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Suarez-Rivera, Roberto (W. D. Von Gonten Laboratories) | Panse, Rohit (W. D. Von Gonten Laboratories) | Sovizi, Javad (Baker Hughes) | Dontsov, Egor (ResFrac Corporation) | LaReau, Heather (BP America Production Company, BPx Energy Inc.) | Suter, Kirke (BP America Production Company, BPx Energy Inc.) | Blose, Matthew (BP America Production Company, BPx Energy Inc.) | Hailu, Thomas (BP America Production Company, BPx Energy Inc.) | Koontz, Kyle (BP America Production Company, BPx Energy Inc.)
Abstract Predicting fracture behavior is important for well placement design and for optimizing multi-well development production. This requires the use of fracturing models that are calibrated to represent field measurements. However, because hydraulic fracture models include complex physics and uncertainties and have many variables defining these, the problem of calibrating modeling results with field responses is ill-posed. There are more model variables than can be changed than field observations to constrain these. It is always possible to find a calibrated model that reproduces the field data. However, the model is not unique and multiple matching solutions exist. The objective and scope of this work is to define a workflow for constraining these solutions and obtaining a more representative model for forecasting and optimization. We used field data from a multi-pad project in the Delaware play, with actual pump schedules, frac sequence, and time delays as used in the field, for all stages and all wells. We constructed a hydraulic fracturing model using high-confidence rock properties data and calibrated the model to field stimulation treatment data varying the two model variables with highest uncertainty: tectonic strain and average leak-off coefficient, while keeping all other model variables fixed. By reducing the number of adjusting model variables for calibration, we significantly lower the potential for over-fitting. Using an ultra-fast hydraulic fracturing simulator, we solved a global optimization problem to minimize the mismatch between the ISIPs and treatment pressures measured in the field and simulated by the model, for all the stages and all wells. This workflow helps us match the dominant ISIP trends in the field data and delivers higher confidence predictions in the regional stress. However, the uncertainty in the fracture geometry is still large. We also compared these results with traditional workflows that rely on selecting representative stages for calibration to field data. Results show that our workflow defines a better global optimum that best represents the behavior of all stages on all wells, and allows us to provide higher-confidence predictions of fracturing results for subsequent pads. We then used this higher confidence model to conduct sensitivity analysis for improving the well placement in subsequent pads and compared the results of the model predictions with the actual pad results.
ABSTRACT Three surveys of an 8km long subsea pipeline laid on a soft clay seabed were performed using side scan sonar profiler. The free span characteristics over the field surveys were examined and compared with the conventional free span design criteria. The comparison results indicate some shortcomings in the conventional design approach, with more refined evaluation of the critical spans allowing for optimization of intervention works. A refined free span acceptance criterion is developed based on the field observations. INTRODUCTION The presence of a pipeline on a seabed promotes local sediment transport that leads to scouring of sediment from around and underneath the pipeline. The scouring causes the pipeline to develop a free span. The scour problem around subsea pipelines has been studied extensively by researchers (e.g. Fredsoe, 1988; Mork, 1999) as well as in the SCARCOST project (Sumer et al., 2001), MOBILEspan Joint Industry Project (Madeley et al., 2015) and research work on studying the existing Woodside North West pipeline behaviour by University of Western Australia (Leckie et al., 2015). The conventional approach to design a pipeline assumes that the seabed itself is stable and so the pipeline span remains stationary. This assumption is difficult to justify because substantial experiments and field evidence have demonstrated that the seabed becomes unstable under severe wave and current condition (Leckie et al., 2015; Teh et al., 2003). Because of the uncertainties of the pipeline span characters, Mork (1999) and Madeley et al. (2015) proposed probabilistic assessment to simulate the span development process. However, the probabilistic approach is not commonly used, which may be because of the limited availability of reliable statistical distributions of span characteristic data to consider in the pipeline design. The objective of this paper is to present the field observation of a pipeline from three surveys and to discuss the shortcomings in the pipeline free span design. It is motivated by questions about what the actual behavior of pipeline free spans is over the design life and its impact on the pipeline integrity.
Zhang, Zhishuai (Chevron Energy Technology Company) | Fang, Zijun (Chevron Energy Technology Company) | Stefani, Joe (Chevron Energy Technology Company) | DiSiena, James (Chevron Energy Technology Company) | Bevc, Dimitri (Chevron Energy Technology Company) | Ning, Ivan Lim Chen (Chevron Energy Technology Company) | Hughes, Kelly (Chevron Energy Technology Company) | Tan, Yunhui (Chevron Energy Technology Company)
Fiber Optic Sensing, including both low-frequency Distributed Acoustic Sensing (DAS) and Distributed Strain Sensing (DSS), can be used to record strain rate or strain for hydraulic fracturing monitoring in an offset well. However, current work focusses on acquisition, processing, and qualitative interpretation. We investigated the modeling of DAS and DSS strain responses to hydraulic fractures during stimulation process. The modeling work provides valuable insights to understand low-frequency DAS and DSS strain measurements during hydraulic stimulation.
We used the Displacement Discontinuity Method (DDM) to model the strain/strain rate field around kinematic propagating fractures. This efficient method provides a quick assessment of models with various fracture extents and net pressures. It also allows simulating the strain responses to a network of fractures in consideration of their interactions. During the stimulation stage of hydraulic treatment, the fracture propagation is modeled by prescribing gradually increased fracture size and calculating the displacement discontinuities that representing fractures at each step. After the stimulation stops, we assume the fracture extent will not change but the net pressure within the fracture gradually decreases due to fluid leakoff. We calculate the displacement discontinuities representing fractures using the fracture extent and the stress boundary conditions on fractures. The strain and stress projected along the monitoring well are calculated from these displacement discontinuities at each time step and converted to strain rate by taking their time derivatives.
We compared and verified our modeling with field observations from the Hydraulic Fracturing Test Site 2 (HFTS2) project, a research experiment performed in the Delaware Basin, West Texas. For a horizontal monitoring well, modeling results explain heart-shaped extending pattern before a fracture hit, polarity flip during stimulation due to fracture interaction, and V-shape patterns when a fracture bypasses the monitoring well from above or below without intersecting. For a vertical monitoring well, modeling shows the different characters of low-frequency DAS and DSS responses when a fracture is near and far away from a vertical monitoring well for both elliptic fractures and layered fractures.
Geomechanical modeling lays the groundwork for quantitative interpretation and fracture-geometry estimation. Our modeling approach provides insight into unraveling the patterns observed by far-field low-frequency DAS and DSS during hydraulic fracturing. Synthetic modeling results of various scenarios can also be used to improve fiber-optic acquisition design for stimulation monitoring.
Low-frequency DAS and DSS modeling and monitoring integrate information on geomechanics, fluid flow, pressure distribution, earth properties, and fracture propagation. The modeling results and field observations can also be compared and validated with engineering data such as pressure and temperature, with geological data such as cores, and with geophysics data such as microseismic and time-lapse seismic, to provide a comprehensive understanding of hydraulic fractures.
Energy companies conduct environmental risk assessments (ERAs) as part of their risk-management processes to ensure acceptable environmental risk for all operations. In some parts of the world, ERAs are required by regulators to assess risk and as a basis for evaluating risk-reducing measures. The new standardized ERA Acute method has been developed that provides quantitative assessment of environmental impact and risk of acute oil spills covering four environmental compartments: sea surface, shoreline, water column, and seafloor. The method uses oil-drift simulations and valued-ecosystem-components (VECs) data as input. Based on a selection of relevant oil spills, impact and recovery times are calculated for VECs in all compartments using continuous functions.
Cheng, Zhiheng (School of Safety Engineering / North China Institute of Science and Technology) | Feng, Jicheng (School of Safety Engineering / North China Institute of Science and Technology) | Zhao, Zhiyan (China Coal Technology and Engineering Group Corp Shenyang Research Institute) | Sun, Fulong (China Coal Technology and Engineering Group Corp Shenyang Research Institute) | Wang, Xin (Itasca Consulting Canada Inc.)
ABSTRACT: Mining-induced fracture fields play important role in gas extraction of underground coal mines. Low concentration of extracted gas has been observed during the mining of gas burst-prone coal seams in Shaqu Coal Mine, Shanxi province, China. Theoretical analysis and field observation are used to quantity the fractures evolution of 4# coal seam to get an optimal borehole design and enhance the efficiency of gas extraction. In this study, pixel extraction and gray value calculation of borehole images are developed using Matlab, which can be used to obtain the 3D gray value distribution for the borehole images. Based on the 3D gray distributions, the development of borehole fractures is identified and then a proper design of gas extraction borehole sets is determined. Based on the analysis, an area of high density of mining-induced fractures with relative stable overlying strata is found about 25 ∼ 30 m above the working face of the protected coal seam. A proper gas extraction borehole depth is estimated and this in turn will assist in enhancing gas extraction efficiency and improving mine safety.
Mining-induced fractures are formed within surrounding rock mass due to influence of in-situ stress redistribution during the underground mining activities. The mining-induced fractures can accelerate the gas desorption processing in coal and rock masses, in the meantime, the fractures can improve the permeability of coal and rock masses. Flow paths of gas are contracted in the mining-induced fracture zones, which plays important role for the gas extraction and therefore more focuses are paid in the fractured zone area. Gas migration law in coal and rock masses is a very complicated problem. Gas flow pattern and gas accumulation law are determined by characteristics of gas flow path in coal and rock masses, such as the density, expansion, length, and extension direction. The migration and accumulation law of gas in fractured rock masses are the fundamental of gas prevention and development for gas extraction technology. In this manner, based on the field condition of mines, it is important to conduct the research of mining-induced fracture distribution (or the gas flow path distribution) to enhance the gas extraction efficiency, prevent gas disasters, and improve mine safety. In this study, the distribution of mining-induced fractures, namely, gas migration channels in surrounding rock is studied during the mining process for the purpose of improving gas extraction efficiency.
ABSTRACT: Over the past decade, rib failures have resulted in 17 fatalities, representing 52% of the ground-fall fatalities in underground coal mines in the United States. In an attempt to control rib failures in underground coal mines, researchers at the National Institute for Occupational Safety and Health (NIOSH) developed a coal-mass model that is capable of capturing the effect of face cleat and the development of rib fracturing. This paper presents research that is part of a continued effort to calibrate the coal-mass model using monitoring data collected at field sites. This paper presents the results of a field study in a longwall mine operating in the Lower Kittanning coalbed in West Virginia. The deformation of the roof and an instrumented coal pillar were monitored using multipoint extensometers, and stress changes at different depths in the instrumented pillar were monitored via borehole pressure cells (BPCs). The monitoring results in conjunction with visual observations were used to calibrate the controlling parameters of the coal-mass model. These parameters are: (1) a dimensionless parameter called “coal-mass scale” (CMS) which varies from 1 to 100. Small values of CMS represent a small-size coal specimen of high strength, and large CMS values represent a large-size coal specimen of lower strength, and (2) critical plastic shear and tensile strains that control rib fracture. The actual behavior of the coal-mass response and the stress transfer were replicated at three different stages of longwall retreat mining. This work provides a basis for continued research aimed at an engineering-based design of coal pillar rib support design.
Rib falls are a serious hazard in underground coal mines. Rib sloughing can be attributed to mining-induced stresses as well as inherent weaknesses in coal and stone layers composing the rib. Based on reports from the Mine Safety and Health Administration (MSHA), rib falls have killed 17 mineworkers since 2008, representing 52% of the ground-fall fatalities in underground coal mines in the United States (MSHA, 2018; Rashed et al., 2018). Also, failing ribs can indirectly contribute to roof and floor instabilities by increasing opening widths across intersections and entryways. Factors affecting rib stability in coal mines are numerous and mutually interacting. These factors include, but are not limited to, mining height and overburden depth, interburden thickness for multiple-seam mining, coal strength, cleat density, entry direction with respect to cleat orientation, existence or absence of partings in the coal, percentage of extracted roof and/or floor rock, and density of rib bolt support (Mohamed et al., 2018). The two main factors that lead to a higher risk of rib falls are thicker coal seams and higher stress levels (Rashed et al., 2019).
An Unmanned Aerial Vehicle (UAV)-based system was developed to acquire a digital elevation model (DEM) of exposed tidal flats based on the structure from motion (SfM) algorithm. Global Position System-Real Time Kinematic (GPS-RTK) was utilized to measure the underwater portion, consisting of 111 points in 16 cross sections. Then entire 3-dimensional topography of tidal creek was acquired by combining these two approaches. This method can be used for detection and spatial analyses of tidal creeks and can provide accurate insights into the processes related to natural and/or human-related development of tidal creeks.
Characterized by large width and gentle slope, the muddy intertidal zone is widely distributed in the world (Zhang et al., 2016). The landward part of the muddy flats is covered primarily by halophytic vegetation which are regularly submerged during high tide, while the seaward part is subject to bare flats with the elevation between the low and high tidal water levels. As a sensitive area of land-sea dynamic interaction, tidal flats have important ecological function, coastal protection and socio-economic value (Chen et al., 2017). Tidal creeks are an important geomorphic unit in tidal flats systems, and are formed by ocean dynamics, especially by tidal actions (Teal, 1962). Distribution, spatial and temporal variations and geometric characteristics of tidal creeks control the flow, nutrients, deposition rate flux and biological growth in tidal flat areas (Lerberg et al., 2000; Mallin & Lewitus, 2004). It is an important link to study the response of tidal flat system to environmental change to grasp the regularity of the tidal creeks morphological change.
Although field observations are laborious in the intertidal mudflats (Gong et al., 2017), they are a formidable tool for improving our understanding of tidal flat evolution and the validation of mathematical and numerical models. Compared with traditional manual measurement, remote sensing is a relatively easy way to obtain field data. At present, remote sensing is the main method to study the morphological changes of tidal creeks, but it is limited to the planimetric morphology of tidal creeks (Fagherazzi et al., 1999; Huang, 2004). In-situ field observation has high-precision but difficult to realize since the muddy flats are hard to walk. Existing methods applied to investigate geomorphologic features of tidal creeks are commonly based on physical experiments (Kleinhans et al., 2012; Stefanon et al., 2010; Tambroni et al., 2005) and/or numerical models (Horton, 1945; Xu et al., 2017; Zhou & Coco et al., 2014; Zhou & Olabarrieta et al., 2014). However, the entire 3dimensional topography of tidal creeks including both exposed and submerged portion after the ebb, has not yet obtained by previous study. On one hand the underwater topography cannot be obtained by remote sensing, on the other hand the water depth in the tidal creek sometimes is too shallow because of ebb to use ship-borne echo-sounder measurement. Therefore, the overall morphological feature and the ontogeny of tidal creeks remain elusive.
Increasing concentration of NO3-N in Kumamoto’s water possibly due to infiltration of toxic elements (e.g. fertilizers) has become a big concern. Some lactic acid bacteria (LAB) have the capability to absorb some metals. The main objective of this research is to detect suitable LAB strain (TOKAI strain) to adopt the biosorption capability of LAB to reduce the amount of NO3-N in Kumamoto’s water. Different incubation conditions are applied and concentrations of NO3-N of samples are measured. Several TOKAI strains have been found to be effective in reducing NO3-N.
Kumamoto is located on the Kyushu island in the southwest part of Japan and was hit by a magnitude 7.3 earthquake in 2016. Kumamoto is very famous for its bays, especially for its contribution to fisheries and seaweed culturing. Kumamoto bay area (i.e. Ariake Bay and Isahaya Bay) is famous for owning majority of Japan’s remaining tidal flats and its sea resources. Ariake Bay is the largest bay of Kyushu area, located in the west coast of the island. However, the bay has witnessed frequent red tides since the 1960s (Tsutsumi et al, 2015). The number of red tides has especially increased since the second half of the 1990s. It is a phenomenon that occurs due to excess of nutrition in the water that leads to overpopulation of algae. The numerous algae discolor the water making it red and deplete oxygen and some algae also release toxin. The lack of oxygen and presence of toxins disrupt the coastal ecosystem by imposing harm on the sea creatures and human beings. In the subtidal areas of the Ariake Bay, a noticeable increase in the amount of the autumn bloom of the phytoplankton has been observed as red tides have covered the inner part of the bay regularly.
The nutrient input from land to bay has fluctuated through years in Kumamoto. However, nutrients have regularly flowed to the bay through the major rivers of Kumamoto for the past three decades. Especially in the year 2000 and 2002, the Nori (Japanese seaweed of the red algae genus Pyropia) culture was severely damaged by large-scale autumn red tide (Tsutsumi, 2006). Since the year 2001, hypoxic water (water lacking in adequate oxygen) has been detected in the bottom layer of Ariake Bay in early summer which has caused huge ecological disturbance. According to Tsutsumi (2006), these occurrences occurred due to the stratification in the salinity level of the water in the bay which had progressed since the last part of 1990s. The Isahaya Bay Reclamation Project to reclaim the tidal flats of approximately 3,500 ha has been underway since 1986 (Tsutsumi, 2006). A decrease in the tidal current in the west part of the bay was noticed after the gates of the dike were closed in 1997’s April. The hydrographical changes resulted from these actions could be related to the development of stratification in water level in Ariake Bay. This type of eutrophication, stratification and ecological imbalance make it imperative to research about the nutrient levels in the water of Kumamoto.
Abstract A thermal steam project has been successfully implemented in a Petroleum Development Oman (PDO) field in the South of Oman. The thermal project developed the crest of the field which has mainly formation A. The thermal response has been favorable as witnessed by the incremental oil recovery. The steam flood is now planned to be expanded further to the South where it will encounter the same formation as currently developed at the crest & to the North where it will encounter two new formations (B & C). The new formations have limited field data on sand production; therefore a sand prediction evaluation for both cold & thermal production conditions is required for these new formations. In this paper we describe the analysis of the sand control potential and the selection process of the sand control technology. The assessment of the potential for sand production and the requirement for sand control was based on a combination of a) actual field data such as sand production, well performance & completion data; and b) a sand prediction model for the hot and cold operating production conditions utilizing rock-mechanical data. In addition, core sieve analysis data were used to determine the Particle Size Distribution (PSD), which was used to select the sand control type and screen slot width. The sand evaluation study demonstrated that for formation A has only the probability of transient sand failure under hot operation conditions. The wells will therefore be completed without sand control. On the other hand, formations B & C have a risk of catastrophic sand failure under both cold and hot operation conditions. A completion with thermally compliant sand control is a must for formation B. In case of formation C the selection of sand control is challenging as the sand distribution shows a high percentage of fines. In this case sand control is obtained through selective perforation, excluding the sand prone intervals. The impact of blanking the high GR intervals on inflow is expected to be low as the average the permeability for these intervals is low. The implementation of the selected Stand Alone Screens for sand control in formation B will be the first thermal application of these screens in PDO.
Nagoo, A. S. (Nagoo & Associates) | Kulkarni, P. M. (Equinor) | Arnold, C.. (Escondido Resources) | Dunham, M.. (Bravo Natural Resources) | Sosa, J.. (Jones Energy) | Oyewole, P. O. (Proline Energy Resources)
Abstract In this seminal work, we reveal for the first time an extensively field-tested, demonstrably accurate and simple analytical equation for the calculation of the critical gas velocity limit (or onset of liquid flow reversal) in horizontal wells as an explicit and direct function of diameter, inclination and fluid properties. For the independently verifiable and first-of-its-kind multi-play field validation study, we carefully assimilate a very large database of actual horizontal gassy oil and gas liquid loading wells from several unconventional U.S. shale plays with different bubble point and dew point fluid systems and varying gas-to-liquid ratios and varying water cuts. The shale plays in our validation database include the Eagle Ford, Woodford, Cleveland Sands, Haynesville, Cotton Valley, Fayetteville, Marcellus and Barnett formations within their associated Western Gulf, South Texas, Arkoma, Western Anadarko, East Texas, Appalachian and Permian basins. Then, after summarizing our comprehensive field testing results, practical production optimization applications of the new analytical equation and advanced use cases of interest are further highlighted in various liquid loading prediction and prevention scenarios. As opposed to prior critical gas velocity calculation methods (droplet reversal-based, film reversal-based, flow structure stability/energy), video observations both in the lab and the field clearly show continuously-evolving, co-existing and competing flow structures even with simple fluids without mass exchanges. Therefore, this work avoids skewed assumptions on demarcating the prevailing or dominant flow structure. Instead, the new analytical equation developed is based on an analysis of the major forces in the flow field, namely the axial buoyancy vector, the convective inertial and the interfacial tension forces, in combination with an assumption of the onset of liquid flow reversal based on flow field bridging (Taylor instability). Since the new analytical equation was formulated using these minimalist assumptions, this unique characteristic results in the highest predictability obtainable for the critical gas velocity calculation because there is the least amount of uncertainties (fudge factors). The consistent accuracy of the equation against our extensive horizontal well liquids loading database verifies this fact. Moreover, the simplicity of form of the equation makes it easy to use in that every practicing engineer in practice can perform fast hand or spreadsheet calculations. In effect, this equates to having a model as simple as the Turner model but now with additional direct functions of diameter and inclination. Also, the results clearly invalidate the need for artificial variables (such as interfacial friction factor) that cannot be directly measured in any experiment. In terms of usage, the new model is used in liquid loading prevention scenarios such as end-of-tubing (EOT) landing optimization and tubing-casing selection. Evidently, this work proves that no complex, computer-only procedure is necessary for accurate critical gas velocity calculation. This finding has significant speed and improved answer-reliability implications in strong favor of the presented simple equation for use in artificial lift, production optimization and digital oilfield software in industry, in addition to being ideally suited for ‘physics-guided data analytics’ applications in real-time production operations environments.