Improving Proppant Placement Success in Horizontal Wells in Layered Reservoirs in the Sultanate of Oman

A gas condensate field in the Sultanate of Oman has been developed since 1999 with vertical wells, with multiple fractures targeting different geological units. There were always issues with premature screenouts, especially when 16/30 or 12/20 proppant were used. The problems placing proppant were mainly in the upper two units, which have the lowest permeability and the most heterogeneous lithology, with alternating sand and shaly layers between the thick competent heterolith layers. Since 2015, a horizontal well pilot has been under way to determine if horizontal wells could be used for infill drilling, focusing on the least depleted units at the top of the reservoir. The horizontal wells have been plagued with problems of high fracturing pressures, low injectivity and premature screenouts. This paper describes a comprehensive analysis performed to understand the reasons for these difficulties and to determine how to improve the perforation interval selection criteria and treatment approach to minimize these problems in future horizontal wells. The method for improving the success rate of propped fracturing was based on analyzing all treatments performed in the first seven horizontal wells, and categorizing their proppant placement behavior into one of three categories (easy, difficult, impossible) based on injectivity, net pressure trend, proppant pumped and screenout occurrence. The stages in all three categories were then compared with relevant parameters, until a relationship was found that could explain both the successful and unsuccessful treatments. Treatments from offset vertical wells performed in the same geological units were re-analyzed, and used to better understand the behavior seen in the horizontal wells. The first observation was that proppant placement challenges and associated fracturing behavior were also seen in vertical wells in the two uppermost units, although to a much lesser extent. A strong correlation was found in the horizontal well fractures between the problems and the location of the perforated interval vertically within this heterogeneous reservoir. In order to place proppant successfully, it was necessary to initiate the fracture in a clean sand layer with sufficient vertical distance (TVT) to the heterolith (barrier) layers above and below the initiation point. The thickness of the heterolith layers was also important. Without sufficient "room" to grow vertically from where it initiates, the fracture appears to generate complex geometry, including horizontal fracture components that result in high fracturing pressures, large tortuosity friction, limited height growth and even poroelastic stress increase. This study has resulted in a better understanding of mechanisms that can make hydraulic fracturing more difficult in a horizontal well than a vertical well in a laminated heterogeneous low permeability reservoir. The guidelines given on how to select perforated intervals based on vertical position in the reservoir, rather than their position along the horizontal well, is a different approach than what is commonly used for horizontal well perforation interval selection.

Reliability of heart rate variability in futsal players

The main aim the present study was evaluated the reliability of the heart rate variability (HRV) indices in futsal players. Additionally the study verifi ed the reliability of different approaches for 5 min interval selection of recording. Eighteen under-20 futsal players underwent 15 min of pre-training RR interval recordings in two different day. Time and frequency domain and Poincaré Plot indices were tested. The indices were calculated using: 1) fi nal 5 min of recording; 2) 5 min of lower variance of recording, by a mathematical algorithm; 3) 5 min segment of lower variance, by an experienced operator. The HRV indices presented a wide range reliability [e.g. RRmean (ICC=0.96, SEM=3.4ms, CV=2.6%), lnRMSSD (ICC=0.88, SEM=5.9ms, CV=4.3%), lnHF (ICC=0.89, SEM=7.5ms, CV=5.9%), LFnu (ICC=0.84, SEM=13ms, CV=9.4%), LF (ICC=0.47, SEM=65.2ms,CV=38.5%) and LF/HF (ICC=0.63, SEM=83.7ms, CV=54.5%)]. The fi nal 5 min of recording was the most reliable. The results suggest that most of HRV indices presented acceptable reliability, however the RRmean, lnRMSSD, lnHF and LFnu were the most reliable.

Reliability of heart rate variability in futsal players

The main aim the present study was evaluated the reliability of the heart rate variability (HRV) indices in futsal players. Additionally the study verifi ed the reliability of different approaches for 5 min interval selection of recording. Eighteen under-20 futsal players underwent 15 min of pre-training RR interval recordings in two different day. Time and frequency domain and Poincaré Plot indices were tested. The indices were calculated using: 1) fi nal 5 min of recording; 2) 5 min of lower variance of recording, by a mathematical algorithm; 3) 5 min segment of lower variance, by an experienced operator. The HRV indices presented a wide range reliability [e.g. RRmean (ICC=0.96, SEM=3.4ms, CV=2.6%), lnRMSSD (ICC=0.88, SEM=5.9ms, CV=4.3%), lnHF (ICC=0.89, SEM=7.5ms, CV=5.9%), LFnu (ICC=0.84, SEM=13ms, CV=9.4%), LF (ICC=0.47, SEM=65.2ms,CV=38.5%) and LF/HF (ICC=0.63, SEM=83.7ms, CV=54.5%)]. The fi nal 5 min of recording was the most reliable. The results suggest that most of HRV indices presented acceptable reliability, however the RRmean, lnRMSSD, lnHF and LFnu were the most reliable.

Hyperspectral Imaging for Tomato Bruising Damage Assessment of Simulated Harvesting Process Impact Using Wavelength Interval Selection and Multivariate Analysis

Highlights The hidden internal damage of falling impact on tomatoes will reduce the quality of products. Hyperspectral imaging and VIS/NIR spectrum analysis, including wavelength selection and classification model construction, have the possibility as a non-destructive and fast method to predict the effect of drop impact grades on tomato bruising damage. Abstract . Mechanical damage usually causes hidden internal damage to tomatoes (Solanum lycopersicum L.), which can reduce the product quality and can cause economic losses to farmers. The visible and near-infrared (VIS/NIR) spectra of tomato fruits were analyzed by using the wavelength selection algorithm (the combination of ant colony optimization and variable importance in projection), and the influence of impact grades of simulated transport on tomato fruit bruising was evaluated. A VIS/NIR hyperspectral imaging system was developed to capture hyperspectral images of tomatoes from 392–1034 nm spectral region and the part used in actual data analysis was 442-984 nm. Multivariate analysis classifier models (partial least squares discrimination analysis and ANN) were set up based on the original spectral dataset. On the basis of selected wavelength intervals, multivariate analysis classifier models were re-established. The overall classification accuracies of all models in the validation set are good, ranging from 64.29% to 100%. Especially in the two types of classification (bruising and normal), the range of correct accuracy is 89.29% to 100%, which shows very high predicted performance. The prediction performance of the model based on the selected wavelengths decreases slightly, but the prediction time is shortened by more than 70%. The results demonstrated that hyperspectral imaging and VIS/NIR spectrum analysis, including wavelength selection and classification model construction, have the possibility as a non-destructive and fast method to predict the effect of drop impact grades on tomato bruising damage. Keywords: ANN, Ant colony optimization (ACO), Partial least squares discrimination analysis (PLS-DA), Variable importance in projection (VIP), VIS/NIR hyperspectral imaging system, wavelength interval selection.