DEVELOPMENT OF A MUD-PULSE HIGH-TEMPERATURE MEASUREMENT-WHILE-DRILLING (MWD) SYSTEM

The overall program objective is to develop a mud-pulse measurement-while-drilling (MWD) tool for oil and gas drilling operations that can be used where downhole temperatures are as high as 195 C (383 F). The work was planned to be completed in two phases: Phase I and an optional Phase II. The objectives of Phase I were first to identify critical components of existing MWD systems that can or cannot operate at 195 C. For components not able to meet the higher standard, one of several strategies was pursued: (1) locate high-temperature replacement components, (2) develop new designs that eliminate the unavailable components, or (3) use cooling to keep components at acceptable operating temperatures (under 195 C). New designs and components were then tested under high temperatures in the laboratory. The final goal of Phase I was to assemble two high-temperature MWD prototype tools and test each in at least one low-temperature well to verify total system performance. Phase II was also envisioned as part of this development. Its objective would be to test the two new high-temperature MWD prototype tools in wells being drilled in the United States where the bottom-hole temperatures were 195 C (or the highest temperatures attainable). The high-temperature MWD tool is designed to send directional and formation data to the surface via mud pulses, to aid in the drilling of guided wellbores. The modules that comprise the tool are housed in sealed barrels that protect the electronics from exposure to down-hole fluids and pressures. These pressure barrels are hung inside a non-magnetic collar located above the drilling assembly. A number of significant accomplishments were achieved during the course of the Phase I project, including: (1) Tested two MWD strings for function in an oven at 195 C; (2) Conducted field test of prototype 195 C MWD tool (at well temperatures up to 140-180 C,3994 ); (3) Tested ELCON hybrid chip with processor, clock, and memory in a custom package for 700 hours at 200 C; (4) Contracted with APS Technology to conduct study of thermoelectric cooling of downhole electronics; (5) Conducted successful Peltier cooling test with APS Technology; (6) Tested and improved the electronics of Sperry Sun's Geiger Muller-based gamma detector for operation at 195 C; (7) Developed two high-temperature magnetometers (one in-house, one with Tensor,3994 ); and (8) Encouraged outside source to develop lithium/magnesium high-temperature batteries (operating temperature of 125 to 215 C). One of this project's greatest achievements was improvement in Sperry Sun's current tool with changes made as a direct result of work performed under this project. These improvements have resulted in longer life and a more robust MWD tool at the previous temperature rating of 175 C, as well as at higher temperatures. A field test of two prototype 195 C MWD tools was conducted in Lavaca County, Texas. The purpose of this operation was to provide directional services on a sidetrack of a straight hole. The sidetrack was to intersect the formation up-dip above the water/gas interface. In addition, the gamma tool provided formation data including seam tops and thickness. Results from these field tests indicate progress in the development of a 195 C tool. Although the pulsers failed downhole in both tools, failure of the pulsers was determined to be from mechanical rather than electrical causes. Analysis of the economics of the 195 C tool highlights the greatest obstacle to future commercialization. Costs to screen individual components, then subassemblies, and finally completed tools for high-temperature operations are very high. Tests to date also show a relatively short life for high-temperature tools--on the order of 300 hours. These factors mean that the daily cost of the tool will be higher (3 to 5 times more) than a conventional tool.

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