Types of Data

Slide 1

• This unit covers the main types of data that we use in industry
• The scale of the data goes from mega-regional (e.g., major lithospheric plates) to microns (e.g., pores in reservoir rocks viewed with SEMs)

Slide 2

• For exploration we may start with regional studies, developing an understanding of the factors influencing tectonics and sedimentation in the basin we are working
• As fields are discovered and we move into development and then production, we focus on studies of much finer-scale
• For each reservoir, how will fluids move as we produce oil & gas?
• Where are the flow barriers and baffles – such as thin shale layers that may segment the field vertically or small faults that might segment the field horizontally (compartments)

Slide 3

• At the mega-regional scale, we would develop and use:
• Geologic maps
• Plate reconstructions
• Gravity & magnetic data and models
• Available seismic lines – typically long, regional lines
• A model of the tectonic evolution of the basin
• A stratigraphic chart that summarizes deposition and highlights potential source, reservoir and seal units
• Paleogeographic maps
• And other information that will help use understand the controls on any hydrocarbon systems

Slide 4

• The typical goals of mega-regional analyses are to:
• Decide which basins hold sufficient potential
• Determine how much to bid for blocks
• Provide regional settings to help understand the characteristics of a field
• Guide step-out wells, i.e., those that extend beyond a known field in search of a similar HC accumulation

Slide 5

• Another main type of data is what we can gather from the surface, either from field measurements and observations or from remote sensing (e.g., satelite data)
• These data include:
• Topographic/Bathymetric maps
• Surface geology (structure & stratigraphy)
• Nearby outcrops (or analogs)
• Heat flow measurements
• HC seeps
• Etc.

Slide 6

• A major source of data is subsurface measurements and the resulting interpretations
• Subsurface Measurements/Observations
• Data from Wells
• Rock samples from cores and cuttings
• Measurements from subsurface rock units via logs
• Interpretations of lithology, ages, geochem, etc.
• Geophysical data, usually collected at the Earth’s surface
• Seismic data (2D, 3D, 4D)
• Gravity & Magnetics

Slide 7

• Data from wells comes from rock samples and measurements at depth from the well bore
• Data from samples includes those from:
• Conventional Cores
• Sidewall Cores
• Cuttings
• Data from measurements taken in the well bore include:
• Wire-line Logs
• Pressure
• Temperature
• Fluid samples
• Flow Properties
• Vertical Seismic Profiles (VSP)

Slide 8

• Our best subsurface data comes from conventional cores
• The coring apparatus is positioned at the bottom of the drill stem
• We often get intact cores of 1 meter or more
• Cores are good for analyzing lithology, sedimentary features, porosity, permeability, paleontology (ages, environments)
• One drawback is that we have to core ‘blindly,’ i.e., we have to decide where to take a core before the interval is drilled and logged
• Another drawback is that cores are very expensive
• To take a core, we have to
• pull out the drill stem
• Attach the coring device and lower the drill stem (1 round trip)
• Obtain the core and pull the drill stem again
• Detached the coring device and send the drill stem down again (a second round trip)
• All of this takes a lot of time, which is expensive (about $1 million per day)

Slide 9

• This slide explains what a sidewall core is
• The tool (pictured on the left) is part of the drill stem
• It has about 30 casings that can be fired into the formation
• The casing captures a small sample of rock
• The samples are retrieved at the end of a logging run
• This does not require very much extra rig time – so is relatively inexpensive
• The drawback is that the sample is small – we get the rock type but nothing about vertical variability, sedimentary structures, etc.

Slide 10

• Cuttings are the ‘rubble’ that comes up the well bore and reaches the surface
• Think of drilling into a block of wood
• Shavings of wood come up as you drill down
• In general, the shavings indicate the property of the wood being drilled – with a built in delay
• The delay relates to the time it takes for a shaving cut at the drill tip to move up to the surface
• Cuttings are the rock ‘shavings’
• There is a delay related to the time it takes for ‘shavings’ cut at a certain time (say high noon) to reach the surface – a distance that can be several thousand feet
• Another problem is that cuttings do not all come from the bottom of the hole
• As drilling proceeds, material can break free anywhere along the well bore and get mixed in with the ‘bottom of the hole’ cuttings
• So the drilling operations are not delayed at all (~ no cost)
• BUT there is a lot of uncertainty about the depth from which the material came from
• The material is also pulverized, so we can not get rock properties such as sedimentary structures, porosity and permeability

Slide 11

• There are many ‘tools’ that can be lowered into a well bore to take measurements
• Usually a section is drilled, a string of tools is lowered to the (current) bottom, and measurements are recorded as the tools are slowly pulled up the well bore
• Some tools work only before the well bore is lined with steel casing – called open-hole logs
• Other tools can work in cased holes
• In the old days, the measurements were recorded on a strip of paper that was registered by the depth of the toll as the measurements were made – a log (right image)
• Now everything is captured digitally, but the data are still displayed as 'logs'
• Photo on left some the wire-line on a drum
• The tools are attacked to the end of the wire-line and lowered into the well bore
• The wire-line is pulled back and measurements are recorded.
• The rotation of the drum is calibrated to translate into the depth of each tool as measurements come in
• The white/blue building houses the recording equipment and the operator

Slide 12

• This photo show SOME of the tools that can be used to take measurements
• We will discuss several of these tools and what they measure in Unit 4

Slide 13

• As a preview of Unit 4, here is a list of some of the rock and fluid properties that we can measure/interpret in a typical logging run
• The recorded data often have to be processed and then interpreted to get the rock and fluid properties
• In many cases, several logs are analyzed jointly to get information
• Log analysis is a complex procedure, larger companies have experts that spent their entire career analyzing well logs

Slide 14

• Geophysical methods provide us with a wealth of data about the subsurface
• Well data is more direct and detailed than the data we get from geophysics
• The problem with well data is that it gives us information at or close to the well bore – what about locations not near a well?
• The biggest advantage of geophysical data is that we can obtain data over very large areas

• The objective:of geophysical data is to take measurements at the Earth’s surface that will give us an image of the subsurface
• As a analogy, think of a sonogram
• We may want to get an image of a baby in a womb
• The technology for this has many parallels to imaging the subsurface:
• Sound waves are used to get the image
• Sound travels down through the mother’s tummy
• Some of the sound waves are reflected (bounce off) the baby’s surface
• Data processing ‘focuses’ the sound waves bouncing off the baby to give us an image
• Unit 5 goes into more detail on how we use sound waves (acoustic energy) to image the subsurface

Slide 15

• As a preview of Unit 5
• We use an energy source at the surface – such as a dynamite explosion
• Sound waves propagate in a radial fashion down through the Earth
• At major rock boundaries (more detail in Unit 5) a small part of the acoustic energy is reflected – most is transmitted (continues downward)
• We have “listening” devices at the surface
• In this simple cartoon, the left device “hears” acoustic energy that bounces off the top of the orange layer at 0.4 seconds
• The right device “hears” acoustic energy that bounces off the top of the brown layer at 0.8 seconds

Slide 16

• This shows the raw data recorded by the two “listening” devices on the previous slide
• The acoustic wave is recorded at device #1 at 0.4 seconds
• The acoustic wave is recorded at device #2 at 0.8 seconds
• To image the subsurface, we use hundreds of shots (explosions) and millions of receivers (listening devices) arranged in lines either on land or offshore

Slide 17

• This first image shows what the raw seismic data for one “explosion” recorded at about 50 “listening” devices looks like
• The raw seismic data is sent to a data processing center
• Here specialists in signal analysis, data analysis, imaging, math, computer science, etc. transform the raw data into an image of the subsurface
• Again at large companies, there are many experts in data processing that can spend an entire career processing seismic data
• Seismic imaging is an area that remains a focus of R&D – obtain better images faster and cheaper
• We cover some basics of data processing in Unit 5
• Once the data are processed and we have an image of the subsurface, the next step is to interpret the data – turn images such as the one in the lower right into a model of the subsurface rocks and fluids
• Several Units focus on sesimic interpretation and data anlysis

Slide 18

• Seismic data accounts for 90%+ of geophysical data collection dollars each year
• There are other geophysical data types
• The other two main geophysical data types are gravity data and magnetic data
• Gravity data is used to interpret the density structure within sedimentary basins and the underlying lithosphere
• Magnetic data gives us information on magnetic susceptibility within sedimentary basins and the underlying lithosphere
• G&M data is often used to map “basement” and thus get the total sediment thickness for an area
• G&M data can also help locate bodies with anomalous densities or magnetic susceptibilities
• An example of a body with an anomalous density is a salt dome
• An example of a body with an anomalous magnetic susceptibility is a volcanic sill