Now that we’ve covered what hydrocarbons are and how they are formed, it’s time to take a look at how oil and gas companies actually go about locating them.
When a company is developing an oil or gas field, knowledge of the spatial arrangement of geologic units and structures is critical to success. Since millions of dollars are spent drilling each well, minimizing the number of failed wells is a key part of a company’s business strategy. In addition to ensuring that wells hit the payzone, an understanding of local subsurface structures allows oil companies to maximize the longevity of initial reservoir drive, avoid environmental contamination, ensure the integrity of the wellbore, and determine proper well spacing.
Subsurface structures are represented by geologic maps, cross sections, and, recently, three dimensional computer models. These tools are all components of a reservoir model – a working geologic description of a region and its associated petroleum systems. Reservoir models are used to help geologists locate oil and gas. As data is collected, a reservoir model is updated and improved. Eventually, a fluid transport behavior model describing the movement of hydrocarbons within the reservoir during production will be developed.
The development of these models is the primary task of a petroleum exploration geologist. Under the guidance of company decision makers, exploration geologists may complete many phases of exploration in order to produce an accurate model. The ultimate goal of an exploration geologist is to put an x on the map that says “drill here”.
The flowchart below shows some of the most common steps and techniques used in reservoir model development.
Exploration can be divided into three phases: Base map development, data collection, and analysis. First, exploration geologists gather existing information and spatial data about the geographic region to create a base map. Second, in the data collection phase, they augment this information using fieldwork and geophysical techniques. In the analysis phase, they produce a geologic map, associated cross sections, and a 3d model of the oil field. Analysis of the maps and models allows them to find promising petroleum systems.
If an economically viable petroleum system is present, exploratory drilling is used to find and extract the oil. During drilling, information from core samples and rock chips can be used to refine the model, adjust future drilling activity, and estimate the total amount of oil and gas that will be recovered.
Why It Matters
Good quality geologic information is important to oil and gas companies and regulators alike. Quality mapping can facilitate appropriate preplanning, identify environmentally sensitive surface features, and waterways, and indicate how geology might impact decision-making in an emergency. While quality information can help with and encourage appropriate planning and preparation, reserve estimation can help identify the potential size and longevity of a play based on the size of the available resource.
The combination of mapping and reserve estimation can help identify areas that may result in new operator behavior that is significantly different from previous development activities. Are the formations bigger, deeper, more complex, or in sensitive areas? Are there caprice protections for ground water? Are there potential gaps in regulation or industry practice? Answering these questions and many more all starts with good quality information.
Learning Objectives
- Read and identify the various features of a topographic map.
- Identify the distribution of rock units on a geologic map.
- Identify strike and dip on a geologic map.
- Recognize faults on a geologic map and classify displacement types.
- Read and analyze an isopach map.
Images: “Oil drilling exploration” by pan demin via Shutterstock