A new control system for managed pressure drilling (MPD) is reducing drilling time significantly compared to planned drilling time on wells in the Haynesville shale. The drilling improvement in the Woodardville field in northwest Louisiana's Red River Parish is the result of faster ROPs and lower nonproductive time (NPT) achieved through the precise monitoring and characterization of very small changes in wellbore pressure and fluid flow. The control system also is enhancing wellsite and personnel safety and reducing risk to the environment.

The computerized MPD control system uses proprietary algorithms to identify bottomhole influxes and losses in the

The main objective was to reduce drilling days with more precise mud weight management. The chart shows actual days to TD for the last hole section compared to planned number of days to drill. This represents a reduction of more than 40% and has been repeated on multiple wells in the area. (Images courtesy of Weatherford International Ltd.)

circulating system. Detection of abnormalities is achieved in real time in a matter of gallons versus barrels. These volume changes, typically less than 20 gal, along with small variations in pressure, are communicated to the driller and MPD system engineer in seconds. Data speed and accuracy are helping wellsite personnel make real-time drilling decisions to precisely manage wellbore influxes and losses before they become a well control event.

As a result of this enhanced control of the wellbore pressure profile and management of equivalent circulating density

(ECD), mud weights in the Woodardville field are being optimized safely to increase penetration rates. In addition, overall rig time is reduced because of less NPT associated with reaction to well-control events. Success in the Haynesville play extends this technology to shale field development applications primarily aimed at optimizing the drilling process and improving safety.

Technology, application objectives
Denver-based Forest Oil Corp. used Weatherford’s Microflux control system in the first application of the technology in the Haynesville shale to reduce drilling time from the planned 31 days to 16 days. Subsequent wells in the drilling program have achieved similar improvements in operational and economic performance.

The Microflux MPD technology operates in a closed-loop circulating system where a rotating control device (RCD) diverts annular fluids through a choke manifold and away from the rig floor. Within this contained, closedloop environment filled with drilling fluid, real-time changes in pressure and flow are identified quickly, and surface and downhole events are easily distinguishable. Using this information, wellbore pressure is controlled by managing annular backpressure with a special automated choke manifold.

Simultaneous surface gas was detected along with a strong downhole influx/kick while drilling in the lateral section. Pressure was added with choke movement (green line) to build surface backpressure, thus minimizing influx volume, and
containing the kick. The application of surface backpressure (as indicated by the white line SBP) also allows bottomhole pressure to be maintained at equivalent pressure levels prior to the influx event.

The system was developed for applications ranging from early kick and loss detection to full constant bottomhole

pressure MPD applications using mud densities that create underbalanced hydrostatic heads when not circulating. Since its initial release, the Microflux MPD system also has been used in pressurized mudcap drilling operations. The system is proven on land, jackup, and offshore floating applications in exploratory, development, and depleted field applications. Globally, more than 80 wells have been drilled successfully using the technology, some of the most challenging being HP/HT applications.

Dynamic wellbore management through precise determination of downhole pore and frac pressure is the main objective in extreme HP/HT applications. An additional benefit has been the enhancement of routine drilling operations such as penetration rates and drilling efficiency by dynamic management of the mud weight and ECD.

Haynesville development wells provided an opportunity to apply these capabilities as the primary objective. The area already has experience with some aspects of MPD systems. Drilling operations commonly use an RCD in a closed-loop drilling system to enhance safety. At times this involves controlling annular backpressure through a manual choke.

The Microflux system provides a stepchange in the capabilities of traditional systems with a high level of precision

After influx occurred, pressure was held on connections (indicated by white line surface backpressure building, due to choke closure indicated by the green line) ensuring no downhole pressure cycles occur. After six connections and no further well influx, events returned to normal connections no longer holding backpressure on connections.

attained through instrumentation and software. The new level of insight into the wellbore environment provides more accurate control achieved not only through the identification and verification of influxes and losses but through feedback on the resulting response and validation of the well.

Planning for Woodardville
Woodardville field drilling operations were approached as a collaborative effort to assess the technology’s capabilities in the Haynesville shale. The system’s speed and precision presents optimization opportunities that vary with specific reservoir characteristics. Precise wellbore information allows the drilling operation to employ an adaptive set of operational procedures that are more responsive to wellbore conditions. As a result, drilling plans are easily adjusted at the well site to suit changing wellbore conditions.

Using the capability took special training. Open communication and constant interpretation were critical to developing and employing the adaptive operating procedures employed by the Forest Oil drilling team.

To effectively use the more accurate and immediate data generated by the system, engineers had to be prepared to actively manage the drilling plan in response to actual conditions. An important aspect of the response was training drilling personnel so procedures could be adjusted as real-time wellbore pressure and flow data were acquired. Quick, precise identification of drilling hazards and events resulted in significant changes in the drilling program, from mud weights to kick response, when compared to previous offset well drilling programs.

Drilling the wells
The key to improving ROP in Haynesville drilling was reducing weight. Early kick and loss detection achieved with the Microflux MPD system provided the capability to lighten the hydrostatic head safely, which reduced mud weight and provided continuous well monitoring and the acquisition of highly accurate pressure readings and ECD calculations at various depths.

Unconventional gas wells in the Woodardville field target the Upper Jurassic formation. The significant microfracturing in the formation that results in high porosities and permeabilities typically causes overpressured zones that are a persistent drilling concern. While drilling, low-volume high-pressure naturally fractured intervals were encountered. The Microflux system easily detected and allowed depletion of natural microfractures in a controlled and safe manner.

The plan for the first well in May 2010 involved drilling the 61?8-in. hole section from 10,712 ft (3,265 m) to 17,230 ft (5,252 m) total depth (TD). A kickoff point was drilled out of the 7-in., 26 lb/ft casing shoe at 10,712 ft, and a leak-off test of 17.5 pounds per gallon (ppg) was performed at the casing point.

While previous wells had been drilled out with 16.5 ppg oilbased mud (OBM), use of the Microflux system led to exiting the shoe with 14.8 ppg OBM with the objective of holding that mud weight to TD. Drilling proceeded with hole angle built at 8 degrees/100 ft (30 m) to horizontal.

The lower mud weight improved ROP. While previous wells were drilled at 12 to 15 ft/hr (4 to 5 m/hr) with 16.5 ppg mud, the reduction to 14.8 ppg increased average ROP to 40 ft/hr (12 m/hr).

While gas presence was significant during operations, drilling was routine, and the system performed as planned without a well-control event. During drilling, the system clearly and accurately identified small, routine variations such as connection gas and other standard oscillations in pressure and flow.

The well reached TD in 16 days versus the planned 31 days, even with two days of NPT recorded due to unrelated rig problems. In addition to faster drilling, there were associated savings in fluid costs due to lower mud weight.

Within one week, the system was deployed on a second similar well in the field, also to drill the 61?8-in section. This application more clearly demonstrated the value of the Microflux system in early kick detection and safe response.

An influx of hydrocarbon was detected while taking gas-cut mud returns. The influx was minimized by managing surface backpressure with the Microflux control system’s automated control of the chokes. The gas was circulated out of the well bore in a controlled manner.

Drilling ahead
With the success of these early wells, Forest Oil has deployed the system on other rigs working in the area and had drilled four wells by mid-August 2010. Positive results mark a new phase in the application of the Microflux technology focused on safety and efficiency in development applications.