Overcoming Drilling Hazards and Pore Pressure Uncertainty, An MPD Approach in West Kuwait Field for the Deepest Well Since 2002 in Kuwait Oil Company (KOC)

Abstract

Comingling Middle and Lower Jurassic Reservoirs to is considered a challenge to drill conventionally, and precisely in West Kuwait Fields, due to a highly uncertain Operative Window, in addition to the challenge of drilling in HPHT (High-Pressure High-Temperature) in West Kuwait Jurassic deep wells, as the main drilling challenge is to comingle the high- pressure formations at top and depleted formations at bottom. Normally, these formations are drilled in two different sections, 9 ¼" hole section covering the Middle Jurassic unconventional virgin pressure reservoir, and 6" hole section covering the lower Jurassic depleted formations through its Flow Zones. This played as an advantage for MPD (Managed Pressure Drilling) to prove the added value of well construction costs, along with the main value added by MPD for this specific well, in the current case having a Pore Pressure difference of 3.7 ppg (ranging from 17.7 ppg to 14 ppg), leading to Well Control and total mud loss incidents compounded with high H2S/CO2 environment and resulting in increased number of NPT (Non-Productive Time).

In cooperation with KOC (Kuwait Oil Company) Drilling Team and Weatherford MPD Team, the risks were analyzed and finalized with a high level MPD Drilling Program and Strategy, to meet the required objectives to drill the assigned well in West Kuwait Field, this resulted in a strategy to employ mud weight of 16.8 ppg with the Equivalent ECD of 18 ppg by the use of MPD CBHP (Constant Bottom Hole Pressure) Application. The strategy included the MPD Dynamic Pore Pressure Tests (DPPT's), as an imperative procedure to ascertain the Pore Pressure limit to adjust the ECD based on real time data. Moreover, to have more certainty of the Pore Pressure between these two different zones, MPD conduct Dynamic pore pressure test to 17.6 ppg in formation A. Upon entering formation B, a high gas concentration was observed, which resulted in an increase in the Equivalent Circulating Density (ECD) to 18.6 ppg. Partial losses were noted; however, through Managed Pressure Drilling (MPD) practices, the ECD was reduced to 18.35 ppg to control the losses. The well encountered a kick at top of formation B, which was controlled with an ECD of 18.7 ppg. Subsequent SIDP measurements confirmed that the pore pressure (PP) was 18.2 ppg. To address this, the MW was increased to 17.5 ppg, leading to an ECD of 18.8 ppg. Drilling resumed with an ECD of 18.8 ppg, and the ECD was gradually reduced from 18.8 ppg to 18.4 ppg based on hole conditions. However, several losses were observed at an ECD of 18.6 ppg. These losses were controlled by reducing the ECD to 18.3 ppg, which also addressed well trickling. MPD successfully managed these conditions, allowing the well to reach TD safely with an ECD of 18.4 ppg, which is the deepest well in west Kuwait since 2002.

One of the main challenges encountered was the need to displace the well to trip MW, for which conventional displacement methods proved inapplicable due the risk of the losses. To address this, MPD introduced an innovative approach: the staged well-killing method. In this approach, MPD first pumps the kill mud (trip mud) to achieve a fully open choke and an ECD of 18.6 ppg. The pumping is then halted, and the drill string is pulled out while maintaining the ECD of 18.6 ppg up to the bit, ensuring it matches the kill mud level in the annulus. Subsequently, pumping of the kill mud is resumed, and this process is repeated as needed; by employing this method, we ensure minimal annular friction applied to the formation, thereby reducing the risk of losses.

The application of an ECD of 18.4 ppg enabled safe and efficient drilling through the challenges typically encountered in a HPHT environment. This was particularly crucial given the narrow operational window of 18.6 to 18.3 ppg in our case. Wells in such conditions are typically un-drillable using conventional methods.

This paper analyzes the efforts in planning a successful execution of drilling two challenging sections commingled with large uncertainty pressure window. This well can be considered a reference well, as the 10 3/4″ casing was accidentally shortened, leading to the use of a 7 5/8″ liner to cover the high-pressure zone that should have been covered by the 10 3/4″ casing. MPD intervened to save the well, successfully commingling two sections with different PP regimes. Without MPD, the well could have ended with high costs for KOC or resulting in well abandon.