Assignment Introduction to Core Analysis
You are your company’s petrophysicist on an upcoming well. Summarize how core plugs from full diameter cores compare to rotary sidewall cores for use in routine core analysis. Describe the basic core plug cutting process.
Solution
Rotary sidewall core plugs are always cut, as a result of the tool’s hardware design, perpendicular to the side of the wellbore, irrespective of the bedding planes’ dip angle and direction. The interval to be cored is selected from either wireline or LWD log responses, with their associated vertical resolution and depth correlation limitations. By contrast, a plug sample from a full diameter core can usually be cut both parallel and orthogonal to the bedding planes, and over an interval determined after careful visual inspection of the whole core, allowing even small vertical changes in rock characteristics to be accommodated by fine-tuning the plug sample location.
Core plug samples are usually cut from a full diameter core with a diamond core bit both parallel and orthogonal to the bedding planes, and trimmed so as to create a cylindrical plug from the center of the core where the minimum amount of filtrate flushing and invasion of mud solids is likely to have occurred. The objective of coring is to recover representative samples of the formation under study. To be fully representative, the samples should not be severely damaged or invaded by non-reservoir fluids. Therefore, sample plugs taken from the center of the full diameter core have the highest chance of being the most representative of the reservoir rock.
Assessment Introduction to Core Analysis
1. Which of the following handling processes are applied to pressure barrel core samples? (Select all that apply.)
A .The metal barrel is milled down its length and the core removed. Correct ✔
B .The drilling mud is chipped from the core surface. Correct ✔
C .The core is weighed, then thawed in evacuated glass chambers. Correct ✔
D .The core is cut into full diameter right cylinders. Correct ✔
E .The core is cleaned with a distilled water and hydrochloric acid mixture.
2. Core plug analysis is most representative and effective in what type of formations?
A .Basement rocks
B .Very heterogeneous formations
C .Homogeneous formations Correct ✔
D .Fractured carbonates
3. Routine core analysis normally provides what basic data about a reservoir core? (Select all that apply.)
A .Porosity Correct ✔
B .Capillary pressure
C .Grain density Correct ✔
D .Permeability Correct ✔
4. Sidewall core samples are __.
A .cut at any angle to the wellbore
B .perpendicular to the side of the wellbore Correct ✔
C .always cut along bedding planes
D .vertical samples of the reservoir
5. What is the primary reason for using a pressure core barrel?
A .To maintain atmospheric pressure on the core when it is in the laboratory for analysis
B .To maintain zero pressure on the core whenever laboratory analysis is being conducted
C .To maintain the reservoir pressure on the core during its recovery to the surface Correct ✔
D .To maintain atmospheric pressure on the core during its recovery to the surface
6. The acquisition of core material is an important activity in what sectors of the oil industry? (Select all that apply.)
A .Development Correct ✔
B .Downstream
C .Appraisal
D .Exploration Correct ✔
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