Hydraulic Fracture Monitoring Research Articles

Catching a (micro)break in Wyoming

SEG convened a forum last spring on the current state of microseismic monitoring of hydraulic fracture well stimulation. The forum was held in scenic Ucross, Wyoming, in the shadow of the Big Horn Mountains, well away from the hurly burly of life in the oil field these days. Cell phones didn't even work. That made for a very full, intense, focused, and refreshing three days and nights for 32 professionals from around the globe who represented service providers, operators, and academia. These engineers, geologists, and geophysicists shared 30 presentations and then continued the debate and discussion late into the evening each night over dinner and a nightly campfire, and with plenty of their favorite after-dinner refreshments. Our host, Apache Corporation, whose facility was borrowed for the event, provided five-star treatment, and many wished the three days had passed not quite so quickly.

Technology Focus: Hydraulic Fracturing (March 2008)

Technology Focus The challenge to minimize our environmental impact falls on every aspect of the global community, including the hydraulic-fracturing industry. In our industry, some companies have taken steps to reduce their effect on the environment. In some cases, the action has even maximized economic value. For example, in Wyoming, "green completions" are performed with fracture-treatment flow-back through separators facilitating in-line cleanup (Mullen et al. 2004). This method maximizes gas sales, allows water recycling for future stimulations, and minimizes the amount of gas flared into the atmosphere. In Pinedale, Wyoming, and North Rulison, Colorado, where well spacing has decreased to as small as 5 acres, fracture treatments can be performed from a central area or pumping station. This manner of stimulation not only reduces costs and improves operational efficiencies but also reduces the topographical effects in environmentally sensitive areas (Colorado River District Water Seminar 2007). Our industry's examples of innovative environmental policy are isolated. In my opinion, much more is needed to avoid our industry facing extreme criticism in a world that will soon demand much higher standards. Our industry must seek government support of environmental initiatives (e.g., research grants and tax incentives); monitor environmental effects and ensure that environmental issues have a prominent role in forming industry/organization/individual goals and objectives; and support development of environmentally friendly technologies, avoiding technologies that fail to meet these requirements. When reading these key papers, consider the need for these hydraulic-fracturing innovations to join with world-class environmental practices to achieve a sustainable outcome for both our industry and our planet. References Colorado River District Water Seminar. 2007. Piceance Basin—Cornerstone Asset. http://www.crwcd.org/media/uploads/Dave_Cesark.pdf. Accessed 7 February 2008. Mullen, M., Dickerman, R., Stabenau, J., Dobson, M., and Ohlson, C. 2004. Integrated Process Improves Production of the Almond Formation in the Wamsutter Field, Wyoming: A Low-Permeability Case Study of Five Years of Continuous Improvement in Well Performance. Paper SPE 90792-MS presented at the SPE Annual Technical Conference and Exhibition, 26–29 September, Houston. DOI: 10.2118/90792-MS. Hydraulic Fracturing additional reading available at the SPE eLibrary: www.spe.org SPE 110068 • "Optimizing the Completion of a Multilayer Cotton Valley Sand Using Hydraulic-Fracture Monitoring and Integrated Engineering" by Jason Baihly, Schlumberger, et al. SPE 106111 • "Effects of Frictional Geological Discontinuities on Hydraulic- Fracture Propagation" by X. Zhang, SPE, CSIRO Petroleum, et al. SPE 106269 • "Development of a Methodology for Hydraulic-Fracturing Models in Tight, Massively Stacked, Lenticular Reservoirs" by Christopher A. Green, SPE, Perenco UK, et al. SPE 110517 • "Microseismic Monitoring Quality-Control (QC) Reports as an Interpretative Tool for Nonspecialists" by U. Zimmer, Pinnacle Technologies, et al.

Detection of repeated hydraulic fracturing (out-of-zone growth) by microseismic monitoring

Hydraulic fracture treatments are commonly carried out in several space- and time-staggered stages which are designed to stimulate isolated segments of a reservoir (i.e., multistage fracturing). However, repeated hydraulic fracturing of reservoir segments fractured in previous stages is commonly observed. In multistage fracturing this problem is also known as out-of-zone or out-of-pay growth, and we shall call it cross-stage fracturing in this article. Cross-stage fracturing can be detected by automated identification of multiplets, i.e., microseismic events with similar source mechanisms and nearly identical location. We applied multiplet identification to detect cross-stage fracturing on two hydraulic fracture monitoring data sets (Canyon Sand and Barnett Shale formations) one of which is described in this paper. We verified this detection method with the initial microseismic events locations. Cross-stage fracturing was detected only a few minutes after the first microseismic events had been detected an...

Wavelet packet polarization method for an automatic detection of P and S wave arrivals

A new method is proposed for detecting P and S wave arrivals in the problem of passive seismic monitoring. This method is based on the wavelet packet decomposition of three-component seismic traces, their automatic quality control, and the calculation of the principal components of the traces in overlapping packet frequency bands and in scale-dependent moving time windows. The wave arrivals times are estimated by means of a robust iterative procedure of adjusting hyperbolic traveltime curves to the initial estimates of arrival times determined from the maximum values of the multilevel measure of the nonstationarity of each trace. The method has been developed for applications in the cases of a large number of bad single-component traces and a high noise level. To illustrate its application, the method is applied to the data set of the Cotton Valley experiment on the seismic monitoring of hydraulic fractures in a fractured gas reservoir.

Active seismic monitoring of hydraulic fractures in laboratory experiments

In scaled laboratory tests, we perform acoustic measurements in a time-lapse sequence to separate the fracture response from the background signal. Using both compressional and shear waves (that are very sensitive to fluid filled fractures) we can, not only detect the hydraulic fracture, but also characterize its shape and geometry during its growth. We show the application of the technique to propagation and reopening of hydraulic fractures. During fracture growth the acoustic waves excite diffractions at the tip of the fracture. Depending on the acquisition geometry, we detect many events related to surface waves propagating along the fracture. Also, we observe that shear waves detect the migration of the fluid front during reopening of a pre-existing hydraulic fracture, in contrast with the compressional waves which are insensitive to the fluid front during reopening.

Acoustic emission monitoring of hydraulic fracturing in laboratory and field

In the hydraulic fracturing tests, water was injected into four kinds of granitic rock specimens with different grain sizes. The fault plane solutions of acoustic emission (AE) indicated that the shear fracturing is dominant in the specimens with larger grains whereas the tensile fracturing is dominant in those of smaller grains. In addition, the experiments were conducted in granitic rock specimens of the same kind, under three different conditions: injection of water, injection of viscous oil and pressurization via a urethane sleeve. The shear fracturing was dominant due to water injection and the pressurization whereas the tensile fracturing was dominant due to viscous oil injection. Further in a field, AE was monitored by a borehole sonde in the hydraulic fracturing to measure rock stress. The AE count rates increased with closing and reopening hydraulically induced cracks. The result suggested that AE monitoring could improve the reliability and the accuracy of hydraulic fracturing stress measurements.

Monitoring the width of hydraulic fractures with acoustic waves

During scaled hydraulic fracturing experiments in our laboratory, the fracture growth process is monitored in a time‐lapse experiment with ultrasonic waves. We observe dispersion of compressional waves that have propagated across the hydraulic fracture. This dispersion appears to be related to the width of the hydraulic fracture. This means that we can apply the dispersion measurements to monitor the width of the hydraulic fracture in an indirect manner. For a direct determination of the width, the resolution of the signal is required to distinguish the reflections that are related with two distinct fluid/solid interfaces delimiting the hydraulic fracture from its solid embedding. To make this distinction, the solid/fluid interfaces must be separated at least one eighth of a wavelength and represent sufficient impedance contrast. The applicability of the indirect dispersion measurement method however, extends to a fracture width that is in the order of 1% of the incident wavelength. The time‐lapse ultrasonic measurements allow us to relate the small difference in arrival time and amplitude between two measurements solely to the small changes in the width of the fracture. Additional experimental data show that shear waves are completely shadowed by hydraulic fractures, indicating that there is no acoustic contact mechanism at the fracture interface. Therefore we think it is appropriate to use a thin fluid‐filled layer model for these hydraulic fractures instead of the standard empirically oriented linear slip model. Nevertheless, the thin layer model is consistent with the linear‐slip model, if interpreted correctly. A comparison of width measurements inside the wellbore and width estimates by means of dispersion measurements close to the wellbore shows that the method can be successfully applied, at least under laboratory conditions, and that small changes in the width of the fracture are directly expressed in the dispersion of the transmitted signal. This opens the way for the important new application of width monitoring of hydraulic fractures.