INTERFERENCE TEST OF SIBAYAK GEOTHERMAL FIELD NORTH SUMATRA - INDONESIA

Abstract

Interference test has been recognized as a valuable technique for evaluating reservoir properties such as permeability thickness and storativity over an area where active and observation wells are located. Interference test can also provide qualitative indications of reservoir heterogenities and communication between two or more wells. The availability of sophisticated pressure recorders encourages providing reliable data and improved accuracy. Interference test of Sibayak geothermal field that has been carried out in December 1998 to September 1999 is examined to prove two major fault which are predicted supporting permeability of this area. The presence of linear boundary can be determined by using a new semi-log type curve matching (Sageev et al, 1985). Log-log type curve (Theis Curve) can also be employed to determine the interwell properties i.e. transmisivity and storativity.
The first test that conducted by measuring SBY-8 response to SBY-5 discharge, does not reflect presenting of either fault F4 or F1. The second test of well SBY-7 response to SBY-5 discharge, indicates shifting of the pressure response to the constant pressure linear boundary curve. It is shown in a log-log plot matching (Theis curve) and more clearly in new semi-log. For Sibayak geothermal field the area between SBY-8 and SBY-5, permeability thickness is 40.3 x 10-12 m3 and storativity is 2.64 x 10-8 m/Pa. The area between SBY-7 and SBY-5, permeability thickness is 48.3 x 10-12 m3 and storativity is 1.63 x 10-8 m/Pa.