Introduction: By vigilantly overseeing and implementing QC procedures, a wellsite geologist helps in acquiring reliable wireline data. This accurate data is essential for informed decision-making throughout the wellbore’s lifecycle, from formation evaluation and reservoir characterization to maximizing well productivity as well as optimizing drilling operations for future wells. In order to witness wireline operations and QC logs in real-time, a wellsite geologist needs knowledge, experience and skills. This article gives a glimpse of ‘how do wellsite geologists witness wireline operations and QC logs’:
One week before a wireline job is expected:
- Geologist calls wire-line engineer in town to update him with the expected date of the upcoming job. On this calls he also discusses logging program to ensure all the tools are available in the base or will be made available by the time logging starts.
- Geologist briefly informs him about expected lithologies and anticipated downhole problems. For example engineer should be informed if the reservoirs are expected to be depleted, or deviation exceeds 50 deg. So that he comes prepared for the challenges.
- If the temperature in hole is expected (although rare) to be above 320 deg. F, geologist must mention this to wireline engineer as this environment requires special tools whose electronics can withstand high temperature.
- More importantly geologist should mention the results of this discussion to operations geologist in town. It is imperative to keep operations geologist informed at all times. Operations geologists do not like surprises.
Three days before the job: call engineer again to update him with current status of well and expected time of TD. Advisable to have wireline crew and tools on board, two days before logging job. So that crew has ample time to take rest and check tools. If it is an offshore location, ensure the chopper flight is booked and tools are on way to rig. Do inform company man and operations geologist about the expected arrival of crew and wireline tools on rig.
One day Before the Job Starts: Wellsite geologist makes sure:
- Wellsite geologist makes sures wireline crew and tools are on board and at least the tools of the first run have been function tested.
- He updates company man with logging program, readiness status and estimated duration of logging job.
- Carries out risk assessments and potential safety issues, prevention measures with wireline engineer.
- Wellsite geologist also ensures that he has taken good rest. Logging operation may take up to 30, 40 or even 50 hours.
- If geologist is estimating it to be long job (longer than 40 hours, he normally requests a junior geologist from town also requests a second wireline engineer. Making a wiper trip just to give a break to wireline engineer is more expensive than paying for second engineer. Also engineer has to handle explosives and radioactive material so from both angles, his demand is well justified for a second engineer.
Before the logging job starts: wellsite geologist has to provide following information to the wireline engineer:
- Company Name:
- Well Name:
- Rig Name:
- Rig floor elevation (from mean sea level):
- Shoe depth, casing type and weight per foot.
- Current TD/TVD
- List of directional Surveys to generate TVDss log
- Time and date of EOC (end of circulation)
- Request mud engineer to provide a sample of mud, mud filtrate and cake. This is to be prepared from mud, collected from flow line just before the circulation stops. Wireline engineer measures resistivity of all three samples and record it on log heading.
- Hole condition: Geologist gives an idea about hole condition during POOH. Points out depths where ever tight hole or abundant caving were encountered
- Temperature of mud out just before the end of circulation
- Percentage of Barite, oil, KCl, mica in the mud, (ask from mud engineer). These may adversely affect certain logs and may require correction
Note:
Density readings are masked by barite in the mud system and in mud cake. GR readings are increased in KCl mud system and in mud that contains mica (both due to potassium content). If a KCl system is used, the log header should have a comment stating concentration of KCl and correction algorithm used, if any.
When Job Starts:
Wireline job starts with a safety meeting, what we call tool box meeting. Actually meeting takes place on rig floor after the rig up but prior to picking up tools. It is attended by wellsite geologist, wireline crew, driller, roughnecks and is conducted by wireline engineer. Important points that are usually reminded in the meeting are: 1. Unnecessary crew to stay away from the rig-floor and moon pool area at the time loading and unloading radioactive sources. 2. People should stay at safe distance from cable. 2. Watch out for potential hazards such as, pinch points, cable tension, anything that can come loose or get entangled etc. etc.
Geologist also informs mudlogging crew to closely monitor well on trip tank. Any significant variation in mud level must immediately be reported to him and company man.
Logging Supervision form: This form is usually available with all consultant geologists. Even some oil companies have their standard form that is to be filled up by geologist during the logging operation. It records in detail, timings of various operations, events and important observations of geologist. It is an important record as it helps understand the efficiency of operation, problems observed and how were they resolved and what lessons can be learned to improve the future operation.
Time Record:
Keep a very detailed time record of the events during wireline logging operation, for example:
- End of circulation at: mention time
- Rig floor clear at: time
- Pre job safety meeting held at: time
- Started Rig up at: time
- Picked up tool at: time
- Loaded radioactive sources and performed before survey calibration at: time
- Start RIH at: time
- Speed RIH: 8000 ft/hr. to 10,000 ft/hr. inside casing.
- Log scales: Ask engineer to show log scales on each track. They should be same as in offset well.
- Time tool at shoe: Checked shoe depth and record shoe depth, (Use Caliper log or resistivity log to pick shoe depth)
- Open caliper: check and note casing ID. If sonic tool is in the tool string; check and note that sonic is reading interval transit time 57 microsec/ft inside casing.
- Tool in open hole section: (note down time and Running speed for log down usually 3000 to 5000 ft/hr.)
- Tool tension and cable tension: Note down just below shoe and then every 1000 ft. or so.
- Tool held up depth: If encountered bridge ( mention depth, look at mudlog, note down lithology and inclination)
- Remarks about hole condition: (Good if no held up, poor if tool speed slowed down occasionally, bad if tool got held up and had to be tried several time to pass through the bridge at varying speeds. Note down attempted tool speeds. Also note down tight spot depths
- Tagged bottom at: note down depth and time. (if shallower, could be due to hole fill) (bottom hole depth is picked looking at tool and cable tension)
- Time started log up: (Record bottom hole temperature BHT)
- Note down tool tension and cable tension at bottom.
- Logging up speed: (usually around 2000 ft/hr. or as discussed with operations geologist)
- Log quality: Check quality of various curves, their consistency, gaps in log, spikes, kinks or straight line on any log, or unnatural looking log curve. Check log readings in known lithologies. If any log looks unusual ask wireline engineer to repeat log over doubtful section at slower speed.
- Time tool at shoe (end of logging)
- Time start POOH. POOH speed inside casing (usually faster 5000 to 10000 ft/hr.)
- Time tool on surface
- Time finished unloading radioactive sources and laying down tool
- Time start picking up tools for run #2
- In remarks mention what was total NPT (non-productive time if any)? Reason for it or how it was prevented or mitigated?
- Also note down lessons learned during the logging operation if any (to be shared with the team). This helps future operation less strenuous and more efficient.
Individual Log QC: Details of individual logs and how to QC them, can be found in the section “Wellsite Geologist Interview Q&A”. Please visit: geoskillz.com.
Conclusion:
Aspiring wellsite geologist must pay attention to the following points to build their knowledge and expertise on the subject:
· To witness the entire logging operation: Make list of established protocols, from tool preparation and deployment to data acquisition and demobilization.
· Monitor data quality in real-time: Gain basic knowledge of individual logs, their utility, recording mechanism and borehole environmental effects on them. Learn how to scrutinize log curves for anomalies, ensure proper tool functioning. (visit: geoskillz.com )
· Maintain clear communication: with logging engineer, drilling supervisor and operations geologist. Learn how to convey observations, concerns, and recommendations and address any data quality issues promptly.
· Learn to document critical observations: Lean how to maintain detailed records of logging operation and timings including wellbore conditions, mud properties, and any deviations from protocol. Some of these notes may be crucial for future reference and data interpretation.