DRILLING AND DRILLING AND COMPLETION METHODSCOMPLETION METHODS

Naturally Fractured ReservoirsNaturally Fractured ReservoirsRoberto AguileraRoberto Aguilera Servipetrol Ltd.Servipetrol Ltd.

KEYS (GOALS) TO SUCCEED IN KEYS (GOALS) TO SUCCEED IN MOST NATURALLY FRACTURED MOST NATURALLY FRACTURED

RESERVOIRSRESERVOIRS::

Intercept the natural fracturesIntercept the natural fracturesDo not damage the natural Do not damage the natural

fracturesfractures

HOW TO ACHIEVE THESE HOW TO ACHIEVE THESE GOALS?GOALS?

Drilling wells that go Drilling wells that go perpendicular to the natural perpendicular to the natural

fracturesfracturesDrilling wells underbalanced. If Drilling wells underbalanced. If

at all possible, avoid at all possible, avoid overbalance drilling in naturally overbalance drilling in naturally

fractured reservoirsfractured reservoirs

ADVANTAGES OF ADVANTAGES OF UNDERBALANCED DRILLINGUNDERBALANCED DRILLING

((BennionBennion et al., 1998)et al., 1998)

Potential reduction in invasive formation Potential reduction in invasive formation damagedamageMinimize the potential for circulation Minimize the potential for circulation losseslossesMinimize the potential for sticking Minimize the potential for sticking differentialdifferentialEliminate need for costly mud systems Eliminate need for costly mud systems and costly disposal of exotic muds (we and costly disposal of exotic muds (we have to be careful with the environment)have to be careful with the environment)

ADVANTAGES OF ADVANTAGES OF UNDERBALANCED DRILLING (2)UNDERBALANCED DRILLING (2)

Reduce extensive and expensive Reduce extensive and expensive completion and stimulation operationscompletion and stimulation operationsRapid indications of productive zones Rapid indications of productive zones during drilling operationsduring drilling operationsEconomic benefits from flush production Economic benefits from flush production while drilling underbalancedwhile drilling underbalancedPotential to flow test while drillingPotential to flow test while drillingIncrease bit life. Larger Increase bit life. Larger ROPROP

DISADVANTAGES OF DISADVANTAGES OF UNDERBALANCED DRILLINGUNDERBALANCED DRILLING

Wellbore stability and consolidation Wellbore stability and consolidation concernsconcernsSafety and well control concerns in high Safety and well control concerns in high pressure or sour environmentspressure or sour environmentsIncreased drilling costsIncreased drilling costsInability to use Inability to use MWDMWD technology technology (partial)(partial)

DISADVANTAGES OF DISADVANTAGES OF UNDERBALANCED DRILLING (2)UNDERBALANCED DRILLING (2)

Failure to maintain a continuously Failure to maintain a continuously underbalanced condition resulting in underbalanced condition resulting in significant invasive damage because of significant invasive damage because of periodic overbalanced pressure pulses periodic overbalanced pressure pulses due to:due to: (1)(1) pipe connections, (2) bit pipe connections, (2) bit trips, (3) localized depletion effects, (4) trips, (3) localized depletion effects, (4) poor knowledge of initial pressurepoor knowledge of initial pressureSpontaneous countercurrent imbibitionSpontaneous countercurrent imbibition

COMPLETIONSCOMPLETIONS

PERFORATED VS. OPEN HOLE PERFORATED VS. OPEN HOLE COMPLETIONSCOMPLETIONS

CLASSIFY RESERVOIR ACCORDING CLASSIFY RESERVOIR ACCORDING TO FRACTURE STORATIVITY TO FRACTURE STORATIVITY

RESERVOIR OF TYPE A, B, or CRESERVOIR OF TYPE A, B, or C

Chart for Evaluating Naturally Fractured Reservoirs (mb = 2.0)

1

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

2

0.00 0.05 0.10 0.15 0.20 0.25 0.30

Matrix Porosity, b

D

u

a

l

-

P

o

r

o

s

i

t

y

E

x

p

o

n

e

n

t

,

m

v=0.05

v=0.10

v=0.20

v=0.30

v=0.40v=0.50

v=0.60v=0.70

v=0.80v=0.90

Total Porosity, 4 6 8 10 12 14 16 18 20 22 24 26 28 30

COMPLETIONSCOMPLETIONSFORMATION DAMAGE INCREASES FORMATION DAMAGE INCREASES

SIGNIFICANTLY AS WE MOVE FROM TYPE SIGNIFICANTLY AS WE MOVE FROM TYPE A TO TYPE C RESERVOIRSA TO TYPE C RESERVOIRS

PERFORATED COMPLETIONS:: PERFORATED COMPLETIONS:: TYPE A AND B RESERVOIRSTYPE A AND B RESERVOIRSOPEN HOLE COMPLETIONS: OPEN HOLE COMPLETIONS: TYPE B AND C RESERVOIRSTYPE B AND C RESERVOIRS

TYPE C RESERVOIRS PLUS CEMENT CAN TYPE C RESERVOIRS PLUS CEMENT CAN LEAD TO MAJOR FIASCOSLEAD TO MAJOR FIASCOS

PERFORATING DAMAGEPERFORATING DAMAGE

Shock stresses resulting from detonation Shock stresses resulting from detonation during jet perforating can cause during jet perforating can cause deformation of the rock surrounding each deformation of the rock surrounding each perforation tunnelperforation tunnelThis in turn can seal a fracture where it This in turn can seal a fracture where it intersects a perforation (intersects a perforation (laboratotylaboratoty work)work)

((HalleckHalleck, 1996), 1996)

So a stimulation might be required So a stimulation might be required following a perforating jobfollowing a perforating job

MULTIPLE HYDRAULIC MULTIPLE HYDRAULIC FRACTURESFRACTURES

These are hydraulic fractures that grow These are hydraulic fractures that grow simultaneously from a wellbore and penetrate simultaneously from a wellbore and penetrate far into the formation during a fracture treatmentfar into the formation during a fracture treatmentThe presence of natural fractures will lead to The presence of natural fractures will lead to more complex systems of multiple hydraulic more complex systems of multiple hydraulic fractures, especially when the created hydraulic fractures, especially when the created hydraulic fracture intersects the natural fracturesfracture intersects the natural fractures

(Gas Research Institute) (Gas Research Institute)

Hydraulic fracturing processHydraulic fracturing process

MicroMicro--fracture stress measurementfracture stress measurement

ADVANTAGES OF HORIZONTAL ADVANTAGES OF HORIZONTAL WELLSWELLS

INTERCEPTING OR AVOIDING NATURAL INTERCEPTING OR AVOIDING NATURAL FRACTURESFRACTURESHIGHER AND MORE RAPID RECOVERIES HIGHER AND MORE RAPID RECOVERIES BY DRILLING INFILL HORIZONTAL WELLSBY DRILLING INFILL HORIZONTAL WELLSBETTER RESULTS IN SECONDARY BETTER RESULTS IN SECONDARY RECOVERY PROJECTSRECOVERY PROJECTSREDUCTION OF GAS AND WATER REDUCTION OF GAS AND WATER CONINGCONINGREDUCTION OF SAND PRODUCTION REDUCTION OF SAND PRODUCTION PROBLEMS PROBLEMS

ADVANTAGES OF HORIZONTAL ADVANTAGES OF HORIZONTAL WELLS (2)WELLS (2)

ENVIRONMENTAL PROTECTIONENVIRONMENTAL PROTECTIONLOW PERMEABILITY RESERVOIRS AS LOW PERMEABILITY RESERVOIRS AS THE HORIZONTAL WELL APPROACHES THE HORIZONTAL WELL APPROACHES THE IDEALIZED CONDITION OF INFINITE THE IDEALIZED CONDITION OF INFINITE PERMEABILITYPERMEABILITYREDUCE TURBULENCE IN GAS (AND OIL) REDUCE TURBULENCE IN GAS (AND OIL) RESERVOIRSRESERVOIRSRESERVOIRS WITH PARALLEL DIPPING RESERVOIRS WITH PARALLEL DIPPING BEDSBEDS

DISADVANTAGES OF DISADVANTAGES OF HORIZONTAL WELLSHORIZONTAL WELLS

MORE EXPENSIVE THAN VERTICAL MORE EXPENSIVE THAN VERTICAL WELLSWELLSCAN PENETRATE DUE TO CAN PENETRATE DUE TO IMPROPER DESIGN (OR IMPROPER DESIGN (OR ACCIDENTALLY) UNWANTED PARTS ACCIDENTALLY) UNWANTED PARTS OF THE RESERVOIR OR OF THE RESERVOIR OR COMPARTMENTS WITH COMPARTMENTS WITH UNDESIRABLE FLUIDSUNDESIRABLE FLUIDS

SIGNIFICANT IMPROVEMENTS SIGNIFICANT IMPROVEMENTS IN PRODUCTIVITYIN PRODUCTIVITY