Arctic and drilling efficiency stretch drilling technology

With Shell Oil beginning its drilling operations in the Chukchi and Barents seas offshore Alaska and ExxonMobil tying up with Rosneft for Arctic research, the industry is moving into even more harsh climates in pursuit of oil and gas reserves. Innovators are trying to anticipate what the industry will need for the Arctic climate. At the same time, deepwater drilling and production is escalating in areas offshore West Africa, East Africa, Brazil, and the US Gulf of Mexico (GoM). Safety is being emphasized in these regions with the best exploration targets.

In many of these areas, deeper reservoirs bring added challenges with high temperatures and high pressures. The industry is tackling these problems with new downhole tools designed to improve operating efficiency in harsher environments.

Also, the increased interest in shale plays worldwide has the industry devising new tools and techniques for maximizing production from those formations.

Arctic drillship

The world’s first ice-class drillship, Stena IceMAX, drilled its first well offshore French Guiana for Shell Oil. (Image courtesy of Stena Drilling)

The first ice-class drillship was built for Stena Drilling by Samsung Heavy Industries at its Geoje shipyard in South Korea. Stena was awarded a five-year worldwide drilling contract by Shell for the newbuild Stena IceMAX, which will be the world’s first dynamically positioned, dual-mast ice-class +1A1 drillship.

The vessel is designed for safe and efficient operations in Arctic conditions. It has a displacement of 98,000 metric tons, an overall length of 228 m (752 ft), and a breadth of 42 m (138.6 ft). The unit is capable of drilling to a total depth of 10,700 m (35,310 ft) in water depths of 3,030 m (10,000 ft) and has accommodation for 180 people with state-of-the-art facilities.

Shell contracted the vessel for five years. The rig drilled its first well in deepwater offshore French Guiana.

Drilling fluids

Guar substitute developed. A guar substitute that addresses two problems – residue from the guar bean and guar supply uncertainty – was developed by Halliburton. The company went to the marketplace and found a polymer that is effective, mimics the behavior of guar systems, and leaves no residue, which is the basis of a product called PermStim.

Ward Dempsey, product champion, Production Enhancement, Halliburton, said, “We also needed good proppant transport because we need to place a lot of sand in those fracture networks. We needed low fluid leak-off to get the frac width. And we needed a good source of supply.”

Halliburton began a controlled introduction of PermStim, starting in the Rocky Mountain region with 29 vertical wells in the DJ basin followed by 40 horizontal wells in the Williston basin and 20 wells in the Green River basin.

The polymer was used by Halliburton in Magnum Hunter Resources Corp.’s wells in the Eagle Ford, resulting in higher flowback and improved production. H.C. “Kip” Ferguson III, executive vice president, Exploration, Magnum Hunter, said, “In adding a PermStim system, we are able to document and figure out how much added advantage we get with clean fluid and less residual fluid. Bottom line, we added about a 20% increase over our average IP [initial production] for our operated wells, which is amazing.”

High-temperature drilling fluid. Another drilling fluid was introduced this year that comes from Schlumberger’s M-I SWACO for new ultra high-temperature applications. The Rhadiant ultra high-temperature nonaqueous drilling fluid system eliminates drilling fluid product degradation, prevents wellbore control issues such as barite sag, and provides a thin filter cake for enhanced logging conditions.

“With wellbores approaching the 260°C [500°F] threshold, there is a need for a drilling fluid that can remain stable and deliver consistent performance throughout the processes of well construction and open-hole logging,” said Joe Bacho, president, M-I SWACO.

The Rhadiant drilling fluid system is specially formulated to maintain a stable rheological profile with little maintenance required. This drilling fluid system maintains extreme temperature stability even during prolonged static conditions. Stable rheologies in tandem with ultra-thin and slick filter-cake deposits clear the path for logging, casing, and cementing operations, according to the company. These characteristics enable accurate perforation placement, optimized completions, and quality reservoir characterization.

Coiled-tubing drilling

The final two wells of a five-well coiled-tubing drilling (CTD) campaign in shallow reserves of the Kansas Niobrara formation on the Kansas-Colorado border were successfully drilled using drilling mud in the vertical bore and air in the horizontal lateral, according to AnTech Ltd.

The build sections of the final two horizontal wells were drilled with mud using an 8½-in. bit. The horizontal sections were drilled with an air mist using a 6?-in. bit. Air was used for these wells because the formations were highly fractured and were unable to hold the pressure of a liquid column.

The first horizontal well was drilled to 332 m (1,090 ft) true vertical depth (TVD) with more than 442 m (1,450 ft) of lateral displacement. Another horizontal well was drilled to 334 m (1,096 ft) TVD with a lateral displacement of 336 m (1,103 ft).

This is the first time that a solid-state gyro has been used for directional measurement while drilling, providing reliable data at all inclinations (vertical, horizontal, and during the build section), which allows orientation to be carried out accurately even while in the casing, according to the company.

Downhole tools

Combination directional accuracy. For optimizing well placement in target zones, PathFinder, a Schlumberger company, introduced the iPZIG at-bit inclination, gamma ray, and imaging service for early bed boundary detection.

Developed specifically for unconventional oil and gas markets and high-efficiency drilling applications, the service allows greater directional control and accuracy while drilling with sensors placed directly behind the drill bit. Changes in lithology and bottomhole assembly orientation are identified, and steering decisions are made to stay in the production zone longer.

“The iPZIG service is the only tool to provide total and imaged natural gamma ray data with dynamic inclination measurements at the bit,” said Derek Normore, president, PathFinder. “Geosteering adjustments in the well trajectory can be made quickly, which reduces directional drilling risks and allows optimal well placement in critical hole sections.”

The service has been successfully field-tested in coalbed methane, heavy oil, and shale plays in North America and Australia. Geological features identified from the real-time images aid in the geosteering interpretation, the company said.

Controlled frac initiation. By using openhole packers to isolate multiple stages and ball-activated sleeves to divert the fracing treatment into the formation, Baker Hughes developed its DirectConnect to control hydraulic frac initiation points and allow increased contact with the reservoir.

A single ball opens five sleeves per stage, with each sleeve including eight DirectConnect ports that are placed 45° apart. After the ball is dropped, the sleeves open, and hydraulic pressure pushes the telescoping ports into the formation at high velocity. The ports act like chisels to initiate fracs at controlled points along the wellbore. Operators can frac through five sleeves per stage with as many as 17 stages per well, connecting the well with the reservoir through as many as 85 sleeves and 680 ports, Baker Hughes said.

Drill bits

Drillable casing bit. As part of its drilling-with-casing (DWC) system, Weatherford designed its new Defyer DPA drillable casing bit specifically for operators charged with overcoming drilling hazards in hard, abrasive formations. The drillable bit helps extend drilling operations to deeper, harder formations at longer intervals without compromising ease of drilling out the casing bit.

The bit eliminates the need for both dedicated drill-out trips and deployment of a special drill bit for the next hole section. The DPA series incorporates polycrystalline diamond compact (PDC) cutting elements mounted on steel-alloy blades and is suited for drilling-with-liner and DWC systems in extended intervals. It is constructed with 80% less steel in the drill-out path compared to its conventional counterpart, imparting additional damage protection.

The system increases efficiency, reduces cost, provides hazard mitigation, increases safety, and is extended to a wider range of formation types, the company said. Applications for the DPA include DWC in medium to medium-hard formations and over short sections in hard formations.

The bit also is well suited for drilling or reaming through trouble zones such as unstable formations or intervals with high-pressure transitions. The system can be used to drill through cement plugs and ream casing or liners through swollen or mobile formations while achieving higher rates of penetration and reduced trip time.

Next-generation shale bit. Smith Bits optimized its steel-body PDC bits for curve and lateral drilling performance. The next-generation Spear PDC drill bit is tailored for unconventional shale plays.

Based on the experience of more than 6,000 Spear bit runs to date, “We incorporated specific design elements into the next-generation bit to deliver an even higher rate of penetration [ROP], further lowering drilling costs in unconventional wells,” said Guy Arrington, president, Bits and Advanced Technologies, Schlumberger.

The range of application-specific features includes improved body geometry and hydraulic enhancements that were engineered to minimize blade packing, improve cutter cleaning, increase ROP, and ensure smooth directional control.

For one customer in the Eagle Ford shale, the next-generation Spear bit design was introduced successfully and set a new performance record. The new bit drilled the entire lateral at an average rate of 24 m/hr (79 ft/hr) compared to median performance of 20 m/hr (65 ft/hr), representing a 22% improvement in ROP.

Mud motors, MWD tools steer systems

Using a mud motor with a bent sub and a standard hostile environment logging/MWD system, Weatherford International devised a technique called targeted bit speed, which controls the bit speed by modulating mud flow. (Image courtesy of Weatherford International)

As an economic alternative to rotary-steerable systems, Weatherford developed the MotarySteerable system to capitalize on two well known directional drilling tools – mud motors and MWD tools – while still offering many of the inherent benefits of rotary-steerable systems (RSSs).

The system consists of a mud motor with a bent sub and standard hostile environment logging/MWD system. A novel technique called targeted bit speed (TBS) is used to achieve the results. This technique controls the bit speed by modulating mud flow.

TBS essentially reduces the sliding commonly required for directional drilling using conventional mud motors, thus reducing hole-cleaning challenges and limiting the creation of ledges that reduce drilling efficiency. In addition, TBS enables full 3-D directional control and near-continuous rotation of the drillstring in much the same manner as an RSS.

Designed for wells ranging in size from 6 in. to 12 1/ 4 in. and with low build rates on the order of 0° to 3° per 30 m (100 ft), the system helps ensure a higher quality and smoother borehole, even in extended-reach drilling scenarios. The system accomplishes this at a lower lost-in-hole cost risk compared to an RSS. An auto-inclination feature allows automatic switching between conventional and TBS drilling modes.

An operator in the Eagle Ford shale play in South Texas selected the system to provide vertical control in a 9.875-in. horizontal hole section while minimizing rig and nonproductive time. The system drilled from 1,125 m to 2,469 m (3,691 ft to 8,100 ft) in a single run, with an average ROP of 45 m/hr (149 ft/hr). The vertically controlled drilling operation required minimal sliding (less than 4% over the entire well section) and saved the operator more than US $200,000 in rig time, Weatherford said.

LWD

Petrophysical measurements. A sourceless LWD formation evaluation service based on pulsed-neutron generator technology that eliminates the need for chemical sources was introduced by Schlumberger. The NeoScope technology provides real-time measurements close to the bit to guide interpretation and decision-making in all drilling environments.

“With its compact design and neutron-on-demand technology, this service saves rig time, reduces risks, and provides a comprehensive suite of petrophysical measurements,” said Steve Kaufmann, president, Drilling and Measurements, Schlumberger.

Schlumberger has field-tested the NeoScope service in more than 200 jobs in more than 30 countries in a wide range of formations and environments from tight carbonates to conventional clastics to validate the measurement response. For example, the service was used to acquire a full suite of petrophysical measurements in a directional exploration well in Africa, where poor borehole conditions prevented wireline tools from reaching the entire interval of interest.

The NeoScope measurements acquired helped save the customer seven days by eliminating the time and cost associated with chemical source deployment while providing the data required to successfully evaluate the well.

LWD sonic tool. Because of shale’s ultra-low permeability, achieving economically viable production rates requires horizontal drilling and hydraulic fracing. Horizontal drilling in complex shale reservoirs requires real-time access to downhole data for successful well placement and maximum hydrocarbon recovery, said Weatherford International.

Operators rely on data from LWD tools to identify sweet spots, optimize wellbore placement, and plan the fracing and stimulation programs.

Understanding the geomechanical properties of the shale, which control both the occurrence of natural fracs and the creation of hydraulically induced fracs, is key to successful stimulation and completion of wells in a shale reservoir. Most organic shales exhibit significant anisotropy in the geomechanical properties, showing variations in both the horizontal plane due to variations in tectonic stress and variations in the vertical plane due to intrinsic bedding features of the formation.

The CrossWave LWD sonic tool provides 360° azimuthally focused measurements of compressional and shear wave velocities that allow 3-D characterization of geomechanical properties (Poisson’s ratio, Young’s modulus, etc.) along the length of the horizontal well-bore in mechanically anisotropic shale reservoirs, according to Weatherford. This allows the operator to select the best areas for frac stage placement while optimizing the frac design and execution.

The LWD azimuthal sonic technology has been successfully tested in horizontal shale reservoir wells in the northeastern US, where vertically transverse isotropic shear wave anisotropy of 5% to 50% was clearly measured in the horizontal sections. Borehole images constructed from azimuthal shear slowness data provided a clear visual indication of the orientation and magnitude of the shear wave anisotropy. Compressional slowness borehole images compared with conventional images from LWD azimuthal gamma ray and density tools can provide information on formation dip and the stratigraphic position of the horizontal wellbore, the company said.

Additionally, the measurements provide geophysicists with key anisotropy parameters, complementing data available from vertical wells to provide a complete 3-D compressional and shear velocity model to enhance seismic data processing and interpretation.

Imaging-while-drilling service. High-resolution laterolog resistivity and full-borehole images in conductive mud environments are provided on a single collar as part of the MicroScope imaging-while-drilling service from Schlumberger.

This service, already successful in more than 150 jobs across 10 countries, addresses the challenges in unconventional shale plays, carbonates, and clastic reservoirs. The MicroScope technology was used in a tight gas carbonate reservoir in Asia; measurements facilitated formation evaluation and clearly identified and defined the structural dips, faults, and fracs along the horizontal section in a complex thin dolomite gas reservoir. The well was completed with an IP rate of gas of 4.2 MMcf/d, which exceeded the production goal.

The MicroScope tool acquires focused laterolog resistivity measurements and images at four different depths of investigation with azimuthal sensitivity. These measurements are essential for calculating reserves estimates, placing horizontal wells, facilitating well placement and frac analysis to optimize hydraulic fracing stage designs, and optimizing completion design, the company added.

Drilling riser

Two syntactic foams have been developed by Balmoral Offshore Engineering for use in drilling risers with operating depths to 4,545 m (15,000 ft). The new foams were designed by the company’s technical and engineering teams in Aberdeen as part of an R&D investment program. “Drilling operations in waters of great depths and high currents, such as the GoM and offshore Brazil, demand the deployment of ultra-heavy riser strings,” said Jim Hamilton, Balmoral’s international business development director. “The essential increase in mechanical performance demanded to operate at these depths cannot be accompanied by reduction in available buoyancy. So foam density reduction was targeted alongside mechanical performance improvement.”

The foams are called Durafloat Superlite and Durafloat Superlite-X.

BOP actuators

Internal BOP actuator. Global Drilling Support International designed an advanced, remote, internal BOP (IBOP) actuator based on a design philosophy that emphasizes a simple compact structure with fewer moving parts. The compact footprint of the actuator allows ample room for elevator links to pass. Its three-cylinder design provides uniform actuation.

The proprietary actuator can open and close the IBOP while in rotation, eliminating problems often associated with having to stop rotation before opening and closing. The unit also provides manual operation through actuation cameras.

ROV actuates subsea BOP. A subsea BOP actuation tool was successfully tested offshore West Africa in more than 1,000 m (3,300 ft) of water by Forum Energy Technologies. The tool closes the BOP remotely using a work-class ROV when the BOP cannot be operated by conventional means.

The actuator can be fitted to an ROV skid assembly or directly to the BOP. It is reportedly able to actuate most BOPs in less than 45 seconds to seal the wellbore, according to the company. It can deliver more than 79 gal/min of hydraulic fluid at pressures up to 7,500 psi. Fluids such as seawater, mineral oils, or glycol fluids can be used.