Home Applied Geology Petroleum Geology What Does a Petroleum Geologist Do?

What Does a Petroleum Geologist Do?

Step 1 – The Petroleum Geologist Prospects

Net Pay Map Made By Petroleum Geologist

Petroleum geologists are scientists that work to discover new oil and gas deposits.  Petroleum geology is a “science of sciences.”  The geologist puts skillsin geology, physics, chemistry, biology, and other fields to the practical task of locating energy sources.

Prospecting is the work the petroleum geologist does to locate a place to drill a test hole, which hopefully can be turned into a producing oil or gas well!

Most petroleum geologists spend 90% of their time in an office, where they have access to a huge amount of data. This includes electric logs, core records, drilling records, scout tickets, and production data. They use the data to construct maps, structural cross-sections, and databases.  These tools help them locate the best places to drill their test holes.

The geologist will construct many contour maps to help her locate the prospect.  She will make many cross-sections and run numerous computer simulations that help her select the next location to drill. She is always thinking about the next drilling location…or prospect!

He will want to know what type of trap he is dealing with, and the composition of the sedimentary rocks he will be drilling through. He needs to estimate the porosity of his prospective “pay zone.” He wants to know if dangerous high pressures can be expected in the new hole. If seismic data is involved in the prospect, he will consult with the geophysicist and get his opinion of the prospect.

In certain areas, it will be necessary to use biostratigraphy to help pinpoint the location.

The petroleum geologist is always interested in anything that happens in her area, particularly news of new discoveries by other companies!  If she sees a promising new area, she will recommend to the land department that an attempt be made to lease the land; the leased acreage will then be available for drilling later.

When the geologist has finally found the best place, she will “spot” or locate the well using the land survey system most appropriate to the area.  She spends much time cross-checking to ensure she has not missed anything. She wants to make sure she is not “surprised” by any of the following:

  • Discovering the selected location was already drilled by another company 40 years ago (and was dry)
  • Discovering that her company has no legal right to drill on the location (lease problems)
  • Unexpected faults or other geologic problems that crop up during drilling and ruin the prospect
  • Discovering that the hole is being drilled in the wrong place after drilling begins (a very bad thing that has actually happened!)

Step 2 – The Petroleum Geologist Packages The Deal


Once the new location is defined, and the geologist is satisfied the prospect is a good one, the work is just beginning. He has a large amount of rough data available in the form of work maps, that he used to satisfy himself of the feasibility.  Now, he must condense this large data mass into a set of presentation materials that can be shown and explained to non-geologists.

To package the deal, he will prepare sets of simplified maps and stratigraphic cross-sections, highly-colored and attractive to the eye. He may use Powerpoint, or other presentation software. Creativity, design sense, and art skills are important during this phase. He needs to anticipate all possible questions, and be prepared to answer each one of them. He must be very sure of himself and his facts before he moves to the next step.

Step 3 – The Petroleum Geologist Sells the Deal

5 steps - Sell The Deal - Petroleum Geologists

Now the geologist must step into a role that is often uncomfortable for him … selling his prospect. It may be uncomfortable because geologists are scientists, with scientific backgrounds and schooling. They are used to talking to other scientists. But now the geologist must become a salesman in order to convince people who are not geology experts of the value of the prospect.  These people may include managers, bankers, engineers, and oil and gas investors.

Of course, the geologist wants to see her prospect drilled.  She will use all of her ability to present it in the best light.  There is a lot of room for interpretation with any prospect (that’s what makes it fun).  But, she will take great pains to ensure all her data is presented accurately and concisely.  She is bound by her own integrity, the integrity of any professional group she is a member of, and the integrity of her profession.

She is looking to convince her clients that

  • the prospect is worth drilling,
  • investors will get a fair return for their money
  • the provided financing will be wisely spent

Even an inexpensive test hole can cost a couple of million dollars, and some exploration tests may run into many tens of millions! So the geologist wants to be very sure of her facts.  All her clients must believe the proposed well has a reasonable chance of being successful.

The geologist will meet with the landman (females in the business are also called “landmen”), who will ensure the company has the legal right to drill in the chosen spot. He will consult with the engineer, who will project the exact cost of drilling and completing the hole.  Marketing personnel will ensure the company has a market (buyer) for the oil, or a pipeline for the gas. Managers, responsible for ensuring the company’s drilling budget is spent wisely, will also approve the test. If outside financing will be used, the geologist will explain the prospect to representatives of the bank or other individuals or partnerships that put up the money.

When he’s done, the geologist will have “sold” his prospect to anywhere from a few to several dozen people.

Step 4 – The Petroleum Geologist Monitors the Drilling of the Test

5 steps - drilling rig

Next comes the part that every petroleum geologist enjoys the most! Drilling the hole! It has now been several months since the geologist started working on his prospect. Now the land owners have been paid, permits acquired, and money raised.  Roads and the drilling location have been built, pipe and supplies have been ordered.  Also, the energy company has engaged a drilling contractor who owns and operates the drilling rig.

The drilling contractor will drill the hole in the exact manner specified by the company. The contractor will have some leeway to select the type of drill bits to be used, hire a drilling crew, and make many other decisions concerning the actual drilling.  Virtually all holes are drilled by contractors.

Drilling a hole is a very complex procedure involving many people and many critical steps. Nearly everything must go right. Dangerous machinery, bad weather, and continuous mechanical failures are faced daily. The work goes on for weeks to months, 24 hours a day.  It is a vigorous, nonstop operation.  A slip-up at any point can ruin the very expensive hole, cost a fortune, or get people killed.

The geologist will closely monitor all aspects of the drilling as it takes place. She will select an electric-logging company, and the proper wireline logging tools to evaluate the hole. She will usually hire a mud logging contractor to “sit” the well day and night.  The mud logger will study the well cuttings, report shows of oil and gas, and keep track of other things on the location. The geologist will monitor the formation tops as they are encountered, and discuss the progress of the drilling with the investors. The geologist will decide where and when to take cores or drill-stem tests. Finally, after the hole is logged with electric logs, she will examine the logs and recommend the hole be completed or plugged.

Step 5 – The Petroleum Geologist Works With The Engineer to Complete the Well

5 steps - completion

At last the hole is drilled!  At this time, a decision must quickly be made to attempt a completion and make the hole a well, or plug the dry hole.  Completion costs are extremely high (often as much or more than the drilling costs), so it must be believed the expensive completion will be worth the money. No one wants to throw good money after bad. Justifying a completion can be a grueling process. It almost always takes place in the middle of the night!

The job of completing the hole is mainly in the hands of the petroleum engineer. The engineer will decide which type of casing to use, and the method of cementing, He will design the completion procedure (which may involve perforating, breakdowns, acid jobs, cementing, fracks, or pumps). However, he will depend on the geologist to advise him on various topics. To start, the geologist will give the engineer a list of formation tops, and tell the engineer exactly which zones should be tested.

The geologist is often the person most familiar with the technical practices of other oil companies in the area. No two companies are exactly alike; some may come up with better ideas for certain processes.  The geologist may be familiar with the most successful fracturing or breakdown procedures of other companies. He might suggest a certain style or method of perforation, or offer advice on cementing techniques. He will relay this information to the petroleum engineer, who will usually be thankful for the help! Working as a team, the geologist and petroleum engineer will get the new well completed, and put it to work providing energy for all of us!