Geophysics
Budget: ₹1,500 – ₹2,000 INR
ATTACHMENT on the following page. Please annotate the attachment to answer the question before scanning or photographing the attachment to include within your answer document.
A company is exploring an extensional basin offshore, and has acquired the attached seismic line. Although there are no wells in the immediate line location, some information has been made available from nearby wells, so that the company has limited information on the velocity of the Tertiary rocks (units 2 to 3). The company is interested in two different locations, targeting the pre-Tertiary below the point marked A, and targeting fault blocks within the Tertiary below the point marked B. As part of your assessment of the potential plays, answer the questions below.
a) Draw an interpretation on the Attachment tracing out the unit boundaries and identifying any faults that are present. Indicate the location of an unconformity and the location of ‘onlap’ relationship.
(10 marks)
b) Velocity for Unit 1 has not been obtained in other wells, which will affect the calculation of true depths for all units in the projected well location A. During early drilling at this location, the base of Unit 1 was found to be 2074 m, so given the water velocity of 1500 m/s and the depth above, calculate the velocity of Unit 1 (present your answer in a table).
c) The company now intends to drill a well at location B. Given the information on unit velocity below, calculate (in a table) the depth to each unit boundary.
UNIT VELOCITY m/s
Unit 2 1894
Unit 3 1946
Unit 4 2003
d) What assumptions is the company making when planning this well, and what effect could an incorrect assumption have?
e) In other wells nearby, potential source rocks have been identified at the base of Unit 3, and potential reservoir rocks at the top of the same unit. The marine source rocks have an average TOC of 8.5% and an average thickness of 180 m. At a nearby location, and a depth of 2400 m, the V0 value was 0.77. Given this information, has the source rock illustrated on the seismic image been buried deeply enough to generate hydrocarbons, and what sort of hydrocarbons are likely to have been generated? Will there be a sufficient volume to trigger primary migration? What type of migration is required to fill available traps above the source rock layer? Describe the full Petroleum Play (excluding the trap – see next question) at this location as part of your answer.
f) Draw a diagram illustrating your idea of the trap type at the location B. What kind of trap is this, and what further information do you need to know whether the trap is likely to be successful in containing hydrocarbons?
g) What effect does the resolution of the seismic image have on your evaluation of the Petroleum Play? What is the typical resolution of seismic images? How does the nature of the seismic reflections help you to determine the different units present on the image?
MAXIMUM Word Count Limit: 1500
ATTACHMENT
A company is exploring an extensional basin offshore, and has acquired the attached seismic line. Although there are no wells in the immediate line location, some information has been made available from nearby wells, so that the company has limited information on the velocity of the Tertiary rocks (units 2 to 3). The company is interested in two different locations, targeting the pre-Tertiary below the point marked A, and targeting fault blocks within the Tertiary below the point marked B. As part of your assessment of the potential plays, answer the questions below.
a) Draw an interpretation on the Attachment tracing out the unit boundaries and identifying any faults that are present. Indicate the location of an unconformity and the location of ‘onlap’ relationship.
(10 marks)
b) Velocity for Unit 1 has not been obtained in other wells, which will affect the calculation of true depths for all units in the projected well location A. During early drilling at this location, the base of Unit 1 was found to be 2074 m, so given the water velocity of 1500 m/s and the depth above, calculate the velocity of Unit 1 (present your answer in a table).
c) The company now intends to drill a well at location B. Given the information on unit velocity below, calculate (in a table) the depth to each unit boundary.
UNIT VELOCITY m/s
Unit 2 1894
Unit 3 1946
Unit 4 2003
d) What assumptions is the company making when planning this well, and what effect could an incorrect assumption have?
e) In other wells nearby, potential source rocks have been identified at the base of Unit 3, and potential reservoir rocks at the top of the same unit. The marine source rocks have an average TOC of 8.5% and an average thickness of 180 m. At a nearby location, and a depth of 2400 m, the V0 value was 0.77. Given this information, has the source rock illustrated on the seismic image been buried deeply enough to generate hydrocarbons, and what sort of hydrocarbons are likely to have been generated? Will there be a sufficient volume to trigger primary migration? What type of migration is required to fill available traps above the source rock layer? Describe the full Petroleum Play (excluding the trap – see next question) at this location as part of your answer.
f) Draw a diagram illustrating your idea of the trap type at the location B. What kind of trap is this, and what further information do you need to know whether the trap is likely to be successful in containing hydrocarbons?
g) What effect does the resolution of the seismic image have on your evaluation of the Petroleum Play? What is the typical resolution of seismic images? How does the nature of the seismic reflections help you to determine the different units present on the image?
MAXIMUM Word Count Limit: 1500
ATTACHMENT
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