to a DC motor. resulting in 1600 H.P. available to drive the winch. 

DC (SCR) Drilling Rig

On a DC drilling rig, alternate current (AC) produced by one or more AC generator sets is converted into direct current (DC) by means of a silicon-controlled-rectifier (SCR) system. They obtain an efficiency of 68%; whose available energy is concentrated in a common bar (PCR) and can be partially or totally channeled to the drilling machinery (rotary, winch and pumps) that is required.

AC (VFD) Drilling Rig On an AC powered rig, AC generator sets (diesel engine plus AC generator) produce alternating current that is operated at variable speed via a variable-frequency drive (VFD)

AC versus DC Drilling Rig

Apart from being more energy efficient, AC powered rigs allow the drilling operator to more accurately control the rig equipment, thus enhancing rig safety and reducing drilling time.

AC Drilling Rig Advantages

- Efficient energy consumption due to a high power factor (minimum 95%).

- Precise speed regulation over a wider speed range.

- Constant high power even at low speed.

- Full torque at zero speed.

- Regenerative braking for safe and efficient control of the drawworks.

- Convenient and safe autodriller system for managing and controlling parameters such as weight on bit (WOB), rate of penetration (ROP), and rotary torque control.

CAT 3512B : Average rating: 1000 kw 

CAT 3512B : Average rating: 1000 kw 

5.- DRILLING BITS

DRILL BITS

BIT PROFILE

BACK RAKE

FUERZAS SOBRE EL CORTADOR: 

LEACHING

CUTTER WEAR

MSE MODEL FOR ROTATING DRILLING WITH PDM

MSE has been defined as the mechanical work done to excavate a unit volume of rock.

Unconfined compressive strength (UCS)

Laboratory experiment showed that MSE was numerically close to the unconfined compressive strength (UCS) of the formation at maximum drilling efficiency [6]. However, the tests were conducted at atmospheric conditions.

Confined compressive strength (CCS) 

In the real drilling process, MSE is numerically close to the CCS of the formation at maximum drilling efficiency. In other words, when drilling achieves a maximum drilling efficiency, the minimum MSE is reached and is roughly equal to the CCS of the rock drilled

Therefore, MSE can be used to detect the peak drilling efficiency by surveilling MSE to see if the MSE(min) is roughly equal to the CCS of the rock drilled. 

Although torque at the bit can be easily measured in the laboratory and with Measurement While Drilling (MWD), the majority of field data is in the form of surface measurement.While in the absence of reliable torque at the bit measurements, the calculation of MSE based on this model contains even large sources of error. Therefore, it is only used qualitatively as a trending tool.

μb   : bit-specific coefficient of sliding friction

Db  : bit diameter (in)

T     : torque at bit (ft-lbf)

Em  : mechanical efficiency of new bit

Ab   : bit area (in2)

DRILLING PERFORMANCE

3D CUTTER

SCHLUMBERGER

BAKER HUGHES

NOV( REED HYCALOG)

VAREL 

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6.- DIRECTIONAL

VIBRATION IN BOTTOM HOLE ASSEMBLY

When drilling a well there is a risk of serious damage caused by drillstring vibrations. Shock and vibration are identified as a cause of premature failure on drill bit and components in the bottom hole assembly (BHA), resulting in lost time for operators and costing service companies several millions in repair each year. The expenditures incurred by drillstring vibrations include reduced rate of penetration (ROP), tripping and poor drilling performance. Currently, several tools and techniques are used in the attempt to minimize shock and vibration. For vibration mitigation to be more effective in the future, the most effective tools and techniques must be designated, implemented and improved.

Predicting bottom hole assembly (BHA) vibrations is a complicated problem. Axial, lateral, and torsional vibrations can be coupled and effects such as stick-slip and whirl can magnify the loads. Fatigue, pipe bouncing, and tool joint washouts demon e the complexity of the problem. One type of vibration that can be isolated and analyzed is the rapid destruction of the BHA caused by operating at or close to resonance. At rotating speeds that reinforce the natural vibration of the BHA, the destructive harmonics generate high stresses resulting in very short fatigue life. While other factors may cause BHA failure, a significant percentage of field failures appear to be associated with harmonic vibration, particularly lateral vibration. A simplified model based on harmonic analysis using finite elements has been found to agree well with field experience. The influence of stabilizer placement, drill string forces, and mass of the drilling mud are included in the finite element vibration model. (SPE-16675-MS)

AXIAL VIBRATION : Can cause bit bounce , which may damage bit cutter and bearing.

TORSIONAL VIBRATION : Can cause irregular down - hole rotation. Stick/Slip is often seen while drilling and is a severe form of drillstring torsional oscillation in which the bit becomes stationary for a period. Torsional fluctuations fatigue Drill collars connections and can damage bits. The use of the mud motor may help to address if the main source of excitation is from the bit but the presences of a motor does not prevent stick/slip . The drillstring and BHA  above the motor can enter into a stick/Slip motion even when the motor is turning the bit a steady rate.  

LATERAL VIBRATION : are most destructive type of vibration and an create large shocks as the BHA impacts the wellbore wall. The interaction between BHA and drillstring contact points may, in certain circumstances , drive the system into backward whirl. Backward whirl is the most severe form of vibration, creating high - frequency and large - magnitude bending moment fluctuations that result in high rates of components and connections fatigue. Imbalance in an assembly will cause centrifugally induced bowing of the drillstring , which may produce forward whirl and result in one - side wear of components.  

   

1.- Schlumberger

2.- Halliburton 

SUMMARY

Stick-slip and whirl are vibrational problems that limit drilling performance in hard formations and extended reach wells. When these vibrations are present, adding roller reamers to the drillstring can significantly reduce their severity and improve performance. Whirl is characterized by lateral vibration at the bit and in the BHA. When whirl becomes severe, lateral vibrations cause significant side forces in stabilizers. Frictional drag then causes high torque levels at the stabilizers, which can result in stick-slip (fluctuations in BHA rotational speed). This is referred to as “coupled stick-slip.” When these conditions exist, the replacement of stabilizers with roller reamers reduces torque generation at the contact points. Consequently, more torque becomes available to the bit and the driller may raise WOB. This results in reduced bit whirl and improved ROP. The reduction of bit whirl and elimination of stick-slip prevent damage to bit and BHA components

Figure5 shows diagram for each of the three BHA configurations. Note that there are two stabilizers configured in BHA-2. The stabilizer is located at the far left to the bit in BHA-3 compare with BHA-2. There is one stabilizer used in BHA-1 near the bit. The detail descriptions are as following:

 

Figure6 provides state vectors display comparison for three of BHA surrogates operation at 100RPM and 80000N of bit weight. The lateral vibration potential simulation for BHA-1 is significantly lower than BHA 2 and BHA-3. Especially for the lateral displacement, the effect is most remarkably, which means that the contacts for BHA-1 with wellbore may be less than other BHA surrogates during drilling process. However, the yellow color curve shows the larger amplitudes of the states for BHA-2 than others, which represents the most severe vibration potential.

Prepared by : O.Bohorquez
Update:24.07.19

7.- DRILLING FLUID

Velocidad Anular: 

Viscosidad

La Viscosidad del Lodo de Perforación cambiará cuando haya un cambio en la tasa de corte. 

LSRYP : Low Shear Rate YP:

Punto de cedencia a baja velocidad de cizallamiento –Medida de la viscosidad del lodo a baja velocidad de cizallamiento. Mide la capacidad del lodo para transportar recortes en el espacio anular. Mientras más grandes sean los recortes más elevado será el valor LSR YP requerido. Se calcula con la expresión :

Como una regla práctica el LSRYP debe estar cerca al diámetro del pozo en pulgadas

Prueba de laboratorio 

                                  

                                

  

Debido a esta naturaleza del lodo se creó el término de  “Viscosidad Efectiva” para compensar el cambio de la tasa de corte de la viscosidad. Por definición, la viscosidad efectiva es aquella viscosidad de un fluido Newtoniano que posee el mismo esfuerzo de corte a una misma tasa de corte.

µea = effective viscosity in the annulus, centipoise

Ka = consistency factor in the annulus, poise

Dh = hole diameter, inch

Do = Outside diameter of pipe, inch

na = power law constant of drilling mud in the annulus

Va = annular velocity in the annulus, ft/sec

Herschel Bulkley

Es un modelo generalizado de un fluido no newtoniano, en el que la tensión experimentada por el fluido se relaciona con el estrés de una manera complicada y no lineal. Tres parámetros caracterizan esta relación: la consistencia k, el índice de flujo n y el esfuerzo de cizallamiento . La consistencia es una simple constante de proporcionalidad, mientras que el índice de flujo mide el grado en que el fluido se está adelgazando o espesando

K : Índice de consistencia
n : Índice de Flujo. 

n = 1: Fluido Newtoniano
n<1 : Fluido Pseudoplástico

Herschel Bulkley mejora el modelo de " Power Law fluid model" respecto al comportamiento del fluido de perforación a un bajo "shear rate "  asumiendo un valor inicial shear stress . La ecuación de Herschel Bulkley puede ser descrita como la ecuación líneas abajo: 

Shear Stress = Yield Stress + K x (shear rate)n

Nota: El Yield Stress puede ser tomado de la lectura de 3 rpm y n y k son tomados de las lecturas de 600 rpm y 300 rpm. 

Número de Reynold: 

El número de Reynolds se define como la relación entre las fuerzas inerciales y las fuerzas viscosas presentes en un fluido. Éste relaciona la densidad, viscosidad, velocidad y dimensión típica de un flujo en una expresión adimensional. Dicho número o combinación adimensional está  relacionado con el hecho de que el flujo pueda considerarse laminar (número de Reynolds pequeño) o turbulento (número de Reynolds grande).

Rea = Reynold Number in the annulus

Va = Annular velocity, ft/min

Dh = Diameter of wellbore, inch

Do = Outside Diameter of tubular, inch

W = mud weight, ppg

µea = effective viscosity in the annulus, centipoise

na = power law constant

Velocidad Crítica: 

Compresibilidad :

 Recordemos que esta propiedad es típica del estado gaseoso, ya que los gases la poseen en grado notable; basta pensar que en primera aproximación (ley de Boyle), a una duplicación de presión corresponde una reducción de volumen a la mitad. 

Pero la Compresibilidad, si bien en grado mucho menor, es también una propiedad de los líquidos. 

Calculo : Para la cementación 

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8.- SOLID CONTROL

EQUIPO DE CONTROL DE SÓLIDOS

CLASIFICACIÓN TAMAÑO (API) DE SÓLIDOS :

1.- COLOIDAL              : < 2 um.

2.- ULTRAFINO            : 2 - 44 um.

3.- FINO                          : 44 - 74 um.

4.- MEDIO                      : 74 - 250 um.

5.- INTERMEDIO          : 250 um.

PUNTOS DE CORTES POR ECS : 

PUNTOS DE CORTES POR ECS :

PUNTOS DE CORTES POR ECS :

PUNTOS DE CORTES POR ECS :

PUNTOS DE CORTES POR ECS :

TAMAÑO DE PARTÍCULAS / PUNTO DE CORTE

EQUIVALENCIAS MESH VS API

D50 BARITA

EFECTO TAMAÑO DE PARTÍCULA vs VISCOSIDAD

GELES

                    

 EFECTO TAMAÑO DE PARTÍCULA vs GELES

HIDROCICLONES

HIDROCICLON -  DESANDER : 

Es un equipo de control de sólidos diseñado para remover arena. Este aparato puede estar formado por uno, dos o tres conos, generalmente de 10 o 12” de diámetro interno, con punto de corte de 44µ. Cada cono procesa aproximadamente 500 gal/min y debe estar en capacidad de procesar el 125% del volumen total en circulación. La cantidad de conos que integran un desarenador se toma con base al caudal máximo a usar durante la perforación del hoyo superficial, y es por ello que la mayoría de los taladros tienen instalados desarenadores de dos conos.

HIDROCICLON -  DESILTER :

Es un equipo de control de sólidos diseñado para remover sedimento. Su capacidad de procesamiento depende del tamaño y cantidad de conos que lo integran. Generalmente tiene varios conos de 4” que manejan aproximadamente 50 gal/min c/u, con punto de corte de 25µ. Un desilter de 10 conos de 4” procesa aproximadamente 500 gal/min, y esta en capacidad de manejar el 150% del volumen total.

BOMBA CENTRIFUGA: 

Las bombas centrifugas son utilizadas en los taladros de perforación para alimentar a los desarenadores y desilter. 

Notas:

1.- La longitud de estas líneas no debe ser mayor a tres veces su diámetro; es decir, para una bomba de 6”x5”, la succión debe ser menor de 18’ (6x3=18) y la descarga menor de 15’ (5x3=15). 

2.- Para evitar problemas de sedimentación o erosión que afecten considerablemente el impeler de las bombas centrifugas, y en consecuencia el caudal y la presión, se requieren velocidades mínimas de flujo de 4 pies/seg en la succión y 10 pies/seg, en la descarga.

3.- La mayoría de los hidrociclones están diseñados para trabajar con 75 pies de carga y con una presión de más o menos cuatro veces la densidad del fluido, es decir: 

                        

                         Presión = 0.052xWxH= 0.052xWx75 = a ± 4W

3 x 4 :    600gpm, 355 ft, 153 psi

4 x 5 :    800gpm, 178 ft, 77 psi

5 x 6 : 1200 gpm, 172 ft, 74 psi

6 x 8 : 1600 gpm, 200 ft, 86  psi 

CENTRIFUGAS

G = (RPM bowl)² (.0000142) (Ø bowl en plg)

Centrifuga de Baja : Esta centrifuga trabaja a ± 1800 RPM, desarrolla una fuerza “G” de ± 1000, con punto de corte de 5µ. Procesa de 10 a 30 GPM, con un factor de dilución de 2 24 a 6 GPM, dependiendo del peso y viscosidad del fluido. A mayor peso, la capacidad de procesamiento de la centrifuga es menor. Este tipo de centrifuga descarta aproximadamente el 40% o mas del fluido procesado, porque mas o menos un 25% de la barita, antes de entrar en circulación, tiene un tamaño de 6µ, el cual se reduce a 5µ una vez que entra en circulación. 

Centrifuga de Alta : Esta centrifuga trabaja a ± 3400 RPM, desarrolla una fuerza “G” de ± 3000, con punto de corte de 2µ. Procesa de 40 a 90 GPM, dependiendo, por supuesto, del peso del fluido. No usa dilución, salvo cuando el fluido tenga alta viscosidad. Al perforar con fluido densificado o no, es decir, con o sin barita, carbonato, se recomienda tener disponible una centrifuga de alta, para solventar problemas de floculación causados por sólidos ultra finos. Este problema es grave, sobre todo cuando se perfora con fluido pesado.

 

DEWATERING SYSTEM