Amangi field reservoir porosity and saturation estimation using seismic and well data

The scientific knowledge of mapping reservoir geometries provide useful displays for understanding the sediment fairway orientation and transport direction, they are not detailed enough to define the best quality well connected reservoir areas needed for planningdevelopment wells. Knowing that that long term development of this field will require excellent subsurface imaging to optimize the placement of future development and production wells, so to plan for this, we used strong reflected primaries (PP) and primary-shear (PS) waves imaging for the reservoir characterization. Porosity of two hydrocarbon reservoirs is investigated for the purpose of planning production operations in Amangi field of the Nigerian Delta. Well log derived porosities were measured at five appraisal wells in the field. Point information about the porosity of the reservoirs were determined from these well log data. However, lateral variations of porosity could not be delineated from measurements made only at the sparsely located wells in the field. A 3D seismic data covering an area of about 20 km x 17.5 km were acquired to delineate the extent of the porous sand. After careful data processing, the lateral variations of seismic amplitudes were transformed to changes in rock impedances, which, in turn, are indirectly related to porosity. In contrast with the sparse well observations, the 3D seismic method provided a dense and regular areal sampling of the acoustic properties of the reservoir intervals. The results of the transformation of the 3D anisotropic seismic reflection data were integrated with petrophysical measurements at the wells to significantly improve the spatial description of porosity in this field.

Nitrates in Groundwater of Small Shallow Aquifers in the Western Side of Hoya de Huesca (NE Spain)

Nitrate is one of the most common groundwater contaminants in rural areas. In this work, the presence of high levels of nitrate in groundwater of the aquifers of the west part of Hoya de Huesca County (NE Spain) has been studied by coupling hydrogeological information with water sampling techniques through a wide areal sampling of 90 surface water and groundwater points belonging to several aquifers. The results showed a general hydrochemistry of calcium carbonate to calcium sulfate waters. Unlike other case studies in Mediterranean areas, in which nitrate pollution was associated with irrigated crops, the highest concentrations in the present study were found in dry farming areas in which winter cereal is grown. A monthly nitrate level monitoring, conducted in 21 selected points between 2016 and 2017, showed that the nitrate evolution pattern followed the N fertilizer application schedules in the sampling points in which the highest concentrations were recorded, whereas an annual regularity could be observed in the sampling points with low nitrate levels. The compilation of data for 16 selected points since 1990 shows that the problem is persistent and points to the need of implementing new aquifer pollution control measures, since the ones currently in force have not been successful.

Application of GPS-RTK Technology in the Measurement of Discontinuity Traces

Rock discontinuities appear as traces on exposures such as natural outcrops or tunnel walls. Discontinuity size which has important effects on rock mass behavior such as rock mass strength, deformability, stability, fluid flow, contaminant transport is related to trace length. Field linear and areal sampling techniques are time-consuming and low accuracy. Real-Time Kinematic GPS (GPS-RTK) developed from GPS is a more secure and fast way, which has some advantages of shorter observation time, high positioning accuracy, unnecessary intervisible and direct result of exact coordinate in field. This paper uses GPS-RTK technology in the measurement of discontinuity traces in Beishan granite rock mass of Gansu province. Through analyzing the processing and results acquired from Beishan granite rock mass discontinuity traces, the paper tries to demonstrate the feasibility and practicality of the method.

Accuracy of the neutron probe for measuring changes in soil water storage under potatoes

The neutron probe (NP) is used widely to measure changes in soil water storage in research and more recently to aid irrigation scheduling. Its accuracy is rarely questioned and most of the relationships between soil water changes and productivity are based on its use. A field experiment was conducted at Cambridge University Farm in 1999 to address whether the NP could accurately measure changes in soil water content (SWC) under irrigation or substantial rain (>10 mm). The experiment was a replicated split-plot design with four irrigation treatments allocated to the main plots, and surface profile (ridge, flat) and crop (potato cv. Saturna, bare soil) treatments allocated to the subplots. The mean results from four NP access tubes per plot installed to measure soil moisture deficit (SMD) across the row-width were analysed. The NP was inconsistent in measuring known irrigation or rainfall input. In relatively dry soil (SMD>40 mm), the NP generally measured 93 to 110% of 18 mm of irrigation within 4 h of irrigation. The NP recorded much less water applied as irrigation in wetter soil, and often only 40 to 70% of the applied irrigation (18 or 36 mm) was measured. There were occasions when the NP did not measure all the water input even when the SMDs before irrigation were greater than the water subsequently applied. Some of the ‘missing’ water might be attributed to drainage, however, results from an additional experiment using an open-topped tank of soil showed that the NP was unable to detect all the water added to the soil, particularly where the water was largely confined close to the soil surface. Replicated measurements of the change in SMD in the field experiment were precise for a given event and treatment (mean S.E. = 1·3 mm) but were not accurate when compared against the input measured in rain gauges. It was concluded, that the NP could not be used reliably to measure changes in soil water storage after irrigation or substantial rain. For periods when there were minimal inputs of water, there was a closer correlation between changes in SMD measured by the NP and those predicted by a modified Penman–Monteith equation than after substantial inputs of water. However, for predicted changes in SMD of c. 20 mm, there was a range of c. ±5 mm in the changes in SMD measured by the neutron probe.The value of the NP for monitoring SMDs where there is irrigation, or substantial rain, must be seriously doubted. Consequently, its limitations for scheduling irrigation, testing models or quantifying the effects of treatments on crop water use in potatoes must be appreciated, especially where the areal sampling limitations of single access tubes positioned only in the ridge centre have not been addressed.

Nonuniform random sampling: an alternative method of variance reductionfor forest surveys

Areal sampling has been used extensively in forest inventories. Prior to the 1950s, areal sampling used fixed-area plots exclusively. The advent of variable radius plot (VRP) sampling provided a substantial improvement in efficiency, both in terms of reducing the variance of the estimator for attributes such as basal area and volume and in the amount of fieldwork required to collect samples. However, since the advent of VRP sampling, there have been few substantial improvements in the efficiency of areal sampling. The purpose of this paper is to illustrate how varying the distribution of sampling points to account for large scale spatial variation can further improve the efficiency of forest inventories. While this is not a new idea, the approach taken here attempts to present the material in such a way as to make it accessible to the broadest spectrum of inventory practitioners. The method, referred to as nonuniform random sampling, is developed using a small forest population where the attribute of primary interest is the total number of trees. A simulation study, drawing samples of 20 fixed-area plots, was performed to compare the new method with current practice. The standard deviation of the estimator of the number of trees was reduced by a factor of about 1.4, meaning that almost 40 sample plots would be needed to achieve equal variance of the estimator using plot locations that were uniformly distributed over the population. To illustrate the potential shortcomings of this approach, the performance of the estimator of the total basal area was studied concurrently. The standard deviation of this estimator actually increased by a factor of more than 2, meaning that fewer than five sample plots would have been needed if the plot locations had been located in accordance with a uniform distribution over the area. Thus, while this technique can substantially reduce the variance for a single or small set of spatially correlated attributes for which the inventory is designed, the estimators of other attributes can be seriously compromised.