DOE Project Deems Feasible Miniaturization Of Key Tools For Microhole Projects

The new technology, which entails integrating a suite of high-tech tools with ultra-small diameter boreholes, promises to slash operators' costs, decrease drilling risks, and dramatically reduce the environmental impacts of oil and gas drilling.

In microhole drilling, slim coiled tubing spooled on a pickup truck is used to drill wells instead of using conventional, wide-diameter drill pipe assembled into massive strings on large, conventional drilling rigs--a traditional method suited only for much larger boreholes. Critical to the initiative is the development of micro-instruments that are small enough to fit into the micro-boreholes yet rugged enough to withstand the harsh downhole conditions.

Two such high-tech tools are a rib steering device (RSD) and a multiple propagation resistivity (MPR) device designed for 2-inch coiled tubing. RSD technology employs a downhole guidance system that continually adjusts the drill bit's course; it uses pads, or ribs, to steer while drilling continuously, enabling the operator to change drilling angles without interrupting the rotation of the drill pipe string. Resistivity measures a formation's resistance to electrical current, which is used to determine whether the formation holds hydrocarbons or water. MPR employs an array of antennas that propagate multiple electromagnetic signals at different frequencies. The technologies are intended to give the operator better control over drilling progress and better information about what the drill bit is encountering downhole.

A first round microhole technology project, managed for DOE by the National Energy Technology Laboratory, seeks to develop an RSD and an MPR device for coiled tubing that is only 2 inches in diameter. Baker Hughes INTEQ, through system concept development and a larger tool field survey, has determined that the appropriate technology is available and can be modified for microhole application.

For the RSD, the problem is primarily one of developing a 2⅜-inch tool that can maintain structural integrity. Modeling and drawing tasks have indicated that, at this stage of the project, construction of a 2⅜-inch RSD is feasible.

For the MPR device, the problems associated with scaling down the size are to maintain structural integrity and still achieve the fidelity of resistivity measurement of the larger tool sizes. The construction of a 2⅜-inch MPR device nevertheless appears to be feasible, according to project investigators.

Several draft designs of these tools are undergoing evaluation to identify the optimum setup. In addition, Baker Hughes INTEQ has performed calculations to evaluate the maximum bending stresses that the new components may encounter when integrated into existing coiled tubing bottom-hole assemblies.

The next step will be to work through the detailed design process to reach a critical decision point: whether or not to enter into the manufacturing stage. A decision is expected by June 30, 2005. If that decision is a "go," then Baker Hughes INTEQ will manufacture two prototypes of each tool and test them in the lab, as well as in the field.

What makes this an important milestone is underscored by the target of DOE's Microhole Initiative. About two thirds of all the oil discovered in the United States remains in the ground. Of that, over half (218 billion barrels) lies in reservoirs shallower than 5,000 feet and is unrecoverable with current technology or because of poor economics. Recovering just 10 percent of that shallow target resource would yield a volume equal to the nation's current level of total proved oil reserves.

America's oil and gas field operators--mostly small producers without access to high-tech solutions--continue to try to squeeze out more oil from aging, nearly depleted shallow oilfields by drilling more infill wells (those spaced between existing producing wells). More than 20,000 shallow infill wells are drilled each year in the United States--and nearly as many low-producing wells are abandoned each year because of eroding economics. The reductions in drilling costs that microhole technology yields--ranging from one third to more than one half--could spawn a wave of infill drilling across the nation's mature, declining oil fields.

Microhole technology offers more than a low-cost means to drill a lot of infill wells. It also reduces exploratory drilling risk by allowing an operator to deploy downhole seismic sensors in a cost-effective way in order to gain a better image of the subsurface. And the environmental benefits of microhole technology are manifested in the smaller "footprint" of the truck-mounted coiled tubing rigs and in the greatly reduced drilling wastes resulting from a smaller hole.

The goal of DOE's microhole initiative is to support reservoir life extension and domestic resource conservation by facilitating efforts to find, characterize, and develop shallow domestic oil and natural gas resources inexpensively. Current projects under the program focus on demonstrating present microhole technology capabilities and developing missing key technology components. Microhole technology consists of techniques and tools used to drill, complete, and characterize reservoirs up to 5,000 feet deep in a 3½-inch diameter borehole.