directional drilling - · pdf file• early drilling for oil and gas was almost always...

Directional Drilling

• - Acknowledgement• - History• - Present Day Applications• - Hardware• - Measurement Sensors• - Error sources and Equipment Limitations• - Mathematics• - Legislation

Acknowledgement

This presentation has been inspired by many of the items discussed in the publication at left.It can be downloaded at: http://www.uhi.ac.uk/en/research-enterprise/energy/wellbore-positioning-download

Additional material has been obtained from publications of;APSG, OGP, EPSG, C-NLOPB and others

History

Rotary drilling techniques were developed in early 20th century.

Deviated wellbores were usually drilled unintentionally.

• Early drilling for oil and gas was almost always performed by drilling vertical wells, usually considered to be within 2°-3° of plumb.

• Wellbores could naturally deviate from the vertical when certain forces were applied and/or geological conditions existed.

• Until the 1970’s downhole surveys were primarily used to monitor lateral deviations of a wellbore and take preventive measures to maintain its verticality should it start to drift off to one side.

• Deliberately causing a wellbore to deviate from the vertical was known as whipstocking and considered illegal.

• In 1930, California driller John Eastman was granted a patent for his techniques of conducting downhole surveys and intentionally deviating a wellbore.

• Founded the Eastman Oil Well Survey Company.

• He achieved fame and credibility in 1934 by drilling a directional relief well to intercept and extinguish another that was burning near Conroe, Texas.

• Similar research by Sperry, a gyrocompass manufacturer, and Sun Oil Company lead to Sperry-Sun Drilling Services.

• Both Eastman and Sperry names live on as directional drilling subdivisions of major Oil industry service companies.

• In 1964 there was a test in Utah running competing survey tools inside an aluminium irrigation pipe installed on a mountain side. This proved the validity of such equipment and several lawsuits were settled as a result.

Present Day Applications

• Large numbers of present day production and development wells are deviated.

• Environmental and economic benefits.

• Allows for enhanced recovery techniques

• Reuse old wellbores

• Drill a relief well as required by regulations

• Sidetrack around broken pipe and ‘fish’

Hardware

Measurement Sensors

Retrievable Magnetic Compass Survey Equipment

Equipment Limitationsand Error Sources

• Measurements are limited to:GyroscopesMagnetometersAccelerometers

• All components have to be small to fit inside wellbore

• Magnetometers cannot be used inside cased hole

• From a surveyor’s point of view, directional surveys are unclosed traverses and thus will always be suspect.

• Despite this, most errors are in the blunder category

Gamma ray sensor installed behind bit to identify rock formations

MWD probe tracks nearby induced magnetic field

Alternative methods of wellbore steering.

Mud Pulsing Data Transmission

Electromagnetic Data Transmission

$$$$$$$$$$$$$$$

Getting the data back can be problematic.

• Mud Pulse TelemetryLow data rate Cannot be used in underbalanced drilling programs

• Electromagnetic TelemetryDepth limitationsNeed to isolate components

• Retrievable ToolsLow data rateTime consuming Small diameter components

• Wired ToolsConnectivity problemsWire damage potential

• Wired Drill PipeHigh capital costA work in progress

Mathematics

Example - Wellbore Survey Calculations

The table below gives data from a directional survey.

Survey Point Measured Depth Inclination Azimuthalong the wellbore Angle Angle

ft I, deg A, deg

A 3,000 0 20B 3,200 6 6C 3,600 14 20D 4,000 24 80

Based on known coordinates for point C we’ll calculate the coordinates of point D using the above information.

Point C has coordinates:

x = 1,000 (ft) positive towards the east

y = 1,000 (ft) positive towards the north

z = 3,500 (ft) TVD, positive downwards

Z

E (x)

N (y)C

D

DzN

D

C

Dy

Dx

I. Calculate the x, y, and z coordinatesof points D using:

(i) The Average Angle method

(ii) The Balanced Tangential method

(iii) The Minimum Curvature method

(iv) The Radius of Curvature method

(v) The Tangential method

Summary of Results (to the nearest ft)

X Y Z

Average Angle 1,100 1,084 3,878

Balanced Tangential 1,097 1,060 3,877

Minimum Curvature 1,098 1,060 3,881

Radius of Curvature 1,095 1,080 3,878

Tangential Method 1,160 1,028 3,865

Even the most elaborate of these five calculations can be written onto an MS Excel spreadsheet

Do try to maintain standards for data exchange as described in: http://www.epsg.org/exchange/p7.pdf

Legislation

• Surface LocationCanada Oil and Gas Drilling and Production Regulations - Section 74Oil and Gas Conservation Regulations (Alberta) – Section 2.020Both require a licenced surveyor to certify plan

• Directional SurveysCanada Oil and Gas Drilling and Production Regulations - Section 32The operator shall ensure that:(a) directional and deviation surveys are taken at intervals that allow the position of the well-bore to be determined accurately; and(b) except in the case of a relief well, a well is drilled in a manner that does not intersect an existing well.

Oil and Gas Conservation Regulations (Alberta) – Section 6.030(1) Unless the Board otherwise directs in writing, the licensee of a well shall make or cause to be made during drilling, tests, at depth intervals not exceeding 150 metres, for the purpose of ascertaining to what extent the well deviates from the vertical. (2) Repealed AR 36/2002 s6.(3) The licensee shall, immediately upon the making of a directional survey, send to the Board the report of the survey (4) The Board may order the licensee to make such further deviation or directional surveys as it deems necessary, and may give directions as to the manner in which such tests or surveys shall be made.

• SummaryNeither jurisdiction requires directional survey data to be tied to surface location.No certification requirement for directional survey.

Nevertheless; directional surveys may be related to legal boundaries!

Legal Cases

• East Texas Scandal 1962Several land owners believed that deviated wells had been drilled beneath their properties from adjacent lands.Surveys were ordered and over 380 wells were found to be deviated across land boundaries.The validity of surveying equipment used was upheld after the Utah tests in 1964.

• Bocardo SA v Star Energy UK Onshore et al 2009Land owner, Mr. Al Fayed, alleged that 17 years earlier Star had drilled a deviated well underneath his property to extract oil and gas.Star denied the ‘theft’ in initial negotiations but admitted it in court several years later.Judgement for trespass in Bocardo’s favour ; awarded 9% of income over a limited period of time.