Slim Hole Drilling In Kuwait (4 1/2" Hole Size)

Abstract

Abstract Slim Hole Drilling in Kuwait Oil Company (KOC) is not a procedure that is planned for in initial well designs. The complexity of drilling conditions in Kuwait has forced KOC to plan and drill such hole sizes as a contingency. First, one must appreciate the drilling conditions that forces the need for slim hole drilling in Kuwait. Highly fractured, extremely weak zones near surface and below or between several productive field horizons are followed by a pressure transition that ends with a salt/anhydrite section with porous layers interbedded, containing H2S gas and water. In order to control the fluid within such layer, mud weight, in excess of 19.0 ppg is required. Below this section is a slight pressure reversal which includes fractured carbonates. Due to such pressure differences between layers and the position of lost circulation layers within productive zones, numerous casing strings are required to isolate pay zones from weak zones, normally pressured zones from high pressured zones and weak zones from other normally pressured zones, to maintain circulation for drilling and well control. Kuwait Oil Company Deep well programs end with 5½" casing set on bottom which requires that the well starts with 42" conductor at surface and 30" as surface casing. Unanticipated hole conditions or well problems that require setting a casing string at an earlier depth than what was actually planned for in the well casing design, will result in slim hole drilling on bottom in order to reach the objective of the well. Often very little allowance is available for problems by the very nature of drilling conditions. Slim hole drilling in Kuwait is drilled in a hostile environment. The slim hole sections are typically in deep, hot hole sections. This environment often finds high pore pressures virtually near frac strengths. The wells are often either flowing or losing mud. To make matters worse, H2S accompanies any influx or drill volume gas. The paper will cite case histories of wells that have included 4½' slim hole sections at depths from 19300 to 20774' in EXW-1 and over long intervals of 15704 to 18683' in DW-01 and in mud weight ranges of 16.0 to 19.3 ppg. Slim hole sections have been drilled using downhole motors as well as with rotary drilling. The case histories will additionally describe the down hole tool selections used along with kick and lost circulation handling. Also, discussions will touch on side tracking and completion on DW-02 where the the original 4 1/2" hole was drilled from 12,620' to 13,800' with 16.0 ppg mud and was side tracked from 12,821' to 13,560’. At the end of the side tracking, 3 1/2" liner was run and cemented as the completion liner and 2.6" bit was run on 1 1/2" coil tubing to clean out inside the liner.