Rotary Drilling Process

           





Michael Aide Imiewarin



ID #:UB26630SP35132





Drilling Engineering:

Rotary Drilling Process - Design and Evaluation of Oil Wells









ATLANTIC INTERNATIONAL UNIVERSITY JULY 2014







TABLE OF CONTENTS

Introduction  -------------------------------------------------------------------------------------------3

The Rotary Drilling Process--------------------------------------------------------------------------4

Types and classifications of Rigs --------------------------------------------------------------------5

Design and Selection of Casings -------------------------------------------------- ------------------7

Casing Liners -------------------------------------------------------------------------------------------8

Pressure/Velocity distributions-----------------------------------------------------------------------10

Directional Drilling ------------------------------------------------------------------------------------13          

Conclusion ----------------------------------------------------------------------------------------------15

Bibliography --------------------------------------------------------------------------------------------16

Introduction

In one of nature's great ironies, one of the most coveted forms of energy, hydrocarbons (Petroleum and Natural Gas), is extracted for our use from inside the ground on where we walk. That is where nature has stored it for our use, under the earth's crust. A much-desired energy resource, for which wars have been fought and people have been slaughtered, may be under our feet all the time. In the United States, planned drilling for oil is recorded as having started from 1859. The first planned oil well being drilled by Edwin L. Drake in Titusville, Pennsylvania. Drilling was earlier carried out by repeated application of force on the drill pipe thereby forcing the bit at the end deeper and deeper until it reaches the petroleum reserves, by the repeated vertical load. This drilling method is known as "Percussion Drilling".

An onshore Percussion process type well.

However, some drilling is done by percussion even today, at conditions, which do not permit the use of other methods. Modern drilling is concerned with 'Rotary Drilling'.

         To acquire an idea about the design and evaluation of well drilling systems and services, it is imperative that the student is conversant with the related sections of Fluid Mechanics and Hydraulics.  In the Oil and Gas sector, practical analytical skills coupled with technical expertise is a must for finding out the  varied design problems as they may and will arise. In this paper, an attempt to impart these basic ideas to the novice engineer, as far as planned petroleum drilling experience is concerned, is the focus.

The Rotary Drilling Process

         As the name itself suggests, this process incorporates a dual effect on the bit as also the well drawstring, which is driven both rotary and forward motion as programmed depending upon the strength of the rock and/or soil cut or debris at different depths. Generally, the derrick has a rigid and rotating turntable from where the draw line starts, the bit being at the other end. The vertical force is provided via thick pipe sections (collars) above the bit and their addition. A fluid is pumped through the bit and the cut-outs are flushed out by the liquid through the annular space between the bit and the drill string. On the surface, the solids are separated out from the original liquid. The revolving drill string that is shaped like a helical conveyor pushes out bigger portions of drill residue by the helix, as it goes down. This is the working philosophy of the Rotary Drilling Process.

Types & Classification of Rigs

         Although drilling rigs can be divided into various groups by a number of different properties, universally the practice of classifying rotary drilling, by projects location on land, water or submersible, portable or fixed nature, inbuilt storage etc. are some of the common grounds 

         Typical chain of command among contractors and clients at a drilling site.







         Different types of Oil well Rotary systems



It needs mention here that in the case of all Petroleum (Hydrocarbons) related work, the default standards are the API standards, API being the acronym for American Petroleum Institute.

The API issued these standards for only American use. However, they were so clear, comprehensible, and technically accurate that people in other countries began to use them as well. Today API standards dominate, for

example, API 610 is the last word in the world

as far as Centrifugal pumps and pumping

systems are concerned. ) Other sub systems in

the Rotary  Drilling Process which the well designer should have a good idea of, are as follows.

Hoisting          system,

         Pumping          system (mud),          

         Fluid          circulation system, at this stage

Design and selection of casings

Casing is a vital item of a well. It prevents walls of the borehole from falling down during drilling and hydraulically isolates the well bore fluids from foreign matter and unknown fluids. It minimizes damage to the subsurface environment by the drilling process and to the well in case an incompatible subsurface is found. Casings act as the conduit for the drilling fluid to the surface. Finally, it can ensure the safe control of formation pressure by providing blowout preventers fitted onto it.



A 'Conductor casing' circulates the drilling fluid around without eroding the shallow sediments below the rig and its foundations.  It provides an annular passage. The conductor casing also protects casing strings from corrosion It can be used to support some of the well load structurally too. Conductors are used in tandem with "Surface casing" which prevents a cave in at the edge of the top and also prevents the drilling fluid to come in contact with the top soil which may harm its fertility and cause other unwanted effects..

Casing Liners

         Liners are casing strings suspended from the bottom of the next larger casing string. A liner hanger is used to suspend the top of the liner in the larger casing size. The liner hanger often can seal the annulus between the liner and the larger casing size.

         Overlaps of several hundred feet of between the liner hanger and the casing seat are typical. The principal advantage of a liner is its low price. Problems can sometimes arise if a hanger fails to suspend the liner correctly or if a seal between the liner and the larger casing is not effective. Moreover, using a liner exposes the casing string above it to additional wear during subsequent drilling. A drilling liner can be used either as an intermediate casing or as production casing. Production casing is usually the final casing string set in a well. It encounters formation fluids below the production packer and with the completion fluid in the tubing-casing annulus above the production packer. This casing string enables the production tubing to be replaced later in the life of a well.

         Production liner is a liner that is set at total depth and is usually exposed to formation fluids below the production packer and to packer fluid above the production packer. Production liners are generally connected to the surface wellhead using a tieback casing string when the well is completed. The tieback casing is connected to the top of the liner with a specially designed seal. Casing wear resulting from deeper drilling operations then affects only the production liner, not the production tieback Intermediate casing is usually required in deeper wells. Intermediate casing is often referred to as "protective" or "drilling" casing.

         The API and ISO standards recognize three length ranges for casing.

Range 1 (R-1) includes joint lengths from 16 to 25 ft.

Range 2 (R-2) covers the 25 to 34-ft range, and

Range 3 (R-3) covers the 34-48 feet range 

These standards also say casing pipes which arrive fresh at a site, 95 % of them  required to have lengths greater than 18 feet for R-1, 28 feet for R-2, and 36 feet for R-3. 95 % of the shipment must have a maximum length variation no greater than 6 feet for R-1, 5 feet for R2 and 6 feet for R-3. Casing is run most often in R-3 lengths to reduce the number of connections in the string. Since these casing pipes are made up in single joints and R-3 lengths can be handled easily by most rigs.



API Drift Diameters Casing

Pressure/ Velocity Distribution

         The determination of pressure at various points in the well is not simple when the drilling mud or the drill string is not at a standstill.  Frictional forces cannot be expressed mathematically unless a lot of things are assumed which is a catch 22 situation. However, in spite of the complexity of the system, the friction head has to be known for use in the calculation of

(1) The flowing bottom hole pressure or ECD during drilling or cementing operations.

(2) The bottom hole pressure or ECD during tripping operations;

(3) The optimum pump head, discharge size, and nozzle bit dia during drilling operations

(4) The cuttings-carrying capacity of the mud

(5) The surface and down hole pressures that will occur in the drill string during well-control operations for various mud flow rates. The basic physical laws commonly applied to the movement of fluids are constant mass equation, the continuity law , the law of entropy etc. energy. All of the equations describing fluid flow are obtained by application of these physical laws using an assumed rheological model and a particular equation derived from an existing law

         Example equations of state are the incompressible fluid model, the slightly compressible fluid model, the ideal gas equation, and the real gas equation. In drilling design, normally only steady-state conditions are considered. Note also that for constant area, which is usually the case, the product of the density and the average velocity is constant. The falling of pressure increases the volume, while density becomes less. This implies that the average velocity increases. In other words, pressure decreases will accelerate a gas in a pipe of constant area or constant volume. With the exception of air, gas, or foam drilling, the drilling fluid, is generally taken as incompressible. Therefore, accumulation or leakage of drill fluid in the surface equipment or underground formations, the flow rate of an incompressible well fluid must be the same at all points in the well.

         The viscous forces present in a fluid are characterized by the fluid viscosity. What is

Viscosity? Viscosity is the property of a fluid which makes it sluggish as it flows. It has got a solid consistency. For example, engine oil is a more viscous fluid than water. Consider the fluid to be of superimposed layers of the fluid, then in an incline each layer will flow at staggered speeds unlike water which will flow as soon as there is an incline.



Let F be the additional force required to keep an area of fluid A , always keep moving at a constant velocity. Then



The term F / A is called the shear stress exerted on the fluid. The constant of proportionality m is called the apparent viscosity of the fluid. Thus, shear stress is defined by



         Here, A is the  area of the plate of fluid acted upon by the force F. The velocity gradient can now be given in terms of the shear rate



We get the following velocity distributions, which gives us the pressure distribution too. From the peak pressure point,

The diameter of the casing can be found out by taking a sufficient safety margin over the

maximum pressure, which may be applicable on casing  and multiplying it with the Factor of Safety.

         This is the Newtonian Laminar flow rheological model

Directional Drilling

         In practical applications, horizontal wells are high-angle wells with inclination angles 100. In an ideal horizontal well the inclination angle is equal inclination angles greater than 90 are sometimes drilled to recover oil and gas located in the formation as well as to enhance production rates (gravity helps to counteract the frictional pressure horizontal wells are drilled in a reservoir partly to maximize wellbore contact with the formation in of higher-production wells. Horizontal wells are also drilled for enhanced oil recovery purposes (water flooding) and for water and gas control. Fig. 8.9 shows a schematic diagram of a horizontal well that consists segment, a first buildup segment, a tangent part, and a second buildup segment, followed by a horizontal Here, the departure is defined as the displacement from vertical until the well reaches the beginning horizontal section. Horizontal displacement is the sum of the length of the horizontal section and the departure. Some horizontal wells consist of one build section connecting the vertical part with a horizontal section. Typically, their radius of curvature, shown as under, classifies horizontal wells











Directional drilling







Long-radius,          with a radius of approximately 1,000- 3,000 ft

         Medium-radius,          with a radius of 200- 1,000 ft

         Short-radius,          with a radius of 30- 200 ft          

There are also ultra-short-radius systems that use high-pressure jetting techniques to turn the well from a vertical to a horizontal orientation. The distinction between the three horizontal well categories is arbitrary, and in engineering practice, the build rates overlap. Some wells can be a combination of long and medium build rates or of medium and short. For example, a 3/100 ft build rate may be used in the upper section of a well, followed by a tangent section, with a 10/100 ft buildup rate below the tangent section to reach a horizontal section.

                                                          

Conclusion

         There are so many intricacies and so many twists and turns that it is not possible to incorporate everything about drilling of an oil well in a single academic paper. The illustration below shows the final process diagram.







Bibliography

API BUL*5C3 94.Bulletin on Formulas and Calculations for Casing, Tubing, Drill Pipe and Line Pipe Properties, 6th Ed. The American Petroleum Institute,10th October 1994.Print.

Bourgoyne, Jr. A.T. Millheim, K.K. Chenevert, M.E. Young Jr.F.S. Applied Drilling Engineering. Society of Petroleum Engineers (2nd Ed), Richardson, Texas, 1991.Print.

Devold, H. An Introduction to Oil & Gas Production. Published by ABB Oil and Gas, Oslo. 2nd May 2009.Print.

Lyons, W. Carter, T., Lapeyrouse, N.J.  Formulas and Calculations for Drilling, Production and Workover. Gulf Professional Publishing, Elsiever MA 02451. 2012. Print.

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