Directional drilling has revolutionized the oil and gas industry, and with geosteering the revolution has notched up a level. Conventional directional drilling involved steering the wellbore path according to a predetermined geometrical plan defined by rigid boundaries and follow it as closely as possible.
Geosteering, on the other hand, involves real-time use of logging tools such as logging while drilling (LWD) and measurement while drilling (MWD) to continually evaluate and place the horizontal wellbore in the optimal position.
The most important part of the geosteering process is the planning stage which if done diligently will help complete the wellbore successfully. During planning crucial points such as strategy for bottom hole assembly (BHA) and stabilizers, the possibility of structural uncertainties of drilled targets, distribution of targets along the wellpath, dogleg severity, etc. need to be considered and understood by every member of the team.
What is Geosteering?
Geosteering is a technology that requires many experts involved in a team effort to steer the well in the right direction and complete the well successfully. Other than the rig crew and the directional team, the geosteering team includes directional drilling engineers, wellsite geologists, exploration and production (E&P) geologists, well planners and geo-modeling staff.
Geosteering is costly, i.e. about three times more expensive than a conventional well, thanks to all the experts needed, and the use of highly advanced electronic tools and equipment. This expense, however, is overshadowed by the return on investment with increased reservoir exposure, increased production level, and oil recovery.
This benefit has made geosteering a method of choice for drilling offshore and in deep water as it maximizes efficiency and offsets the additional cost of an offshore drilling operation.
Geosteering is not just a method for the most expensive horizontal wells but can be used to improve the odds of success by remaining in the productive zone for longer drilling periods. The method is also great for optimizing horizontal wellbore positioning in the sweet spots within the reservoir.
A few essential facts and reality checks for geosteering professionals are mentioned below as published in an SES (Software Engineering Software v5.11) user manual:
- Wellbore/stratigraphic certainties are limited and sporadically located along a wellbore path.
- Wellbore/stratigraphic certainties near current total depth (TD) and beyond are unknowable.
- Geosteering purpose attempts to maximize wellbore/pay zone exposure and avoid troublesome drilling/ completion/ production conditions.
- Geosteering purpose attempts to add economic value, geologic knowledge and imagination (art) with systematic and intellectual reasoning.
- It's best to carefully consider the full drilling/completion/ production risks and trade-offs before making planned well path changes while drilling.
- Strong working knowledge of the areas geology/drilling/production leads to better geosteering/steering decisions and increased odds of favorable results.
Geosteering has been around for a while but was performed mostly as an inference from cutting samples, well logs, maps, rough drawings, and 2D trigonometry. That has changed now as geosteering has incorporated modern hi-tech electronic equipment that is able to relay real-time approximation of the location of nearby geologic beds in relation to a wellbore or coordinate system.
The real-time information is obtained using MWD that steers the drill and LWD that generates logs representing various rock formation properties at depth.
In order to steer the well correctly, certain downhole tools are an essential part of the drilling assembly.
Measurement While Drilling (MWD)
MWD works by using magnetometers, gyroscopes, and accelerometers that measure the azimuth and inclination of the borehole at a particular location and is transmitted to the surface. It also provides drill bit information, wellbore position, and directional data.
The tool measures and surveys the geometric properties of the wellbore and passes on the information in real-time to the computers located at the surface. The exact position of the drilling assembly should be known at all times in order to make decisions and direct the drill bit.
Logging While Drilling (LWD)
This tool also has many electronic components and sensors that can measure a wide range of rock properties such as conductivity, resistivity, resonance, porosity, density, and acoustic properties. It is located behind the drill bit and passes on real-time data allowing geologists to know the rock properties while geosteering is in progress.
Drill Bit
This is the cutting component of the downhole tool, and its design and properties are very essential for a successful geosteering operation. The bit should be balanced, smooth, compatible with the drive system, and respond predictably to steering inputs to steer the well correctly.
Geosteering is Trending Up
To meet the global need for energy security, production levels of natural oil and gas have to be boosted. This can help economies, especially in developing countries, to continue to function smoothly while striving for their goal to become developed nations. Geosteering is the right solution for meeting the demands of the energy industry while creating a lighter footprint for alleviating environmental concerns.
The remote placement of wells in real-time has also reduced the need for hundreds of rigs and many people working on them often in risky conditions that threaten their lives.
Geosteering is safer and cost-effective and as days go by, it may bring in many more environmental and economic benefits as technology and innovation continuously improve electronic drilling equipment and tools.