Modern oil field operators demand access to a great quantity of information regarding the parameters and conditions encountered downhole. Such information typically includes characteristics of the earth formations traversed by the borehole and data relating to the size and configuration of the borehole itself. The collection of information relating to conditions downhole, which commonly is referred to as “logging,” can be performed by several methods including wireline logging and “logging while drilling” (LWD).
In wireline logging, a probe or “sonde” is lowered into the borehole after some or all of the well has been drilled. The sonde hangs at the end of a long cable or “wireline” that provides mechanical support to the sonde and also provides an electrical connection between the sonde and electrical equipment located at the surface of the well. In accordance with existing logging techniques, various parameters of the earth's formations are measured and correlated with the position of the sonde in the borehole as the sonde is pulled uphole.
In LWD, the drilling assembly includes sensing instruments that measure various parameters as the formation is being penetrated, thereby enabling measurements of the formation while it is less affected by fluid invasion. While LWD measurements are desirable, drilling operations create an environment that is generally hostile to electronic instrumentation, telemetry, and sensor operations.
In these and other logging environments, measured parameters are usually recorded and displayed in the form of a log, i.e., a two-dimensional graph showing the measured parameter as a function of tool position or depth. In addition to making parameter measurements as a function of depth, some logging tools also provide parameter measurements (e.g., resistivity or acoustic impedance) as a function of azimuth. Such tool measurements have often been displayed as two-dimensional images of the borehole wall, with one dimension representing tool position or depth, the other dimension representing azimuthal orientation, and the pixel intensity or color representing the parameter value.
In certain environments (e.g., air-drilling operations) such tools perform poorly. Moreover, even when such tools operate normally, operators often still feel ‘blind’ when it comes to understanding exactly what is happening downhole.
A better understanding of the various disclosed embodiments can be obtained when the following detailed description is considered in conjunction with the following drawings, in which:
While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description are not intended to limit the invention to the particular illustrated embodiments, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the scope of the appended claims.
Accordingly, there are disclosed herein various systems and methods for downhole optical imaging while drilling. Such systems and methods enable operators to obtain images and/or video inside the borehole during drilling and/or wireline logging operations. In at least some system embodiments, the image or video data is communicated to the surface in real time to enable operators to better control the drilling operation and steer the drilling assembly. Operators are able to analyze the borehole shape, borehole breakouts, tool offset, fracture patterns, formation texture and composition, bed boundaries, fluid (including gas) inflows, flow patterns, as well as simply monitoring for unusual downhole conditions (e.g., well intersections, whipstock malfunctions, or caverns).
In some embodiments, a downhole optical imaging tool includes a light source and a camera enclosed within a tool body having at least two sidewall windows. A first window transmits light from the light source to a target region in the borehole, while a second window passes reflected light from the target region to the internal camera. As explained in greater detail below, the target region is spaced along the borehole away from the second window in a direction opposite the first window. In some embodiments, this configuration is provided by angling the first and second windows with respect to the sidewall, or by shaping the windows to cast and receive light from a “forward” direction. Some tool embodiments include motion and/or orientation sensors that are employed by a processor to combine separately captured images into a panoramic borehole image.
Some method embodiments include: using a drillstring to convey an optical imaging tool into a borehole containing a fluid; illuminating a target region via a first window in a sidewall of said tool; and capturing an image of the target region via a second window in the sidewall of said tool. The fluid can be, for example, a gas or a substantially transparent liquid. The second window is downhole from the first window, and the target region is downhole from the second window. Images captured by the camera can be used to determine fracture size and orientation, to steer the drillstring, to monitor and optimize a stimulation process, to monitor clean up, to determine tool orientation or position (e.g., relative to a whipstock, muleshoe, multilateral window, or lost string), to operate a downhole device or monitor its operation (e.g., a safety valve, a sliding sleeve, or an isolation device), to monitor downhole tests (e.g., seals during a pressure test), to inspect casing for corrosion, scale buildup, methane hydrate formation, tar accumulation, or even to conduct a milling operation.
The disclosed systems and methods are best understood in the context of the larger systems in which they operate.
A LWD tool 26 is integrated into the bottom-hole assembly near the bit 14. As the bit extends the borehole through the formations, logging tool 26 collects measurements relating to various formation properties as well as the tool orientation and various other drilling conditions. The logging tool 26 may take the form of a drill collar, i.e., a thick-walled tubular that provides weight and rigidity to aid the drilling process. As explained further below, tool assembly 26 includes a downhole video tool that captures images and/or video of the borehole walls. A telemetry sub 28 may be included to transfer images and measurement data to a surface receiver 30 and to receive commands from the surface. In some embodiments, the telemetry sub 28 does not communicate with the surface, but rather stores logging data for later retrieval at the surface when the logging assembly is recovered. In both approaches, limitations are placed on the amount of data that can be collected and stored or communicated to the surface.
At various times during the drilling process, the drill string 8 may be removed from the borehole as shown in
An alternative drilling technique is drilling with coil tubing.
Surface computer system 66 is configured to communicate with supervisory sub 64 to set logging parameters and collect logging information from the one or more logging tools 65 such as a downhole video logging tool. Surface computer system 66 is preferably configured by software (shown in
In each of the foregoing logging environments, the logging tool assemblies preferably include a navigational sensor package that includes directional sensors for determining the inclination angle, the horizontal angle, and the rotational angle (a.k.a. “tool face angle”) of the BHA 26. As is commonly defined in the art, the inclination angle is the deviation from vertically downward, the horizontal angle is the angle in a horizontal plane from true North, and the tool face angle is the orientation (rotational about the tool axis) angle from the high side of the wellbore. In accordance with known techniques, wellbore directional measurements can be made as follows: a three axis accelerometer measures the earth's gravitational field vector relative to the tool axis and a point on the circumference of the tool called the “tool face scribe line”. (The tool face scribe line is typically drawn on the tool surface as a line parallel to the tool axis.) From this measurement, the inclination and tool face angle of the BHA can be determined. Additionally, a three axis magnetometer measures the earth's magnetic field vector in a similar manner. From the combined magnetometer and accelerometer data, the horizontal angle of the BHA may be determined.
The optical image sensor 80 can include a single sensor that sweeps around the borehole as the tool rotates, or it can include an array of sensors to image around the borehole circumference without requiring any rotation. In some embodiments, the optical image sensors can be paired to provide binocular or 3D vision. Tool 74 shields the optical image sensor(s) with a window that is transparent for at least some of the wavelengths that can be sensed by the sensors. If desired, the window can be provided curvature to act as a camera lens. In at least some embodiments, the optical image sensor takes the form of a digital camera having, e.g., a charge-coupled device (CCD) sensor. In other embodiments, the optical image sensor employs wavefield sensors that measure light phase and/or direction in addition to light intensity at each point.
The illustrated tool 74 has the illumination window 1202 and viewing window 1204 (
It should be noted that the above disclosed techniques are also applicable to wireline tools. Where rotation is desired, the wireline tool can be fitted with a rotating head. Since wireline tools are coupled to the surface via a cable, fiberoptics can optionally be used to convey light downhole and/or images to the surface.
For use of the foregoing technology, it is helpful for the borehole fluid to be relatively transparent to the light wavelengths in use. In many cases, the borehole fluid includes a large volume fraction of nitrogen, air, natural gas, light oil, or water. It is expected that there will normally be a sufficient quantity of cuttings and/or contrasting fluid phases (e.g., bubbles or droplets) to make the flow patterns of the borehole fluid visible. Nevertheless, a mist or smoke stream can be generated if desired to assist with borehole fluid flow visualization. Conversely, where the borehole fluid is too opaque, a clear fluid can be used to flush the region immediately in front of the sensors to enable imaging.
As the downhole optical imaging while drilling tool progresses along the borehole, it rotates or employs an azimuthally-distributed array to collect optical image measurements as a function of azimuth and depth to form a map of the borehole wall as shown in
It should be noted that the particular utility of the downhole optical image logging tool is not limited to generating a fixed image of the borehole wall. When video data is acquired, the time component of the signal can be used to observe, map, and display inflow and fluid flow patterns in a dynamic format.
For example, in
In
The foregoing technologies enable the operators to view borehole shapes, formation fractures and laminations, and fluid (and gas) influxes into the borehole. Suspended particulates or contrasting fluid phases enable visualization of flow patterns in the borehole. Computer software enables automated mapping of fractures or fluid flow patterns from the video signal stream.
Note that the described tool has a multitude of applications, including imaging borehole wall in terms of the formation heat capacity or cooling rate. If the light source operates in the infrared, the borehole walls will heat slightly when illuminated. By monitoring the time rate of change of the temperature in response to the illumination, information can be learned about the properties of the formation in the target region. In an alternative embodiment, the light source can be cycled on and off, enabling the camera to record both heating and cooling rates. In yet another embodiment, the temperature of the borehole fluid can be cycled up and down to alternately heat and cool the borehole wall. An infrared camera can monitor the temperature versus time for each “pixel” in the borehole wall image to estimate at least a qualitative heat capacity or thermal conductivity of the formation.
Numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. For example, the illumination window and viewing window could be at different angles, or only one might be angled, or they could even be angled towards each other to image a target region between them. It is intended that the following claims be interpreted to embrace all such variations and modifications where applicable.
The present application claims priority to Provisional U.S. Application No. 61/246,115, titled “Downhole Video While Drilling”, and filed Sep. 26, 2009, by inventors Roland Chemali and Ron Dirksen. This provisional is hereby incorporated herein by reference.
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