Near-balanced drilling gets increased attention

The IADC Well Control Conference held recently in Houston and the Well Control Workshop held earlier at Louisiana State University, showed increasing interest in using near-balanced, and not necessarily under-balanced, drilling scenarios for the Gulf of Mexico.

The IADC Well Control Conference held recently in Houston and the Well Control Workshop held earlier at Louisiana State University, showed increasing interest in using near-balanced, and not necessarily under-balanced, drilling scenarios for the Gulf of Mexico. The question being asked is: "Will there be enough flexibility in the current federal regulations to effectively evaluate these technologies for application in the Gulf of Mexico?"

Federal regulations allow for new technologies to be used, as long as existing standards are met or exceeded. A US Minerals Management Service representative at the conference emphasized there has been some flexibility already demonstrated to encourage the development of near-balanced drilling techniques. Also, there is a clear message from the MMS that offshore oil and gas operators have been given the opportunity to develop and prove that near-balanced drilling technologies can be used safely.

Technology testing ground shifting to Brazil, West Africa

Recent trends in the industry indicate that the training and development ground for some new technologies, notably near and under-balanced drilling technologies, may be shifting from the Gulf of Mexico and the North Sea to areas such as offshore Brazil and West Africa. Technology advances are coming at a rapid-fire pace to accommodate the much-needed push into deepwater and current regulations in the Gulf of Mexico limit the ability to effectively test these new technologies.

The current safety margin set in the US Code of Federal Regulations for drilling operations well control is 0.5 ppge overbalance. Discussions are currently underway within the MMS to lower this margin to 0.3 ppge, giving operators more flexibility in evaluating near and under-balanced drilling technologies. This is still an over-balanced situation, and eliminates the possibility of testing under-balanced drilling systems. The harder, lower permeability geology of offshore Brazil is an ideal environment for testing near and under-balanced drilling (UBD) equipment and techniques. The argument that the difference in geological environments of the respective areas renders any comparison questionable, isn't really the issue. The underlying issue is the lack of confidence in existing technologies to maintain current well control regulatory guidelines.

This geologic environment will be an excellent proving ground for these new technologies and techniques. Once initial development and evaluation is completed, the West African offshore areas can be considered for further evaluation. The higher permeability geology of this area is similar to the Gulf of Mexico depositional environment, and should yield good comparative examples. Offshore regulations in this area are less restrictive and will give technology developers more flexibility in testing and design changes. The knowledge and experience gained from these areas will play a critical role in the future implementation of this technology in the Gulf of Mexico.

Rotary steerable update:

The rotary steerable tool market continues to grow. Unique designs are offering subtle differences in tool applications. Large and small service providers are working furiously to provide alternatives in this fast developing market. In the feature section of this issue, a case study demonstrates the application of a rotary steerable tool run in conjunction with a conventional mud motor to achieve an aggressive well design. Other applications and tools will appear in later issues.

Vertical rotary steerable kick off in soft formation

A recent well example by Steerable Rotary Tools, a subsidiary of Superior Energy Services, Inc., demonstrated the ability of their steering-while-on-rotary-drilling system (SWORD) tool to effectively deviate a wellbore from vertical, in soft formation.

After directionally orienting to N 78° E, and hydraulically cycling the tool to the directional configuration (kick position), drilling commenced. Low weight-on-bit (WOB) was maintained for the first 60 ft after kick off. Steering efficiency was assumed to be low, based on the weak strength of the formation. Weight-on-bit increased 40 ft later, and drilling continued to the next connection. A measurement-while-drilling (MWD) survey was taken, showing 2.8° of inclination. This survey depth was immediately below the soft formation originally drilled through, implying that low WOB did not completely eliminate the ability of the tool to deviate the well bore from vertical. Drilling continued, with the tool in the straight configuration, to the next drilling connection where another MWD survey showed an inclination of 3.3°. Extrapolation of this survey to the bit estimated the inclination at the bottom of the hole to be 5°.

Operational parameters during this drilling sequence included a pump rate of 300 gpm, surface weight on the bit of 20 klb, and a rotary speed of 60-80 rpm.

The mechanical, orienting valves have operated successively each time at pump start up. Pump pressures and differential pressures between straight and deflected modes have been clear and consistent. Differential pressure of 250-300 psi has been easily recognized by the directional driller (DD) on the rig floor, indicating that the tool was, or was not, in the directional (deflected) mode.

The first phase of development and evaluation has been completed with the confirmation that the design can effectively deflect the bit. The second part will be to implement and MWD link up capability and provide a realtime tool face while rotating.

Operating on the "tilt-the-bit" principle, the tool mechanically changes the axis of the bit relative to the axis of the borehole to change hole direction and/or inclination. Bit deflection is achieved by an actuator valve that responds to hydraulic pressure commands created by cycling of the mud pumps. Tool configurations are "straight" and "directional". The straight alignment maintains the shaft straight and rotationally locked to the housing - basically acting as a three blade near-bit stabilizer. In the directional configuration, the housing is rotationally unlocked from the shaft, normally after directional orientation, so that the shaft can rotate through it. This same action transversely displaces the shaft's midsection relative to the housing with the shaft and drill bit angularly deflected 1.25° by way of a ball and cup arrangement near the drill bit end of the housing. The present prototype is designed to build angle at a dogleg of 10 - 12°/100 ft. Different cam arrangements can be fitted at the service center for greater, or lesser build rates, according to specific well plan needs.

More in Home