Petroleum Exam 2 Review

Formation/Pore Pressure

fluid pressure found within pore spaces of the formation

Fracture Pressure

Pressure to induce fractures in the rock at a given depth.

Causes of overpressure

compaction effects, diagenetic effects, differential density effects, migration effects

Compaction effects

pore fluid provides support to the overburden

Diagenetic effects

chemical and physical changes that produce H20 and allow for production of hydrocarbons

Differential density effects

pore fluid density variation in the vertical direction

ways to estimate abnormal formation pressure

predictive, methods while drilling, verification methods

Predictive methods

correlation of available offset well data, seismic interpretation

Overpressure Detection while drilling

drilling rate (reducing overbalance), seismic while drilling (change in dt), resistivity (porosity change), mud conductivity (fluids entering mud), shale cuttings density (compaction), influx into well (kick)

Formation pressure is estimated from _____ dependent parameters obtained from well logs

porosity

Fracture Gradient Prediction

relate fracturing pressure gradient to the pore pressure and horizontal matrix stress

Overburden pressure gradient

1 psi/ft

Predictive Hubbert and Willis Method

F=((S-P)/Z)(v/(1-v)) +P/Z

Directional Drilling

science and art of deviating a well bore along a planned course to a subsurface target whose location is a given lateral distance and direction from the vertical

Purpose of Directional Wells

drilled with intentional control to hit a pre-determined target: inclination (angle), azimuth (direction)

Kick off point (KOP)

where the wellborn begins to deviate from vertical (deviates at surface casing shoe)

Well Inclination

angle by which the wellborn deviates from vertical

End of Buildup EOB

where wellbore has finished increasing

Hold Angle

where the inclination of the borehole is held constant

Tangent Section

occurs after a build where the inclination of the borehole is held constant for a certain distance

Start of Drop

where borehole starts dropping inclination

End of drop

where wellborn finishes dropping inclination

Target Displacement

lateral distance from the surface location to the target

Target Location

point defined in space by geographical coordinates at a given true vertical depth

Drop of Rate (DOR)

rate that the inclination decreases

Build Up Rate (BUR)

change of inclination of a wellborn where the angle is increased

Turn Rate

rate a well profile turns in azimuth direction

Dog-leg severity (DLS)

normalized estimate of the overall curvature of an actual well path between two consecutive directional surgery stations

TVD

depth at any point or a station along a wellborn is the vertical distance from the well surface reference point to the station of interest

Measured Depth (MD)

the distance from the well surface reference point to the station of interest along the actual well path

Horizontal Displacement (HD)

the distance between two points along a wellborn projected into a horizontal place or plain view

Vertical section (VS)

distance between any two points along a wellborn projection into a vertical section plane

Azimuth

Angle in the horizontal plane measured from a fixed reference direction such as geographic north, grid north, or magnetic north) measured clockwise

Vertical Directional well

most common type, deviation from 0 to 8 deg is always considered vertical

Type I-J Type

moderate depth, used in deeper wells without large lateral displacement, single zone no int. casing, wellborn penetrates the target at an angle equal to maximum build up level, lowest inclination angle

Type II - S Type

wells in multiple pay zones, wells with lease or target limitation, can present some problems, wellborn penetrates the target vertically for the multiple pay zones, J type can be modified to the S-type by building holding dropping the assemblies

Type III Horizontal

Kick off point well below surface, fault and salt dome drilling, redials or sidetracks, highest inclination of all, limitations of deviation

Coiled Tubing (CT)

continuously milled tubular product manufactured in lengths that require spooling onto a take up reel

Drilling Cost

Pre spud costs, casing and cementing, drilling (rotational cost), Drilling (non rotational costs), trouble costs

Pre-Spud costs

license, surveying, buy/rent equip, personnel, gov papers

Casing and cementing

material costs

trouble costs

emergencies

AFE (Approval for Expenditure)

detailed cost estimate that is submitted for management approval to allocate money

Reservoir Engineering purpose

use petrophysical and fluid properties, determining fluids in place, identifying production drive mechanisms, forecast reservoir performance

Total Petroleum Initially in Place

quantity of petroleum which is estimated to exist originally in naturally occurring accumulations.

Reserves

quantities of petroleum which are anticipated to be commercially recovered from known accumulations

Recovery Factor

Rf= production/OHIP

Proved Reserve

Quantities of petroleum that can be estimated with reasonable certainty to be commercially recoverable.

Developed Reserves

Resources expected to be recovered from existing wells

Producing Reserves

recovery from currently open completion intervals

Nonproducing reserves

reserves shut in or behind pipe so they are expected to be commercially recoverable

Underdeveloped Well

resources expected to be recovered from new wells, deepening existing wells, expensive additional efforts

Unproved Reserves

technical, contractual, economic, or regulatory uncertainties prevent definition as proved.

Probably Reserves

engineering data suggests reserves are more likely than not commercially recoverable.

Possible Reserves

Reserves that can be commercially recoverable depending on favorable geological and economic factors.

Estimated Ultimate Recovery (EUR)

quantities of petroleum that are estimated on a given date, to be potentially recoverable from an accumulation, plus those quantities already produced therefrom

Primary Recovery

Refers to production using energy inherent in reservoir from gas under pressure or a natural water drive

Secondary Recovery

Usually refers to water flooding, which used to be termed an EOR method

Enhanced oil recovery

Term applied to methods that recover oil beyond that recoverable by primary and secondary means.

Sidewall Core

percussion (hollow projectile), Rotary (Hollow Diamond coring system)

Net Pay Thickness

thickness of a porous medium in hydraulic communication contained between two layers

Porosity

ratio of pore volume to the bulk volume, storage capacity of fluids

Effective Porosity

actual connected pore space, that from which oil or gas may be produced

Total Porosity

includes unconnected pore spaces. This is the porosity measured by a neutron porosity tool

Porosity Depends on

particle shape, packing, particle size, cementing materials, overburden stresses, fractures and bugs

Permeability

ability of fluids to flow in the porous medium

Permeability Darcy Assumptions

single fluid, no rock fluid interaction, incompressible fluid, laminar flow

Darcy's Law

q=kA(P1-P2)/muL

mobility

k/mu

Mobility ratio

water mobility/ oil mobility

Effective Permeability

measure of conductance of a porous medium for one fluid phase when the medium is saturated with more than one fluid

Absolute Permeability

if rock is 100% saturated

effective permeability

when two or more fluids coexist in a rock, always less than or equal to absolute permeability

relative permeability

ratio of effective permeability for a particular phase to the absolute permeability

Darcy Flow vs. Non Darcy Flow

q/A vs (p1-p2)/L where slope is k/mu, linear part is Darcy and laminar and non Darcy is the curved part turbulent

Saturation

fraction of the pore volume. Ration of the volume that a fluid occupies to the pore volume is called saturation of that fluid.

Methods of Determining Saturations

Conventional core analysis, capillary pressure measurements, well log analysis

What controls areal extent

heterogeneity, isotropy/anisotropy, discontinuity/bourdaries

fluid density

mass occupied by fluid per unit volume

isothermal oil compressibility

change in volume per unit volume for a unit change in pressure c=-1/V*dV/dP

Gas Solubility (Rs Scf/STB)

number of standard cubic feet of gas which will dissolve in one STB of crude oil at certain pressure and temperature

Oil Formation Volume Factor (Bo RB/STB)

ratio of vol of oil at the prevailing reservoir temperature and pressure to the volume of oil at standards conditions

Gas formation volume factor (Bg)

ratio of volume of gas at the prevailing reservoir temperature and pressure to the volume of gas at standard conditions

Total formation volume factor

ratio of volume of oil and gas at the prevailing reservoir temperature and pressure to the volume of oil and gas at standard conditions

Limitation of material balance methods

no distribution of pressures and saturations, no indication of uncontested areas, no spatial info, reserve properties are average properties, reservoir is a tank, zero dimensional method

Sources of primary driving reservoir energy

liquid and rock compressibility, gas in solution, gas in cap, water influx, gravity segregation

DDI

depletion drive index

SDI

segregation (gas cap) drive index

WDI

water drive index

where is bubble curve on phase diagram

top left curve

where is dew curve on phase diagram

right outside curve

Production Engineering

part of petroleum engineering that optimizes production or injection in a cost effective manner

VFP

goes between surface and wellbore

IPR

between reservoir and wellbore

Steady State flow

bubble point pressure, strong aquifer or gas cap

Pseudo Steady State flow

when you reach the boundaries

Unsteady State

beginning and end of production

Skin effect

region near the wellbore of improved or reduced permeability compared to bulk formation permeability

s>0

damaged ks

s<0

stimulated ks>k