ABSTRACT
As exploration continues, the number of areas having hydrocarbon potential that have yet to be tapped by the drill are rapidly decreasing. Concomitant with the rising costs of subsurface evaluation, these areas have diminished to the most inaccessible, requiring the development of new practices and technology. Most of the unexplored areas are offshore, and require evaluation of the geology from increasing water depths. The successful drilling and completion of rank wildcat wells is thus becoming more difficult but also more important. Much of the success of a well is determined in the planning stage, and it is here that careful interpretation of seismic data can provide extremely useful information on potential drilling hazards such as shallow gas, geopressures, and fluctuating fracture pressures, all of which provide information for the casing and mud program.
A good well plan begins with the prospect generation by the geophysicists and geologists, and then involves further analysis for engineering hazards by joint interpretation. Good communication and cooperation at this point is essential. Based on the results of these interpretations, the well plan outline may be drawn up; the final operations being contingent upon the actual conditions encountered by the borehole.
The interpreters must be aware that the limitations of their initial plan are dependent upon the resolution of the available data. Flexibility in the well plan is thus a major requirement. It is to be expected that errors in the prognosis (due to errors in the seismic interpretation) will occur; therefore, extra margins are necessary in materials and emergency contingencies. Errors in the predicted depths of events, magnitudes of geopressures, and the occurrence of unexpected lithologies and phenomena must be within the capabilities of the operation.
