Operators of unconventional plays today are drilling more extended-reach drilling (ERD) wells, often combined with multilaterals, hoping to reduce total well count without sacrificing production. However, drilling numerous ERD wells on an urgent schedule can dramatically increase operational complexity. Technical challenges include identifying the most productive zone within a reservoir, designing the optimal well plan, and geosteering the bit to ensure maximum reservoir contact.

Along a 3,000-m to 6,000-m (10,000-ft to 15,000-ft) well path through a long, thin shale bed, there are plenty of opportunities to wander from the sweet spot and reduce overall producibility. For this reason, many operators are looking for effective geosteering tools they can apply to ERD wells in unconventional plays.

Three geosteering solutions

Until recently, two primary geosteering options have been available to choose from: high-end services or low-end software tools. Consultants with large oilfield service providers offer sophisticated geosteering services using advanced proprietary systems. Operators of very costly wells rely on these high-end services to position complex well bores in thin target zones having significant potential . Such services can be extremely effective, but they may be too expensive for many unconventional drilling campaigns. Moreover, these geosteering systems are not commercial, so operators cannot bring them in-house.

On the other hand, low-end geosteering software tools are available to correlate gamma ray curves from LWD data in an ERD well bore with a type log from an offset well. Some of these geosteering applications are available commercially, while others have been developed internally by oil and gas companies.

Though they provide valuable tools, many have significant limitations. Most, for example, are standalone software packages lacking a common underlying database. As a result, users cannot incorporate vital seismic data or link directly with mapping software. They must import, export, and reformat data for use in other standalone applications, so subsurface interpretations cannot be easily updated during real-time operations. When expected target depths are incorrect, the drill bit may exit the most productive reservoir zone numerous times, lowering ultimate recovery. Because unconventional drilling is so fast-paced, geotechnical professionals struggle to capture new information from one well and use it to guide subsequent operations. Typically it takes too much time.

Fortunately, a third type of geosteering solution is emerging. As part of an integrated multi-domain workspace for asset teams, this new geosteering approach combines next-generation interpretation, mapping, horizontal well correlation, and well planning technologies with a comprehensive data management system to improve ERD in shale plays. Integrated workflows allow geoscientists and engineers to build a dynamic 3-D framework, plan optimal ERD wells in correct spatial context, and update both the subsurface model and look-ahead well plan during real-time geosteering operations. These new capabilities enable operators to keep the drill bit in the sweet spot, even in long, thin formations.

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Iteratively adjusting targets revises the look-ahead well plan, keeping the well in the sweet spot and guiding subsequent well operations while developing the field

Next-generation geosteering workflows

Real-time geosteering workflows within a unified workspace begin with construction of a dynamic 3-D subsurface model prior to drilling. New tools and automated processes enable geologists and geophysicists to build a geometrically correct 3-D “framework” – a consistent series of structural and stratigraphic surfaces properly integrated with faults – while they are interpreting well and seismic data. Subsequent real-time geosteering workflows leverage this integrated, multisurface framework, which includes a powerful capability called dynamic updating or “automated workflow re-execution.” With this capability, changes made to one part trigger instant and automatic revisions to the entire model. Since all surfaces within the 3-D framework are integrated, any change made to one surface – repicking a top, shifting an unconformity, or adding a new data point during geosteering — dynamically cascades throughout the model, updating every associated surface while honoring all the hard data.

After building the 3-D subsurface model, asset teams use collaborative well planning tools to automatically generate and visualize any number of pad and horizontal well plans in proper geologic context. A scenario planning engine tests various well spacings, azimuths, and wellbore lengths and optimizes the number of wells per pad and pads per lease. One feature that can assist with geosteering operations is the look-ahead well plan, which indicates where the well bore will go if it proceeds along its current trajectory.

Once drilling operations have begun and the bit lands in the target reservoir, operations geologists can leverage the 3-D framework, dynamic updating, look-ahead well plan, and horizontal well correlation technology to maximize reservoir contact.

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Adding new horizontal well correlation points to an integrated 3-D framework automatically updates target reservoir maps while drilling. (Images courtesy of Landmark Software and Services)

New horizontal well correlation (HWC) software generates predicted well log curves for the active portion of the horizontal well bore based on a type log in the pilot hole or an offset well. While drilling, the HWC tool compares the real-time LWD curve with the predicted curve. The unified workspace displays correlations in linked 2-D and 3-D views of the subsurface along with interpreted seismic data where available. Curves that do not match help identify local, and often unexpected, variations in formation dip that directional drillers must quickly take into account. Geologists can manipulate the structural framework until points on the two curves match, enabling them to pinpoint the current stratigraphic position of the well bore. The software uses each new LWD correlation as a hard data point to trigger an update of the entire 3-D subsurface model, automatically shifting top and base maps of the target reservoir up or down accordingly. If an unexpected sub-seismic fault is encountered while drilling, adding the fault pick also dynamically re-grids all affected surfaces.

Automatically updating the structural framework means the positions of predetermined targets within the reservoir also need to be revised. Targets that are too high or low can be fine-tuned simply by moving them onscreen. In this case, the integrated well planning module immediately projects an updated look-ahead well path from the current bit location to the optimal target location ahead of the bit. Alternatively, geologists and engineers can establish a set distance between the well path and a local reference surface such as the top of the reservoir. Any time new data points modify the structural interpretation, the software automatically revises the 3-D framework, the targets, and the look-ahead well plan to maintain the proper distance without any manual intervention whatsoever. By incorporating new horizontal well correlations while drilling, reinterpreting the structure, and iteratively updating the well plan, asset teams can stay in the sweet spot all the way to total depth.

The ability to track subsurface formations in real time and steer the drill bit through the most productive zone also is essential to technical and financial success. With next-generation geosteering solutions, not only can operators maximize individual well productivity, but they also can dynamically update formation maps on the fly and capture new knowledge rapidly enough to boost the accuracy of the next well in the campaign, no matter how fast-paced the activity.