Fracture Geometry Calibration Using Multiple Surveillance Techniques

An accurate Mechanical Earth Model (MEM) is of vital importance in tight gas reservoirs where hydraulic fracturing is the only way to produce hydrocarbons economically. The Barik tight gas reservoir is the main target in Khazzan and Ghazeer Fields at the Sultanate of Oman (Rylance et al., 2011). This reservoir consists of multiple low-permeability sandstone layers interbedded with marine shales. A good understanding of the fracture propagation in such a reservoir has a major effect on completion and fracturing design. The MEM derived from sonic logs and calibrated with core data needs to be further validated by independent measurements of the fracturing geometry. Multiple surveillance techniques have been implemented in the Barik reservoir to validate the MEM and to match observations from hydraulic fracturing operations. These techniques include closure interpretation using a wireline deployed formation testing assembly, the use of mini-frac injection tests with deployed bottomhole pressure gauges, execution of post injection time-lapse temperature logging, the injection of radioactive tracers, associated production logging, subsequent pressure transient analysis and other techniques. A cross-disciplinary team worked with multiple sources of data to calibrate the MEM with the purpose of delivering a high-confidence prediction of the created fracture geometry, which honors all available surveillance data. In turn, this validation approach provided a solid basis for optimization of the completion and fracturing design, in order to optimally exploit this challenging reservoir and maximize the economic returns being delivered. For example, combination of stress testing with radioactive tracers provided confidence in stress barriers in this multilayered reservoir. Pressure transient analysis allowed to calibrate mechanical model to match fracturing half-length that is contributing to production. This paper provides extensive surveillance examples and workflows for data analysis. Surveillance of this degree in the same well is uncommon because of the associated time and cost. However, it provides unique value for understanding the target reservoir. This paper demonstrates the Value Of Information (VOI) that can be associated with such surveillance and provides a concrete and practical example that can be used for the justification of future surveillance programs associated with the hydraulic fracturing operations.

Simulation evaluation on a compact monitor for gamma-emitting tracers in plant stems

Non-destructive monitoring of radioactivities derived from radioactive tracers at multiple points in plant stems can be used to evaluate the velocity of element transport in living plants. In this study, we calculated absorption-efficiency distributions for several detector geometries to determine appropriate shapes for non-destructive monitoring of radioactivities in the stem. The efficiency distributions were calculated by Monte Carlo simulations, and the flatnesses and spatial resolutions were evaluated. It was found that the placement of four detectors around the stem could limit the percentage of standard deviation to the mean of the pixel values to less than 5%. We could determine a compact detector geometry with the spatial resolution of 1.35 cm using four small detectors. The detection efficiencies were 0.014, 0.0030 and 0.00063 cm at the initial gamma-ray energies of 0.5, 1 and 2 MeV, which is sufficiently applicable to detect 10 kBq/cm of radioactivity.

Fiber Optic Deployed Behind Cemented Casing in a Vertical Deep Tight Gas Well Used to Enhance Hydraulic Fracturing, Monitoring and Diagnostics

The use of fiber optic (FO) to obtain distributed sensing be it Distributed Temperature Sensing (DTS), Distributed Acoustic Sensing (DAS) or Distributed Strain Sensing (DSS) is a well & reservoir surveillance engineer's dream. The ability to obtain real-time live data has proven useful not only for production monitoring but during fracture stimulation as well. A trial the first of its kind in Petroleum Development Oman (PDO) used fiber optic cable cemented in place behind casing to monitor the fracture operations. Several techniques are used to determine fracture behaviour and geometry e.g. data fracs, step down test and after closure analysis. All these use surface pressure readings that can be limited due to uncertainty in friction pressure losses and the natural complexity in the formation leading to very different interpretations. Post frac data analysis and diagnostics also involves importing the actual frac data into the original model used to design the frac in order to calibrate the strains (tectonics), width exponent (frac fluid efficiency) and the relative permeability. Monitoring the frac using DAS and DTS proved critical in understanding a key component in fracture geometry; frac height. The traditional method to determine fracture height is to use radioactive tracers (RA). But these are expensive and the data only available after the job (after drilling the plugs and cleaning the wellbore). In contrast fiber optic can provide real time data throughout the frac stages including the proppant free PAD stage which tracers can't. The comparison of DTS and Radioactive Tracers showed very good agreement suggesting that DTS could replace RA diagnostic. Hydraulic fracture stimulation operations in well-xx was the first one of its kind to be monitored with fiber optic. The integrated analysis of the available logs allowed us to benchmark various information and gain confidence in the conclusions. This helped fine tune the model for future wells for a more optimized zonal targeting and hydraulic fracture design. In this paper we will share the detailed evaluation of the fracture propagation behaviour and how combining the fiber optic data with the surface pressure, pumping rates and tracer logs in conjunction with a fracture simulation platform where a detailed geomechanical and subsurface characterization data is incorporated to get a more accurate description of fracture geometry.

Preclinical Testing of Radiopharmaceuticals for the Detection and Characterization of Osteomyelitis: Experiences from a Porcine Model

The development of new and better radioactive tracers capable of detecting and characterizing osteomyelitis is an ongoing process, mainly because available tracers lack selectivity towards osteomyelitis. An integrated part of developing new tracers is the performance of in vivo tests using appropriate animal models. The available animal models for osteomyelitis are also far from ideal. Therefore, developing improved animal osteomyelitis models is as important as developing new radioactive tracers. We recently published a review on radioactive tracers. In this review, we only present and discuss osteomyelitis models. Three ethical aspects (3R) are essential when exposing experimental animals to infections. Thus, we should perform experiments in vitro rather than in vivo (Replacement), use as few animals as possible (Reduction), and impose as little pain on the animal as possible (Refinement). The gain for humans should by far exceed the disadvantages for the individual experimental animal. To this end, the translational value of animal experiments is crucial. We therefore need a robust and well-characterized animal model to evaluate new osteomyelitis tracers to be sure that unpredicted variation in the animal model does not lead to a misinterpretation of the tracer behavior. In this review, we focus on how the development of radioactive tracers relies heavily on the selection of a reliable animal model, and we base the discussions on our own experience with a porcine model.

Radiotracers for Bone Marrow Infection Imaging

Introduction: Radiotracers are widely used in medical imaging, using techniques of gamma-camera imaging (scintigraphy and SPECT) or positron emission tomography (PET). In bone marrow infection, there is no single routine test available that can detect infection with sufficiently high diagnostic accuracy. Here, we review radiotracers used for imaging of bone marrow infection, also known as osteomyelitis, with a focus on why these molecules are relevant for the task, based on their physiological uptake mechanisms. The review comprises [67Ga]Ga-citrate, radiolabelled leukocytes, radiolabelled nanocolloids (bone marrow) and radiolabelled phosphonates (bone structure), and [18F]FDG as established radiotracers for bone marrow infection imaging. Tracers that are under development or testing for this purpose include [68Ga]Ga-citrate, [18F]FDG, [18F]FDS and other non-glucose sugar analogues, [15O]water, [11C]methionine, [11C]donepezil, [99mTc]Tc-IL-8, [68Ga]Ga-Siglec-9, phage-display selected peptides, and the antimicrobial peptide [99mTc]Tc-UBI29-41 or [68Ga]Ga-NOTA-UBI29-41. Conclusion: Molecular radiotracers allow studies of physiological processes such as infection. None of the reviewed molecules are ideal for the imaging of infections, whether bone marrow or otherwise, but each can give information about a separate aspect such as physiology or biochemistry. Knowledge of uptake mechanisms, pitfalls, and challenges is useful in both the use and development of medically relevant radioactive tracers.

Comparing and Combining Camera, Tracer and Distributed Temperature and Acoustic Sensing DAS+DTS for a Holistic Understanding of Stimulation and Production Performance

In the present cost-constrained environment, it is critical that operators effectively complete their wells while minimizing capital expenditure. Optimization efforts focus on increasing recovery factor by managing landing zone, increasing the number of effective fractures, increasing the size of the fractures, and increasing the length of the lateral, while reducing the total number of stages and job size, without sacrificing efficient proppant and fluid delivery. The same pressure to reduce expenditure also impacts decision making on diagnostic evaluation, reducing operators to ‘free’ or low-cost feedback, like surface production rates and decline curves. Operators are responding to these challenges by utilizing a combination of lower cost, post-completion diagnostics like deployed fiber optics, downhole camera evaluation of perforations and radioactive tracers. These less expensive options allow for a broader scope and number of diagnostic inquiries, whereas a permanent fiber may prove to be cost-prohibitive, reducing diagnostic focus to one well, in one part of a play. Combining differing diagnostic technologies enhances the overall description of the well and reservoir behaviors and improves confidence in their interpretation of stimulation and production efficiency; furthermore, where a single diagnostic measurement may be unlikely to justify dramatic change in a completion strategy, a combination of data points from different domains can and does support design change that leads to rapid, real world performance improvements. Care is needed in the conclusions drawn when utilizing complimentary diagnostics due to the differences in depth of investigation and the non-unique interpretation of some data types. This paper discusses three post-completion diagnostic technologies, perforation evaluation by downhole camera, radioactive tracers, and distributed acoustic and temperature sensing (DAS+DTS) data and their respective physical measurements, strengths and weaknesses and how they can be combined to better understand well and reservoir behavior. It concludes with a review of completion optimization efforts from the Rockies area, where these post-completion diagnostic technologies were applied in the evaluation of eXtreme Limited Entry (XLE) trials. A statistical analysis of the RA tracer, downhole camera measurement of perforation area and deployed fiber optic acquisition of DAS+DTS reveals no correlation between diagnostic answers, indicating no one diagnostic measurement can accurately predict the other, such that it could substitute for that diagnostic and provide the same answer. Asking the right question can often enhance the value of diagnostic descriptions of the system in question. Those answers often lead to the next question and clear the path forward in advancing completion optimization. Complimentary diagnostics facilitate a more complete understanding of stimulation and production performance when compared, increasing confidence when they agree. When one or more appear to disagree, the different respective physical measurements and depths of investigation often reveal a more complete and complex understanding of stimulation and production efficiency. As an aggregate they provide clarity on the effect of efforts to create conductive pathways into the reservoir, allowing operators increased control over the resulting production.

The role of seagrass leaf litter in the SGD-derived nutrient fluxes in Cala Pudent (Menorca, western Mediterranean)

<div> <p>The assessment of the biogeochemical cycles in coastal environments often relies on riverine inputs as the main source of nutrients and other dissolved compounds from land to the ocean. However, the discharge of groundwater through continental margins, commonly known as Submarine Groundwater Discharge (SGD), is also recognized as relevant sources of nutrients to the coastal ocean, particularly in oligotrophic and semi-arid environments, such as the Mediterranean Sea. In this study, we use radioactive tracers (radium isotopes and radon) to i) quantify the magnitude of SGD-driven nutrient fluxes to a Mediterranean cove (Cala Pudent, Menorca, Balearic Islands) and ii) characterize the nutrient transformations occurring in the beach before groundwater discharges to the sea. Cala Pudent is a limestone coastal cove with a restricted connection to the open sea. In this system, groundwater from a permanent spring infiltrates through an organic substrate dominated by thick deposits of seagrass (Posidonia oceanica) leaf litter and flows into the sea. This substrate, together with the dynamic groundwater-seawater mixing, are chiefly influencing the nutrient enrichment and transformation occurring in the beach and thus modulating the SGD-derived nutrient input to the sea. The ecological implications of these inputs are also assessed, particularly for the Posidonia oceanica and Cymodocea nodosa meadows located near the study site.  </p> </div><div> <p> </p> </div>