W2- O&G Geology

Question 1

Rock suitability for reservoir

Answer 1

particle size, sorting (uniformity), composition, rounding, sphericity

Question 2

Mud logging

Answer 2

Process of monitoring reservoir rock;
Drill cutting emergence safe indicators

Question 3

Main rock types

Answer 3

Igneous: formed from magma as cools and hardens;
limited porosity/permeability, i.e. granite basalt, obsidian

Sedimentary: layers of material deposit over time;
interconnected pores to trap organics, i.e. limestone, sandstone

Metamorphic: formed after physicochemical transformation of igneous/sedimentary under high T&P, i.e. slate, marble

Question 4

Reservoirs

Answer 4

Porous rock regions (mainly sedimentary) filled with HCs after organic material buried under extreme T+P

Organisms dies at bottom of lake- sediments accumulate & rock later buried deeper and T&P increase

Kerogen formed (via organic material decay anaerobically)

Constant T&P increase over Ma converts Kerogen to HCs

Question 5

Reservoir formation (5 methods)

Answer 5

Source rock: sedimentary porous rock carries trapped organics and is buried under more sediment & decays under anoxic conditions to kerogen.
Under high T&P kerogen -> HCs

Migration: movement of HC out source rock into reservoir;
Primary(to reservoir) or secondary (to cap/trap)

Accumulation: HC migrates and accumulates from source to reservoir rock

Cap rock containment: non porous/low permeability material atop reservoir to prevent HC flow out = capillary seal;
membrane (buoyancy P) or hydraulic seals

Traps- sealing: Trap formed when change in subsurface geology that cuts off reservoir from any formations;
Structural, stratigraphic, hydrodynamic

Question 6

Reflection seismology

Answer 6

Energy release and transmission after shock events;
Produce waves that travel and reflect off rock under seabed

Waves: Primary (P waves) & secondary (S waves)

Question 7

Porosity, total, effective and ineffective porosity

Answer 7

Porosity: Ratio of pore volume (void space) in reservoir rock to total volume as a percentage

Total: total pore volume/total volume

Effective porosity: vol of all pores/total volume

Ineffective porosity: vol of completely disconnected pores/total volume

Question 8

3D & 4D seismic techniques

Answer 8

Pressure and composition changes monitor how reservoir responds

More expensive setup, but higher recovery possible & increase reservoir yield as stagnant regions targeted

Question 9

Absolute & relative permeability

Answer 9

Absolute: ability for petroleum reserves to flow through rock - saturation of a single fluid

Relative: permeation of more than one fluid

Question 10

Darcy law

Answer 10

Q = [kA/muL)]*(P1-P2)

k = absolute permeability (m2)
A = CS area (m2)
L = length (m)
P1-P2 = flowing pressure drop (N/m2)

Question 11

Inclined flow darcy law

Answer 11

Q = (kA/mu)[((P1-P2)/L) - pgsina]

Question 12

Radial flow darcy law

Answer 12

Q = (kA/mu)(dP/dr)

-> Q = {[2PIkh(Pe-Pwf)]/[mu*ln(re/rw)]}

Question 13

Absolute permeability: Parallel flow

Answer 13

Q = Q1+Q2+Q3
h = h1+h2+h3

-> kavg = {[sum(kihi)]/[sum(hi)]}
-> kavg = {[sum(kiAi)]/[sum(Ai)]}

where Ai = sum(Wi*hi)

Question 14

Absolute permeability: Series flow

Answer 14

Q = Q1=Q2=Q3
L/kavg = L1/k1 + l2/k2 + L3/k3

-> kavg = {[sum(Li)]/[sum(Li)/Ki]}