Drill Well on Paper (DWOP) meetings are held, a wide range of data is shown, however after the meeting some of that data is rarely referred to again until trouble arises during drilling.  Constant review of data and input from members of the development, drilling and completion teams throughout the well will achieve the best outcome.  Keeping open lines of communication is a key factor while drilling.

Today we take for granted that data is easy to share and we sometimes assume that everyone on an asset team (including service providers supporting the team) have access to it.  This is not always the case.  We find that during troublesome wells other data becomes available that could have resulted in a better steer or potentially avoided a hazard altogether.  Additional type logs, seismic sections, cross sections, cutting, reports, etc. are reviewed in order to figure out where we went wrong and where to go next.  It’s best to use this information prior to spudding and through out the drilling operations to anticipate anything that could hinder an ideal lateral placement.  Data and good planning allows the team to be proactive and increases the wells overall chance of success.

Sometimes various professions rely much too heavily on one piece of data and make all decisions based solely on it.  All forms of data have different strengths and weaknesses and should be weighed for their pros and cons.  Sharing data with the team and keeping open and active lines of communication will lead to better results.

Geosteering is best suited to low-energy deep marine deposits (i.e. unconventional shales). In these depositional environments, lithology and thicknesses are typically very consistent therefore one can expect rather smooth continuous correlations with transitions in API values more gradual as the wellbore cuts through different lithologies. Therefore, one way of detecting faults via geosteering is to look for sharp changes in gamma ray character corresponding to a “break” in the correlation.

Identifying a fault while geo-steering example:

Data are correlating well to the type log and up-hole data producing high confidence in stratigraphic position and formation dips up to this point.

2 survey points (179’) correlation falls apart with a sharp “knife edge” change in gamma character from high to low API readings, therefore a fault is hypothesized. Notice that I am careful with my verbiage by selecting the word hypothesized as multiple different factors can cause this same sharp knife edge change in gamma character such as the MWD tool not being calibrated after Bottom Hole Assembly, tool failure while in the hole, erroneous MWD data, crossing naturally sharp vertical facies changes (i.e. clean blocky sand overlain by a hot shale), etc. Therefore, it is important to recognize if you should be anticipating faults in the area that you are drilling in based on your models.

So now the easy part is done and we have identified a potential fault. Now we are faced with the challenge of deciding on where to offset the data on our type log post faulting. A great way to do this is instruct the directional driller to either cut up or down section with steeper drilling inclinations than anticipated formation dip. This is where having sound geological knowledge/models of the area is critical. If you cross a down-faulted block this will place the wellbore higher in section across the fault boundary, therefore you’ll want to cut down stratigraphy to aid in tying back into your type log with confidence, and vice versa for crossing an up-faulted block. In this example we know to expect normal faulting with down-faulted blocks heading south, therefore the rig is instructed to slide down with steeper inclinations than anticipated. As they slide down section and more data comes in, we are able to resolve stratigraphic position after the fault as the data starts correlating well to the type log/up-hole data. In this case a 25’ fault was interpreted and identified using geosteering methods.

As shown above, geosteering is an extremely powerful tool that can be used to identify faults on the fly in the subsurface. If faulting is expected/known in an area that has already been developed using horizontal wells, one can do look-backs on the area using geosteering to refine models to include faults that may have been missed.

One of the first concepts we learn in university, as geology students, are Steno’s laws of Stratigraphy. Basically, these four laws describe patterns in which sedimentary rocks are deposited. One of the four laws; the law of lateral continuity can have major implications when it comes to geosteering. Particularly when geosteering horizontal wells in formations where the sedimentary layers may not be as laterally continuous as we may see in formations such as the EagleFord. The Middle Bakken of the Williston Basin is one such formation where we see relatively small-scale changes in the lateral continuity due to the ancient depositional environment. On the large scale, we can see markers such as the Upper and Lower Bakken tops that extend laterally for long distances. However, due to the relatively small-scale lateral variability of the Middle Bakken, it can be difficult to know exactly where we are vertically, when drilling long horizontal wells. Having experience in the Middle Bakken, and expecting to see these changes along the course of the lateral helps geosteering professionals navigate the complexities of drilling long horizontals in the Williston Basin. Correlating large-scale trends and not getting bogged down correlating every little change is just one method that can be used to accurately steer the Middle Bakken Formation of the Williston Basin.

Because of the lack of character through most of the formation, staying in-zone can be a struggle, as geosteering becomes difficult. Therefore, the cleaner gamma ray and slightly higher resistivity of the limestone directly above the characteristic interval are utilized as benchmarks to solidify the geosteering interp.

By specifically placing a drill window above/below these distinct benchmarks, and intermittently targeting them during drilling, geosteering can present an accurate and high confidence interpretation of the apparent formation dips. This translates to a useful drilling target, less chance to get too high/low in formation and require a side track, and a higher in-zone completion percentage.

Figure 1: By strategically targeting the clean limestone benchmarks just outside the zone (blue arrows), drilling was able to provide steerable data to the geosteering team. With the distinct gamma ray traces, geosteering was able to confidently interpret structure, and provide useful target information.

A perfect example of this is pictured below. In this well, the client had strong vertical offset well control near the heal and toe, this led to an over confident position in the average formation dip, and in turn the expected apparent dips. The drill plan is the blue dashed line, and the geosteering interpreted apparent dips in black. In terms of drilling, the team was very successful in staying on target, unfortunately the geology did not follow this target. Pre-drill planning calculated an expected average dip of around 1.3°. The actual average dip of the interpretation ended being not far off, roughly 1.25°. The unexpected undulating and faulted structure, coupled with the operator’s reluctance to deviate from plan and follow apparent dip, resulted in a poorly drilled section, and a final in-zone wellbore percentage of 31%.

This could have been easily prevented. Instead of over confidently following the plan, regardless of the geology. Higher value should have been placed in the LWD data collected, and interpreted by the geosteering. Especially when geosteering can present a high confidence correlation.

 Figure 1: An operator’s reluctance to deviate from plan, despite high confidence geosteering suggestions, led to poor in-zone percentage.

 (BC1H)

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Early 2016 has been dedicated to visiting clients, promoting our services, listening to feedback and speaking with industry professionals. This has left us feeling optimistic about the future and armed with ideas to further our success in all things geo-steering.

In addition to continuing to expand our geo-steering knowledge and experience, our Geo-Direct software has been under constant development with our experts. Our latest release features numerous user-friendly developments, including backward and forward projections.

Expect to see us in Calgary at the AAPG ACE, slated for June 19-22 at the BMO Centre. As always, stop by to take our software for a test ride and learn about our services.

Our team hit the ground running this year, perfecting our geo-steering services and further improving our innovative Geo-Direct geo-steering software.

We’ll be bringing our expertise to Houston, TX, for NAPE Summit (Feb. 10-12 at the George R. Brown Convention Center). Come by our booth to learn more about our services and software, and to have all your geo-steering questions answered by our professionals.

From there, we’ll be off to Calgary’s GeoConvention (March 7-9).

Make sure to stop by and visit us at either of these events.