Divine Somiari,S Well Bore Stability Presentation

WELLBORE STABILITY

JUMA . E. OIL & GAS SERVICES

TRADITIONAL WELL DESIGN

Traditional well design is based on pore and fracture pressure

estimate from offset wells and log-based analysis

This method is typically less reliable when drilling • Deviated wells• In tectonic areas• Dipping weak bedded formations • In depleted reservoir

And costs the industry a lot of money, approximately $8.00 billion yearly.

Case Study, Niger Delta, NigeriaComparison Between Traditional & Geo-

mechanics method of Well Planning • Below is a table (table 6) showing mud

weight values estimated for a well using traditional method. While drilling with the estimated mud weight value of 0.53 to 0.57psi/ft, by the traditional method, it was not possible to drill to TD.

• With geo-mechanics used, a mud weight of 0.36 psi/ft was estimated (table 2). These mud weight was able to drill a sidetrack of the well to TD, with out any non productive loss time due to well bore instability problems.

TABLE 1

Fracture Gradient (psi/ft) Mud Weight (psi/ft) Mud Overbalance (psi/ft)

0.603133333333333 0.526666666666667 0.0764666666666666

0.6048 0.536956307031351 0.0867563070313506

0.6068 0.5285 0.0783

0.608133333333333 0.529166666666667 0.0789666666666667

0.609133333333333 0.529666666666667 0.0794666666666666

0.610133333333333 0.530166666666667 0.0799666666666667

0.6118 0.531 0.0808

0.642906666666667 0.566633333333333 0.0762733333333333

0.64424 0.5673 0.0769399999999999

0.644906666666667 0.567633333333333 0.0772733333333333

0.646906666666667 0.568633333333333 0.0782733333333333

0.64724 0.5688 0.07844

HOW CAN WELLBORE STABILITY ADD VALUE TO THE INDUSTRY?

By reducing expensive drilling problems • Well bore instability and fracture pressure prediction • Reduce stuck pipe, losses, side tracks, reaming, etc• Under balanced drilling, feasibility.

By increasing reservoir performance.• Production from natural fractures • Sand production prediction. • Reduce casing shear and collapse • Compaction / subsidence

By reducing exploration risk• Fault leakage analysis

THE GEOMECHANICAL MODEL

This based on the principal stress tensor

Description of a geo mechanical model for a reservoir

involves detailed knowledge of:• In situ stress orientations• In situ stress magnitudes • Pore pressure • Rock Mechanical properties

Other consideration: Mud chemistry, weak bedding planes,

Fractures, thermal effects.

BUILDING A GEOMECHANICAL MODEL

Data required to construct a geo mechanical model:

• Vertical or overburden stress from integrated density log• Pore pressure from log-based (sonic, resistively)• Seismic (ITT, Velocity cubes) and Measurement (RFT,

PWD, etc)• Magnitude of Minimum horizontal stress from LOT,

XLOT, etc)• Rock Strength from Logs, core test, etc

PORE PRESSURE, FRACTURE, PRESSURE, AND WELL BORE STABILITY

THE COMPLETE PICTURE

Well planning and drilling should incorporate:

Geomechanics to reduce wellbore instability and lost circulation risk.

This is especially important for high angle wells, tectonic areas and

depleted reservoirs.

Pore pressure and well bore stability prediction should be performed

Together as these will give clearer picture of the formation.

WELL BORE STABILITY

Aim:

Reduce drilling costs by incorporating Geomechanics into well

planning and drilling process:• Optimizing mud weights and mud properties • Minimizing casing strings • Optimizing wellbore trajectory • Optimizing surface location

Case Study, Niger Delta, Nigeria.

• Wellbore Stability Analysis Plots to illustrate the use of geo-mechnics to add value to the planning and drilling of a well in Niger Delta.

TABLE 2

Depth (ft)Overburden Stress (psi/ft)

Pore Pressure (psi/ft)

8240 0.909 0.45

8710 0.914 0.45

9283 0.92 0.45

9753 0.924 0.45

10043 0.927 0.45

10347 0.93 0.45

10917 0.935 0.45

12584 0.948 0.45

13204 0.952 0.45

13614 0.954 0.45

14368 0.96 0.45

14498 0.961 0.45

TABLE 3Minimum Horizontal Stress (psi/ft)

Well Inclination(deg)

Well azimuth(deg)

0.469666667 0 0

0.471333333 5 5

0.473333333 10 10

0.474666667 15 15

0.475666667 20 20

0.476666667 25 25

0.478333333 30 30

0.482666667 35 35

0.484 40 40

0.484666667 45 45

0.486666667 50 50

0.487 55 55

TABLE 4

Poisson's Ratio Friction angle(deg) UCS (psi/ft)

0.25 25.4 0.289

0.25 26.7 0.3596

0.25 24.9 0.2243

0.25 25.4 0.2393

0.25 25.4 0.2324

0.25 25.4 0.233

0.25 26.2 0.2633

0.25 26.7 0.2487

0.25 28 0.294

0.25 27.2 0.2518

0.25 29.7 0.3291

0.25 29.7 0.3261

TABLE 5

Compressional Velocity Shear Velocity Maximum Horizontal Stress (psi/ft)

45 5 0.667366666666667

56 10 0.670533333333333

67 15 0.674333333333333

78 20 0.676866666666667

89 25 0.678766666666667

100 30 0.680666666666667

111 35 0.683833333333333

122 40 0.692066666666667

133 45 0.6946

144 50 0.695866666666667

155 55 0.699666666666667

166 60 0.7003

TABLE 6

Collapse Pressure (psi/ft) Fracture Gradient (psi/ft) Mud Weight (psi/ft)

0.479896447759961 0.469666666666667 0.474781557213314

0.56093485246493 0.471333333333333 0.516134092899132

0.417355126422702 0.473333333333333 0.445344229878018

0.440704205542267 0.474666666666667 0.457685436104467

0.439936355143774 0.475666666666667 0.45780151090522

0.447046417631349 0.476666666666667 0.461856542149008

0.489090182237921 0.478333333333333 0.483711757785627

0.483988464233271 0.482666666666667 0.483327565449969

0.53901938462006 0.484 0.51150969231003

0.487310584993971 0.484666666666667 0.485988625830319

0.575089388054011 0.486666666666667 0.530878027360339

0.560433280276301 0.487 0.523716640138151

TABLE 7

Mud Overbalance (psi/ft)

Distance from Fault (ft)

Open Hole Time (Second(s))

Deplected Pore Pressure

0.224781557213314

10000 0.234989743562158 0.25

0.266134092899132

10000 0.292395542508484 0.25

0.195344229878018

10000 0.182381313083017 0.25

0.207685436104467

10000 0.194578012575863 0.25

0.20780151090522 10000 0.188967530809154 0.250.211856542149008

10000 0.189455398788868 0.25

0.233711757785627

10000 0.214092731764416 0.25

0.233327565449969

10000 0.20222127759138 0.25

0.26150969231003 10000 0.239055310059773 0.250.235988625830319

10000 0.204741928819901 0.25

0.280878027360339

10000 0.267595586873032 0.25

0.273716640138151

10000 0.265156246974463 0.25