Kill Line Base Fluid Lost Circulation Management Methodology

Abstract

The loss of drilling and completion fluids during well operations are not uncommon occurrences; the major challenge is the loss rate and duration of these events. Studies and experiences have shown that several factors contribute to loss events and are broadly classified into human and natural factors, and in most cases a combination of both. Agbami well operation is not an exception; while drilling well CZ46, an oil producer well in the Agbami field, severe losses in the magnitude of 350 bph was encountered. This happened while drilling the 12-1/4" hole section in the top part of the KMY reservoir. The solution to this loss circulation event is based on the a relatively simple well control principle; manage the reduction of the bottom hole pressure (BHP) to stop or drastically reduce losses without taking influx. Previous works provided a comprehensive description of the Agbami field and its reservoirs1,2. In line with conventional drilling engineering practices3,4,5,6 the choice of the mud weight was informed by pore pressure prognosis which was not accurately predicted in the case of this well. The losses were initially slowed down by intermittently pumping sized calcium carbonate and some other LCM pills; however, it soon became obvious that the pills will not cure the losses for wellbore drilling to continue. This event was happening at a time when the Deepwater Horizon/Macondo incident7 was still very fresh in the minds of most drilling folks especially those working in deepwater operations. The major pre-occupation for the drilling operations personnel on this well when the loss event happened was not to lose the primary means of well control which is the drilling mud hydrostatic pressure. The three main challenges that this loss rate posed were: how to reduce the loss rate in order not to run out of mud at surface; what lighter mud weight to displace the hole with; and how to carry out the displacement to a lighter mud weight. All the challenges must be resolved without taking influx or negatively impacting wellbore stability. The systematic method of displacement developed by the rig-site drilling operations personnel presented here was successfully implemented and has evolved to be called "Kill Line Base Fluid Displacement Method". The method can be adapted for use in severe loss circulation event in the deepwater environment and its success can be credited to treating the situation like a response to a well control event, although it is more of trying to avert one.