| Abstract |
Currently, PT. Pertamina Geothermal Energy is developing Ulubelu geothermal field, located at Tanggamus, Lampung, Indonesia. This field is producing steam that is dedicated to supply PLN Geothermal of Unit 1&2. Steam is produced from several wells, one of them is from well pad D. All of the wells at pad D are non-artesian wells that mean the fluids cannot be discharge naturally to the surface, thus, it should be stimulated by air compression system. The probability of successfull well discharge rates can be predicted by Af/Ac method, where Af and Ac are the area of flashing and condensation respectively. The numbers of Af and Ac are calculated from well pressure and temperature (P&T) down hole measurements. The well will be successfully discharged when the number of Af/Ac more than 0.85. In addition, the total enthalpy of the wells also can be calculated from P&T data. Main feed zones of the wells are determined by the pivot point of the pressure in a certain depth; furthermore, by checking the temperature in a steam table, it will result the total enthalpy. Besides that, the mass flow of wells can be predicted by the injectivity graph which is calculated from other well testing. However, this prediction has 50% error and can be applied if the casing and well head arrangement are identic. From the experiences at Ulubelu field, the accuracy of enthalpy prediction from P&T data analyses is varying between 92.88% to 99.16%. According to the results, the method of total enthalpy by P&T data is valid. Moreover, Af/Ac method is valid for well discharge evaluation because the accuracy is 100% that mean it is applicable for other wells. The result of the injectivities graph are varying from 49% to 94% which indicating the total mass flow prediction using the well injectivities are not quite accurate and need further research for the improvement. |