Binder, Gary (Colorado School of Mines) | Titov, Aleksei (Colorado School of Mines) | Tamayo, Diana (Colorado School of Mines) | Simmons, James (Colorado School of Mines) | Tura, Ali (Colorado School of Mines) | Byerley, Grant (Apache Corporation) | Monk, David (Apache Corporation)
In 2017, distributed acoustic sensing (DAS) technology was deployed in a horizontal well to conduct a time-lapse vertical seismic profiling (VSP) survey before and after each of 78 hydraulic fracturing stages. The goal of the survey was to more continuously monitor the evolution of stimulated rock throughout the treatment of the well. From two vibroseis source locations at the surface, time shifts of P-waves were observed along the well that decayed almost completely by the end of the treatment. A shadowing effect in the time shifts was observed that enables the height of the stimulated rock volume to be estimated. Using full wavefield modeling, the distribution of time shifts is well described by an equivalent medium model of vertical fractures that close as pressure declines due to fluid leak-off. Converted P to S waves were also observed to scatter off stimulated rock near some stages as confirmed with full wavefield modeling. The signal-to-noise ratio is a limitation of the current dataset, but recent improvements in DAS technology can enable stage-by-stage monitoring of the stimulated rock height, fracture compliance, and decay time as a well is completed.
Distributed Acoustic Sensing (DAS) has opened new possibilities for seismic monitoring of unconventional reservoirs. Using a laser interrogator to launch light pulses down a fiber optic cable, dynamic strain changes can be sampled along the cable from the phase shift of light backscattered to the interrogator (Hartog, 2017). Since the fiber optic cable can be permanently cemented outside the casing in a borehole, highly repeatable vertical seismic profiling (VSP) surveys can be acquired frequently without costly wireline geophone deployments that interfere with well treatment activities (Mateeva et al., 2017; Meek et al., 2017).
As described by Byerley et al., 2018, a unique interstage DAS VSP survey was conducted in 2017 during the stimulation of a horizontal well targeting the Wolfcamp formation in the Midland Basin, Texas. Using two vibroseis source locations offset about 1 mile from the heel and toe of the well, DAS data was acquired in the treatment well before and after each of 78 hydraulic fracturing stages. At the expense of fewer source locations, this type of acquisition allows the evolution of the stimulated rock volume (SRV) to be monitored on a stage-by-stage basis as the well is treated.
Carr, Timothy (West Virginia University) | Ghahfarokhi, Payam (West Virginia University) | Carney, BJ (Northeast Natural Energy, LLC) | Hewitt, Jay (West Virginia University) | Vargnetti, Robert (USDOE National Energy Technology Laboratory)
The Marcellus Shale Energy and Environment Laboratory (MSEEL) involves a multidisciplinary and multi-institutional team of universities companies and government research labs undertaking geologic and geomechanical evaluation, integrated completion and production monitoring, and testing completion approaches. MSEEL consists of two legacy horizontal production wells, two new logged and instrumented horizontal production wells, a cored vertical pilot bore-hole, a microseismic observation well, and surface geophysical and environmental monitoring stations. The extremely large and diverse (multiple terabyte) datasets required a custom software system for analysis and display of fiber-optic distributed acoustic sensing (DAS) and distributed temperature sensing (DTS) data that was subsequently integrated with microseismic data, core data and logs from the pilot holes and laterals. Comprehensive geomechanical and image log data integrated with the fiber-optic data across individual stages and clusters contributed to an improved understanding of the effect of stage spacing and cluster density practices across the heterogeneous unconventional reservoirs such as the Marcellus. The results significantly improved stimulation effectiveness and optimized recovery efficiency. The microseismic and fiber-optic data obtained during the hydraulic fracture simulations and subsequent DTS data acquired during production served as constraining parameters to evaluate stage and cluster efficiency on the MIP-3H and MIP-5H wells. Deformation effects related to preexisting fractures and small faults are a significant component to improve understanding of completion quality differences between stages and clusters. The distribution of this deformation and cross-flow between stages as shown by the DAS and DTS fiber-optic data during stimulation demonstrates the differences in completion efficiency among stages. The initial and evolving production efficiency over the last several years of various stages is illustrated through ongoing processing of continuous DTS. Reservoir simulation and history matching the well production data confirmed the subsurface production response to the hydraulic fractures. Engineered stages that incorporate the distribution of fracture swarms and geomechanical properties had better completion and more importantly production efficiencies. We are working to improve the modeling to understand movement within individual fracture swarms and history match at the individual stage. As part of an additional MSEEL well pad underway incorporates advanced and cost-effective technology that can provide the necessary data to improve engineering of stage and cluster design, pumping treatments and optimum spacing between laterals, and imaging of the stimulated reservoir volume in the Marcellus and other shale reservoirs.
Is the Cloud Mature Enough for High-Performance Computing? Data volumes are growing at an exponential rate. How can high-performance computing solutions help operators manage these volumes? This paper describes interpretation results of a 4D seismic-monitoring program in a challenging Middle East carbonate reservoir. This paper discusses a project with the objective of leveraging prestack and poststack seismic data in order to reconstruct 3D images of thin, discontinuous, oil-filled packstone pay facies of the Upper and Lower Wolfcamp formation.
Distributed acoustic sensing (DAS) is a rapidly evolving fiber optic technology for monitoring cement curing, perforation performance, stimulation efficiency, and production flow and, more recently, for performing vertical seismic profiling (VSP). VSP data can be acquired and processed to determine velocity models that are used in surface seismic imaging for reservoir characterization, or for microseismic monitoring of hydraulic fracturing operations. The limitation of conventional VSP data acquisition has been well accessibility, with wireline-conveyed tools deployed during openhole or casedhole logging campaigns before well completion or during workovers. Fiber optic cable conveyance by coiled tubing (CT) expands the opportunity for VSP data acquisition during planned CT interventions. This paper presents an example of a CT DAS VSP acquisition. The processing steps are shown to overcome some of the noise challenges inherent in CT DAS data, such as persistently strong borehole tube waves induced from the surface operations activities. A case study is shown for the depth tie between surface seismic data and the CT DAS VSP derived corridor stack image, demonstrating the viability of CT deployed fiber to acquire DAS VSP data.
Amer, AimenAi (Schlumberger) | Sajer, Abdulazziz (Kuwait Oil Company) | Al-Adwani, Talal (Kuwait Oil Company) | Salem, Hanan (Kuwait Oil Company) | Abu-Taleb, Reyad (Kuwait Oil Company) | Abu-Guneej, Ali (Kuwait Oil Company) | Yateem, Ali (Kuwait Oil Company) | Chilumuri, Vishnu (Kuwait Oil Company) | Goyal, Palkesh (Schlumberger) | Devkar, Sambhaji (Schlumberger)
Producing unconventional reservoirs characterized by low porosities and permeabilities during early stages of exploration and field appraisal can be challenging, especially in high temperature and high pressure (HPHT) downhole conditions. In such reservoirs, the natural fracture network can play a significant role in flowing hydrocarbons, increasing the importance of encountering such network by the boreholes.
Consequently, the challenge would be to plan wells through these corridors, which is not always easy. To add to the challenge, well design restrictions dictate, the drilling of only vertical and in minor cases deviated wells. This can reduce the possibility of drilling through sub-vertical fracture sets significantly, and once seismic resolution is considered, it may seem that all odds are agents encountering a fracture network.
This article addresses a case where a vertical well is drilled, in the above-mentioned reservoir setting, and missed the natural fracture system. The correct mitigation can make a difference between plugging and abandoning the well or putting it on production.
The technique utilized is based on a borehole acoustic reflection survey (BARS) acquired over a vertical well to give a detailed insight on the fracture network 120 ft away from the borehole. Integrating this technique with core and high-resolution borehole image logs rendered an excellent match, increasing the confidence level in the acoustically predicted fracture corridors.
Based on these findings new perforation intervals and hydraulic stimulation are proposed to optimize well performance. Such application can reverse the well decommissioning process, opening new opportunities for the rejuvenation of older wells.
Wang, Herbert (University of Wisconsin-Madison) | Fratta, Dante (University of Wisconsin-Madison) | Lord, Neal (University of Wisconsin-Madison) | Zeng, Xiangfang (Institute of Geodesy and Geophysics, Chinese Academy of Sciences) | Coleman, Thomas (Silixa LLC)
Each of the Wisconsin field trials used active sources that ranged from a hammer source to fixed and truck-mounted 40-270 kN swept-frequency sources. Two of the field trials were near highways where traffic was a source of ambient noise. Geophones were colocated near the DAS cable to benchmark and complement the DAS response. The goals of the studies were to understand the ground motions recorded by DAS and to prototype DAS applications using active sources, ambient or traffic noise, and earthquakes. Introduction Distributed Acoustic Sensing (DAS) technology can image the subsurface using dense arrays whose spatial resolution is on the order of ten meters and whose dimensions can be tens of kilometers given the relatively low cost of fiberoptic cable and currently available interrogator and processing technology (Parker et al., 2014). The flexibility of fiberoptic cable allows for many possible geometric configurations.
Chalenski, D.A. (Shell International Exploration and Production Inc.) | Lopez, J. (Shell International Exploration and Production Inc.) | Hatchell, P. (Shell International Exploration and Production Inc.) | Grandi, S. (Shell Global Solutions International B.V.) | Broker, K. (Shell Global Solutions International B.V.) | Hornman, K. (formerly with Shell Global Solutions International B.V.) | Anderson, B. (ASV Global Inc.) | Marzolf, T. (ASV Global Inc.) | Chance, S. (ASV Global Inc.) | Jurisich, J. (ASV Global Inc.) | Hibben, T. (WGP Group Ltd.) | Shute, R. (WGP Group Ltd.)
We present recent work on developing an autonomous, unmanned marine seismic concept for 4D reservoir surveillance called Rapid Autonomous Marine 4D (RAM4D). It aims to reduce the total cost and footprint of the source side of seismic acquisitions by combining standard geophysical equipment with an Autonomous Surface Vessel (ASV), resulting in a lower anticipated day rate and reduced exposure to humans and the environment in deepwater operations. We present the ongoing development of RAM4D and results of a lake field trial completed in October 2017 in Lafayette, LA (USA) during which we acquired autonomous, unmanned 4D baseline and monitor surveys. We discuss technological improvements under development to adapt the current generation of autonomous vessels to the demands of 4D seismic. We also introduce a model for the cost of DAS VSP surveys enabled by RAM4D, which shows that dual RAM4D vessel operations are more robust to downtime. We conclude that market forces will be required to achieve an aspired survey cost that would disrupt the traditional seismic vessel market enough to enable wide adoption.
Presentation Date: Monday, October 15, 2018
Start Time: 1:50:00 PM
Location: 204C (Anaheim Convention Center)
Presentation Type: Oral
ABSTRACT: Polarized shear wave travel times and spectral changes are used to determine natural fracture intensity and orientation. The study develops this concept for fracture density mapping associated with laboratory hydraulic fracturing experiments in pyrophyllite, a fine grained monomineralic metamorphic rock comprised of the mineral pyrophyllite, and hence an analogy for natural shale. A 6” long horizontal cylindrical pyrophyllite sample (wellbore parallel to bedding plane) is hydraulically fractured using water under uniaxial conditions with an effective maximum stress of 830 psi applied perpendicular to the bedding plane (breakdown pressure – 1914 psi). The pyrophyllite sample exhibits a P-wave anisotropy of 18% and displays transverse anisotropy. Acoustic emissions (AE) were recorded using sixteen 1-MHz piezoelectric P-wave transducers; the spatial acoustic emission density was mapped. Berryman’s strong anisotropy model was used to build an anisotropic velocity model for AE event locations. Post-fracturing shear wave velocity measurements were conducted using an array of seven pairs of polarized shear wave transducers which were systematically stepped across the end faces of the cylinder producing 931 discrete shear wave velocity measurements for every polarization. These arrays are used to record shear wave travel time with polarizations parallel and perpendicular to the direction of maximum stress before and after hydraulically fracturing the sample. Fourier analysis of the post-failure recorded shear waveforms mapped attenuation associated with the SRV which was consistent with the shear wave velocity analysis. The geometry of experiment reflects hydraulic stimulation in a horizontal wellbore condition. Orthogonally polarized shear velocities show measurable differences which reflect a preferred fracture orientation, with more than 32% post fracture reduction in shear velocity, in the fractured plane. The polarized shear wave map is consistent with the AE event locations recorded during the fracturing process. Secondary microfractures appear normal to the primary fractures in the horizontal plane.
Hydraulic fracturing in combination with horizontal drilling has made the extraction of hydrocarbon from certain geologic formations economically feasible, thereby boosting the available energy resources in US. It has induced an oil and gas “boom” in various parts of the country.
There are arguments that state that the physical laws governing fractures are known and fracture models are accurate, but the emergence of ‘new mechanisms’ every few years suggests that the basic physics incorporated into models has not been as comprehensive as required to model a fracture fully (Warpinsky, 1996).
It has become critical to understand the location of fracture and the extent to which it stimulates a reservoir to plan future drilling and completions. Thus, mapping hydraulic fracture is essential. There have been various methods that have been used to map the fracture propagation. Commonly used method in the field is to record the microseismic events generated because of release of elastic energy during the fracturing process, as established by Albright and Pearson, 1982, Rutledge and Phillips, 2003 and Warpinski et al., 2004. Acoustic emission (AE) techniques had been utilized in mapping hydraulic fractures and assessing fracture mechanisms in laboratory studies as well (Matsunaga et al., 1993, Masuda et al., 2003, Damani et al., 2012). Other methods include using temperature sensors to monitor the fracture propagation in real time (Holley et al., 2010). Third common method is to use Scanning Electron Microscope (SEM) to map the stimulated reservoir volume of the fracture generated by taking out a chip out of the fractured sample for analysis (Damani et al., 2012).
ABSTRACT: We imaged confining-pressure induced changes in dry, unconsolidated quartz sand with micro X-ray computed tomography (CT) while simultaneously recording ultrasonic P-wave velocities. Increasing confining pressure (atmospheric pressure to 27.6 MPa) leads to 30% reduction in porosity, over 60% decrease in grain size due to extensive grain damage and changes in coordination number and contact radius. We used image-derived porosity, grain radius, contact number and contact radius to compute P-wave velocities with the Hertz-Mindlin model. Our observations showed that numerous assumptions of the widely used Hertz- Mindlin model are violated in this type of sediment and the model drastically overpredicts velocities. Our results indicate that the Hertzian contact model should be applied with caution to angular, unconsolidated sediments.
The need for understanding of elastic properties in unconsolidated sediments ranges from soils, structural and civil engineering applications to unconsolidated petroleum reservoirs. Since seismic imaging is the most commonly used exploration method, there is a need to understand and model pressure dependent elastic moduli and velocities of unconsolidated granular media. Studies of this pressure dependence are subject to numerous uncertainties.
The Hertzian contact model is commonly used to describe elastic properties of unconsolidated granular media (Mindlin, 1949, Digby, 1981, Murphy et al., 1984, Zimmer et al., 2006, Bachrach and Avseth, 2008). It is a theoretical model for the elastic properties of a pack of identical spheres. Despite being a widely applied model for unconsolidated sediments, discrepancies between measured velocities and model predictions are common (Prasad and Meissner, 1992, Bachrach et al., 2000, Zimmer et al., 2006). Walton, 1987 reduced these mismatches by allowing rotation and slipping of the grain contacts. One of the model's assumptions is pressure- independent, constant grain size. However, pressure- dependent grain crushing and accompanying changes in grain size and sorting have been documented for the type of sediments that the Hertz-Mindlin model is commonly applied to (Prasad and Meissner, 1992, Chuhan et al., 2002, Chuhan et al., 2003, Perry et al., 2016). Grain crushing during burial of sediments occurs until the onset of cementation and is hence important for reservoir quality of consolidated sandstones (Milliken, 1994, Storvoll and Bjorlykke, 2004, Makowitz et al., 2006). In order to image grain texture and gain important insights into the microstructure, rocks are often characterized by 2D-imaging methods, like cathodoluminescence or thin section microscopy which allow important insights into the microstructure. However, such images do not yield quantitative descriptors, such as grain size, size of contact areas and coordination number (number of contacting grains per grain), which are necessary to model the elastic properties. Three dimensional imaging is needed to quantify the changes caused by grain crushing and compaction. Insights into the development of fractures and packing rearrangement with increasing burial are still largely unknown due to a lack of in-situ imaging during pressurization.
ABSTRACT: Monitoring mining-induced seismicity can provide valuable insights into the rock mass response to mining. There are many approaches to monitoring seismicity in mining depending on the mining method, mining geometry, data quality requirements, and acceptable cost of monitoring. One flexible, inexpensive monitoring method is a temporary surface seismic deployment. The National Institute for Occupational Safety and Health has conducted temporary deployments above longwall panels at two longwall coal mines in the western United States. This study evaluates the effectiveness of these deployments in meeting basic monitoring objectives and examines the seismicity recorded at each mine. A total of 901 events were detected at the first mine and 30 events were detected at the second mine. Event magnitudes ranged from 0.1 to 1.6 for one mine and from 0.4 to 0.7 at the other. The two deployments were successful in their goals; however, the results highlight the importance of well-designed arrays and accounting for seismic velocity changes caused by mining. Although the deployments only lasted a few weeks, notable seismic features of each panel were observed. The two mines exhibit starkly different responses to similar mining methods, quantified by the rates, magnitudes, and locations of the events.
Mining-induced seismicity (MIS), the release of seismic energy in response to mining, is a common occurrence in many mining operations, especially those employing caving methods such as longwall mining. The occurrence of seismic events rarely implies a hazardous situation; however, the monitoring and analysis of these events can be useful to detect and understand potentially hazardous conditions when they do arise. Detecting these conditions is essential in employing effective mitigation strategies to protect mine workers.
Seismic monitoring is widely employed in mines outside of the United States. For instance, underground gold mines in the Witwatersrand Basin in South Africa have monitored seismicity since the early 20th century. A large number of active mines in the region own and operate in-mine microseismic systems (Reimer and Durrheim, 2012). Many of the advances in mining seismology have come from the region and continuing efforts are focused on understanding MIS mechanisms and developing effective measures to manage seismic risk (e.g., Potvin, 2009, Reimer and Durrheim, 2012). Hardrock mines in Western Australia and Canada also deploy seismic monitoring and hazard assessment techniques (ex., Simser et al., 2015; Knobben, 2017). Seismic monitoring is not limited to hardrock mines. Seismic monitoring is also practiced in the Upper Silesian Coal Basin of Poland, where several mine-operated stations complement a regional seismic network run by the Central Mining Institute (CMI) (Stec, 2007), and in Chinese coal mines, where bursts and bumps are a significant issue (Qi et al., 2015).