Well control is primarily achieved using mud hydrostatic column to overbalance reservoir pressures. The overbalance from mud can be lost in a well due to following reasons; encountering unexpected higher pore pressure, reduction in mud column due to down hole losses, reduction in mud weight due to dilution and loss of hydrostatic head due to poor drilling practices. Emergency situation is created when escalation of any of the scenarios results to the loss of primary well control. In such instance, the secondary well control equipment such as blow out preventers and wellheads are activated to enable restoration of overbalance and return of drilling operation to normalcy. As part of emergency preparedness, it is important to regularly confirm the pressure integrity of the secondary well control equipment in order to guarantee their availability whenever required. As part of the pressure integrity assurance process in Shell operations, pressure test of the critical equipment is mandatorily carried out every 21days whenever the wellbore is exposed to hydrocarbon bearing reservoir.Drilling operation has been successfully carried on GXH-1 HPHT well across the hydrocarbon bearing hydrostatic interval. Pressure test that was carried out on the well control equipment after installing the 9 7/8Љ production casing and prior to drilling into the high pressure interval of the well revealed loss of pressure integrity at the flange connection between the 15,000psi rated BOP and fastlock drilling adapter on the 15,000psi rated wellhead. Upon observation, the loss of pressure integrity was discovered to be due to washout on the flanges of the BOPs and the wellhead as well as the ring gasket. The well was suspended with plug to allow safe repairs of the damaged flanges.The damages on the flanges were successfully repaired and pressure tested to full rated working pressure before recommencement of drilling operation. This paper reviews the relevant drilling operations that preceded the loss of pressure integrity of the secondary well control equipment and the root cause analysis carried out on the failure. It also enumerates recommendations from lessons learnt from the incident that will ensure prevention of future re-occurrence of the type of failure.

The management of human factor and the utilization of advanced Annular Pressure Monitoring (APM) tool enhanced the performance of Managed Pressure Drilling (MPD) in a highly permeable and narrow margin high pressure (HP)exploration gas wells in the Niger Delta. The pore pressure prognosis (PPP) indicated narrow drilling window in the HP section which necessitated the deployment of MPD for safe project execution. The MPD mud design entailed drilling with a mud weight that balanced the expected pore pressure prognosis (PPP) and the application of MPD surface back pressure (SBP) to balance the highest PPP case. During the drilling of the first of a three-well-campaign, a kick was taken with pore pressure equivalent to the highest predicted case. The evaluation of the pre-kick Equivalent Static Density (ESD) data indicated that the bottom hole pressure (BHP) was not maintained at the programmed set point unknown to the MPD operator. Transient dips in the BHP below the set point and pore pressure resulted to significant gas influx from the gas reservoir with permeability of 124 - 204mD and reservoir mobility of 112 – 1000mD/cp. Incident causal analysis revealed the contribution of human factor and limitations of conventional APM tool. This paper details how human factor was effectively managed using procedures and training, and how the advanced APM tool enhanced MPD process optimization in the second deployment resulting in the achievement of BHP values within the range for safe drilling.

Application of Managed pressure drilling (MPD) technology with other techniques to maintain constant Bottom Hole pressure (BHP) has been found to enhance drilling operations in applications where the margin between the pore pressure and fracture gradient is narrow and the reservoir permeability is high. Classic examples of such applications are deep water drilling, high pressure and high temperature (HPHT) regime and depleted reservoir environments. In the Niger Delta, HPHT reservoirs can be found in well depths up to 17000 ftss with a drilling window range of 0.4 to1.6ppg. Typical reservoir characteristics are formation permeability of 124 – 204mD and reservoir mobility of 112 – 1000mD/cp. Generally in this type of environment and essentially where there are high uncertainties in the reservoir pressures and formation characteristics, significant process safety incidents have been found to occur during pumps off events as a result of variations in BHP outside the allowable limits of pore pressure (lower limit) and fracture gradient (upper limit). The risks of exceeding the allowable limits are the possibility of taking significant influx volume if BHP falls below the pore pressure and loss of well bore integrity if the BHP exceeds the fracture pressure. Consequences of any of these events are high nonproductive time (NPT), well cost escalation and inability to achieve well objectives. This paper illustrates how in the recent HPHT exploration campaign carried out in Niger Delta, managing BHP was identified as a critical success factor. Hydrocarbon reserves of the exploratory objectives were successfully and safely unlocked by using MPD to maintain BHP within the allowable limits. The paper also illustrates how MPD application was enhanced by the use of high resolution pressure while drilling (PWD) technology.

Data from Measurement While Drilling (MWD) tools are critical to successful drilling operations, because they aid real time assessment of down-hole conditions and support critical decision-making. De-risking lithology and pore pressure uncertainties while drilling exploration wells are reliant on these measurements. The reliability of MWD tools is known to be affected by mud properties, such as concentration of low- and high-gravity solids, mud viscosity and gel strength. The high mud density required for deep well drilling operations requires an unavoidable increase in solids content, which can lead to tool failure if the fluid design or quality of constituents is suboptimal. The upper part of the 8 ½" section of the BGG-S1 HPHT well was drilled with mud weight of 16 lb/gal. The mud weight was increased to 16.3 lb/gal because of the higher pore pressure prognosis across the deeper reservoirs. The increase in mud weight resulted into higher solids content as a result of addition of more weighting agent to the fluid. After the mud weight was increased, multiple BHA runs were made because the power module of the MWD tool was not responsive. Further investigation of the repeated failures identified the root cause as solids drop-out when flowing mud through the MWD tool. The poor quality of locally sourced barite used in the operation contributed to the poor performance of drilling fluid, because it resulted in higher solids content in the mud. The solids deposition challenge was resolved by conditioning the mud to an emulsification specification that is higher than conventional industry practice. The well was eventually drilled successfully to TD after the treatment, using a single BHA run with continuous MWD data acquisition and transmission. This paper reports the impact on the mud system associated with the quality of barite, the failure mode of the MWD power module, and the treatment of the mud to ensure technical success of the drilling operations on BGG-S1.