Field Validation of a Non-logging Alternative Method for the Prediction of the Location of Water-Cresting in Horizontal Wells for Water-Drive Reservoirs.

A previously reported method for a non-logging alternative method for the prediction of the location of water-cresting in horizontal wells for water-drive reservoirs is validated in a field test for the first time in this study. Using this method, the wellbore trajectory, variation in the reservoir permeability, and the pressure gradient data were used to calculate what is called the breakthrough coefficient for the different segments along the length of a set horizontal well with the largest calculated breakthrough coefficient corresponding to the most likely location of the actual water-cresting occurrence. This method was field-validated and found to be in good agreement with log testing for a group of seven wells in an oilfield in Northern China. Another calculated parameter derived from the breakthrough coefficient which is called the variation of the breakthrough coefficients that characterize the effect of the variation of water production along the length of the horizontal well due to the effect of the variation of the wellbore trajectory, permeability, and pressure gradient on the oil production is also introduced. This field validation found variation of the breakthrough coefficients to be weakly and inversely correlated to the oil production in application to a group of 27 wells in the same field.

Method of Predicting the Location of Water Cresting for Horizontal Wells in a Water-Drive Reservoir for Early Prevention.

A method of prediction of location of water cresting and characterizing its intensity in a horizontal well in a water-drive reservoir is introduced for the first time. A mechanistic model for water cresting derived from Darcy's equation incorporating the main parameters reported in the literature affecting water cresting-viscosity, well distance to the aquifer, wellbore pressure gradient, and reservoir heterogeneity-is introduced with two new characterizing parameters. First is a model-derived parameter, called the breakthrough coefficient, which is defined as the ratio of the average time of breakthrough to the time of breakthrough for a segment of the well, with the model-predicted location of water cresting corresponding to the well segment with the largest breakthrough coefficient. The second is the Cresting index, which is the ratio of the maximum breakthrough coefficient to the minimum breakthrough coefficient as a characterizing parameter, with a well with a higher cresting index corresponding to a faster breakthrough in a group of similar wells. This methodology was validated through a series of sophisticated experimental corefloods and found to predict 78% of the location of the water cresting accurately. The cresting index is found to be weakly correlated with the speed of breakthrough among similar wells.

Interplay between Rock Permeability and the Performance of Huff-n-Puff CO2 Injection.

The CO2 huff-n-puff experiments are often conducted on a rock sample with a given permeability. However, there is a need for understanding the production performance of CO2 huff-n-puff over a range of rock permeability values. In this study, CO2 huff-n-puff corefloods were conducted by using 30 cm long artificial cores over a permeability range between 0.7 and 240 mD. After that, the cores and produced oil were analyzed by NMT tests and gas chromatography tests. The effects of rock permeability on primary parameters, such as ultimate oil recovery, gas and oil ratio (GOR), pressures, residual oil distribution, and produced oil composition, were studied in detail. The experimental results indicate that the overall CO2 huff-n-puff efficiency increases with permeability, while the production dynamics also changes with permeability. The oil production is greater and realized faster in high permeability core samples than low-permeability rocks; hence, maintaining the same production efficiency for low-permeability samples needs more production cycles and a longer production time. Fortunately, the GOR of CO2 huff-n-puff in low-permeability samples is lower, which is favorable in long-term production. In contrast, a larger produced GOR is realized in high-permeability core samples, especially beyond the optimal cycle. Moreover, although the CO2 front occurs at a shorter distance from the inlet as rock permeability decreases, CO2 huff-n-puff can simultaneously produce oil from different pore sizes of different permeability core samples. The permeability of core samples also has a significant influence on the composition of the produced oil. The CO2 extraction capability is stronger in samples with a lower permeability.

Experimental study on factors affecting the end effect in gas viscosity measurement using capillary-tube viscometer.

Because of its simple principle and high adaptability to severe operational conditions, the capillary-tube viscometer has been widely used for viscosity measurement. However, difficulties in accurately correcting the end effect induced measurement deviation will result in great uncertainty for measurement results. In order to solve this problem, in this work, we studied factors affecting the end effect by conducting the high pressure nitrogen viscosity measurement at low flow velocity with an improved capillary-tube viscometer. The experimental results indicated that the influence of the end effect became less significant with the decrease in flow velocity (v) and tube inner diameter (d) and varied inversely with the length of tube (L). We defined the ratio of measured viscosity to standard viscosity obtained from the NIST database as the viscosity deviation coefficient (Ce). From the Ce vs v, Ce vs d, and Ce vs L curves, we have observed that there existed a threshold velocity (vthreshold), a threshold diameter (dthreshold), and a threshold length (Lthreshold) at which Ce got closer to 1.0. It suggested that under certain experimental conditions, the influence of the end effect on gas viscosity measurement became negligible. Based on that, we established end effect free capillary-tube viscometry and compared the nitrogen viscosity results measured by this method with the data provided by the NIST database. The results presented a good match with error within 1.2%. These insights will contribute to improving the accuracy of a capillary-tube viscometer especially under high pressure.

Determination of ozonization reaction rate constants of aromatic pollutants and QSAR study.

Rate constants of ozone with 39 aromatic compounds in aqueous solution were determined at 298 K. And optimized calculation was carried out at B3LYP/6-311G** level with DFT method. 10 molecular parameters obtained from calculations were selected as the descriptors to establish QSAR models for predicting the rate constants. These descriptors include structural, electronic and thermodynamic parameters. The optimum model was -logk' = 4.656 + 0.015CMA-1.684E (LUMO)-3.057qH(+), of which square regression coefficient R² = 0.791, standard deviation SD = 0.126. Stability of the model was checked by leave-one-out cross-validation and variation inflation factor. The QSAR model showed that the main contribution to degradation was the CMA parameter.