Title of Invention  "A METHOD OF DRILLING A BORE HOLE AND AN APPARATUS THEREOF" 

Abstract  The present invention provides a method of drilling a borehole from an above ground surface to one or more subsurface targets according to a reference trajectory plan, said method comprising: determining at predetermined depths below the ground surface, a present location of a drill bit for drilling said borehole; calculating a new trajectory plan to said one or more subsurface targets based on coordinates of said present location of the drill bit; and proceeding with the drilling in accordance with the new trajectory plan using a drilling apparatus such as herein described, the said new trajectory plan being calculated in a three dimensional space and being determined independently of the reference trajectory plan. The invention further provides an apparatus for implementing the aforesaid method. 
Full Text  Field of the Invention: The present invention provides a method for drilling a borehole and an apparatus thereof. This invention provides an improved method and apparatus for detennining the trajectory of boreholes to directional and horizontal targets. In particular, the improved technique replaces the use of a preplanned drilling profile with a new optimum profile that maybe adjusted after each survey such that the borehole from the surface to the targets has reduced tortuosity compared with the borehole that is forced to follow the preplanned profile. The present invention also provides an efficient method of operating a rotary steerable directional tool using improve*! error control, and minimizing increases in torque that must be applied at the surface for the drilling assembly to reach the target Background Controlling the path of a directionally drilled borehole with a tool that permits continuous rotation of the rlrillstring is well established. In directional drilling, planned borehole characteristics may comprise a straight vertical section, a curved section, and a straight nonvertical section to reach a target. The vertical drilling section does not raise significant problems of directional control that require adjustments to a path of the downhole assembly. However, once the drilling assembly deviates from the vertical segment, directional control becomes extremely important. Fig. 1 illustrates a preplanned trajectory between a kickoff point KP to a target T using a broken line A The kickoff point KP may correspond to the end of a straight vertical segment or a point of entry from the surface for drilling the hole. In the former case, this kickoff point corresponds to coordinates where the drill bit is assumed to be during drilling. The assumed kickoff point and actual drill bit location may differ during drilling. Similarly, during drilling, the actual borehole path B will often deviate from the planned trajectory A. Obviously, if the path B is not adequately corrected, the borehole will miss its intended target. At point D, a comparison is made between the preplanned condition of corresponding to planned point on curve A and the actual position. Conventionally, when such a deviation is observed between the actual and planned path, the direcţional driller redirects the assembly back to the original planned path A for the well. Thus, the convenţional direcţional drilling adjustment requires two deflections. One deflection directs the path towards the original planned path A. However, if this deflection is not corrected again, the path will continue in a direction away from the target. Therefore, a second deflection realigns the path with the original planned path A. There are several known tools designed to improve direcţional drilling. For example, BAKER INTEQ'S "Auto Trak" rotary steerable system uses a closed loop control to keep the angle and azimuth of a drill bit oriented as closely as possible to preplanned values. The closed loop control system is intended to porpoise the hole path in small increments above and below the intended path. Similarly, Cameo has developed a rotary steerable system that controls a trajectory by providing a lateral force on the rotatable assembly. However, these tools typically are not used until the wellbore has reached a long straight run, because the tools do not adequately control curvature rates. An example of controlled direcţional drilling is described by Patton (U.S.P. 5,419,405). Patton suggests that the original planned trajectory be loaded into, a computer which is part of the downhole assembly. This loading of the trajectory is provided while the tool is at the surface, and the computer is subsequently lowered into the borehole. Patton attempted to reduce the amount of tortuosity in a path by maintaining the drilling assembly on the preplanned profile as much as possible. However, the incremental adjustments to maintain ah'gnment with the preplanned path also introduce a number of kinks into the borehole. As the number of deflections in a borehole increases, the amount of torque that must be applied at the surface to continue drilling also increases. If too many corrective turns must be made, it is possible that the torque requirements will exceed the specifications of the drilling equipment at the surface. The number of turns also decreases the amount of control of the direcţional drilling. In addition to Patton '405, other references have recognized the potenţial advantage of controlling the trajectory of the tool downhole. (See for example, Pattern U.S.P. 5341886, Gray, U.S.P. 6109370, W093U2319, and Wisler, U.S.P, 5812068). It has been well recognized that in order to compute the position of the borehole downhole, one must provide a means for defiringthe depth of the survey in the downhole computer. A variety of methods have been identified for defîning the survey depths downhole. These include: 1. Using counter wheels on the bottom hole assembly, (Patton, 5341886) 2. Placing magnetic markers on the formation and reading them with the bottom hole assembly, (Patton, 5341886) 3. Recording the lengths of drillpipe that will be added to the driUstring in the computer while it is at the surface and then calculating the survey depths from the drillpipe lengths downhole. (Witte, 5896939). While these downhole systems have reduced the time and Communications resources between a surface drilling station and the downhole drilling assembly, no technique is known that adequately addresses rnimmizing the tortuosity of a drilled hole to a direcţional or horizontal target. Summary of the Invention Applicant's invention overcomes the above deficiencies by developing a nov.l method of computing the optimum path from a calculated position of the borehole to a direcţional or horizontal target. Referring to Fig. l, at point D, a downhole calculation can be made to recompute a new trajectory C, indicated by the dotted line from the deviated position D to the target T. The new trajectory is independent of the original trajectory in that it does not attempt to retrace the original trajectory path. As is apparent from Fig. 1, the new path C has a reduced number of turns to arrive at the target Using the adjusted optimum path will provide a shorter less tortuous path for the borehole than can be achieved by readjusting the trajectory back to the original planned path A. Though a downhole calculation for the optimum path C is preferred, to obviate delays and to conserve Communications resources, the computation can be done downhole or with normal direcţional control operations conducted at the surface and transmitted. The transmission can be via a retrievable wire line or through Communications with a nonretrievable measmewhiledrilling (MWD) apparatus. By recomputing the optimum path based on the actual position of the borehole after each survey, the invention optimizes the shape of the borehole. Drilling to the target may then proceed in accordance with the optimum path determination. The invention recognizes that the optimum trajectory for directional and horizontal targets consists of a series of circular arc deflections and straight line segments. A directional target that is defined only by the vertical depth and its north and east coordinates can be reached from any point above it with a circular arc segment followed by a straight line segment. The invention further approximates the circular arc segments by linear elements to reduce the complexity of the optimum path calculation. Statement of the Invention Accordingly, the present invention provides a method of drilling a borehole from an above ground surface to one or more subsurface targets according to a reference trajectory plan, said method comprising: determining at predetermined depths below the ground surface, a present location of a drill bit for drilling said borehole; calculating a new trajectory plan to said one or more subsurface targets based on coordinates of said present location of the drill bit; and proceeding with the drilling in accordance with the new trajectory plan using a drilling apparatus such as herein described, characterized in that said new trajectory plan being calculated in a 3D space and being determined independently of the reference trajectory plan. The present invention also provides an apparatus for drilling a borehole from an above ground surface to one or more subsurface targets according to a reference trajectory plan, comprising: a device such as herein described for determining at predetermined depths below the ground surface, a present location of a drill bit for drilling said borehole; and a device such as herein described for calculating a new trajectory plan to said one or more subsurface targets based on coordinates for said present location of the drill bit, characterized in that the said new trajectory plan being calculated in three dimensional space and being calculated independent of the reference trajectory plan. Preferred Embodiments of Invention Preferred embodiments of the invention are set forth below with reference to the drawings where: Fig. 1 illustrates a comparison between the path of a conventional corrective path and an optimized path determined according to a preferred embodiment of the present invention; Fig. 2 illustrates a solution for an optimized path including an arc and a tangent line; Fig. 3 illustrates a solution for an optimized path including two arcs connected by a tangent line; Fig. 4, illustrates a solution for an optimized path including an arc landing on a sloping plane; Fig. 5 illustrates a solution for an optimized path including a dual arc path to a sloping plane; Fig. 6 illustrates the relationship between the length of line segments approximating an arc and a dogleg angle defining the curvature of the arc to determine an optimized path according to a preferred embodiment of the invention; Fig. 7 illustrates a first example of determining optimum paths according to a preferred embodiment of the invention; By recomputing the optimum path based on the actual position of the borehole after each survey, the invention optimizes the shape of the borehole. Drilling to the target may then proceed in accordance with the optimum path determination. The invention recognizes that the optimum trajectory for directional and horizontal targets consists of a series of circular arc deflections and straight line segments. A directional target that is defined only by the vertical depth and its north and east coordinates can be reached from any point above it with a circular arc segment followed by a straight line segment. The invention further approximates the circular arc segments by linear elements to reduce the complexity of the optimum path calculation. Statement of the Invention Accordingly, the present invention provides a method of drilling a borehole from an above ground surface to one or more subsurface targets according to a reference trajectory plan, said method comprising: determining at predetermined depths below the ground surface, a present location of a drill bit for drilling said borehole; and calculating a new trajectory plan to said one or more subsurface targets based on coordinates of said present location of the drill bit. characterized in that said new trajectory plan being calculated in a 3D space and being determined independently of the reference trajectory plan. The present invention also provides an apparatus for drilling a borehole from an above ground surface to one or more subsurface targets according to a reference trajectory plan, comprising: a device for determining at predetermined depths below the ground surface, a present location of a drill bit for drilling said borehole; and a device for calculating a new trajectory plan to said one or more subsurface targets based on coordinates for said present location of the drill bit, characterized in that the said new trajectory plan being calculated in three dimensional space and being calculated independent of the reference trajectory plan. Preferred Embodiments of Invention Preferred embodiments of the invention are set forth below with reference to the drawings where: Fig. 1 illustrates a comparison between the path of a conventional corrective path and an optimized path determined according to a preferred embodiment of the present invention; Fig. 2 illustrates a solution for an optimized path including an arc and a tangent line; Fig. 3 illustrates a solution for an optimized path including two arcs connected by a tangent line; Fig. 4, illustrates a solution for an optimized path including an arc landing on a sloping plane; Fig, 5 illustrates a solution for an optimized path including a dual arc path to a sloping plane; Fig. 6 illustrates the relationship between the length of line segments approximating an arc and a dogleg angle defining the curvature of the arc to determine an optimized path according to a preferred embodiment of the invention; Fig. 7 illustrates a first example of determining optimum paths according to a preferred embodiment of the invention; current location of a drill bit and a target. In each of the tables, the variables are defined as follows: Nomenclature AZDEP — Azimuth of the direction of dip for a sloping target plane deg North AZ — Azimuth angle from North deg North BT = Curvature rate of a circular arc deg/lOOft BTA = Curvature rate of the upper circular arc deg/lOOft BTB — Curvature rate ofthe lower circular arc deg/100 ft DAZ — Difference between two azimuths / deg DAZt — Difference between azimuth at the beginning and end of the deg upper curve DAZ2 = Differencebetween azimuth at the beginning and end of the deg lower curve DEAS = Easterly distance between two points ft DIP — Vertical angle of a sloping target plane measured down from a deg horizontal plane t)MD ~ Distance between two points ft DNOR — Northerly distance between two points ft DOG — Total change în direction between ends of a circular arc deg DOG1 = Difference between inclination angles of the circular arc deg DOG2 = Difference between iriclination angles of the circular arc deg DOG A — Total change in direction of the upper circular arc deg DOGB — Total change in dkection of the lower circular arc deg DTVD = Vertical distance" between two points ft DVS — Distance between two points projected to a horizontal plane ft EAS = East coordinate ft ETP = East coordinate of vertical depth measurement position ft HAT = Vertical distance between a point and a sloping target plane, (+) ft if point is above the plane INC = Inclination angle from vertical deg LA = Length oftangent lines that represent the upper circular arc ft LB  Length oftangent lines that represent the lower circular arc ft MD = Measured depth along thewellbore from surface ft MDL = Measured depth along tangent lines ft NOR = North coordinate ft NTP = North coordinate ofvertical depth measurement position ft TARGAZ = Target azimuth for horizontal target deg North TVD = Vertical depth from surface ft TVDT = Vertical depth of a sloping target plane at north and east ft coordinates TVDTP = Vertical depth to a sloping target plane at NTP and ETP ft coordinates Fig. 2 and Table l show the process for designing a direcţional path comprising a circular arc followed by a straight tangent section that lands on a direcţional target. Table l SingleCurveand Tangent to a Direcţional Target GIVEN: BTA Starting position: MD(1), TVD(l), EAS(l), NOR(l), INC(l), AZ(1) Target position: TVD(4), EAS(4), NOR(4) (Table Removed) Fig. 3 and Table 2 show the procedure for designing the path that requires "' two circular arcs separated by a straight line segment requked to reach a direcţional target that includes requirements for the entry angle and azimuth. Table 2 Two Curves with a Tangent to a Direcţional Target GIVEN: BTA, BTB Startingposition: MD(1), TVD(l), EAS(l), NOR(1), INC(l), AZ(1) Target position: TVD(6), EAS(6), NOR(6), INC(6), AZ(6) (Table Removed) Fig. 4 and Table 3 show the calculation procedure for determining the specifications for the circular arc required to drill from a point in space above a horizontal sloping target with a single circular arc. In horizontal drilling operations, the horizontal target is defined by a dipping plane in space and the azimuth of the horizontal well extension. The single circular arc solution for a horizontal target requires that the starting inclination angle be less than the landing angle and that the starting position be located above the sloping target plane. Table 3 Single Curve Landing on a Sloping Target Plane GIVEN: TARGAZ, BT Starting position: MD(1), TVD(l), NOR(l), EAS(l), INC(l), AZ(1) Sloping target plane: TVDTP, NTP, ETP, DIP, AZDIP (Table Removed) For all other cases the required path can be accomplished with two circular arcs. This general solution in included in Fig. 5 and Table 4. Table 4 Double Turn Landing to a Sloping Target GIVEN: BT, TARGAZ Starting position: MD(l),TVD(l),NOR(1), EAS(l), INC(l), AZ(1) Sloping Target: TVDTP @ NTP & ETP, DIP, AZDDP (Table Removed) In summary, if the direcţional target specification also includes a required entry angle and azimuth, the path from any point above the target requires two circular arc segmente separated by a straight line section. See Fig. 3. When drilling to horizontal well targets, the goal is to place the wellbore on the plane of the . formation, at an angle that parallels the surface of the plane and extends in the preplanned direction. From a point above the target plane where the inclination angle is less than the required final angle, the optimum path is a single circular arc segment as shown in Fig. 4. For all other borehole orientations, the landing trajectory requires two circular arcs as is shown in Fig. 5. The mathematical calculations that are needed to obtain the optimum path from the above Tables 14 .are well within the programming abih'ties of one skilled in the art. The program can be stored to any computer readable medium either downhole or at the surface. Particular examples of these path determinations are provided below. Direcţional Example Fig. 7 shows the planned trajectory for a threetarget direcţional well. The specifications for these three targets are as follows. Vertical Depth North Coordinate East Coordinate Ft. Ft. Ft. Target No. l 6700 4000 1200 Target No. 2 7500 4900 1050 Target No. 3 7900 5250 900 The position of the bottom of the hole is defined as follows. Measured depth 2301 ft. Inclination angle l .5 degrees from vertical Azimuth angle 120 degrees from North Vertical depth 2300 ft. North coordinate 20 ft. East Coordinate 6 ft. Design Curvature Rates. Vertical Depth Curvature Rate 2300 to 2900 ft 2.5 deg/100 ft 2900 to 4900 ft 3.0 deg/100 ft 4900 to 6900 ft 3.5 deg/100 ft 6900 to 7900 ft 4.0 deg/100 ft The required trajectory is calculated as follows. For the first target we use the Fig 2 and Table l solution. BTA = 2.5 deg/100 ft MDL (1) = 2301 ft INC (1) = 1.5 deg AZ (1) = 120 deg North TVD (1) = 2300 ft NOR(l) = 20 ft EAS(l) = 6ft LA = 1121.7 ft DOGA = 52.2 deg MDL (2) = 3422.7 ft TVD (2) = 3420.3 ft NOR (2) — 5.3 ft EAS (2) = 31.4 ft INC (3) — 51.8 deg AZ (3) = 16.3 deg North aziinuth MDL (3) = 4542.4 ft MD (3) — 4385.7 ft TVD (3) = 4113.9 ft NOR (3) = 850.2 ft EAS (3)  278.6 ft MD (4) = 8564.0 ft MDL (4) = 8720.7 ft INC (4) = 51.8 deg AZ (4) = 16.3 deg North TVD (4) = 6700 ft NOR (4) = 4000 ft EAS (4) = 1200 ft For second target we use the Fig. 2 and Table l solution BTA =3.5 deg/100 ft MD (1) — 8564.0 ft MDL (1) = 8720.9 ft INC (1) =51.8 deg AZ (1)  16.3 deg North TVD (1) = 6700 ft NOR(l) — 4000 ft EAS (1) = 1200 ft LA = 458.4 ft DOGA — 31.3 deg MDL(2) = 9179.3 ft TVD (2) = 6983.5 ft NOR (2) = 4345.7 ft EAS(2) = 1301.1ft INC (3) = 49.7 deg AZ(3) = 335.6 deg North MDL (3) = 9636.7 ft MD (3)  9457.8 ft TVD (3)  7280.1 ft NOR (3) =4663.4ft EAS(3) = 1156.9 ft MD (4) = 9797.7 ft MDL (4) * 9977.4 ft INC (4) = 49.7 deg AZ(4) = 335.6 deg North TVD (4) =7500 ft NOR (4) =4900 ft EAS(4) = 1050 ft For the third target we also use the Fig 2 and Table l solution BTA = 4.0deg/100ft MD(1) = 9797.7 ă MDL (1) = 9977.4 ft INC (1) = 49.7 deg AZ(1) = 335.6 deg North TVD (1) = 7500 ft NOR(l) =4900fi EAS(l) = 1050 ft LA = 92.8 ft DOGA = 7.4 deg MDL(2)  10070.2fi TVD(2) = 7560.0 ft NOR EAS (2) = 1020.8ft INC (3) = 42.4 deg AZ(3) = 337.1 deg North MDL(3) = 10163.0 ft MD(3) = 9983.1ft TVD (3) = 7628.6 ft NOR (3) = 50221 ft EAS (3) =996.4 ft MD(4)  10350.4 ft MDL(4) = 10530.2 ft INC (4) = 42.4 deg AZ(4)  337.1 deg North TVD (4) =7900 ft NOR (4) = 5250 ft EAS(4) = 900ft Horizontal Example Fig. 8 shows the planned trajectory for drilling to a honzontal target In this example a direcţional target is used to align the borehole with the desired horizontal path. The direcţional target is defined as follows. 6700 ft Vertical depth 400 ft North coordinate 1600 ft East coordinate 45 deg inclination angle 15 deg North azimuth The horizontal target plan has the following specs: 6800 ft vertical depth at O ft North and O ft East coordinate 30 degrees North dip azimuth 15 degree North horizontal wellbore target direction 3000 ft horizontal displacement The position of the bottom of the hole is as follows: Measured depth 3502 ft Inclination angle 1.6 degrees Azimuth angle 280 degrees North Vertical depth 3500 ft North coordinate 10 ft East coordinate 20 ft The design curvature rates for the directional hole are: Vertical Depth Curvature Rate 35004000 3 deg/100 ft 40006000 3.5 deg/100 ft 60007000 4 deg/100 ft The maximum design curvature rates for the horizontal well are: 13 deg/100 ft The trajectory to reach the directional target is calculated using the solution shown on Fig. 3. BTA = 3.0 deg/100 ft BTB =3.5 deg/100 ft MDL(1) = 3502 ft MD (1) = 3502 ft INC (I) = 1.6 deg AZ(1) = 280 degrees North TVD(l)  3500 ft NOR(l) = 10 ft EAS(l) = 20 ft LA = 672.8 ft LB = 774.5 ft DOGA = 38.8 deg DOGB = 50.6 deg MDL(2) = 4174,8 ft TVD(2) = 4172.5 ft NOR(2) = 13.3 ft EAS(2) = 38.5 ft INC (3) = 37.2 deg AZ(3) = 95.4 deg North MDL(3) = 4847.5 ft MD (3) = 4795.6 ft TVD(3) = 4708.2 ft NOR(3) = 25.2 ft EAS(3) = 366.5 ft INC (4) — 37.2 deg AZ(4) = 95.4 deg North MDL(4) = 5886,4 ft MD (4)  5834_5 ft TVD(4) = 5535.6 ft NOR(4) — 84.7 ft EAS(4) = 992.0 ft MDL(5) = 6660.8 ft TVD(5) = 6152.4 ft NOR(5) = 129.0 ft EAS(5) = 1458.3 ft MD (6) = 7281.2 ft MDL(6) = 7435.2 ft INC (6) =45 deg AZ (6) = 15 deg North TVD(6) = 6700 ft NOR(6) = 400 ft EAS(6) = 1600 ft The horizontal landing trajectory uses the solution shown on Fig. 4 and Table 3. The results are as follows. The starting position is: MD (1) = 7281.3 ft INC(l) = 45 deg AZ (1) = 15 deg North TVD (1) = 6700 ft NOR (l = 400 ft EAS (1) = 1600 ft The sloping target specification is: TVDTP = 6800 ft NTP = Oft ETP = Oft DIP = 4 deg AZDIP = 30 deg North The horizontal target azimuth is: TARGAZ= 15 deg North The Table 3 solution is as follows: DNOR = 400 ft DEAS = 1600 ft DVS = 1649.2 ft AZD = 76.0 deg North TVD (2) — 6880.2 ft ANGA = 15 deg X = 193.2 ft TVD (3) = 6893.2 ft NOR (3) = 586.6 ft EAS (3) = 1650.0 ft LA = 273.3 ft AZ(5) = 15 deg North INC (5) = 86.1 deg DOG = 41.1 deg BT = 7.9 deg/100 ft DVS = 272.6 ft DNOR = 263.3 ft DEAS = 70.6 ft DTVD = 18.4 ft NOR (5) = 850.0 ft EAS (5) = 1720.6 ft TVD (5) = 6911.6 ft MD (5) = 7804.1 ft The end of the 3000 ft horizontal is detennined as follows: DVS — 2993.2 ft DNOR = 2891.2 ft DEAS = 774.7 ft DTVD = 202.2 ft NOR = 3477.8 ft EAS  2495.3 ft TVD  7113.8 ft MD = 10804.1 ft It is well known that the optimum curvature rate for direcţional and horizontal wells is a function of the vertical depth of the section. Planned or desired curvature rates can be loaded in the downhole computer in the form of a table of curvature rate versus depth. The downhole designs will utilize the planned curvature rate as defined by the table. The quality of the design can be further optimized by utilizing lower curvature rates than the planned values whenever practicai. As a feature of the preferred embodiments, the total dogleg curvature of the uppermost circular arc segment is compared to the planned or desired curvature rate. Whenever the total dogleg angle is found to be less than the designer's planned curvature rate, the curvature rate is reduced to a value numerically equal to the total dogleg. For example, if the planned curvature rate was 3.5°/100 ft and the required dogleg was .5°, a curvature rate of .5/100 ft should be used for the iniţial circular arc section. This procedure will produce smoother less tortuous boreholes than would be produced by utilizing the planned value. The actual curvature rate performance of direcţional drilling equipment including rotary steerable systems is affected by the manufacturing tolerances, the mechanical wear of the rotary steerable equipment, the wear of the bit, and the characteristics of the formation. Fortunately, these factors tend to change slowly and generally produce actual curvature rates that stay fairly constant with drill depth but differ somewhat from the theoretical trajectory. The down hole computing system can further optimize the trajectory control by computing and utilizing a correction factor in controlling the rotary steerable system. The magnitude of the errors can be computed by comparing the planned trajectory between survey positions with the actual trajectory computed from the surveys. The difference between these two values represents a combination of the deviation in performance of the rotary steerable system and the randomly induced errors in the survey measurement process. An effective error correction process should nunimize the irtfluence of the random survey errors while responding quickly to changes in the performance of the rotary steerable system. A preferred method is to utilize a weighted running average difference for the correction coefficients. A preferred technique is to utilize the last five surveys errors and average them by weighting the latest survey fivefold, the second latest survey fourfold, the third latest survey threefold, the fourth latest survey twofold, and the fifth survey one time. Altering the number of surveys or adjusting the weighting factors can be used to further increase or reduce the infl uence of the random survey errors and increase or decrease the responsiveness to a change in true performance. For example, rather than the five most recent surveys, the data from ten most recent surveys may be used during the error correction. The weighting variables for each survey can also be whole or fractional numbers. The above error determinations may be included in a computer program, the details of which are well within the abilities of one skilled in the art, The above embodiments for direcţional and horizontal drilling operations can be applied with known rotarysteerable direcţional tools that effectively control curvature rates. One such tool is described by the present inventor in U.S.P. 5,931,239 patent. The invention is not limited by the type of steerable system. Fig. 9 illustrates the downhole assembly which is operable with the preferred embodiments. The rotarysteerable direcţional tool l will be run with an MWD tool 2. A basic MWD tool, which measures coordinates such as depth, azimuth and inclination, is well known in the art. In order to provide the improvements of the present invention, the MWD tool of the inventive apparatus includes modules that perform the following functions. 1. Receives data and instructions from the surface. 2. Includes a surveying module that measures the inclination angle and azimuth of the tool 3. Sends data from the MWD tool to a receiver at the surface 4. A twoway radio link that sends instructions to the adjustable stabilizer and receives performance data back from the stabilizer unit 5. A computer module for recalculating an optimum path based on coordinates of the drilling assembly. There are three additional methods that can be used to make the depths of each survey available to the downhole computer. The simplest of these is to simply download the survey depth prior to or following the surveying operations. The most efficient way of handling the survey depth information is to calculate the future survey depths and load these values into the downhole computer before the tool is lowered into the hole. The ieast intrusive way of predicting survey depths is to use an average length of the drill pipe joints rather than measuring the length of each pipe to be added, and determining the survey depth based on the number of pipe joints and the average length. It is envisioned that the MWD tool could also include modules for taking GammaRay measurements, resistivity and other formation evaluation measurements. It is anticipated that these additional measurements could either be recorded for future review or sent in realtime to the surface. The downhole computer module will utilize; surface loaded data, minimal instructions downloaded from the surface, and downhole measurements, to compute the position of the bore hole after each survey and to determine the optimum trajectory required to drill from the current position of the borehole to the direcţional and horizontal targets. A duplicate of this computing capability can optionally be installed at the surface in order to nunimize the volume of data that must be sent from the MWD tool to the surface. The downhole computer will also include an error correction module that will compare the trajectory determined. from the surveys to the planned trajectory and utilize those differences to compute the error correction term. The error correction will provide a closed loop process that will correct formanufactiiringtolerances, tool wear, bit wear, and formation effects. The process will significantly improve directional and horizontal drilling operations through the following: 1. Only a single bottom hole assembly design will be required to drill the entire direcţional well. This eliminates all of the trips commonly used in order to change the characteristics of the bottom hole assembly to better meet the designed trajectory requirements. 2. The process will drill a smooth borehole with minimal tortuosity. The process of redesigning the optimum trajectory after each survey will select the minimum curvature hole path required to reach the targets. This will eliminate the tortuous adjustments typically used by direcţional drillers to adjustthe path back to the original planned trajectory. 3. The closed loop error correction routine will minimize the differences between the intended trajectory and the actual trajectories achieved. This will also lead to reduced tortuosity. 4. Through the combination of providing a precise control of curvature rate and the ability to redetermine the optimum path, the invention provides a trajectory that utilizes the minimum practicai curvature rates.,This will further expandthe goal of minimizing the tortuosity of the hole. While preferred embodiments of the invention have been described above, one skilled in the art would recognize that various modifications can be made thereto without departing from the spirit and scope of the invention. WE CLAIM: 1. A method of drilling a borehole from an above ground surface to one or more subsurface targets according to a reference trajectory plan, said method comprising: determining at predetermined depths below the ground surface, a present location of a drill bit for drilling said borehole; calculating a new trajectory plan to said one or more subsurface targets based on coordinates of said present location of the drill bit; and proceeding with the drilling in accordance with the new trajectory plan using a drilling apparatus such as herein described, characterized in that said new trajectory plan being calculated in a 3D space and being determined independently of the reference trajectory plan. 2. The method as claimed in claim 1, wherein said new trajectory plan comprises a single curvature between said present location of the drill bit and a first sub¬surface target of said one or more subsurface targets. 3. The method as claimed in claim 2, wherein said single curvature is determined based on a present location of the drill bit and a position of said first subsurface target. 4. The method as claimed in claim 3, wherein said single curvature is estimated by a first tangent line segment and a second tangent line segment, each of the first and second tangent line segments having a length (LA) and meeting at an intersecting point, where the length is determined based on a radius of a circle defining said single curvature (R), and an angle defined by a first and second radial line of the circle defining said single curvature to respective nonintersecting endpoints of the first and second tangent line segments (DOG) in a manner such as herein described. 5. The method as claimed in claim 3, wherein said new trajectory plan comprises said single curvature and a tangent line from an end of the said single curvature which is closest to said first subsurface target. 6. The method as claimed in claim 1, wherein a first of said subsurface targets comprises a target, having requirements for at least one of entry angle and azimuth, and said new trajectory plan comprises a first curvature and a second curvature. 7. The method as claimed in claim 6, wherein said first and second curvature is estimated by a first tangent line segment A and a second tangent line segment B, each of the first and second tangent line segments having a length (LA) and said tangent line segments meeting at an intersecting point C, wherein the length is determined based on a radius of a circle defining at least one of said first and second curvature and an angle defined by a first and second radial line of the circle defining said at least one of said first and second curvature to respective nonintersecting endpoints of the first and second tangent line segments (DOG) in a manner such as herein described. 8. The method as claimed in claim 7, wherein said first and second curvature are interconnected by a straight line joining a nonintersecting endpoint of the first and second tangent line segments corresponding to said first curvature with a nonintersecting endpoint of the first and second tangent line segments corresponding to said second curvature. 9. The method as claimed in claim 4, wherein said first subsurface target comprises a horizontal well with a required angle of entry and azimuth and said present location of said drill bit is at a depth which is more shallow than said first sub¬surface target. 10. The method as claimed in claim 1, wherein determining said present location of the drill bit comprises ascertaining coordinates for a borehole depth and measuring an inclination and an azimuth, wherein the borehole depth is predetermined based on a number of drill segments added together to drill said borehole to said present location. 11. The method as claimed in claim 1, wherein determining said present location of the drill bit comprises ascertaining coordinates for a borehole depth and measuring an inclination and an azimuth, wherein the borehole depth is determined based on a communication of a depth measurement provided from a drilling station located above ground. 12. The method as claimed in claim 1, comprising measuring inclination and azimuth angles of a new borehole drilled according to the new trajectory plan at at least a first location, a second location and a third location in said new borehole, calculating actual trajectories of the new borehole between the first location and the second location, and between the second location and the third location, comparing the actual trajectories with the new trajectory plan used to drill the new borehole between said first, second and third locations, and determining an error between the actual trajectories and the new trajectory plan to determine an error correction term, wherein said error correction term is calculated as a weighted average, which weights more recent error calculations more heavily than less recent error calculations. 13. The method as claimed in claim 1, wherein the predetermined depths are anticipated depths, said method further comprising loading the anticipated depths into a processor that is lowered into the borehole, said loading occurring while the processor is at the above ground surface prior to being lowered into the borehole. 14. The method as claimed in claim 13, wherein the anticipated depths are determined based on an average length of drill pipe segments. 15. An apparatus for drilling a borehole from an above ground surface to one or more subsurface targets according to a reference trajectory plan as claimed in claim 1, comprising: a device such as herein described for determining at predetermined depths below the ground surface, a present location of a drill bit for drilling said borehole; and a device such as herein described for calculating a new trajectory plan to said one or more subsurface targets based on coordinates for said present location of the drill bit, characterized in that the said new trajectory plan being calculated in three dimensional space and being calculated independent of the reference trajectory plan. 16. The apparatus as claimed in claim 15, wherein said device for determining said present location of the drill bit comprises means such as herein described for ascertaining coordinates for a borehole depth, wherein the borehole depth is predetermined based on a number of drill segments added together to drill said borehole to said present location. 17. The apparatus as claimed in claim 15, wherein said device for determining said present location of the drill bit comprises means such as herein described for ascertaining coordinates for a borehole depth, wherein the borehole depth is determined based on a communication of a depth measurement provided from a drilling station located above ground. 18. The apparatus as claimed in claim 15, comprising: means such as herein described for measuring at least one of an azimuth and inclination angle of a new borehole drilled according to the new trajectory plan at least a first location, a second location, and a third location in said new borehole; means such as herein described for calculating actual trajectories of the new borehole between the first location and the second location, and between the second location and the third location; and means such as herein described for determining an error between the actual trajectories and the new trajectory plan used to drill said new borehole between said first, second and third locations to determine an error correction term. wherein said correction term is calculated as a weighted average, which weights more recent error calculations more heavily than less recent error calculations. 19. A method of drilling a borehole from an above ground surface to one or more subsurface targets such as herein described with reference to the accompanying drawings. 20. An apparatus of drilling a borehole from an above ground surface to one or more subsurface targets such as herein described with reference to the accompanying drawings. 

01937delnp2003correspondenceothers.pdf
01937delnp2003Description (Complete)06062008.pdf
01937delnp2003description (complete)16062008.pdf
01937delnp2003description (complete)17062008.pdf
01937delnp2003description (complete).pdf
1937DELNP2003Abstract(06062008).pdf
1937delnp2003abstract(17062008).pdf
1937DELNP2003Claims(06062008).pdf
1937delnp2003claims(16062008).pdf
1937delnp2003claims(17062008).pdf
1937DELNP2003CorrespondenceOthers(06062008).pdf
1937delnp2003correspondenceothers(16062008).pdf
1937DELNP2003Drawings(06062008).pdf
1937DELNP2003Form1(06062008).pdf
1937delnp2003form1(17062008).pdf
1937delnp2003form13(16062008).pdf
1937DELNP2003Form2(06062008).pdf
1937DELNP2003Form3(06062008).pdf
1937delnp2003form5(17062008).pdf
1937DELNP2003Petition137(06062008).pdf
Patent Number  221587  

Indian Patent Application Number  01937/DELNP/2003  
PG Journal Number  31/2008  
Publication Date  01Aug2008  
Grant Date  25Jun2008  
Date of Filing  17Nov2003  
Name of Patentee  THE VALIDUS INTERNATIONAL COMPANY  
Applicant Address  LLC OF 5430 LBJ FREEWAY, SUITE 1550, DALLAS, TX 75240, UNITED STATES OF AMERICA.  
Inventors:


PCT International Classification Number  E21B  
PCT International Application Number  PCT/US02/03386  
PCT International Filing date  20020220  
PCT Conventions:
