Monitor Water Movement Research Articles

The Second Las Cruces Trench Experiment: Experimental Results and Two‐Dimensional Flow Predictions

As part of a comprehensive field study designed to provide data to test stochastic and deterministic models of water flow and contaminant transport in the vadose zone, several trench experiments were performed in the semiarid region of southern New Mexico. The first trench experiment is discussed by Wierenga et al. (this issue). During the second trench experiment, a 1.2 m wide by 12 m long area on the north side of and parallel to a 26.4 m long by 4.8 m wide by 6m deep trench was irrigated with water containing tracers using a carefully controlled drip irrigation system. The irrigated area was heavily instrumented with tensiometers and neutron probe access tubes to monitor water movement, and with suction samplers to monitor solute transport. Water containing tritium and bromide was. applied during the first 11.5 days of the study. Thereafter, water was applied without tracers for an additional 64 days. Both water movement and tracer movement were monitored in the subsoil during infiltration and redistribution. The experimental results indicate that water and bromide moved fairly uniformly during infiltration and the bromide moved ahead of the tritium due to anion exclusion during redistribution. Comparisons between measurements and predictions made with a two‐dimensional model show qualitative agreement for two of the three water content measurement planes. Model predictions of tritium and bromide transport were not as satisfactory. Measurements of both tritium and bromide show localized areas of high relative concentrations and a large downward motion of bromide relative to tritium during redistribution. While the simple deterministic model does show larger downward motions for bromide than for tritium during redistribution, it does not predict the high concentrations of solute observed during infiltration, nor can it predict the heterogeneous behavior observed for tritium during infiltration and for bromide during redistribution.

The Las Cruces Trench Site: Characterization, Experimental Results, and One‐Dimensional Flow Predictions

A comprehensive field trench study was conducted in a semiarid area of southern New Mexico to provide data to test deterministic and stochastic models of vadose zone flow and transport. A 4 m by 9 m area was irrigated with water containing a tracer using a carefully controlled drip irrigation system. The area was heavily instrumented with tensiometers and neutron probe access tubes to monitor water movement and with suction tubes to monitor solute transport. Approximately 600 disturbed and 600 core samples of soil were taken to support deterministic and stochastic characterization of the soil water hydraulic parameters. The core sample‐based saturated hydraulic conductivities ranged from 1.4 to 6731 cm/d with a mean of 533 cm/d and a standard deviation of 647 cm/d, indicating significant spatial variability. However, visual observation of the wetting front on the trench wall shows no indication of preferential flow or water flow through visible root channels and cracks. The tensiometer readings and the neutron probe measurements also suggest that the wetting front moves in a fairly homogeneous fashion despite the significant spatial variability of the saturated hydraulic conductivity. In addition to the description of the experiment and the presentation of the experimental results, predictions of simple one‐dimensional uniform and layered soil deterministic models for infiltration are presented and compared to field observations. These models are presented here to provide a base case against which more sophisticated deterministic and stochastic models can be compared in the future. The results indicate that the simple models give adequate predictions of the overall movement of the wetting front through the soil during infiltration. However, the models give poor predictions of point values for water content due to the spatial variability of the soil. Comparisons between the one‐dimensional infiltration model predictions and field observations show that the use of the layered soil model rather than the uniform soil model does not consistently improve the accuracy of the predictions for this particular field application. This result illustrates that increasing the spatial resolution of the deterministic characterization of the site in the vertical direction does not always improve the model predictions. Uncertainties due to horizontal spatial variability and due to other difficulties associated with experimental characterization appear to be more significant.

Statfjord Field: Development Strategy and Reservoir Management

Summary This paper reviews reservoir performance and management of the Statfjord field after 8 years of production. The reasons behind the reservoir development strategies and field experiences are presented. The field comprises three reservoirs produced simultaneously with designated wells for each reservoir: the Upper and Lower Brent and the Statfjord. The two Brent reservoirs are produced with a waterflood, while the Statfjord reservoir is produced with a high-pressure miscible gasflood. The original development plans have been refined on the basis of field performance through an extensive monitoring program and use of reservoir simulation. The induced gamma ray spectra (IGRS) log is used to monitor water movement in the Brent reservoirs, while the compensated neutron tool (CNT) is the main tool used to monitor the gasflood in the Statfjord reservoir. The acquired data have improved the geologic model and the knowledge of fluid movements in all three reservoirs. This resulted in a large and complex reservoir simulation model with more than 20,000 gridblocks. Introduction The Statfjord field, the largest producing oil field in Europe, is located in the prolific northern part of the Viking graben, 125 miles [200 km] northwest of Bergen, Norway, on the U.K./Norwegian boundary (Fig. 1). The field was discovered in March 1974 with the drilling of Well 33/12-1 and was delineated with drilling of 11 additional wells. The field lies mainly in Norwegian Blocks 33/12 and 33/9, but also extends into U.K. Blocks 211/24 and 211/25. The field was unitized in 1976 with Mobil as operator. The equity redetermination of 1979 resulted in 84.1 % of the field being in the Norwegian sector and 15.9 % in the U. K. sector. The operatorship was transferred from Mobil to Statoil in Jan. 1987. The Statfjord field, which is 15 miles [24 km] long and averages 2.5 miles [4 km] in width, is located in a westerly tilted and eroded Jurassic fault block. The main recoverable reserves, about 75 %, are located in the Middle Jurassic Brent group, while the remaining 25 % is in the Lower Jurassic/Upper Triassic Statfjord formation. Both Brent and Statfjord have exceptionally good reservoir characteristics. The estimated ultimate recovery is around 3 × 109 bbl [475 × 106 M3] of oil and 3 × 10 12 Scf [85 × 109 std M3] of gas. Both Brent and Statfjord reservoirs contain highly undersaturated low-sulfur crude oil. Reservoir data and fluid properties are given in Tables 1 and 2. The Statfjord field is being developed with three gravity-based Condeep-type platforms and single-point mooring for offshore oil tanker loading. Production from Platform A commenced in Nov. 1979, while Platform B came on production in Nov. 1982 and Platform C in June 1985. Regular gas sales by pipeline to the U.K. and the European continent began in Oct. 1985. Eighty-nine development wells have been drilled to date to achieve the current average daily oil-production and water-injection rates of 750,000 STB/D [119 000 stock-tank M3 /d] and 1,050,000 B/D [ 167 000 M 3 /d], respectively. As of Dec. 1987, nearly 1.2 × 109 bbl [190 × 10(6) M3] Of oil. or about 40% of the recoverable reserves, has been produced.

A Microlysimeter Field Study of Solute Transport through a Structured Sandy Loam Soil

AbstractA 49‐d field experiment monitoring water and solute movement through a structured sandy loam is reported. Two field plots, each 15 by 30 m2 in area were instrumented with a 3 by 6 grid of small lysimeters containing undisturbed soil. Each lysimeter was weighed before and after irrigation and had effluent concentrations and drainage volumes recovered periodically. At the beginning of the experiment a pulse of KBr was added to the field and lysimeters with a mechanical lawn spreader and was leached into the soil with three water irrigations per week. Each plot received the same amount of water per irrigation but at intensities of 5.5 and 9.5 mm/h. Effluent breakthrough curves were constructed for each lysimeter. Substantial indication of preferential flow through part of the wetted pore space was observed in each lysimeter and the average breakthrough curves reflected substantial bypass. A statistical analysis of the drainage concentrations as a function of time showed the two fieldwide breakthrough curves to be identical. This not only showed that no intensity effect was apparent for solute movement on these plots but also indicated that the plot areas were large enough to incorporate all of the field scale variability within them. A calculation of solute flux from each lysimeter showed no correlation between instantaneous drainage and instantaneous solute concentration. As a consequence, we were able to show that the traditional method of estimating field scale solute flux as the product of average drainage and average concentration was adequate to describe solute leaching below the fields. Thirty‐six soil cores were taken in the two plots at the conclusion of the experiment. The average concentration depth patterns were similar for the two treatments and showed evidence of movement to at least 1.2 m during the lifetime of the experiment, implying that preferential flow continued to occur to greater depths.

Monitoring Water Movement Through Strip Mine Spoil Profiles

ABSTRACT TWO, 3.6-m deep, 2.4-m diameter caissons were used to measure water movement in re-constituted spoil profile. In here we present details of instrumentation and propose methods for deter-mining spoil-water-retentivity curve and hydraulic conductivity as a function of water content and/or tensiometer pressure including a correction for coarse fragment content. This correction may be significant when modeling flows in spoil materials. During water application we found that on spoil alone, water infiltrated faster and less of it was retained in the profile after drainage than on topsoiled spoil. More sediment moved with infiltrating water in the topsoiled profile, and oxygen concentrations after application of water were lower than on spoil alone. Similar situations may prevail in the field. During the initial wetting, settlement was consider-able and changes in temperature and bulk density were good indicators of water movement within the spoil and topsoiled spoil profiles. However, flow through larger channels did contribute significant amounts of water to the water table in the spoil without being detected by radioactive probes, temperature probes, or tensiometers.