In collaboration with Drillmar Inc., Huisman-Itrec has developed and constructed the LOC250, a containerized, 250-ton hook-load land and offshore rig — a new concept. The LOC 250 is designed to take advantage of today’s emerging casing-while-drilling (CWD) technology to reduce the costs and environmental impact of drilling a well. Demand for faster operation and deeper wells triggered development of its successor. The LOC400 is an easy-to-transport drilling rig that can combine conventional drillpipe (DP) drilling with the advantages CWD. The rig includes several design features that facilitate more effective and cost-efficient drilling.

Low transport costs, fast rig moves
The entire, compact-size LOC400 rig can be broken down into 22 modules, which are certified

Figure 1. Drillers panel with fully integrated control systems for all rig equipment. (All figures courtesy of Huisman)
20-ft and 40-ft (6.1-m and 12.2-m) ISO container units. Within 24 hours (including limited transportation time) and without cranes, a five-man crew with three trucks can demobilize the rig and rebuild it in another location. Because standard container ships, trains and oilfield trucks can transport ISO containers rapidly and economically, the LOC400 rig can be used to drill wells anywhere in the world.

Deployment configurations
The LOC400 rig to be used in various ways: on land, on skids for jungle use, on offshore platforms or on barges for drilling in lakes or swamps. On offshore platforms, the modules of the LOC400 can be fitted compactly on to a skid unit using a crane, which enables two-dimensional movement of the complete rig over the platform’s array of wells.

CWD
In CWD, a well is drilled using standard oilfield casing instead of drillpipe. This enables the operator to simultaneously drill and case a well. Drill bits and other tools can be lowered inside the casing to the bottom of the hole on a wireline, where they are latched to the last joint of casing, while mud circulation continues. Retrieval of the bits and the tools occurs the same way. The CWD process eliminates tripping and its associated blowout risks. There are several possible configurations for CWD systems: the casing rotates during drilling but there are various rotation speed options, and the drilling tools may be integrated into the casing string or be part of an assembly that extends below the casing shoe. A top-drive system is used to rotate the casing, which remains in the hole at all times and is eventually cemented in place when the casing point is reached. The benefits of CWD include:
• Reduced drilling flat time (no tripping);
• The casing is always on bottom, which eliminates the risks associated with open holes;
• Improved circulation;
• Drilling through difficult layers such as depleted zones and unstable formations is made easier; and
• Improved wellbore stability, which often means that a casing string can be eliminated.

Experience has shown that drilling efficiency can be improved 20 to 50% with CWD. Because the casing remains in the well and circulation is maintained at all times, wellbore integrity is preserved, and unscheduled events such as well control problems, swelling or sloughing formations and washouts are avoided.

Automated casing, drillpipe handling
The LOC400 is equipped with a fully automated pipe handler, which enables highly efficient handling of both casing and DP. When the pipe handler has upended the tubulars, they are
Figure 2. Drilling with casing; no drillpipe is found on this rig.
taken over by elevators in the rig. A top drive spins the tubulars in torques the connections. Fully automated power slips acting as a backup tong are integrated within the rotary table. The LOC400 is capable of tripping DP at 1,700 ft/hr (518.5 m/hr), which makes the LOC400 as efficient as existing conventional DP drilling rigs and more efficient than other specially designed CWD rigs. The DP drilling and CWD processes (including pipe and casing handling) are fully controlled from the control room without personnel on the drill floor. As DP handling is identical to casing handling and uses the same equipment, the same team can carry out both tasks. While a conventional drilling rig needs a crew of 10, the LOC400 requires only a five-man crew for full and safe operation.

BOP testing and BHA handling
To further reduce non-productive time, the blowout preventers (BOPs) are pressure tested offline on a dedicated test stump, which also serves as a mouse hole. The control hoses do not have to be disconnected after testing to move the BOP onto the wellhead. Only the wellhead has to be tested in the critical path of rig operation. In addition, bottom-hole assemblies (BHA) can be assembled and taken apart offline using the LOC400’s crown-mounted service crane as a stand builder. An area for storage of up to eight stands of BHA is available. A new BHA is ready when the previous one is pulled out.

Save energy, improve safety
Statistics show that pipe and material handling cause almost 50% of the recorded accidents during well drilling. The fully automated pipe handling of the LOC400, with its automated drill floor, obviates the need for personnel on the drill floor. In addition, the simple rig-assembly process — smaller loads, less rig crew involvement and improved overview and visibility — effectively mitigates the risk for the crew and the potential for accidents and damage during rig moves.

The LOC400 has a significantly lower adverse impact on the environment when compared with conventional rigs. Because drilling a well with the LOC400 requires less drilling time and lower mud pump pressures and flow rates, two 800-hp mud pumps are sufficient, compared to the three 1000-hp pumps required for conventional DP drilling. This means a 45% lower fuel consumption per day of drilling and a reduction in hydrocarbon emissions per well of up to 75%. Mud and cement costs are reduced by 10 to 20%. Because the LOC400 has only a single 124.6-ft (38-m) mast, its silhouette does not impact significantly on the horizon. The footprint of the LOC400, at 7,534 sq ft (700 sq m), is 75% smaller than the 32,291 sq ft (3,000 sq m) required for conventional rig.

Integrated design
Many conventional rigs are combinations of components and subsystems developed and maintained by different suppliers. The LOC400 is a fully integrated drilling rig offered as a complete package. All components, including drawworks, top drive, mud pumps, power unit, mud system, BOPs and an integrated control and monitoring system, have been carefully selected and tested.

A complete and integrated Geolograph is also included. The monitoring system includes satellite-linked remote diagnosis and troubleshooting, which enables Huisman engineers to help customers to solve any problems. Each LOC400 is customized to meet the customer’s specific needs and is fully tested and commissioned before delivery. Additional modules such as extra mud tanks or mud pumps can be installed on request.

Field experience
The first LOC 250 unit has been in operation for more than a year, has drilled more than 18 wells and has proven to be a quality drilling machine. Small modifications have improved
reliability and operator friendliness. Modifications include improved BOP handling, additional cooling of electrical system and additional suction dampeners for mud pumps. Also based on field experience the LOC 400 uses AC electrical drive for main drive systems, leaving hydraulics only for auxiliary functions. This improves power efficiency, lowers noise levels and reduces maintenance cost and downtime.

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