A new propagation resistivity tool has been designed and built with a measure point only 15 feet from the bit. Measurements of near-bit inclination and gamma ray are also provided. All of these measurements are in a package that includes a mud motor. The primary purpose of this tool is to provide a means for staying in a target formation during horizontal drilling. The propagation resistivity measurement of this reservoir navigation tool has the ability to see radially much deeper than focused resistivity devices. The radial direction is the direction of interest in horizontal drilling because the distance between adjacent beds is in the radial direction (relative to the tool). Devices which attempt to see beyond the end of the bit have limitations in a horizontal environment because the distance to the adjacent bed is very large in the direction of the borehole. In addition to the standard 2 MHz frequency, this new propagation resistivity tool has a second frequency of 400 kHz which has a much greater depth of investigation than the 2 MHz frequency. Measuring amplitude and phase at both frequencies produces 4 different depths of investigation at the same measure point. Modeling has shown that adjacent conductive beds can be detected as much as 12 feet away with the 2 MHz frequency and about 32 feet away at the lower frequency. These detection distances refer to the true vertical distance from the borehole to the adjacent bed, but the borehole may not intersect this bed for several hundred feet in horizontal drilling because the borehole is nearly parallel to the bed boundary. In addition, new state-of-the-art electronics and the use of a second transmitter have greatly improved the precision of the resistivity measurements. The result of these improvements is better accuracy in highly resistive formations. Therefore, this tool is able to provide both geosteering and a propagation resistivity measurement as accurate as the best wireline induction tools.

A new method and tool design for borehole compensated electromagnetic propagation resistivity logging while drilling (LWD) are presented. The method provides borehole compensated resistivity measurements at multiple depths of investigation using a shorter antenna array than existing compensation methods. The compact array is typically 40% shorter than conventional antenna arrays for borehole compensated measurements, resulting in a shorter, lower cost bottom hole assembly (BHA). This paper presents the theoretical basis of the compact array design, as well as electromagnetic modeling results demonstrating performance in downhole conditions of interest. Results from field tests of a downhole tool are also presented. The compact array design has been applied to create a shorter, lower cost resistivity logging while drilling collar. The three resistivity measurements enable determination of true resistivity (Rt), diameter of invasion, and flushed zone resistivity (Rxo) while drilling, geosteering, and formation evaluation in horizontal or deviated wells where application of wireline tools is difficult. The initial downhole antenna array design is some 44% shorter than equivalent conventional antenna arrays for borehole compensated measurements. Electromagnetic modeling results are presented for the three-receiver and two-transmitter antenna array to demonstrate performance of the shallow, medium, and deep resistivity outputs from phase-difference measurements. Modeling and field test data are used to show equivalent performance of the compact array to existing compensated antenna arrays in rugose boreholes and at bed boundaries. Modeling results are also presented which demonstrate the limitations and advantages of multi-frequency operation. Test data for a new method for compensation of electronics error are also shown. The paper presents a new approach to LWD borehole compensated resistivity methods that reduces the overall length of the antenna array and associated cost. The compact antenna array provides improved invasion profiling and determination of true resistivity when compared to existing borehole compensated array designs. Introduction For over twenty years, resistivity logging while drilling (LWD) using electromagnetic propagation techniques has been commercially available. The first propagation tools were simple systems based on a phase-difference measurement from one transmitter and two receivers, providing a single resistivity value[1]. As the technology matured, additional measurements were added to provide additional resistivities at different depths of investigation. Measurement of signal amplitudes at the two receivers was added to give a deeper resistivity measurement based on attenuation2. Extra transmitters at different transmitter-receiver spacings were also added to provide resistivity measurements at multiple depths of investigation3. Multiple operating frequencies were further added as a means to obtain multiple depths of investigation4. In addition to new measurements for multiple depths of investigation, the receiver antennas in most of the later generation tools were placed in the middle of an array of transmitters to provide compensation for errors due to borehole irregularities (rugosity) and cancellation of electronics errors[2]. A recent survey of LWD resistivity tools5 shows that the original three antenna propagation measurement has evolved into much more complex systems which can include as many as nine antennas. Figure 1 shows this evolution. Tools with six or seven antennas are now common. These more complex systems support attributes considered essential for propagation resistivity logging: multiple depths of investigation, borehole compensation, cancellation of electronics errors, and operation at multiple frequencies. However, with added complexity comes added cost, both for initial manufacturing of the equipment and also operation and maintenance. In this paper, a new method for borehole compensated resistivity logging while drilling based on electromagnetic propagation is introduced. The new method reverses the trend toward ever increasing length and complexity by minimizing the number of antennas required to provide borehole compensated measurements at multiple depths of investigation with cancellation of electronics errors. Tools designed using this method also provide multiple frequencies of operation and support higher rates of penetration.

TX 75083-3836, U.S.A., fax 1.972.952.9435. AbstractA new method and tool design for borehole compensated electromagnetic propagation resistivity logging while drilling (LWD) are presented.The method provides borehole compensated resistivity measurements at multiple depths of investigation using a shorter antenna array than existing compensation methods. The compact array is typically 40% shorter than conventional antenna arrays for borehole compensated measurements, resulting in a shorter, lower cost bottom hole assembly (BHA). This paper presents the theoretical basis of the compact array design, as well as electromagnetic modeling results demonstrating performance in downhole conditions of interest. Results from field tests of a downhole tool are also presented.The compact array design has been applied to create a shorter, lower cost resistivity logging while drilling collar. The three resistivity measurements enable determination of true resistivity (Rt), diameter of invasion, and flushed zone resistivity (Rxo) while drilling, geosteering, and formation evaluation in horizontal or deviated wells where application of wireline tools is difficult. The initial downhole antenna array design is some 44% shorter than equivalent conventional antenna arrays for borehole compensated measurements.Electromagnetic modeling results are presented for the three-receiver and two-transmitter antenna array to demonstrate performance of the shallow, medium, and deep resistivity outputs from phase-difference measurements. Modeling and field test data are used to show equivalent performance of the compact array to existing compensated antenna arrays in rugose boreholes and at bed boundaries. Modeling results are also presented which demonstrate the limitations and advantages of multi-frequency operation. Test data for a new method for compensation of electronics error are also shown.The paper presents a new approach to LWD borehole compensated resistivity methods that reduces the overall length of the antenna array and associated cost. The compact antenna array provides improved invasion profiling and determination of true resistivity when compared to existing borehole compensated array designs.

The original objective of the project, to deliver an integrated 3 1/8" diameter Measurement While Drilling (MWD) and Logging While Drilling (LWD) system for drilling small boreholes using coiled tubing drilling, has been achieved. Two prototype systems have been assembled and tested in the lab. One of the systems has been successfully tested downhole in a conventional rotary drilling environment. Development of the 3 1/8" system has also lead to development and commercialization of a slightly larger 3.5" diameter system. We are presently filling customer orders for the 3.5" system while continuing with commercialization of the 3 1/8" system. The equipment developed by this project will be offered for sale to multiple service providers around the world, enabling the more rapid expansion of both coiled tubing drilling and conventional small diameter drilling.The project was based on the reuse of existing technology whenever possible in order to minimize development costs, time, and risks. The project was begun initially by Ultima Labs, at the time a small company (~12 employees) which had successfully developed a number of products for larger oil well service companies. In September, 2006, approximately 20 months after inception of the project, Ultima Labs was acquired by Sondex plc, a worldwide manufacturer of downhole instrumentation for cased hole and drilling applications. The acquisition provided access to proven technology for mud pulse telemetry, downhole directional and natural gamma ray measurements, and surface data acquisition and processing, as well as a global sales and support network. The acquisition accelerated commercialization through existing Sondex customers. Customer demand resulted in changes to the product specification to support hotter (150 deg. C) and deeper drilling (20,000 psi pressure) than originally proposed. The Sondex acquisition resulted in some project delays as the resistivity collar was interfaced to a different MWD system and also as the mechanical design was revised for the new pressure requirements. However, the Sondex acquisition has resulted in a more robust system, secure funding for completion of the project, and more rapid commercialization. In October, 2007 Sondex was acquired by General Electric. This also resulted in some additional project delays as Ultima Labs was relocated to a nearby existing GE facility.GE remains fully committed to commercialization of the resulting products.The resulting downhole system now in production consists of a mud pulser, probe-based directional and gamma sensors, and resistivity collar with multiple depths of investigation. A near bit sensor with wireless communications to the MWD/LWD system above the mud motor remains under development. The surface system consists of a mud pulse detection and depth tracking system with PC-based software for mud pulse message decoding, real time log plotting, and processing of memory data from the resistivity collar at the end of the job.

With the increase in slimhole wellbores ranging from 93.2 mm to 123.8 mm being drilled, specifically within Russia, comes the need for logging while drilling (LWD) technology to provide real-time formation evaluation data to better analyze the reservoir and enable improved well placement. The authors describe the development of a 79.4 mm propagation wave resistivity system designed to facilitate the low cost drilling of small, shallow boreholes using coiled tubing drilling (CTD) technology, from which an 88.9 mm system was developed to address the Russian slimhole market. The technology described is available to all service companies, including those without the internal product development capabilities who previously relied on third party equipment to provide services.The paper details the design and development of the LWD system which provides borehole compensated resistivity measurements from three sensor spacings. A description of the environmental testing performed on the tools to verify the design, along with the results of field tests in the United States are provided.Logs acquired during the field test show how borehole compensated resistivity measurements can be calculated and presented without the need for the transmitter antennae to be positioned symmetrically either side of the receiver antennae. This unique antenna spacing design reduces the length of the collar when compared to other resistivity offerings in the industry, potentially enabling measurements to be positioned closer to the bit.