Dynamic Multiphase Kick Tolerance Allows Safe Drilling Which Led to Huge Gas Discovery in a HPHT Exploration Well in Malaysia.
Authors: Umar Lawrence , Yun Thiam Yap , B A Murad M Syazwan , Woo Wing Keat , Nas Steve William , Escalono Brenda , Eka Andi 
Published: March 2015

TTD-1 well is located in offshore block SK in East Malaysia and this High Pressure High Temperature (HPHT) well proved to be a challenging well to drill with a pore pressure ramp exceeding 15psi/ft and a bottom hole pressure exceeding 14,000psi. Due to the predicted steep pressure ramp and the resulting narrow margin between the pore and fracture pressures advanced dynamic kick simulations and Managed Pressure Drilling (MPD) was used to drill TTD1 well.

This paper details the importance of dynamic kick tolerance calculations in getting the well to the targeted drilling depth. In order to optimize casing setting depths in a narrow margin HPHT drilling environment, dynamic flow checks and dynamic formation integrity tests using managed pressure drilling technology were used to define the lower and upper boundaries. The dynamic well control simulations take an influx followed by standard well control procedure of shutting down the pumps and closing the BOP before circulating out the influx. The kick tolerance of a well is governed by fracture pressures, influx volumes and kick intensity. The kick tolerance limits are defined by the operator and if the limits are reached the next casing has to be installed before drilling can proceed.

In addition to the dynamic kick tolerance analysis conducted in the planning phase, a simplified version of the software was installed on the rig. Drilling supervisors and well control specialists were trained to operate the software. The purpose of the rigsite kick simulator was to enable the drilling supervisors to quickly determine if an influx could be circulated out safely without exceeding surface or downhole pressure limits during a well control situation. The simplicity coupled with realistic multiphase technology permits simulations to be performed as soon as an influx is taken.

The multiphase dynamic kick model is able to simulate a well control event more realistically when compared to the common single bubble kick calculations. These more realistic calculations allowed drilling to proceed whilst maintaining pre-determined kick tolerance volumes. This allowed the deeper targets to be achieved in the TTD-1 well.

Introduction

The SK field proved to be challenging to drill due to the high pore pressure ramp in the 8-1/2" hole. The high pore pressure ramp resulted in a narrow pore - fracture pressure margins as drilling progressed.

The TTD1 HPHT exploration well was drilled in 2012 offshore East Peninsular Malaysia. Seismic studies predicted a pore pressure ramp of 5psi/ft. More detailed pore pressure analyses based on regional data were perfomed prior to drilling and this study estimated a 15psi/ft pore pressure ramp. Whilst drilling the 8-1/2" hole section (4173m to 4823m), dynamic flow checks utilizing the MPD system were performed and real time pore pressure engineers predicted that the pore pressure ramp could be exceeding 15psi/ft. Formation Pressure tools later confirmed that the pore pressure ramp was at 17psi/ft. The mud weight at total depth of the well was 18.0ppg which gives a static bottom hole pressure (BHP) close to 15,000psi. The casing schematic for the TTD1 well is shown in figure 1.