The Use of Horizontal Drilling in International Exploration

Abstract

Internationally (outside the USA) more than 300 horizontal wells were drilled in 1991. Horizontal well reservoir targets generally consist of a preponderance of clastic reservoirs over carbonates in the ratio of approximately 60% to 40%. The concept of using horizontal wells as an exploration tool can be defined as a means not only of proving new reserves in undrilled plays, but as a means of re-exploring previously drilled and poorly productive terrains. The Austin Chalk play in South Texas is the prime example of this concept in action. Exploration in this case can be defined as the adding of multiple orders of additional reserves value. International basin selection criteria are discussed which can optimise the chances of finding high value additional reserves in the initial stages of an exploration campaign by using horizontal drilling (with the important help of previous subsurface coverage or pilot drilling). These criteria include the presence of self sourcing carbonate reservoirs, the presence and predictability of regional fracturing, the mechanical properties of the reservoir rocks, the presence of significant original oil or gas-in-place and the reservoir depth criteria in which horizontal drilling technology is practicable and cost-effective.