By Dan Geary, Gavin Fluke, Jeff DeJarnett, Callie Brehm, Kara Syvertsen, Marc Russell, Kit Clark, and Demola Soyinka, Anadarko Petroleum Corp.; Jeffrey Kok, Eric Vauter, Chad McMillan, and John Taylor, PathFinder, a Schlumberger company; and Judd Tudor, April Wisebaker, and Stephanie Chow, Schlumberger

The Permian Basin of West Texas and New Mexico is a prolific area of brownfield hydrocarbon reservoirs. It comprises several component basins, of which the Midland Basin is the largest and the Delaware Basin the second largest. The Delaware Basin contains the Bone Spring formation, which has been producing oil and gas for decades. This heterogeneous formation, composed of interbedded sandstones, carbonates, and shales, has enjoyed several cycles of E&P attention.

Conventional-quality sandstones were the first targets. High-rate wells were then brought in from carbonate lenses, followed by a spate of vertical drilling in low-permeability sandstones. Horizontal drilling now is tapping accumulations in thin sand formations, shales, and other tight facies. There were more than 30 rigs working in the Bone Spring formation during 2010, targeting intervals including the Avalon shale; Leonard shale; and the 1st, 2nd, and 3rd Bone Spring sand reservoirs.

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The Delaware Basin lies in West Texas and New Mexico. (Images courtesy of Schlumberger)

Developing The Bone Spring Sands

Anadarko Petroleum Corp. has been particularly active in the 3rd Bone Spring sand, a sand-silt sequence which, although possibly eolian in source, was deposited in relatively deep water. As many as eight separate reservoir sand units, typically ranging from 6 to 12 ft (2 to 4 m) in thickness, historically were bypassed because of lack of production in vertical wells. To produce economically, these beds require maximum reservoir contact from a horizontal well path within a single thin layer and then stimulation to commingle the multiple reservoir layers.

Initially, the curve and lateral sections were drilled with mud motors and geosteering decisions based on standard MWD gamma ray measurement. Initially, it took 72 days to drill the well from spud to rig release. For maximum wellbore contact within these thin reservoirs, distinct log responses across the reservoir are needed for lateral correlations and well trajectory steering. Along with many reservoirs in the Permian Basin, the Bone Spring sands commonly exhibit low reservoir bed-to-boundary resistivity contrasts (usually as low as a 2-ohm difference), with few, if any, features within the bed that standard gamma ray measurements can differentiate. This has frequently resulted in the well bore steering out of zone, often requiring openhole sidetracks or long out-of-zone intervals to re-enter the reservoir.

Vertical sections of Bone Spring wells encounter hard abrasive rocks and are prone to deviation from the intended trajectory while drilling. Anadarko has fine-tuned its drilling processes and bit selection methodology to deliver time- and cost-effective solutions for the well-construction phase. The company recognized that by using a rotary steerable system (RSS), it could accelerate drilling in lateral sections. It outsourced this phase of well construction to a specialized drilling contractor, including deployment of the Schlumberger PowerDrive X5 RSS.

Deep Azimuthal Resistivity Measurements


To improve horizontal drilling efficiency, Schlumberger applied its deep azimuthal electromagnetic resistivity LWD system, called the PeriScope bed boundary mapper. This tool makes 360-degree deep directional measurements that can indicate the distance to and orientation of formation boundaries 21 ft (6.4 m) from the borehole using a combination of tilted coil technology and multiple frequencies and spacings. Conventionally requiring a degree of change in formation property response for steering applications, these deep directional curve measurements are considerably more sensitive to provide more information than is possible when using conventional MWD systems in low-measurement-contrast reservoirs.


During drilling operations, LWD measurements are transmitted in real time to the surface. These unique symmetrized directional measurements, with maximum sensitivity to formation or fluid boundaries, make it possible to map boundaries in real time, independent of anisotropy and dip. Real-time bed mapping and curve interpretation are performed by expert well-placement engineers with proprietary geosteering software called real-time geosteering software (RTGS). The system helps to place laterals accurately within thin target reservoirs, reducing the potential for costly sidetracks and improving drilling efficiency and lateral exposure in zone for optimum completion and production.

Building Geological Knowledge


Knowledge gained from interpreting real-time LWD data has not only been used for proactively geosteering to stay in zone but also has contributed to updating geologic models to improve overall understanding of reservoir morphology and plan future well path trajectories.

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Boundary detection based on azimuthal resistivity curves was used to generate the boundary mapping PeriScope inversion canvas with RTGS. Note the flat resistivity and gamma ray response across the target interval and also the difference between planned and drilled trajectories.

The Bone Spring sands have been found at similar depths in many wells across West Texas and were assumed to be relatively flat. However, with growing experience, it is clear that the formations exhibit considerable local structural variation with significant differences between wells spaced closely together, making it impossible to predict optimum well trajectories without a high degree of uncertainty.

Beyond Technology


Major improvements in drilling efficiency were achieved in the Bone Spring through the application of optimized technology, but these improvements would not have been possible without highly dedicated people and the continual fine-tuning of processes. Close collaboration among drillers, engineers, geologists, and other geoscientists within Anadarko and the service company has been a key contributor to success, along with consistency within the team. Drilling engineers and other crew members have been dedicated to the project for long periods of time, enabling them to share and build expertise and learn from experience.


Schlumberger drilling engineering experts have provided 24/7 support for operations, from developing initial well plans to preparing post-project reports. These experts were both local – i.e., Oklahoma City, Okla., and Midland, Texas – and around the world. All team members have been able to share data through the InterACT secure connectivity, collaboration, and information system irrespective of their location.


Dedicated operations support has helped to drive continuous improvement in drilling efficiency through improved processes and identifying the most fit-for-purpose technology. Several benefits have been realized through changes to bottomhole assembly components, such as identifying drill bits that are more resistant to abrasion in this particular geological environment.


Bed boundary mapper azimuthal measurements, combined with the use of an RSS in the lateral, have enabled wells to be placed accurately within thin target sand layers that differ significantly from prognoses. To date, more than 97% in-zone has been achieved from all laterals drilled, with no sidetracks required.


Growing experience in the Bone Spring area has led to the identification of an optimized drilling target window within some sand units. Drilling within this window helped mitigate high shock and vibration to the tool string, allowing the operator to optimize drilling mechanics and improve drilling ROP, maximizing efficiency.


Prior to deploying RSSs and bed boundary mapping technology, wells could take more than 70 days from spud to rig release. Using the technology to steer in-zone, this quickly dropped to around 51 days and has continued to improve. Best composite time targets have been challenged and reduced for subsequent wells. The latest record for spud to rig release of a well was 25 days.