October 1999 Vol. 220 No. 10  Exploration

Perry A. Fischer,  Engineering Editor

Tiny exploration wells and half-inch geophones

Imagine drilling an exploratory well at only 2% to 4% of the cost of a conventional well. Imagine further, driving along a route to check on several autonomous coiled-tubing drilling units, each punching a 1-in. hole to depths up to 10,000 ft. While such wells may not enable much production, they give new meaning to the term wildcat. Direct evaluation of traps and/or gathering of subsurface geophysical data become possible at such costs.

These are some of the benefits envisioned by the EES-4 group at the Los Alamos Microhole Drilling and Instrumentation program. The program is supported by the U.S. DOE, Defense Department, Texaco, Phillips, Mark Products, Input / Output, Mobil and the DeepLook Collaboration (BP, Chevron, Shell, Conoco, Unocal, CiDRA, Baker Hughes, Halliburton, Schlumberger and others).

Program goals include reducing the cost of deploying downhole geotechnical instruments by using appropriately scaled, conventional and new drilling technology, sensors and instrumentation; providing a small-footprint unit to develop and test the integration of instrumentation and drilling systems. These will be highly automated, optimally controlled, look-ahead drilling systems that can be deployed in remote, unattended operating modes. This research is aimed at future exploitation of commercial and currently non-commercial (due to cost) resources, planetary exploration and national security needs.

There is evidence that strongly supports the feasibility of using coiled tubing to drill microboreholes as small as 1-1/8 in., and these will need to be up to 10,000 ft deep. Wells this small would primarily be exploratory in nature, but many wells could be drilled because of reduced costs, e.g., only one-fortieth as much drilling fluid is needed. These systems will need to provide well stability, pressure and directional control. Micro-completion technology must include miniaturized surface- and intermediate-casing strings, cementing of very small annuli, micro-perforating and cased-hole logging technology.

Commercially available components were assembled into several bottomhole drilling assemblies and tested at Los Alamos. Motor, thrust and bit performance showed that off-the-shelf components were suitable for coiled-tubing drilling of 1-3/4- and 2-3/8-in. bores using mud motors.

Field testing 2-3/8 drilling assemblies began in September 1998. A coiled-tubing drilling rig was modified to explore technical hurdles of microhole drilling in shallow-well tests up to 400 ft deep. Drilling 1-3/4-in. holes to 1,000 ft on 3/4-in. coiled tubing is anticipated, while 1-1/8-in. holes, drilled to 1,750 ft, is under study. Thus far, 2-3/8 in. is the smallest hole size yet attempted with coiled tubing.

During the past year, DeepLook Collaboration funded the first development phase of 1-1/8 to 1-3/8-in. drilling assemblies. In conjunction with this project, miniature downhole sensors are being developed for passive and active seismic measurement (Microhole Instrumentation Project). Microtool-access tubing was deployed in a stripper well in Texaco’s Humble field. This allows repeated access to the well for microsensor seismic measurements without having to pull the production string. Thus far, 1-gram geophones, a hydrophone and a micromachined silicon accelerometer have been packaged and tested. Development of other micrologging tools, including micro resistivity, induction, gamma and borehole-orientation tools has now begun.

A 400-ft-long, 1-in.-OD section of coiled tubing is being equipped with telemetry and electric power cables to operate a 2-in. rock-melting drill. This drilling demonstration is intended to show the synergy of continuous drillstem and thermal drilling and provide the first downhole instrumentation run on a rock-melting drill.

This project is reviewed annually by oil and gas industry representatives to the National Gas and Oil Recovery Partnership. In 1998, the Microhole Drilling Project was ranked first out of the 12 national laboratory proposals in drilling and completion.

European version. The Euroslim Drilling System is Europe’s answer to reduce the cost of exploration drilling. The project’s main sponsors are Forasol-Foramer and Security DBS, while collaborating partners are Elf Aquitane and IFP.

This is essentially a slimhole system, which ranges from 3 to 5 in., and while less ambitious then the microhole system above, it is now at the commercial stage of development. New drill pipe had to be designed to achieve an 11,400-ft depth target. A dedicated rig was built to take full advantage of reduced slimhole requirements, including smaller rig footprint, reduced crew, less weight and fluid volume.

New fluid and cement formulations were field tested to account for reduced annuli. The rig integrated an instrumented wireline winch, dedicated for coring and other inhole operations. A new coring tool is latched to the drill pipe when cutting the core, then unlatched and pulled up through the drill pipe by wireline, saving significant rig time. This project is nearly commercial, and results indicate a 25% to 50% reduction in costs, depending on the drill site.

Seismic mobile information. Veritas DGC Inc. has successfully deployed its new Seismic Mobile Information and Control System (Seis-MICS) remote survey capability. This is a component of Veritas DGC’s Millennium II project. It enabled GPS survey data to be continuously uploaded and transmitted in near real-time, via satellite, from a field crew in western Wyoming, to a remote Information and Control Center (ICC) in Calgary, almost 1,000 mi away.

At the ICC, before the data is processed and recorded, data quality control is performed in near real-time while the survey crew is still in the field. Although still in beta-testing mode, this the first deployment of this kind of technology in the geophysical industry.

Seis-MICS transmits small packets of survey data, in the form of e-mail messages, directly from a surveyor’s GPS backpack to the ICC. The new system will allow clients the convenience of using PCs to follow the progress and status of projects by using a secure or dedicated internet connection.

Comments? Write: fischerp@gulfpub.com

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Copyright © 1999 Gulf Publishing Company