Patent Application
20190234198
Tiltmeters are used in oil and gas wells to detect minute deformations in the formation caused by hydraulic fracturing or other sources of pore pressure changes. The data can be used to identify where and how injected fluids have been placed within the reservoir, fracture detection and characterization, and other information.
Hydraulic fracturing is a worldwide multi-billion dollar industry, and is often used to increase the production of oil or gas from a well. The subsurface injection of pressurized fluid results in a deformation to the subsurface strata. This deformation may be in the form of one or more large planar partings of the rock, in the case of hydraulic fracture stimulation, or other processes where injection is above formation parting pressure. The resultant deformation may also result from cases where no fracturing is occurring, wherein the subsurface strata (rock layers) compact or swell due to the poroelastic effects from altering the fluid pressure within the various rock layers.
A variety of applications can induce pore pressure changes, fluids are injected into the earth, such as for hydraulic fracture stimulation, waste injection, produced water re-injection, or for enhanced oil recovery processes like water flooding, steam flooding, or CO2 flooding. In other applications, fluids are produced, i.e. removed, from the earth, such as for oil and gas production, geothermal steam production, or for waste clean-up.
The preparation of a new well for hydraulic fracturing typically comprises the steps of drilling a well, cementing a casing into the well to seal the well from the rock, and creating perforations at a desired target interval. Perforations are small holes through the casing, which are formed with an explosive device. The target interval is the desired depth within the well, which typically is at the level of a pay zone of oil and/or gas. A bridge plug is then commonly inserted below the perforated interval, to seal off the lower region of the well.
Hydraulic fracturing within a prepared well bore comprises the pumping of fluid, under high pressure, down the well. The only place that the fluid can escape is through the formed perforations, and into the target zone. The pressure created by the fluid is greater than the in situ stress on the rock, so fractures (cracks, fissures) are created. Proppant (usually sand) is then pumped into the prepared well, so that when the fluid leaks off into the rock (via natural porosity), the proppant creates a conductive path for the oil/gas to flow into the well bore. Creation of a hydraulic fracture, therefore, involves parting of the rock, and displacing the fracture faces, to create fracture width. The induced deformation field resulting from the hydraulic fracturing radiates in all directions.
Surface and offset well tiltmeter fracture mapping have been used to estimate and model the geometry of formed hydraulic fractures, by measuring fracture-induced rock deformation.
There is a need though for better and lower cost approaches for gathering the needed data for this application. The approach to be described herein consists of a MEMS inclinometer array with wide range and sensitivity, coupled with downhole micro seismic receivers, all conveyed on a fiber optic wireline. These can be used in both horizontal and vertical sections of the well, by using clamp on EAT technology and DAS telemetry.
Elements in the figures have not necessarily been drawn to scale in order to enhance their clarity and improve understanding of these various elements and embodiments of the application. Furthermore, elements that are known to be common and well understood to those in the industry are not depicted in order to provide a clear view of the various embodiments of the application, thus the drawings are generalized in form in the interest of clarity and conciseness.
In the following detailed description, reference is made to accompanying drawings that illustrate embodiments of the present disclosure. These embodiments are described in sufficient detail to enable a person of ordinary skill in the art to practice the disclosure without undue experimentation. It should be understood, however, that the embodiments and examples described herein are given by way of illustration only, and not by way of limitation. Various substitutions, modifications, additions, and rearrangements may be made without departing from the spirit of the present disclosure. Therefore, the description that follows is not to be taken in a limited sense, and the scope of the present disclosure will be defined only by the final claims.
Various inventive features are described below that can each be used independently of one another or in combination with other features. However, any single inventive feature may not address any of the problems discussed above or only address one of the problems discussed above. Further, one or more of the problems discussed above may not be fully addressed by any of the features described below.
The description of embodiments of the disclosure is not intended to be exhaustive or to limit the disclosure to the precise form disclosed. While the specific embodiments of, and examples for, the disclosure are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the disclosure, as those skilled in the relevant art will recognize.
The EAT sensors and EAT sensing technology described in this disclosure is a recently developed technology and has been described in a recently published PCT application: WO2015020642A1.
EAT Sensors represent a new approach to fiber optic sensing in which any number of sensors, electronic or fiber optic based, can be utilized to make the basic parameter measurements, but all of the resulting information is converted at the measurement location into perturbations or a strain applied to an optical fiber that is connected to an interrogator. The interrogator may routinely fire optical signal pulses into the optical fiber. As the pulses travel down the optical fiber back scattered light is generated and is received by the interrogator.
The perturbations or strains introduced to the optical fiber at the location of the various EAT sensors can alter the back propagation of light and those affected light propagations can then provide data with respect to the signal that generated the perturbations.
The possible advantages from using the above described EAT systems in a variety of configurations may include using a variety of sensors, either electrical or fiber optic based, to measure for example a micro seismic event, a chemical concentration, a pH, a temperature, or a pressure and using a common optical fiber connected to a interrogator to measure perturbation signals from each EAT sensor assembly location distributed along that common optical fiber and analyzing those signals to extract values of the parameters being measured. The approach can significantly reduce manufacturing complexity, reduce very expensive labor intensive production with expensive equipment like splicers and fiber winders, improve reliability, and widen industry acceptance by allowing the use of sensing technologies of choice.
A typical system is shown in
The same optical fiber is used for telemetry of micro seismic information back to the surface. Low cost electronics within the EAT sensor system are then used to convert the sensor signal to a frequency, and the frequency is converted to an acoustic frequency signal. Multiple frequencies could be used to differentiate between X/Y/Z components in a 3D sensor package, as well as different data from micro seismic sensors. The EAT transmission frequencies could be selected to be outside the seismic signal range of interest. The typical seismic range of interest for reflection seismic is in the 0-250 Hz range and 0-2,000 Hz for micro-seismic applications.
The combination of the tiltmeter meter data and the micro seismic data provides excellent insight on actual formation deformation, resulting in improved accuracy in determining fracture characteristics. These characteristics may include depth coverage, number of fractures, orientation, and other features of interest.
The processor combines the downhole and surface tiltmeter information as well as the micro seismic sensor data to create fracture maps of the well and other information for increasing reservoir productivity and reducing completion costs.
The magnitudes of the deformations are very small and require highly sensitive instruments. Typical tilts are of the order of 100 nanoradians (100 parts in a billion) at the observation well, and so highly sensitive tiltmeters are required. Traditionally sensors based on the same principal as the carpenter's level have been used—a bubble in a fluid inside a bent glass tube. While these are extremely sensitive, their trade-off is that their range is very limited, typically to half a degree or less, and once out of range, they must be physically reoriented back into the operating range. This requires a motorized system that pivots the sensor to the center of its operating range. However, even this mechanism may be limited, and unable to cope with large deviations such as horizontal wells. As a result, tiltmeters have not to date been used commercially in horizontal sections of the well. Having tiltmeters in the horizontal sections of the well should provide much larger and stronger signals compared to the surface tiltmeters, which will improve the accuracy of the fracture mapping.
Two lateral arrays 310 are shown. The first lateral sensor 320 is mounted perpendicular to the board for vertical sections of the well. Each subsequent sensor is mounted at the angle of the previous one minus the range of the sensor. For example if the range is +/−5 degrees, then the second sensor is mounted at 10 degrees to the first, the third is mounted 10 degrees to the second, and so on, until 90 degrees 330 is reached, suitable for horizontal wells. Thus 10 sensors would cover the full 90 degrees. If the range needs to be +/−1 degree to get the required sensitivity, then 45 sensors can be used. So whatever the lateral angle, there is a sensor in its sweet spot.
Similarly an axial array 340 for measuring tilt along the axis of the tool is provided. In this case two rows of tiltmeters provide up to +/−50 degrees of range.
For horizontal locations in the well, the circuit board is mounted in a rotatable cylinder along its long axis—see
As previously described in the discussion of
In some cases the EAT tiltmeter instrument may be designed to operate only in a near horizontal orientation. In this case a simpler tiltmeter assembly can be employed. This is shown generally as 600 in
In this version two arrays of tiltmeters perpendicular to each other are mounted on a small signal conditioning board. In addition, a MEMS tiltmeter/accelerometer chip is also included, although with lower sensitivity than the array tiltmeters. Each successive array tiltmeter is mounted at a different angle from the previous one, so that a wide overall range is covered by the array. Each tiltmeter in the array has a narrow range but high sensitivity to angular change. Since the sensor array is designed specifically for horizontal wells, its range can be much smaller than the universal array described previously, and fewer MEMS tiltmeters are required, thus simplifying the device and reducing cost.
A complete horizontal EAT tiltmeter assembly is shown in
In some cases the EAT tiltmeter instrument may be designed to operate only in a near vertical orientation. For this, the horizontal EAT tiltmeter can be further simplified as shown in
Instruments using electrolytic sensors are limited to the angle they can measure in a well, and require mechanical mechanisms to adjust for even a small range. By using MEMS based tiltmeters in arrays, a wide range in both axial and lateral measurement is possible, at high resolution, both in vertical and horizontal portions of the well. The horizontal measurement close to the fractured well is unique and will provide more accurate mapping and interpretation. By using multiple EAT sensors in the horizontal section, a much wider area of detection is possible when compared to vertical well detection.
The MEMS sensors are very small, rugged and low cost, and can be built up in arrays. The centering motor is only used once at the beginning of the run. The sensors use nano watts of power, so can be deployed for long periods without recharging.
The use of the tiltmeter array with EAT technology along with micro seismic sensors represents a significant reduction in size, complexity and cost compared to current tiltmeter designs. With fewer moving parts the tiltmeters are also more reliable.
Using DAS technology provides dual use for the fiber—both as a well monitoring system over its entire length, as well as providing point specific measurements of inclination. Providing both at the same time is a unique service.
Although certain embodiments and their advantages have been described herein in detail, it should be understood that various changes, substitutions and alterations could be made without departing from the coverage as defined by the appended claims. Moreover, the potential applications of the disclosed techniques is not intended to be limited to the particular embodiments of the processes, machines, manufactures, means, methods and steps described herein. As a person of ordinary skill in the art will readily appreciate from this disclosure, other processes, machines, manufactures, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufactures, means, methods or steps.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2016/050829 | 9/8/2016 | WO | 00 |
