Geosteering - Fundamentals, Evolution and Future

Preface

With plenty of material currently available online / offline on geosteering subject, but there's still enough room to write on this subject. People with geoscience-related discipline generally develop geosteering skill over the period of time with their past knowledge and experience in related discipline. Occasionally, people ask me to provide them with some material or a book on geosteering but I can not, due to the fact that any comprehensive information on geosteering in a single book is hardly available in a free market. However, some experts have recently published books on this subject that are available on purchase.

With over 20 years of international experience in oil and gas industry, more pronounced in geosteering technologies continuously since 2006, I would like to share my learnings and experience with my audience for their benefit.

It is a known fact that the age of easy oil is over, so where do we look now? The answer is drilling horizontal wells in previously ignored thin layers enriched with hydrocarbons, and explore unconventional basins, utilizing advanced and state-of-the-art horizontal drilling technology. The new directional drilling technology has a cost to drill horizontal wells, and to minimize the cost, the horizontal wells have to be placed precisely in thin target zones to maximize production and reduce non productive time. Geosteering technology supports accurate horizontal well placement in target zones.

Current era of digital transformation is accelerated by COVID-19 pandemic, subsequently, many organizations have shifted their operations to remote work. Furthermore, the world will embrace a new era of remote work after embracing 5G technology.

Fortunately, the geosteering operations are being run remotely ever since I started my career in it. Now that we understand the value of geosteering and remote operations, let's talk about it. It may require a series of articles to cover the entire subject. I hope to keep posting on this subject and would appreciate the feedback from the audience.

What is Geosteering?

"The accurate placement of a high angle (HA) / horizontal (HZ) wellbore in a specific geological target zone, making real-time decisions based on real-time LWD downhole measurement(s) in comparison with available offset well(s) (vertical / deviated) data coupled with geological surfaces, occasionally utilizing drill cuttings, rock geochemistry and biostratigraphy information".

Components of Geosteering

Geosteering operation is a multi-disciplinary approach with following components:

1. Directional tools - a conventional mud motor or an RSS tool allows building wellbore directions (up/down/left/right) and transmits directional surveys at certain intervals or on-fly.
2. LWD tools - an LWD tool comprises minimum of a gamma ray sensor, and it may have additional tools from triple combo to penta combo in a drill string that can provide GR-Res-Den-Por-borehole Images. Currently, LWD ultra deep azimuthal resistivity tools having 150-250 feet depth-of-investigation is available in the market.
3. Geosteering software - an excel template or a strip log works to geosteer a well with gamma ray only. However, for medium to large projects and for complex geosteering jobs, a purpose-built geosteering software is indispensable. (I have a plan to write an article on geosteering software in future)
4. Trained Geosteering specialist - a geosteering specialist is an extremely responsible person, due to the fact that he has to process real-time information, choosing the best possible scenario and has to make decisions in time. Any confusion has to be discuss with client's geologist to avoid losing geosteering control. The geosteerer has to communicate with directional drillers, LWD engineers, company geologists, drilling engineers, etc., therefore, he has to be a trained and experienced in his profession. Geosteering being a client-facing position, it is important to develop technical skills as well as soft skills to bring real value of the position.
5. 24/7 communication - effective and efficient communication with all relevant departments throughout the drilling of a lateral section is a key to successful geosteering job.

A geosteering center (or desk) is a hub of all cross-domain information exchange

Cross-domain knowledge is required for superior performance and excellent geosteering results

Let me briefly list down the cross-domain knowledge required in a geosteering process, the items listed at the top takes highest priority:

1. Geology - it is recommended for a geosteering specialist to have a geoscience or petroleum engineering related degree to perform geosteering job due to the fact that the main point of contact is client's geologist and he/she would like to hear and discuss geology using geological terms.
2. ?Petrophysics - LWD tools transmits measurements that are petrophysical in nature and without petrophysical knowledge of logging curves and their interpretation, it is barely possible to achieve results.
3. Directional drilling - one of the closest and direct contact of a geosteering specialist is directional driller, hence, it is importance to have sound knowledge of directional drilling concepts, terminologies, coordinate systems, doglegs, vertical depth and survey concepts, survey methods etc., in order to communicate with him effectively. Any confusion may lead to an error and the responsibility falls on the geosteerer.
4. ?LWD tools - without proper knowledge of LWD tool's function, mechanism, specification, telemetry, data transmission and type of data transfer etc., the geosteering process cannot be optimized.
5. Geophysics - a basic understanding of geophysical interpretation is essential due to the fact that the geological information is tied to the geophysical information and the geophysicist interacts occasionally.
6. Drilling engineering - the drilling engineers often communicate with geosteerers to discuss wellbore profile, BHAs, doglegs, perforation zones, packer intervals for zonal isolation, multilateral pads etc. It is advisable to learn what is expected and answer accordingly.
7. Other services at rigsite - mudlogging, gas detection system, wireline logging, biostratigraphy, chemostratigraphy might be the part of a horizontal drilling, it is important to develop understanding on those operations for better communication and to optimize geosteering operations, utilizing all the available information.
8. Rigsite operations - owing the fact that geosteering jobs are being done remotely, many geosteerers haven't seen the rig operations directly and when they receive any non-drilling operations update from the rigsite they get confused. The proper understanding of rigsite drilling operations is quite useful.
9. Software knowledge - several third-party geosteering software are available in open market, it is recommended to learn the software very well before using it in real-time. And keep the contact of a person or tech-support who has command on software use, to get assistance in case of error or glitch in software while drilling.
10. Real-time data transmission- there are number of ways to transfer data from LWD data acquisition unit at rigsite to geosteering computer (at remote location). The most common method is WITSML protocol. It is critical to latch right data from data streaming hub to geosteering software and learn basic troubleshooting for continuous data streaming through server to avoid inconvenience in case of unexpected disruption in data transfer and keep the contact of concerned IT person.

Qualification required for geosteering geologist position

There is a range of qualifications and experience required for a geosteering position depending on the job responsibilities. However, in general, the companies look for the following qualifications:

• Bachelors or Masters degree in Geoscience or related profession
• 5-7 year of experience in geoscience field (>10 years on a senior position)
• Mudlogging or wellsite geology experience
• Experience on any geosteering software
• LWD or wireline experience is considered as an additional value

The Evolution of Directional Drilling, LWD and Geosteering Technology (Past, Present and Future)

Directional drilling technology

The history of directional or slanted wells drilling dates back to 1920s, when most of the wells were actually drilled crooked holes while some of them were deviated on-purpose, using whipstock. The major breakthrough in directional technology occurred in 1970's with the development of downhole mud motors, coupled with survey tools and improved BHA design. A piece of bent sub was fixed in mud motors that allowed the direction of the wellbore to be changed instead of pulling it out completely for a whipstock. Nevertheless, the economic viability of the directional / horizontal wells was achieved only during 1980s after hydrocarbon production from a horizontal well was successfully increased three to four-fold while the cost was increased less than two-fold. One of the most revolutionary technology in directional drilling was the development of Rotary steerable system (RSS) tool during 1990s, that has proven significant value in drilling horizontal and long lateral wells. RSS technology has great advantages over its predecessor mud motor in a way that it produces accurate results, smoother wellbore, reduced wellbore tortuosity, better directional control, reduced drilling time and faster rate of penetration. The later generation of RSS tools have been developed with two-way communication (closed-loop) and precise directional control in 3D with greater steerability in all types of geological formation. RSS tools broadly falls into two categories based on their function i.e.; push-the-bit and point-the-bit. However, the discussion on this subject is beyond the scope of this article. (sources: offshore magazine, drilling contractor (IADC), IHS Energy group, World Oil magazine, Oil & Gas Journal)

The drilling of horizontal wells has been significantly increased globally over the last two decades and North America is leading the horizontal drilling technology and activity, see fig.1 and fig.2 below.

Fig.1 US Horizontal wells count from 2008 (28,000) to 2018 (140,000). (source: Statista 2020)

Fig. 2 Comparison of rigs drilling horizontal and vertical wells. Notice the number of horizontal drilling rigs surpassed the number of vertical drilling rigs in Canada in 2010 (source: CER, Govt. of Canada)

LWD technology

Fig.3 A collar based LWD tool

Similar to directional drilling, logging while drilling (LWD) technology has been developed remarkably over the period of time since its start with simple gamma ray and basic resistivity tool during 1980s to the more advanced azimuthal borehole imaging, density, neutron porosity, borehole sonic, nuclear magnetic resonance, deep and ultra deep azimuthal resistivity tools etc., till recent.

The latest LWD tools are designed to proactively geosteer horizontal wells precisely in thin geological layers, utilizing advanced algorithms and inversion technologies. The reservoir boundary mapping tools are the examples and are often called as geosteering tools.

A purpose-built robust geosteering software is essential to utilize the full potential of such state-of-the-art tools.

Data transmission / Telemetry system

Fig. 4 LWD tools and telemetry systems on rack for calibration and programming

To transmit MWD / LWD tool downhole measurements to surface computers in real-time, a smart telemetry system is crucial to accomplish the task. The directional drilling companies offer a range of telemetry systems that includes, mud pulse telemetry (positive / negative), electromagnetic (EM) and the most recent one is wired drill pipe. The wired drill pipe telemetry is similar to a wireline cable in terms that it connects the downhole tools with surface processing computer through a wire. The wired drill pipe transmits all downhole data to surface computer in a matter of milli-seconds without compromising the data quality and data resolution, beside that it allows simultaneous data transmission from surface to downhole tools. The higher rate of data transfer and the flexibility of transferring large amount of downhole data through wired drill pipe make it a niche technology comparing it with mud pulse and EM telemetry. However, the application of telemetry system involves couple of factors in order to make the job cost-effective and efficient.

Geosteering technology

Ever since the horizontal drilling technology has emerged, the geosteering technology developed in parallel to place the horizontal wells in geological target layers.

Geosteering often referred to as well placement or reservoir navigation. The main objective of the job is to place a directional / horizontal wellbore in a geological target zone based on the interpretation of real-time LWD measurements, keeping a smooth wellbore profile in order to maximize hydrocarbon production, minimize non-productive drilling time and reduce drilling and completion cost.

In past during 1990s, the wellsite geologists and operations geologists were responsible to place the horizontal wells in geological target zone based on; drill cuttings, drilling parameters, hydrocarbon gas and gamma ray or resistivity measurements. The lateral sections were short, the target zones were thick, ~10m. and the drilling speed was slow, despite that it was difficult to place a horizontal wellbore accurately in target zone due to limited downhole information.

I was involved in a horizontal well project as a Mudlogger in Qatar during early 2000, the operations geologist was struggling to place the horizontal well in carbonate target zone. Mudlogging unit was the center for making geosteering decisions as the decisions were based on cuttings, gases and drilling parameters. The client was satisfied with the well placement of little more than fifty-percent in zone. The geosteering technology was in early stage of development with limited real-time information and unavailability of advanced geosteering software. The well correlations were made on printed logs and the type-log overlays were utilized. Another example of horizontal well drilled in Turkey during 2001, where I worked as pore pressure engineer. The client's operations geologist was steering horizontal well in target zone. After drilling a few hundred feet in zone, the formation was lost with no success finding it, hence, it was decided to drill a sidetrack hole to drill the rest of the section in zone. After drilling some footage, the sidetrack hole accidently entered in previous hole. There were couple of reasons for the mishap, the main reason was high degree of inaccuracy in surveys, lack of horizontal well understanding, and limited knowledge of true stratigraphic depth (TSD). Most of the geologists were exercising true vertical depths (TVD) instead. Excel templates were being utilized for geosteering that had its own limitations. In general, it was difficult to make geosteering decision accurately and timely during that time due to the above mentioned limitations.

Geosteering with azimuthal LWD tools

With the development of gamma ray, density and resistivity azimuthal tools, and the advancement in LWD telemetry systems, geosteerers were enabled to determine wellbore position in relation to the stratigraphy. Although the geosteering decisions were improved with the development of azimuthal tools, but the poor resolution of borehole images in real-time (with only four to eight sector data) and missing image data in sliding intervals was still affecting the precise and timely decisions. The second challenge was the increase in sensor-to-bit-distance, that was increased due to additional tools in the drill string. The depth-of-investigation of LWD tools was not great. Hence, the geosteering decisions were reactive that means the decisions were made after the tool contact the target boundary. With this advancement, the geosteering job was considered successful with two-third of the well placed in zone.

The next generation of LWD tools overcame the limitation of previous generation LWD tools. The depth-of-investigation (DOI) of deep azimuthal resistivity tools was successfully increased to 15 feet for the first time, and subsequently to 18 and 20 feet in a competitive environment. That increase in DOI allowed proactive geosteering and it became possible to avoid the approaching boundary even if the tool was 25 meter behind the bit.

First deep azimuthal resistivity tool was patented in 2000 and was commercialized during 2002-2003. The telemetry was improved further which enables the transfer of large amount of downhole data in compressed form along with multiple sets of 16 and 32 sectors image data transfer in real-time. Geosteering software were revamped to accommodate azimuthal data, inversion calculations, forward modelling and distance-to-bed-boundary calculations. The development of deep azimuthal resistivity tool was a remarkable achievement in the progress and performance of geosteering technology, that lead into a higher degree of accuracy in timely geosteering decisions and carved a way for proactive geosteering.

The parameters of job success have been considerably changed over the period of time, from a satisfaction of more than fifty percent of wellbore in zone in the past - to a question of why the ten percent of wellbore is out of zone as of now.

Measurement of Geosteering work performance

The assessment of geosteering work quality and performance is necessary not only to justify the payment to the contractor but also to analyze if the job tasks were done correctly, following are the metrics to measure geosteering performance.

• Percent of wellbore in-zone - one of the most basic and instant criteria to measure the success of well placement job. The parameters of job success have been considerably changed over the period of time, from a satisfaction of more than fifty percent of wellbore in zone in the past - to a question of why the ten percent of wellbore is out of zone as of now.
• Smoother wellbore profile - in recent times, the length of lateral section is increased to few kilometers, so it is necessary to keep the wellbore smooth with minimum doglegs in the hole in order to complete the well without high torque and drag. Smooth wellbore profile allows running casing / liner smoothly to the bottom and completing wells.
• Hydrocarbon production - one of the most important performance measurement metrics is the well production. A successful geosteering job results in a higher well production. The production results speak louder!
• Cost-saving - The faster the wellbore drills in-zone, the lesser the drilling costs. To reduce drilling cost, avoid unnecessary stopping and slowing down drilling. Avoid abrupt change in geosteering decision to keep the borehole smooth and drill faster. Analyze interpretations in coordination with operations geologist in case of complexity to avoid boundary exit. Optimize the wellbore position in a porous layer to drill fast. Make recommendation of Fit-for-purpose LWD tools to minimize the cost.

Remote Geosteering operations center

The geosteering operations turned mostly remote following the technological advancements and digitalization during mid 2000's. The proactive geosteering decisions effectively placed horizontal wellbore in zone, utilizing latest LWD and RSS technology resulted in fast drilling and smoother wellbore. The remote geosteering was proved to be cost-effective and enabled rigsite safety. One geosteerer could effectively geosteer 2-3 wells or more depending on the wellbore objectives and complexity, so it is also cost-effective.

A range of third-party geosteering software have been developed for third-party geosteering. However, the concept of third-party geosteering was successfully progressed in North America with the limited concept in other parts of the world. The operators in other part of the world consider geosteering, a part of directional drilling services. Some large operators have successfully established their own remote geosteering centers.

Ultra Deep Azimuthal Resistivity (UDAR) - Reservoir Boundary Mapping tool

During 2010's, the progress in the development of LWD tools reached a new milestone when Schlumberger announced it's first ultra deep azimuthal resistivity tool (Geosphere) with its 100 feet of depth-of-investigation (DOI) followed by Baker Hughes designed its UDAR tool (VisiTrak) with similar DOI. I was working for Baker Hughes when VisiTrak tool was developed with advanced resistivity inversion calculations. Later on after few years, Halliburton introduced its groundbreaking technology with the development of ultra deep resistivity tool (Earthstar) having 250 feet depth-of-investigation. Schlumberger enhanced its Geosphere to Geosphere HD with comparable DOI.

The competition in tools technology is never-ending, not only increasing DOIs but also improving real-time resistivity inversion in 2D / 3D, and enhancing automation.

Third party geosteering software

Couple of third-party advanced and robust geosteering software are recently developed that are designed specifically for Proactive multi-well and larger multilateral geosteering projects. The software are LWD tool vendor independent and have the ability to process advanced LWD tools data with the option of real-time data streaming through WITSML. Those software are the best-fit for third party geosteering, utilizing high-end LWD tools.

Next Generation of Geosteering

The next generation of geosteering will involve cross-domain functions to deliver fully optimized integrated drilling and geoscience operations. The enabled real-time remote operations centers fulfill the objectives of integrated remote jobs with the involvement of geosteerers, operations geologists, directional drillers, LWDs, geomechanics, geomodeller, reservoir characterization specialist, data analysts, etc.

The adaptation and incorporation of machine learning and artificial intelligence in operations center will create great value to integrated operations that results in significant cost-savings.

I would say the new era will pave the way to third-party remote operations center.

GazServ Inc. is a proACTIVE third-party geosteering company, based in Calgary with extensive global experience in advanced proactive geosteering and specializes in the interpretation of advanced deep azimuthal resistivity LWD tools of all vendors. Belloy Petroleum Consulting is GazServ's strategic partner for integrated geological and drilling solutions.

Stay tuned, for next articles!

Fig.5 Our Remote Geosteering Centre in Calgary