A new series of land rigs has been introduced in China that features an award-winning variable frequency drive and digital control functions. Ten of the new rigs have been delivered to Uzbekistan, and additional units are going to Pakistan.

In May, SPA CNPC, mobilized the first of two new HH2600ED series rigs built by Honghua Co., Ltd. (HH) (Fig. 1). The 2,600 hp land rig spudded its first well in Pakistan.

HH's second rig (No. 70E-2), currently under construction in HH's yard in China, is scheduled for completion and delivery at the end of September. Huabei Oilfield currently holds a contract with HH for the rig.

Rig No.70-1, rated 22,965 ft (7,000 m), comes with a number of improvements to make it one of the most efficient and advanced land rigs available. It has a newly designed substructure, drawworks, climate-controlled driller's cabin, system controls connected through programmable logic controllers and cabling, and other overall designs to reduce manual labor, optimize processes and performance, and improve safety in operations. The sophisticated data acquisition, storage, processing and setup system makes it possible for automatic and continuous-loop drilling.

Drawworks

The drawworks is an HH JC-2600ED powered by two YJ31 motors (Fig. 2). Each motor is rated to 1,300 hp. The AC drives provide regenerative braking and more precise control of the drillstring than conventional silicone control rectifier (SCR)-drive systems. Regenerative braking eliminates the need for an auxiliary brake, allowing less weight and smaller footprint. The hydraulic brake works only for parking, positioning and emergency stop. All parameters including tripping speed, block positioning and automatic bit feed are digitally controlled. The AC technology allows greater control of the drilling process and improves efficiency during tripping operations. A small 40-hp AC motor is used for automatic bit feed and emergency hoisting if the main motor system is out of service. The sophisticated single-shaft drawworks simplifies the drive and makes it easy for maintenance.

Mast and substructure

HH built both the mast and substructure with new designs to increase ease of rig-up, thus reducing the time required to raise them. The mast and substructure are rated for 1 million-lb hook-load capacity (Fig. 3).

The drill floor height of 35 ft (10.6 m) meets the requirements for underbalanced drilling. The independent rotary drive system is integrated in the substructure, thus making the drill floor wider and clearer. A 36 ft by 36 ft (11 m by 11 m) floor area is available.

The substructure is pinned together at ground level and raised to working position together with the mast. The mast is pinned to the substructure at eight points to improve its stability.

The mast is a 147-ft (44.8-m) cantilever type and can accommodate a Varco TDS-11 500-ton top drive. The poles used for raising the mast and substructure work as a rear part of the structure when rig-up is completed, simplifying the substructure and reducing the weight.

Driller controls

HH2600VFD uses the HH Digital Driller (D-Driller) for integrated controls and rig data monitoring. The driller occupies a single-seat climate-controlled cabin near the rig floor where he controls the drawworks, rotary table, mud pumps and rig power plants, blowout preventer, and hydraulic catheads by using touch-screen computer controls and a joystick (Fig. 4).

The D-Driller system provides steady weight-on-bit (WOB) while drilling based on downhole conditions and permits control of parameters including WOB and rate of penetration (ROP). As compared to a conventional auto-drilling system, often producing bit-weight fluctuations of 2,000 lb to 3,000 lb, the system has reduced fluctuations to less than 1,000 lb noted by the data acquisition system. These developments in controlling drilling parameters have improved bit life and penetration rates.

Other benefits of D-Driller system include:

• Rotary torque-up inhibitor, which senses drillstring torque;
• Surge-swab limitation, which monitors and controls tripping speed in and out of open hole; and
• Drillstring over-pull and drag limitation, which monitors and controls over-pull on the drill pipe when tripping out of the hole.
The drilling monitors have the following views:
• Drilling: Monitors WOB, torque, ROP, hook load, pump strokes and pressure, well depth, bit depth, flow rate, and tank volumes parameters, etc.
• Tripping: Monitors trip tank volume, flow rate, block position, etc.
• Trend page: Displays with graphs and logs by selected functions that can be stored for backup reference.
• Others: Monitors spooling of drawworks drum, racking platform, shale shakers and pumps.

Other equipment

Each of the HH2600VFD series of rigs utilizes an HH 371/2-in. rotary table, independently powered by a YC23 800-hp AC motor. This rotary table system replaces the conventional mechanically powered, vertical-chain rotary drive. Two F-1600 mud pumps are employed. Each pump is driven by a YC31A 1600-hp AC motor via V-belt drive. Four electronically controlled Caterpillar 3512B generator sets, each rated at 1,200 kW, supply AC power to the HH-ABB VFD house for powering mud pumps, rotary table and auxiliary equipment. One Caterpillar electronically controlled 3412E, rated at 400 kW, works as the auxiliary generator set.

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