temperature and pressure in the svartsengi ... - Orkustofnun

7~6 EVOLUTION WITH TIMEThe production from the Svartsengi reservoir started inOctober 1976. The history of the productIon now coversabout 2600 days. Fig. 6 shows the first 2000 days of thisproductIon. During the first two years the mass flow ratefrom the reservoir Is 50 kg/s, but In 1979 the flow rateincreases to approximately 100 kg/so The next increase inmass flow rate Is in 1981, when the winter flow Isincreased to about 300 kg/so The productIon rate has beenat this level during the last three years. In the summertime the mass withdrawn from the reservoir Is about halfof the winter flow rate. The total mass taken out of thereservoir In Svartsengi Is now about ~xl010 kg.The pressure drawdown In the reservoir has beensubstantial. Fig. 6 shows that in 1982 the water level inthe reservoir is 90 m lower than at the start of produc ­tion. There is a simple relation between the pressuredrawdown in the reservoir and the total mass wi thdrawnfrom the reservoir as shown in Fig. 6~.The Svartsengi geothermal reservoir is a typical liquiddominated reservoir where the ther mal fluid in theformation is in liquid phase. The temperature of the fluidin the undisturbed state was close to 2~OoC. However,during the natural surface discharge in the area wherewells SG - 2, SG - 3 and SG-l0 are located, the system wasboiling and two - phase conditions are still present atshallow depths. During the exploitation of the field. wherethe pressure in the system has decreased with time, theboiling at shallow level around wells SG - 2, SG - 3 and SC - l0has increased wi th time. These cond i t ions were descr i bedin Chapter 4 (see Fig. 12 , 13, 14 , 15, 31 and 32) . Thelower level of the boiling zone is now at approximately500 - 550 ID depth.The top of the main reservoir in Svartsengi is, however, atapproximately 600 m depth. The caprock in the geothermalsystem is most likely the hyaloclastite formation as shown