Drilling high angle wells into a heavily fractured, highly pressured, sour Jurassic reservoir may be the key to unlocking substantial reserves of light oil for Kuwait. One of the main risks to effectively developing this unconventional reservoir is the ability of wells to access a permeable, interconnected, vertical fracture network, without which the oil will not flow. Less than 50% of the vertical wells drilled to date have been successful due to a failure to intersect fractures or due to formation damage suffered during drilling. High angle or horizontal wells, while more technically challenging and expensive, will ensure fractures are encountered and will ideally penetrate multiple large, oil bearing fractures, to provide high productivity and reserves recovery per well. This paper discusses the challenges of designing a high angle well into the Jurassic which has so far proved difficult to drill vertically. These challenges can broadly be divided into three major categories - the high pressure nature of the well, the directional challenges imposed by the high angle in the reservoir, and the metallurgy aspects of operating in a highly corrosive environment.
The approach to coping with the high pressures (12,500 psi at 12,500 ft) has been to combine local experience with some of the learning from other parts of the world, notably HPHT drilling in the North Sea. The prediction of a pressure window in which to operate without gains or losses has been generated by analyzing local offset data. The task of staying within that window is crucial to being able to cross open fractures and was aided by utilizing the latest drilling technologies such as Pressure While Drilling (PWD).
Directional planning again builds on local knowledge to evaluate different options for achieving the objectives of the well. The latest tools and technologies was required to meet some demanding angle build rates in the lower part of the well in hard rock and through large open fractures. Experience gained in other parts of the world was used as the basis for design since there is no prior application of the technologies in Kuwait.
The presence of high concentrations of H2S and CO2 (5,000 – 20,000 ppm & 10,000 ppm respectively) at high pressure has made the metallurgy design a task of finding a way to resolve the conflicts between designing for high pressures, longevity, high levels of H2S and staying at reasonable cost. The final design has achieved a satisfactory balance by using risk assessment to minimize the use of expensive alloys.
This was the first well of its kind in Kuwait and could pave the way for the exploitation of a very substantial volume of light crude oil.