Publications

Panen is one of the prospective areas in the Jabung Block. Gas discoveries were reported from Panen-1 and Napal-1 wells. The surface geochemistry studies which have been conducted in this area also confirm some prospectively. The head space gas method was applied to predict hydrocarbon presence to reduce the risk of exploration failure. The data used for this study were integrated of geophysical data (Seismic section and subsurface map) and drilling data (mudlog, and wireline logs). One of the advantages of using surface geochemistry during the exploration phase is its assistance in the screening large areas rapidly, economically, and qualitatively for overall petroleum source potential. Zones of favorable thermal environments for petroleum formation can be defined by identifying areas containing thermogenic hydrocarbons in soilgas (Richers & Maxwell, 1991). Head space gas is one of surface geochemistry methods which calculates the total surface gas present, and to identify its origin and stage of maturity (early catagenetic or catagenetic). The principle of this method is recognizing hydrocarbon traces by measuring the amount hydrocarbon present in shallow samples. Each Sample should be taken at 25-30 m depth, and then put into a container and mixed with water (3/4 parts from one container) & ten drops of bactericide. Subsequent laboratory analyses will provide gas parameters such as C1, C2, C3, iC4, nC4, wetness gas, & iC4/nC4 (Geoservices, 2009). The next step is using cross plots to define origin of surface gas or to define gas characteristics. This enables the construction of contour maps to illustrate the gas distribution. Two hundred and fifty samples were taken from the Panen area. All samples had gone through analyses, combined with the use crossplot parameters (C3/C1, iC4/nC4, and wetness) vs number of samples, were used make the contourmaps of surface gas distribution (C1, C2,C3,iC4,nC4, wetness gas & iC4/nC4) The contour maps of surface gas distribution shows the areas of gas characteristic of early diagenetic (biogenic) and catagenetic (thermogenic). The samples containing thermogenic gas are related to active producing well areas, while the samples containing early diagenetic are related to deep and non producing active wells. Overlays of head space gas anomalies with subsurface maps or depth structure map show that traps are associated with head space gas anomalies and that these areas also have thermogenic gas characteristics (based on crossplots of gas parameters vs. number of samples). Conversely these overlays also identify the closures with no hydrocarbons or only hydrocarbon shows (etc: Panen-2 well) does not exhibit a head space gas anomaly. Surface gas anomalies can be a useful guide for hydrocarbon presence, especially area which have fault pattern until to surface, because they are often coincident with traps containing hydrocarbons. areas without hydrocarbons found also doesnt show gas anomalies. The usefulness of surface geochemistry is maximized when it is integrated with additional geophysical and geological data.