Near-Bit Propagation Resistivity for Reservoir Navigation

Abstract

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.

Prediction and Early Detection of Karsts—An Overview of Methods and Technologies for Safer Drilling in Carbonates

“…As can be seen in the figure, the drill bit cannot be completely isolated from the BHA as there is a contact with the bearing section of the rotary steerable system or with the mud motor [54] depending on the configuration of the BHA. Therefore, with the increased length of the electrode, it becomes challenging to distinguish responses from multiple chaotically distributed points of contact with borehole walls.…”

Successful Geosteering in Ecuador Using the Bright Spot Phenomenon from Deep Resistivity Images

“…100 KHz to 2 MHz) and the relative dip of the boundary is high. Because polarization horns appear on the real-time logs before the boundary is crossed, they are used for geosteering (Meyer, 1994). This application preceded the development of azimuthal wave resistivity by approximately one decade.…”

Complex Permittivity Logging Tool Excited by Transient Signal for MWD/LWD

“…Although dry rocks' electric properties are frequency independent below radio frequency, the existence of high porosity and moisture can lead to polarization which causes mixture permittivity dispersion [8][9][10]. In the past twenty years, many authors presented induction tools comparing the apparent resistivity achieved at several hundred kHz and 2 MHz for detection of porous formation resistivity dispersion [11,12]. But unfortunately, other factors such as invasion, dielectric effects and different antenna structures were found to explain these differences more suitably than resistivity dispersion [13].…”