# US 2014/0196949 A1 · Autodriller system

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- Number: US 2014/0196949 A1
- Document ID: US20140196949A1
- Status: Published application
- Kind: A1
- Application number: 14/124,699
- Filed: 2012-06-29
- Published: 2014-07-17
- Earliest claimed: 2011-06-29
- Assignees: University of Calgary
- Inventors: Geir Hareland; Mohammad Fazaelizadeh; Zebing Wu
- Web page: https://patentgrep.com/patent/US20140196949A1

## CPC

- E21B 44/00: Automatic control systems specially adapted for drilling operations, i.e. self-operating systems which function to carry out or modify a drilling operation without intervention of a human operator, e.g. computer-controlled drilling systems; Systems specially adapted for monitoring a plurality of drilling variables or conditions
- E21B 44/02: Automatic control of the tool feed ({E21B44/005,} E21B44/10 take precedence)
- E21B 47/007: Measuring stresses in a pipe string or casing (for locating blocked portions of pipes E21B47/09)
- E21B: EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS

## Abstract

An autodriller provides an automatic self calibration system to predict both axial and rotational friction coefficients from the surface measurements such as hookload and surface torque while a drill bit is off bottom. The friction coefficients are used to calculate the friction forces between drillstring and the wellbore while the bit is on bottom during drilling operation to estimate downhole weight on the bit and bit torque, and use the estimates to alter the drilling process.

## Claims

### Claim 1

A method of drilling a formation, the method comprising:
drilling the formation with a drilling system that includes a drillstring and a bit;
estimating a friction force on the drillstring;
estimating a downhole weight on bit using a surface measurement and the estimated friction force; and
taking an action to change drilling of the formation based on estimated downhole weight on bit.

### Claim 2 (depends on 1)

The method of claim 1 in which estimating a friction force on the drillstring comprises applying a friction model.

### Claim 3 (depends on 1)

The method of claim 1 in which the action comprises modifying drilling by modifying a drilling parameter.

### Claim 4 (depends on 1)

The method of claim 1 in which the friction force is estimated according to the friction model and according to a first surface measurement conducted while the bit is off bottom.

### Claim 5 (depends on 4)

The method of claim 4 in which the first surface measurement is a hook load measurement.

### Claim 6 (depends on 5)

The method of claim 5 in which the surface measurement is a hook load measurement.

### Claim 7 (depends on 1)

The method of claim 1 in which the drilling parameter is one or more of surface torque, drillstring rotation rate, hook load and mud weight.

### Claim 8 (depends on 1)

The method of claim 1 in which estimating the downhole weight on the bit comprises:
(a) determining the static weight of drillstring;
(b) determining an axial friction coefficient including pipe rotation effect;
(c) determining the effect of downhole weight on the bit on value of axial friction force during drilling; and
(d) determining downhole weight on the bit using axial friction coefficient and surface hookload measurements.

### Claim 9 (depends on 1)

The method of claim 1 incorporated in an autodrilling system in which the autodrilling system automatically adjusts surface WOB utilized by the autodrilling system.

### Claim 10 (depends on 1)

The method of claim 1 in which taking an action comprises the autodrilling system displaying surface WOB from hook load measurements and estimated downhole weight on bit.

### Claim 11 (depends on 1)

The method of claim 1 further comprising identifying a founder point where estimated weight on bit is non-zero and rate of penetration is not increasing.

### Claim 12 (depends on 1)

The method of claim 1 further comprising calibrating the axial friction coefficient and the rotational friction coefficient from the surface measurement and identifying a drilling problem.

### Claim 13 (depends on 12)

The method of claim 12 in which the drilling problem is one or more of string sticking and insufficient hole cleaning.

### Claim 14 (depends on 8)

The method of claim 8 wherein the static weight of drillstring is calculated using survey data, drillstring specification and local buoyancy factor at any bit depth which are given by mud logging unit on the rig site.

### Claim 15 (depends on 8)

The method of claim 8 wherein the axial friction coefficient including the drillstring rotation effect is estimated using surface measured hookload determined when the bit is off bottom.

### Claim 16 (depends on 15)

The method of claim 15 wherein the surface measured hookload is determined while the bit is off bottom and has a drillstring rotation, and the bit is sufficiently close to bottom that the drillstring rotation is the same as the expected drillstring rotation in the formation to be drilled.

### Claim 17 (depends on 1)

The method of claim 1 in which, during drilling, different equations are employed to determine the downhole weight on bit depending on whether a part of the drillstring in a curved section is in compression or tension.

### Claim 18 (depends on 1)

The method of claim 1 further comprising:
calculating hookload by using axial friction coefficient and estimating the weight on the bit;
comparing calculated hookload with measured hookload value; and
if the difference between calculated hookload and measured hookload value is negligible, the estimated downhole weight on the bit is taken as downhole weight on the bit, and if the difference is not negligible, another value will be estimated for downhole weight on the bit and this procedure is repeated to determine the downhole weight on the bit.

### Claim 19 (depends on 8)

The method of claim 8 further comprising estimating downhole torque on bit comprising the steps of:
(a) determining the rotational friction force while drilling bit is off bottom;
(b) determining the rotational friction coefficient including axial pipe movement effect from surface torque measurements while bit is off bottom;
(c) determining the effect of downhole weight on the bit on value of rotational friction force during drilling; and
(d) determining downhole bit torque by using rotational friction coefficient and estimated downhole weight.

### Claim 20 (depends on 19)

The method of claim 19 in which taking an action comprises determining when to pull the bit off the bottom and pulling the bit off bottom.

### Claim 21 (depends on 19)

The method of claim 19 wherein the rotational friction coefficient including the drillstring axial movement effect is estimated while the bit is off bottom and there is no torque at the bit.

### Claim 22 (depends on 21)

The method of claim 21 wherein the measured surface torque is measured while the bit is moving downwardly and sufficiently close to bottom that the drillstring rotation at the point of measurement is the same as drillstring rotation in the formation to be drilled.

### Claim 23 (depends on 19)

The method of claim 19 in which, during drilling, different equations are employed to determine the downhole torque on bit depending on whether a part of the drillstring in a curved section is in compression or tension.

### Claim 24 (depends on 19)

The method of claim 19 wherein rotational friction force while bit is on bottom is estimated by using rotational friction coefficient and downhole weight on the bit.

### Claim 25 (depends on 1)

The method of claim 1 used in sliding drilling using a mud driven motor.

### Claim 26 (depends on 25)

The method of claim 25 further comprising finding K, where K is the estimated downhole weight on bit divided by pressure differential across the mud driven motor.

### Claim 27 (depends on 26)

The method of claim 26 in which K is used to improve drilling performance.

### Claim 28 (depends on 1)

Computer readable media containing, in non-transient form, instructions for instructing an autodriller system to carry out the method of claim 1.

### Claim 29 (depends on 1)

A drilling system comprising a rig, a drill string connected downwardly into a borehole, and an autodriller system, the autodriller system being configured to carry out the method of claim 1.