Overview of Petroleum Industry Chapter 2 – Petroleum Exploration PTRT 1301 Overview of Petroleum Industry Chapter 2 – Petroleum Exploration

Introduction Historically a matter of good luck and guesswork Most successful by drilling near oil seeps at the surface Modern techniques utilize surface, subsurface and above surface technologies to help determine where to drill an exploratory well Fragments (cuttings) and special tools run into the hole (logging) provide more information about subsurface structures that may contain hydrocarbons

Technologies being utilized for Exploration Aerial photography Satellite imaging Remote Sensing infra-red ultraviolet radar other Various geophysical instruments Gravitometer Magnetometer Seismometer

Surface Geographical Studies Examination and correlation of data Interpreting Information Topography Initial studies of natural and man-made features of the land Sometimes surface features can reveal clues to the underlying structure of geological features that drive the accumulation of petroleum and natural gas Aerial photography limitations large numbers of photos varying angles and lighting conditions difficult to correlate Remote Sensing Utilization of other means besides photography to map and area

Satellite Imaging Wide coverage Uniform conditions over a wide area Landsat continuous mapping since 1972 Recent upgraded satellites include Geophysical applications Resolution of 100 feet (30 meters) Augmented with traditional exploration

Colors can represent different rock types or mineral deposits

RADAR - RAdio Detection And Ranging Radio waves (microwaves) are bounced off surface Detects potential oil-trapping structures Side-Looking Airborne Radar (SLAR) are carried by aircraft Performed by satellite RADARSAT – Canadian Satellite

Side Looking Airborne Radar (SLAR)

Oil & Gas Seeps Obvious signs of a subsurface petroleum source Petroleum and or gas “oozing” into surface soil/water. Bacteria action and weathering may hide the presence of the seeps. Also seep may not occur directly above formation. Many of the great oilfields of the world were initially discovered by oil seeps

Oil seep Updip from reservoir

Geophysical Surveys Geophysics Petroleum Geologists most interested in “geo”- Earth “physics” - How & Why Petroleum Geologists most interested in Magnetism Gravity seismic vibrations Variations in these properties of the Earth can point to probable oil-bearing formations

Magnetic and Electromagnetic Surveys Like rocks have like magnetic fields Slight variations in magnetic response of the Earth indicate the presence of different minerals in the rock Basement rock often contains magnetic minerals Magnetic surveys can help map the sub-structure of these formations and indicate geological features Faults Arches folds

Magnetometer Surveys Magnetometer detects slight variations in Earth’s magnetic field (anomalies) Towed array 300 ft above the ground To separate the sensor package from magnetic field of the airplane Micromagnetics is an efficient exploration method that narrows down the size of areas for seismic surveys

Magnetotellurics Measure electrical properties of rock Capacitance conductivity Both magnetic and magnetotellurics do not assure that all traps containing hydrocarbons are located They do give a general idea of where oil-bearing rocks are most likely to be found

Gravity Surveys Minute variations in the Earth’s Gravitation field indicate density differences between subsurface structures Old method - torsion balance and pendulum New methods - gravitometer

A gravimeter measures minute differences in the pull of gravity at the Earth's surface.

Airborne Gravitometer

Seismic Surveys “reflection” or “refraction” Time of flight @”speed of sound”(in rock) different rocks have different vs. Ball dropped on road vs ball on sand. Difference reflection spirals “Shot”- artificially produced earthquakes using explosives or thumpers

Seismograph – ID strip chart In Figure 2.5 one of the vertical lines is a seismograph This is called a Seismic section Now called 2D seismic Why? New technique called 3D seismic Obtained by running numerous 2D surveys spaced along a line or around a surface 2-3 miles(3-5 km) apart Paste the surveys together. 4D seismic – 3D run periodically to study changes in time 1841 seismometer devised by David Milne 1845 L. Palmier developed a seismograph During WW I - L. Mintrop tried to determine range to artillery pieces using 3 seismographs Error occasionally due to changes in time for subsurface effects (changes in geological status ) After the war he reversed the process set off the explosion a known distance for the seismograph.

3-D seismic imaging technology

Two Primary Methods Explosion Methods “shot” placed in a shallow hole & exploded (see figure 2.7) “Geophones” pick up the reflected “echo” from the shot Notes: lines are not quite accurate

Thumper Large steel mass dropped on the ground. (Fig 2.8) Measure time it takes for the echo to return to the recorder (geophone) Speed of sound in air ~ 330 m/s Speed of sound in water ~1400m/s Speed of sound in rock ~ 5,000m/s Echoes reflect off of boundaries between layers, faults, etc

The seismic crew (doodlebug) party chief geologist or geophysicist surveyors drillers loaders shooters jug hustlers (geophone techs)

Other methods Vibroseis- Conoco Marine methods (Fig 2.10) Hydraulic vibrator creates low frequency sound waves Can also mount geophones to the wall of the bore to avoid surface noise Marine methods (Fig 2.10) similar to land methods “hydrophones” “bird” towed behind a ship Air gun is the standard method for producing the sound pulse Can also use a steam pulse

Well Logging Log = Record of information about the formation through which a well has been drilled Drillers log = Record as a function of depth of the kinds of rocks and fluids encountered Wireline log = metal line dropped into the hole with a tool attached to the bottom end If it carries electrical signals then its called a conductor line (sometimes still called a wireline) Many different tools use but the procedure is the same Drop a “sonde” into the well bore on a conductor line or a wireline

Well Logging The sonde is recovered to the surface at a constant rate (speed) Data is collected as a function of depth Electric Logs Radioactivity Logs Acoustic Logs

Electric Logs Spontaneous Potential (SP)Log Measures weak electric currents in the rock next to the well bore Actually measures voltage Fig 2.13 (left side) No transmitted signal Resistivity log - resistance Induction log – conductivity Saltwater conducts electricity better than oil/gas or rock these logs help determine: How much water the formation holds (sp) How freely the water can move (ρ) How saturated the formation is (with water) (σ)

Nuclear Logs Gamma-ray log Neutron Log Measures the natural radioactivity from the rock (U235 decay) Neutron Log Radioactive source (Co60) or others emit neutrons that react with the rock and create neutrons that collide with H and get slowed down. The detector “sees” the slow neutrons and detects the presence of H.

Acoustic Logs Measures speed of sound in the rock. Higher density (less porosity) = Higher speed Also called sonic log Measure the time for the echo

Core Samples

Drill cuttings Core samples Most accurate information about underground formation at the well location Context (60 to 70 foot samples) Relative location of minerals is preserved Drill cuttings Not as useful but statistics can help sort out those from the drilling area from debris coming off the side walls

DRILL STEM TEST(DST) Primary means of testing formation that has just been drilled $$ but can yield good return on investment Bottom Hole Pressure (BHP) Bottom Hole Temperature (BHT) Fluid sample recovery

Drill Stem Tests use a perforated pipe tool in the borehole to test formation pressure and fluid composition. This Drill Stem Test (DST) tool is the permeability measurement tool for use in coal seam methane studies.

Stratigraphic Test (Strat Test) Exploratory well drilled specifically to uncover geologic information for down hole Stratigraphic correlation - comparing geologic formation compare known areas with unknown areas (nearby) predict where oil/gas reservoirs might be Compare data from different wells drillers log sample logs electric logs comparing fossils Composition electric data to matchup formation with one another Understand the origin of various features and how they might have been formed

Maps Base Maps: Depict existing wells, property lines, roads, buildings, etc. Topographic Maps: Depict surface features Geological Maps: Depict rock types on surface Bouguer Maps: Depict gravity surveys Contour Maps: Depict varying depths or thicknesses of strata and formations using concentric circles Vertical Cross Sections: Depicts structural and stratigraphic patterns via a cross section of the formation.

Contour map Isopach map

Standard Map Isopach Map Contour maps representing the depth of specific information from the surface Display high and low limits of a buried surface feature Isopach Map Shows variation in thickness of a formation gray scale false colors

Vertical Cross Sections Slice through a section of the crust Note SP log superimposed onto each well location

Computer Graphics and Models