The goal of this project is to develop a high-resolution single-well seismic survey and monitoring system to efficiently and correctly 3D/4D image, characterize, and monitor sub-surface geological formations, structures and properties such as fractures, faults, thin-bed and discontinuous lithologies, stress fields, fluid saturations and anisotropy at both large and small scales. The single-well seismic system consists of clamped multi-component high-frequency vibratory seismic sources and high-fidelity receivers. The seismic data from this novel borehole seismic system will allow for both efficient and environmentally prudent development of Unconventional Oil and Gas (UOG) by simultaneously deploying two break-through seismic technologies in single UOG wells. The first technology is an ultra-sensitive, large-bandwidth, large-aperture, fiber-optic-based borehole 3C seismic vector sensor array that can be deployed in both vertical and horizontal wells to image the fracturing process and the location of the proppant in the fractures using data from passive and active seismic sources. The second technology is comprised of an ultra-large bandwidth, clamped borehole vector seismic source which is simultaneously deployed with the downhole receivers. This combined technology will image and monitor the geological formation and the hydraulic fractures with an ultra-high resolution. The source-receiver system will detect and locate the changes in the formation generated by the fracturing process and injection of the fluids and the proppant in the stimulated formation. On the receiver side of the system, the 3C vector seismic receiver array will be combined with a large distributed array of enhanced acoustic sensors with a dense spatial sampling of 6 ft which will complement the more sensitive vector sensors with the less-dense spatial sampling of 25 ft. The sensors will allow high-resolution 3D time-lapse monitoring of reservoir dynamic processes such as hydraulic fracturing, stimulation, and production. The receiver arrays will also monitor the injection of small high-frequency Injectable Acoustic Micro Emitters (IAME) into the fracture network. The small proppant-sized high-frequency seismic sources will be mixed with proppant and used for tracking the true location of the proppant injected into the fracture network. This will allow differentiation of the formation which is only fractured versus the formation that is fractured and propped. It will also monitor the injection process by recording and locating the microseismic events generated by the primary hydraulic fracturing of the reservoir rock, then track the proppant through the recording of microseismic events caused by the injection of the proppant and its movement through both new and old fractures. This will allow separate mapping and monitoring of the fracturing process and the proppant injection process.
In summary, this project is developing a multi-reservoir attribute mapping and monitoring system to provide a new level of understanding of shale reservoirs that will increase production and resource recovery rates, while making the shale gas and oil production processes more sustainable and safe for surrounding communities through improvements in production efficiency and process control. By moving the seismic source into the borehole, a significant improvement will be achieved in terms of imaging resolution. The effective source frequency will be increased by a factor of 10–20 X relative to surface seismic sources by using 5–1,600 Hz seismic sweeps that simultaneously generate P and S waves.
Paulsson, Inc., 16543 Arminta Street, Van Nuys, CA 91406-1745
TdVib LLC, 2121 Industrial Park Road, Boone, IA 50036
Seismic Source, 9425 E. Tower Rd., Ponca City, OK 74604
Terves LLC, 24112 Rockwell Drive, Euclid, OH 44117
Pierce Ranch Oil Field Properties, 1181 Pierce Ranch Rd, Pierce, TX 77467
Attribute Imaging LLC, PO Box 838, Simonton, TX 77476
In the U.S., very large UOG resources are found in shale deposits. According to a 2018 estimate in the Annual Energy Outlook 2020 by the Energy Information Administration (EIA), the volume of technically recoverable gas from gas shale is 2,829 trillion cubic feet (TCF) – enough for 92 years of consumption at the 2018 level of 31 TCF. EIA also estimates that in 2018 the U.S. possessed 44 billion barrels of technically recoverable shale oil. However, production of these shale gas and oil resources is often very inefficient, with UOG oil recovery rates reported being as low as 5 – 8%. Thus, a tremendous additional resource is available at known locations if an improved recovery can be designed and implemented. The first step in this process is to generate better images that will lead to an improved understanding of these complex reservoirs. The lack of a detailed understanding of the reservoir and production processes are currently creating a significant environmental impact that can be lessened while improving the economics of gas resource extraction. This can be accomplished by mapping the natural fractures in greater detail than what is possible today and monitoring at much greater resolution than is possible with today’s surface based imaging technologies, the induced hydraulic fracturing and proppant distribution in the fractures as well as the subsequent production.
It has been shown that seismology, using surface seismic sources and receivers, is technically able to image geology in 3D, albeit in low resolution, and monitor the production process using seismic data from surface seismic vibratory sources (VibroSeis). It is thus the resolution that is currently lacking.
It is well established that if large volumes of high quality borehole seismic data is recorded in vertical and horizontal boreholes drilled to and into shale gas and oil reservoirs, the data can be used to image and monitor the reservoirs in 3D/4D in higher resolution. Using borehole seismic receivers to record the data will improve the resolution by 2 – 4 times over the resolution provided by the surface seismic sources and receivers since the seismic data only needs to penetrate the near surface attenuating formation once. If the surface layer is avoided all together by placing both the sources and the receivers in boreholes, further improvement in the resolution by a factor of 10 – 20X is possible. This will lead to a step change in producers’ understanding of the Oil & Gas extraction process that is only possible by applying large arrays of advanced seismic mapping and monitoring technologies recording a full suite of high quality seismic data.
Borehole seismic acquisition and imaging techniques are the most effective and highest resolution techniques to investigate complex UOG reservoirs. Therefore, Paulsson’s (PI) approach to improve the UOG production process is to design, develop, and laboratory and field test a more sensitive and more effective high temperature seismic imaging and monitoring system. We design and build fully operational prototype vector borehole seismic sources which are engineered for deployment with seismic vector receivers in the same well. PI’s single well seismic system will detect very small changes in fracture properties and orientation, volumetric stress, pore pressure, fluid conductivity and types, proppant distribution, fluids, and saturation. The system will also be able to monitor and map passive seismic data from fracturing or fluid flow as well as data from surface seismic sources. Vibratory seismic sources are preferred since they couple high frequency signals much more effectively into the survey formation than impulsive sources.
Our new borehole seismic system will have a profound effect on our ability to produce our oil and gas reservoirs. High resolution true depth imaging and monitoring of shale gas and oil reservoirs are critical to effectively produce and manage UOG reservoirs. In the past, borehole seismic imaging and monitoring have shown great potential to provide the high fidelity information necessary to better manage these reservoirs. However, legacy seismic techniques have in many ways fallen short; the amount of data has not been sufficient, the quality of the data has many times been poor, and the modeling and processing technologies have fallen short.
PI will build a borehole seismic system that overcomes the shortfalls of the existing borehole seismic acquisition and processing technologies. The new borehole seismic system will allow deployment in both vertical and horizontal wells, which is not possible with commercial systems today without using expensive and fragile well tractors for the deployment. Our new single-well seismic source-receiver system will have a bandwidth from 5 to 1,600 Hz using active vibratory seismic vector sources, which will provide for much broader bandwidth data than available from any existing commercial or research seismic system. The receivers will also record microseismic data extending the useful bandwidth to at least 8,000 Hz. The new all optical based vector sensor system will be about 100 times more sensitive than geophone based seismic systems. The new system will deploy sensors with an 80 dB rejection of out-of-plane seismic energy allowing for a precise location of reflections and microseismic events. The Fiber Optic Seismic Vector Sensor (FOSVS) system will also allow for source and receiver deployment in deeper wells, at higher pressures and temperatures than what is possible today. In combination, our new fiber optic based seismic sensor and downhole seismic sources will record far superior multi-component high-fidelity data, allowing for superior imaging, detection, and location of all seismic events.
The downhole source and receiver system will integrate the IAME into the overall seismic system. The development of IAMEs, together with the means to record the high-frequency seismic data the IAME generate, will for the first time provide operators of UOG resources with a proppant tracking technology that potentially allows the operators to calibrate and tune the hydro-fracturing, proppant injection and oil production processes, and thereby significantly increase the recovery of the hydrocarbon resources.
Under this project, PI is developing a broad-bandwidth downhole seismic vibratory source that will be combined with our existing FOSVS. The new source is designed to be clamped to the inside of the borehole wall and generate and couple non-destructive seismic energy in three modes: Axial, Torsional and Radial into the geologic formation. The three source motions will generate complimentary seismic wavefields, enabling the combination of 3C seismic sources with 3C optical accelerometers thereby generating 9C seismic data. Together, the source and the receivers will be able to image vertical faults and salt domes and monitor reservoir changes that are invisible to surface seismic techniques.
The clamped multi-component seismic vibratory source system has been designed and an axial prototype has been built. The prototype downhole seismic source was tested in a laboratory setting and in a small-scale field test achieving 10–1,600 Hz sweeps and a maximum force of over 339 lbf (1,509 N). We expect to be able to achieve a force in excess of 2,248 lbf (10,000 N) in the same broad frequency band during the next phase of the development project.
PI has designed the borehole seismic vibratory sources to be deployed using the same clamping system that secures our optical seismic vector receivers to the borehole wall, thereby effectively coupling the seismic energy to the borehole. This deployment system has also been shown to eliminate any tube waves which is critical capability for a single well seismic system. The first source tested generates a borehole axial oscillating point force. Other directional seismic sources that will be included in the future will use torsional and radial source motions that generates complimentary radiation patterns. The new single well seismic system has been designed to be deployed using our existing small diameter drillpipe, so the sensor arrays can be deployed in vertical, deviated and long reach horizontal wells. The source will be deployed on the same system concurrently with the receivers.
The power of vibratory seismic sources is two-fold. First, the time distributed energy providing a low instantaneous non-destructive force compared with impulsive sources, (i.e. low instantaneous stress), which enables an effective elastic coupling of the energy. This issue is particularly important when the source is deployed in a high cost borehole. Any source induced damage to the casing-cement interface would render the borehole seismic source unacceptable to any oil and gas field operations. Second, the correlation process used during the processing of seismic vibrator data improves the signal-to-noise ratio by an estimated 40 dB. This improvement in the Signal to Noise ratio allows for a longer-range detection of data transmission and reflection targets.