Optimizing Deepwater Well Locations To Reduce the Risk of Shallow-Water-Flow Using High-Resolution 2D and 3D Seismic Data

Abstract

Abstract Interpreting possible overpressured sands with geophysical data, inpractice, is best accomplished by doing a combined interpretation using bothconventional exploration 3D and high-resolution 2D seismic data. The use ofhigh-resolution ‘hazards’ 2D seismic data, can, if interpreted together with 3Dseismic data on a workstation, significantly aid in optimizing well locationsto reduce the risk of overpressured sands. Introduction Drilling through overpressured sands in the tophole section of deepwaterwells can result in a difficult and expensive well-control problem known as"shallow-water-flow"(SWF). SWF-prone sediments are common in the deepwater Gulfof Mexico. And, it is often common for these problem intervals to cover thedrilling target so that the interval cannot be easily avoided. High-resolution2D seismic data is routinely acquired for obtaining a permit for drilling, butthe data are usually interpreted only for that purpose. High-resolution 2D datasets, however, are very useful in SWF assessment studies. Exploratory 3Dseismic data can image overall SWF-prone intervals, but in many cases lack theresolution to identify sand-prone sections in the required detail. High-resolution 2D seismic data, interpreted together with 3D seismic data, canbe used to identify well locations where SWF would not be expected or would beless severe. The first part of this paper reviews the seismic data types that arecommonly used in SWF pre-drill assessment studies and their respectiveresolutions. The basic SWF model and the associated seismic facies that arecommonly the source of SWFs are also reviewed. Finally, two pre-drill SWFstudies, one from the middle continental slope at a water depth of 1,014 m(3,328 ft) and the other from the abyssal plain at the foot of the Sigsbee Escarpment at a water depth of 2,026 m (6,647 ft), both in the Gulf of Mexico, are discussed.