Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Notes on this paper
National Exams, 98-Pet-B1, Well Logging and Formation Evaluation — May 2014, 3 hours, closed book (calculators permitted), 12 questions, all marked, 100 marks total.
Reference texts: Bassiouni, Theory, Measurement, and Interpretation of Well Logs (SPE Textbook Series Vol. 4); Asquith & Krygowski, Basic Well Log Analysis, 2nd ed. (AAPG); Ellis & Singer, Well Logging for Earth Scientists, 2nd ed.; Schlumberger, Log Interpretation Charts / Log Interpretation Principles and Applications.
Log quality — how faithfully a recorded curve represents the true formation property — is degraded by conditions at the borehole wall, in the mud system, and in the acquisition itself. Four characteristics dominate:
Borehole condition (rugosity, washouts, non-gauge hole). Pad-contact tools (density, microresistivity, some neutron sondes) need firm wall contact; a washed-out or irregular hole (exactly the condition Question 6's caliper log shows) leaves a mud-filled standoff between the pad and the formation, biasing density readings low (mud is less dense than rock) and degrading microresistivity/dielectric readings. A rough or elliptical hole also degrades centralization of mandrel tools (induction, sonic).
Mudcake thickness and mud properties. A thick, high-filtrate-loss mudcake attenuates pad-tool signals and biases shallow resistivity readings toward Rmc; a highly conductive (saline) or highly resistive (oil-base) mud changes which tool (induction vs. laterolog) is even usable, and barite-weighted mud attenuates the SNP/density source-to-detector count rate, requiring the environmental corrections applied in Question 7.
Depth of investigation vs. invasion depth. If the invaded zone is deep relative to a tool's depth of investigation, the tool reads a blend of Rxo and Rt rather than either cleanly (Question 1), and different tools in the same suite can appear to disagree even though each is reading correctly — a quality issue of interpretation, not of the hardware.
Logging speed, tool centering, and statistical (nuclear) count-rate noise. Nuclear tools (gamma ray, neutron, density) count discrete radioactive/scattering events; logging too fast for the counting-time constant used degrades vertical resolution and introduces statistical "noise" streaks, while a poorly centralized or eccentered tool (again tied to hole condition) biases both nuclear and sonic readings.
