A pedological study of the reservoir bed of Al-Khoud Dam, Oman, revealed an unusual sedimentation pattern which evolved into an intricate composition of silt blocks surrounded by vertical cracks and horizontal layers filled with a "proppant" sand. The discovered soil morphology reflects the complex topology of water motion (infiltration-seepage-evaporation) through the sand-filled cracks/layers and blocks during both the rare flood events and ensuing periods of ponding, and the long, intervening dry periods. These naturally formed soils demonstrate an ability to preserve a large quantity of water inside the silty blocks at depths of 0.5 to 1.5 m, despite the high temperature and dryness of the topsoil. The hydrological optimality and "smartness" of these soils is attributed to the unique block-crack system. Natural, lush vegetation was found in adjacent zones of the reservoir bed, and acted as a footprint of the shallow "fractured perched aquifer". Planted "ivy" (Convolvulaceae) in the vertical face of one pedon showed intensive growth without irrigation. Soil moisture content data confirmed the hydrological immobility of water in the blocks if not depleted by transpiration. The novel phenomena reported unveil the possible alteration of soil heterogeneity for optimization of the soil-water system in arid zone soils.Key words hydropedology; capillary barrier; arid zone; 3D block-fracture composition; evapotranspiration; infiltration Sédimentation préférentielle en blocs et fissures: structure originale et évolution naturellesRésumé Une étude pédologique du lit du réservoir d'Al-Khoud, Oman, a révélé un mode de sédimentation inhabituel conduisant à une formation complexe de blocs de limon entourés de fissures verticales et d'ouvertures horizontales remplies de sable jouant un rôle d'agent de soutènement. La morphologie des sols découverts reflète la topologie complexe des mouvements de l'eau (infiltration-percolation-évaporation) à travers les blocs et les fissures pendant les rares épisodes de crues suivis de la formation de flaques superficielles puis enfin au cours des longues périodes de sécheresse habituelles. Ces sols formés naturellement ont démontré une capacité à conserver une grande quantité d'eau à l'intérieur de leurs blocs limoneux à une profondeur de 0,5 à 1,5 m, malgré la température élevée et la dessiccation de leur surface. La configuration du sédiment doit ses propriétés hydrodynamiques à des barrières capillaires. L'optimalité hydrologique et « l'astuce» de ces sols sont attribuées à l'existence d'un unique système matriciel de fissures. Signe de l'existence d'un « aquifère perché fracturé » superficiel, une végétation naturelle luxuriante a été observée dans les zones de réservoirs voisines. Une plantation de lierre (Convolvulaceae) sur la face verticale d'un pédon a connu une croissance intensive sans irrigation. Les données de teneur en humidité des sols ont confirmé la rétention de l'eau dans les blocs si elle n'est pas prélevée par la transpiration. Les nouveaux phénomènes rapporté...
Joint research between Sultan Qaboos University, Oman, and Petroleum Energy Center, Japan; sought to develop and establish a process whereby the large quantities of produced water from Omani oil fields can be effectively treated and utilized for irrigation. During pilot plant operation, oil contamination ranging from 50–300 ppm, was reduced to below 0.5 ppm. Irrigation with treated water showed no significant detrimental effects on the growth of three different salt tolerant species of plants. Introduction Produced water is the largest single associated waste product of oil production. It is a common phenomenon to find a water layer below an oil layer. Thus, oil production is usually accompanied by water. Total production of water is expected to be more than ten times that of oil, during the economic lifetime of an oil field1. A salient feature of oil production in Oman is the fact that the output of water already exceeds that of oil in most of the wells. During 1999, Petroleum Development Oman (PDO), which holds roughly 95% share of total oil production in Oman, produced an estimated 450,000 m3/day of water as an associated co-product of its oil output of 135,000 m3/day. This volume of water is expected to increase steadily and double to 900,000 m3/day within ten years2. While in the northern oil fields of Oman, the separated water is re-injected into the oil bearing strata to maintain the reservoir pressure; in the southern oil fields, produced water has been disposed into the shallow water bearing strata in the past. However, due to fears of contamination of groundwater for human use with continued long-term shallow disposal, the government has prohibited this practice and all water disposal is being switched to deeper water bearing strata. Table 1, shows the PDO disposal history and forecast in the main oil fields in southern Oman. Beyond the year 2000, produced water disposal from these fields is expected to exceed 300,000 m3/day2. This volume is sufficient to irrigate 3000 hectares in an arid climate such as Oman. Although produced water is separated from oil in gravitational separation tanks and CPI separators, such water still contains 100–300 ppm oil. Table 2, shows the average oil concentration in produced water of south Oman oilfields2. While continued disposal of such produced water to shallow aquifers will result in groundwater contamination, disposal to deep aquifers is costly.
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