One of the major concerns when drilling deepwater wells is fluid loss since the fracture gradients are typically lower than their onshore counterparts. Failure to minimize the fluid loss can significantly increase the cost of drilling, and even lead to abandonment of the well. Successful management of lost circulation should incorporate accurate estimation of loss zone location, followed by corresponding lost circulation control procedures.
This paper presents an innovative way to estimate the location of mud loss by interpreting distributed temperature measurement which is facilitated by a recently developed drilling microchip technology. Firstly, a transient wellbore thermal model is presented to predict the effect of mud loss on the change in circulating mud temperature profile for tubular fluids. The model is developed based on heat balance equations with variable local flow rates along the wellbore due to the mud loss. The effects of heat transfer above the seabed between riser and the drilling muds are included. Downward shifts in the temperature curves are noted in both the drillpipe and annulus. With distributed temperature measurement data, the derivative of annulus temperature with respect to depth can be used to effectively identify the location of the loss zone. A case study has been conducted to identify the location of a loss zone in a deepwater well. According to the results, a jump in the derivative coincides with the location of loss and is sufficiently significant in magnitude to be identified. The seawater-riser heat transfer has minimum effect on the loss zone prediction; furthermore, the effect of the same amount of loss is more conspicuous if the loss occurs at a shallower depth, in which case the loss zone can be more reliably located.