The Revolution RSS is the only system in the industry rated to 347°F (175°C) and can handle the hostile environment areas of the Haynesville. (Images courtesy of Weatherford)
The learning curve for both operators and service companies was long in 2008, considering the depth of the zones of interest, temperatures, and varying characteristics in different areas of the Haynesville shale trend. Later in 2008 and into 2009, wells are being drilled faster and more economically.

The industry learned quickly that each county or parish presents its own unique characteristics and challenges, such that each could almost be treated as a separate play altogether. For example, an operator can drill in Louisiana’s Caddo and DeSoto parishes with relatively few temperature issues. However, temperature becomes more of a concern in Red River parish and farther to the southwest, in Shelby and San Augustine counties in Texas. These areas are on the very fringe of the Haynesville, where it appears to be the deepest.

Yet one puzzling scenario has shown that the deepest wells are not always the hottest. Two wells in very close proximity can yield a 15ºF difference, with the hotter borehole sitting 350 ft (107 m) total vertical depth higher.

As service companies became more efficient at drilling horizontal wells, a plateau was reached. Instead of performance improving dramatically and cutting numerous days off of drilling time, the time savings became more modest on a well-to-well basis. Operators were now drilling 6,000-ft (1,829-m) laterals in the time previously required to drill a 2,500-ft (762-m) lateral.

Rotary steerables gain acceptance

The maximum temperatures encountered in the Haynesville vary significantly by county and parish.
Rotary steerable system (RSS) technology became an obvious enabler of improving drilling performance. Initially, operators resisted using RSS technology because of its higher cost of deployment and the fact that much was still being learned about the drilling prospects. A few operators who were new to the region used rotary steerables right away in early 2009 and saw excellent results. Established operators were more hesitant to modify their entrenched methods. Eventually, rotary steerables gained wider acceptance and have become increasingly popular for drilling Haynesville wells.

On average, decreases of five to nine drilling days per well have been seen using rotary steerables in various capacities. In addition to the obvious reduction in sliding and consequent increase in average rate of penetration (ROP), there are several other factors making RSS technology a growing favorite in the Haynesville.

Those factors include:
• LIH exposure. Mud systems have been perfected to a point where it is very rare to see a “sticky” hole or lost-in-hole (LIH) occurrence, making the risk of putting high-dollar equipment in the borehole much more acceptable;
• Hole quality. Rotary steerables reduce “ledging” and create a smoother radius dogleg severity while improving hole cleaning;
• Running production casing. The inherent “gun barrel” hole produced by a point-the-bit RSS allows better centralization and cementing, which significantly reduces risks associated with running the production string;
• On-the-fly steering. Using negative pulse telemetry, the rotary steerable can be controlled while on bottom by varying the rotary speeds to reduce time spent setting the tool. Time saving is significant compared to the traditional method of orienting with a mud motor. The tool face orientation of the RSS can be controlled either by a negative mud pulse surface to downhole controller or by varying the rotary table speed while off bottom;
• Longer laterals. Unlike conventional mud motor assemblies, RSS do not require high weight to the bit. RSS are much more efficient at transferring weight to the bit than oriented drilling with a conventional steerable system using a mud motor. As a result, the operator can drill significantly longer laterals, which equates to more pay in a single well bore with much less torque;
• Longer life expectancy. Long mud motor runs are rare at high temperatures. Conversely, a rotary steerable can drill the lateral from landing point to total depth (TD) in one run, usually eliminating two or three bottomhole assembly trips. It is believed that soon an RSS will be able to drill a Haynesville well from kick-off to TD in a single bit run; and
• Sensor package closer to the bit. Because rotary steerables are shorter than mud motors, the formation evaluation and directional packages are located closer to the bit, allowing for more effective geosteering.

Currently, rotary steerable technology does not allow for doglegs greater than 8º to 10º per 100 ft (30 m). Some operators initially balked at of the thought of sacrificing some vertical section to use a rotary steerable. Very quickly, however, they realized that the benefits of the technology far outweighed losing some vertical section footage. Additionally, it was much easier to get the production footage on the back end of the well due to the rotary steerable’s ability to drill longer laterals.

Next steps

Although a thick shale formation may be initially viewed as homogeneous, this is not necessarily the case, especially when drilling horizontally or parallel to the bed boundaries. Instantaneous ROPs are sometimes unpredictable due to silt stringers and whether calcite or pyrite is encountered. To address these issues, the next step for Weatherford in its Haynesville RSS strategy will be to insert a mud motor in the string using its proprietary DualPulser wireless telemetry technology. The higher RPMs generated by the mud motor could allow for faster ROPs in the curve and lateral sections.

LWD

The Haynesville shale may be faulted in some areas, and knowing where these faults are located is important, especially to the completions group. Using Weatherford’s high-temperature azimuthal gamma ray logging-while-drilling (LWD) sensor, a real-time and recorded octant image is available. These images are invaluable in choosing bed boundaries and dips and in possibly identifying faults without running expensive logging suites.

Typically, while drilling a conventional horizontal in a sand formation bounded by shale, the sweet spot is obvious when using a passive gamma ray sensor. When drilling a shale formation, it is harder to determine the sweet spot without using additional formation evaluation sensors. A traditional gamma sensor measures the natural radioactivity in a formation. Shale naturally gives off higher radiation due to the uranium, thorium, and potassium elements present in the rock. A spectral azimuthal gamma ray (SAGR) sensor measures the three components independently. It has been discovered in the Barnett Shale that uranium content is much higher at intervals that are more conducive to producing natural gas. The SAGR sensor can possibly be used to identify these zones in the Haynesville Shale.

Drilling mechanics sensor packages have proven successful in the Haynesville as well. A bore and annulus pressure sensor has been useful for several operators to dial in the appropriate mud system characteristics. Due to the high temperature in some regions, the mud properties at the bottom of the well bore were not acting as they were modeled. This sensor allowed some experimentation in real time and has improved ROPs and hole cleaning, especially in long laterals.

Slow drilling in the Travis Peak has been a specific topic of performance improvement. Weatherford’s tri-axial vibration monitor has been used to track downhole vibration and RPMs while varying surface weight-on-bit and RPMs to determine the optimum combination and yield the fastest ROP possible. The company also has worked with several operators in developing an ultra-slow-speed motor to optimize drilling the Travis Peak formation with one or two bits. This represents a dramatic performance increase considering that some areas of the Travis Peak once required four to five bits and many days to drill a well.

The Haynesville is becoming more cost-effective to drill and produce. As the service sector strives to improve performance and introduce new technologies, operators ultimately benefit. The quick learning curve and successes to date have resulted from operator/vendor partnerships and trust, which are testament to the adage that, in the end, it takes the operator and service company working together to drill a successful well. Nowhere is this more evident than in the Haynesville Shale.