Duties and Responsibilities Of Wellsite Geologist

Duties and Responsibilities :

The Wellsite Geologist is an important member of the wellsite team. They are required to monitor vital perations during the course of the well, make sure that all client requirements are carried out, and perform formation evaluation activities to ensure the well is drilled and evaluated in the most safe, efficient manner, and cost-effective.

In today’s wellsite work environment, with personnel being moved around the globe at a moments notice, it is always necessary to review the well prognosis with oil company personnel as soon as possible. This is because many times the client engineers or company man will supervise certain operations in one geographical area, but not in others, and it is best to get everyone “on the same page” before decisions are made.

A generalized list of duties and responsibilities include:

• Supervision of “Formation Evaluation” contractors (Mud Logging Geologists, MWD Logging Engineers, Wireline Logging Engineers, Coring and Well Testing Personnel)
• Logistics concerning the formation evaluation cont ractors and their equipment.
• All safety aspects for the well and personnel during these evaluation operations.
• Quality control of all evaluation results and logs prior to accepting the data or logs from those contractors.
• Providing relevant correlation and well data to those contractors during their operations.
• Checking all reports and logs from the evaluation contractors prior to sending them to oil company offices.
• Monitoring and supervising the collecting, processing and dispatching of formation evaluation samples.
• Safe-guarding the collection, storage and transmission of information and reports at the wellsite.
• Wellsite interpretation of the formation evaluation data .
• Checking and occasionally approving and signing of service reports and invoices of the formation evaluation contractors.
• Keeping the drilling superintendent and o perations geologist fully informed of all formation evaluation operations.

Since teamwork is required, the geologist must work closely with the drilling team (Company Man, Drilling Engineer, Toolpusher and Rig Crew) providing advice when necessary to assist in safe, cost-effective drilling and non-drilling operations.

Wellsite Visits:

There will be occasions when additional oil company personnel will be on location (“new” staff will visit the wellsite for orientation and training). More often though, this will happen when:

• They are to witness an operation at the wellsite.
• They are to gain immediate access to data, reports or logs.
• They are to advise the Wellsite Geologist on alternative methods to achieve the well program objectives Regardless of their reason, remember to be flexible when dealing with both the client and contractor, and maintain professional standards at all times. In all cases, oil company staff members do not assume any of the Wellsite  Geologist's responsibilities (except when personally communicated by the Operations Geologist).

 Any advice given to the Wellsite Geologist from the specialists, which may affect the well program, should be conveyed to the Operations Geologist.

 Programs Modifications:

 The Wellsite Geologist usually has the authority to make minor changes to the geological aspects of the well program (e.g. sampling intervals, logging sequence), without consultation with the Operations Geologist. Such changes are decided upon by:

• The Wellsite Geologist's reasoned initiative.
• On advice from the specialists, after consultation The Wellsite Geologist should inform the Operations Geologist of any modifications at the earliest opportunity. Any major changes to the geological aspects of the well program (e.g.different coring intervals, additional logs, extra formation tests) must have the approval of the Operations Geologist. When discussing such changes, the Wellsite Geologist should state their reasons behind the proposed change (i.e. operational constraints, advice from specialists, their own experience) and provide additional information which may prevent delays in reaching a decision (i.e. cross-checking data).
• Since it is sometimes difficult to distinguish between minor changes and major changes, it is best to inform the Operations Geologist if there is any doubt concerning the changes. Even better, discuss the clients preferences before operations start.

Rigsite Information Sources:

Service companies have different ways of collecting and displaying data. Most commonly, a log-type format is used with cuttings descriptions and drilling parameters displayed graphically on a litholog/striplog or when using a spreadsheet-based format. All formats and information displayed should be discussed and agreed upon by the contractor.

There are many sources of information at the rigsite and the following is a brief list of some of the sources. The data sets available will depend upon the type of service used and the ability of the service contractor to obtain the data.

Wireline Logging Unit

VSP                     Used to “look ahead”, formation top confirmation 

RFT                     Fluid sampling, Pressure determination,Oil/Water/Gas gradients

Resistivity            Water Saturation, Porosity, Hydrocarbon evaluation 

Density                Lithology confirmation, Correlation, Porosity,Overpressure detection, Gas/Oil contacts 

Sonic                   Porosity, Mechanical properties, Over pressure 

Dipmeters            Structure, Well trajectory, Facies analysis,Sedimentology 

Sidewall Cores    Biostratigraphy, Geochemistry, Lithology confirmation Hydrocarbon evaluation.

Mud-Logging Unit

Cuttings              Geochemistry, Lithology, Correlation, Density, Calcimetry, Hydrocarbons, Shale Factor (C.E.C.), Hole Stability, Bit Condition

Hydrocarbons    Total gas, Chromatograph, Gas Ratios, Connection gases, Trip gases, Oil shows

Gases                 CO2, H2S

Engineering       Dxc, Torque, Drill Rate, Formation Pressures

MWD/FEMWD unit data

Directional                 Borehole Trajectory (MWD), Dogleg Severity

Gamma Ray              Lithology Determination, Shale Content,

Resistivity                  Correlation, Hydrocarbon Evaluation, Pressure Indication, Sw Estimations

Density                     Lithology, Correlation, Pressure Indication, Gas/Oil Contact

Others                       Coring Biostratigraphy, Reservoir analysis, Porosity, Permeability

Wellsite Materials

At the client's pre-spud meeting, the length of the well will be estimated. This will dictate the amount of supplies you will require, both from a personal standpoint and a business standpoint. If re-supplying will be impossible, then your preparations before going to the wellsite must be thorough.

The amount of time spent at the wellsite will depend on several factors. Generally, it is best to be there a few days prior to spud to acquaint yourself with the rig crew, to observe the contractor's rig-up, and to converse with the personnel responsible for geologic data.

Review the list of contractor companies and see if they will have the supplies you will need. Most contractors will be happy to meet any “ext ra” requirements you may have.

Regional Geology:

It is important that the Wellsite Geologist be familiar with the regional geology of the area where the drilling is taking place. This will allow timely interpretation of data, especially if it should deviate from the prognosis. Particular aspects are:

• Nature and depth of b asement within the basin.
• Geologic age of the section.
• Depositional environments and expected lithologies.
• Tectonic setting within the basin.
• Formation pressure anomalies.
• Hydrocarbon occurrences within the basin.
• Basin correlations.
• Copies of geologically related articles should be brought to the wellsite. Reprints and books can be obtained from the American Association of Petroleum Geologists (AAPG) and local geological societies. 

Well Prognosis and Prospect Description:

The Wellsite Geologist should be completely familiar with all aspects of the drilling prognosis. Particular attention should be paid to any sections which may require geological decisions. These include:

• Determination of Primary and Secondary Objectives. 
• Determination of Casing Points 
• Detection of Overpressured Intervals.
• Detection of Lost Circulation Zones 
• Correlation and Detection of Marker Horizons.
• Determination of Geologic Basement or Economic Basement.
• Selection of Logging Run Intervals.

A complete set of correlation logs and reports should be compiled for use at the wellsite. Mudlogs, lithlogs and wireline logs should be used as sources of information.

 Company Requirements:

Prior to arrival at the wellsite, the geologist should be aware of their responsibilities and their authority. Decisions that are to be made at the wellsite and those that are made by the drilling foreman or the exploration office must be differentiated. It is important that all channels of communication for every situation be clear and well defined. A list of names and, where applicable, office and home contact numbers and addresses should be compiled. Contact numbers for contractor personnel are also useful.

Material Requirements:

• The Wellsite Geologist should be self-sufficient in terms of material supplies at the wellsite. The actual requirements will vary, depending on the reporting formats and descriptive requirements of the client. The following is a comprehensive list of possibilities:
• Copy of the well prognosis.
• Copy of prospect footage.
• A copied set of correlation logs.
• Set of company report forms, including: - Morning Report Forms Afternoon Report Forms - Cuttings Description Forms - Sidewall Core Description Forms - Core Description Forms - Wireline Quality Control Forms - Mud-Logging Quality Control Forms.
• Set of data transmittal forms.
• Grain size comparator.
• Rock Color Chart.
• Wireline/MWD Log Chart books (company s pecific).
• Set of log sepias and paper copies (if required).- Lith Log - Core Log - Pressure Evaluation Log - Temperature Log.

Many companies use computers for wellsite data storage and reporting. If the Wellsite Geologist requires a computer, check on office space availability at the rigsite or if a mud-logging unit is to be used. Power supply and plug/socket compatibility must be checked. Back-ups of software, blank disks, software/hardware manuals and anti-virus software are necessary.

Sampling Requirements:

Once the sampling requirements have been ascertained, they should be passed on to the mud-logging contractor. Sufficient sample boxes, sample bags, sample envelopes, and sample vials should be present at the wellsite. If they are not, it is essential that the geologist be aware of the lead time required for their acquisition. Particular care should be taken over bulky items such as geochemical cans or core boxes as these may require special transportation. In addition to those required for the sample intervals, extra bags or envelopes should be available for “spot” or “hot shot” samples.

A sample is useless if the test/drilling conditions and depth data are not indicated on the sample container. Also, the names and addresses of sample recipients should be obtained for the efficient dispatch of the samples.

Sample catching and packaging is usually the job of the mud-loggers, however the geologist must be aware of the correct methods, intervals and requirements to ensure that data quality is maintained.

It is always best to take more samples of anything that may be required (for later reference), even without specific instructions. These samples can always be removed if deemed unnecessary.

Pre-Well Responsibilities:

Generally, the Wellsite Geologist will be notified that they will be responsible for a well some time before the well is spudded. This time period should be spent, either collecting all available information or reviewing the already collected information.

If the geologist has the responsibility to collect the information pertaining to the well, the process should be exhaustive and thorough. General information concerning a field or specific information for a well can be obtained from the oil company owning the field, well log libraries, production reporting services, oil industry journals, regulatory agencies, and from communication within the oil company.

Once collected, the information is used by the Wellsite Geologist to come up with a “most probable” scenario as to what the subsurface adjacent borehole will look like. An open mind must be maintained when looking for hydrocarbons. Since the unknown is frequently confused with the unattractive. It is also important to guard against negative thinking, resulting from limited data. At the same time, it is important to remain optimistic and realistic when reviewing the data. It should be remembered that oil and gas are common substances in sedimentary basins.

Geologic Maps:

During the preliminary stages, much of the geological effort is directed towards drafting subsurface maps or reviewing previously drafted maps, covering the perspective field. Whether drafting or reviewing, it must be remembered that a map is never finished, but the map must be as complete as possible with the data available at the present time. It is best to remember that the subsurface is usually much more complex than is generally envisaged.

With regards to early subsurface maps, many early rotary holes were drilled unintentionally crooked by as much as 40 to 50 degrees, with no surface indications apart from “pay dirt” being absent or it occurring much deeper than expected. Consequently, early geological data and subsurface maps require very thorough investigation.

Dry Holes:

Dry holes should never be considered fruitless, because valuable data can be obtained from the well even if no hydrocarbons were indicated. Successful exploration, in many cases, requires that many dry holes be drilled (even though the aim of the industry is to drill as few dry holes as possible).

When reviewing well data, it is prudent to note that dry holes may be due to the following:

1. The trap was absent or open: This can be due to poor seismic quality or incorrect interpretation of data.
2. The trap shifted position: This may be due to faulting or folding.
3. A crooked hole: Traps formed by faults, and those around the flanks of salt diapirs require highly accurate directional drilling,and reservoirs can be missed by slight deviations from the projected borehole trajectory.
4. The reservoir rock may be absent due to: Shaling Out, Faulting Out, Erosion off a structural high, Failure to drill deep enough.
5. No oil or gas in the reservoir: Even more difficult than attempting to justify why hydrocarbons should be present (the pre-well proposal), is explaining why, when all the requirements for the generation and accumulation of hydrocarbons are present, the well was found to be dry. 

This can occur because there was no supply of hydrocarbons available, the trap developed after the hydrocarbons had migrated out of the reservoir, or the hydrocarbons may have “spilled-out” or had been flushed out of the re servoir.

6. Failure to recognize hydrocarbons during drilling: This can be due to excessive mud weights causing flushing of the formations and a thick filter cake build-up. Small diameter holes causing only a small volume of rock being crushed and carried to the surface for observation. Poor log quality or incorrect interpretation techniques. Drilling fluid contaminants masking hydrocarbon shows. Failing to test a suspected reservoir.

Summary

When the Wellsite Geologist arrives at the wellsite, they should be fully confident in their abilities, have an idea of how the well is to be drilled and evaluated. They should know where wellsite information can be gathered, and who to look to for assistance and advice.

Drilling, evaluating and completing a well is a team effort and the Wellsite Geologist is a valuable member of this team.