Publications

In early 1998 Unocal Indonesia acquired the 5,050 square kilometer Ganal production sharing contract (PSC). A tactical decision was made not to acquire a 3D survey over the block until a functioning hydrocarbon system was proven. Instead, a 4,850 line kilometer 2D seismic survey was acquired. The interpretation of these data provided the basis for the generation of a portfolio consisting of eleven deepwater prospects. Ten of these prospects were subsequently tested with five of them resulting in commercially viable discoveries, for an overall success rate of 50 percent.The drilling of these prospects, in conjunction with the later acquisition of 3D seismic, provided some classic examples of the pitfalls of using 2D seismic. The crest of one structure, the Gandang prospect, was actually several kilometers miss-located from the 2D interpretation. In the case of another, the Gada prospect, an amplitude fit-to-structure from the 3D survey suggests the principal reservoir of the structure may have just been missed. Certainly 3D data provide a superior quality of interpretation relative to 2D data. However, there is no question that on the Ganal PSC, 2D interpretation proved adequate to identify large prospects and allow drilling of exploration wells that proved the existence of a viable hydrocarbon system. Now that the system is proven, 3D data will be used to formulate plans of development, and to identify more subtle prospects on the Ganal Block.