Precise Gain and Loss Detection Using a Transient Hydraulic Model of the Return Flow to the Pit

Abstract

Abnormal variations of pit volume are a prime indicator of mud losses and formation fluid influxes. However the detection of gain and loss at the pit level can be difficult because of the transient behavior of several components in the hydraulic loop. For instance, during circulation the compressibility of the drilling fluid changes the total volume of mud needed to fill the well compared to static conditions. Similarly, changes of the drilling fluid temperature modify the volume of mud due to its thermal expansion. Furthermore, the transport and separation of cuttings also influences volume variations in the pit. Finally, the retention capacity of some of the mud transport and treatment equipment (e.g., return flow-line, shakers, sand-trap, degasser, transfer pit) has a direct impact on the active pit level. All of these effects are transient and can cause substantial variations of the active pit volume that may be interpreted as gain or loss while they actually have natural origins.Most of these effects are well known and are dealt with in a pragmatic way by using finger printing between the current pit volume variation and a reference pattern obtained in similar drilling conditions. Nevertheless, the finger printing method has its limitations when the current drilling condition variation does not have an obvious reference pattern. In addition, it necessitates a selection of the reference pattern by an operator and therefore is rather difficult to automate. This paper describes in detail a transient hydraulic model of the downhole and surface equipment effects on the pit volume variations. Several use cases are also described including early kick detection with small margins during pump shutdown and detection of tiny gains during draw-down tests used in an MPD (Managed Pressure Drilling) operation.

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“…An early indication of kick and fluid loss can be detected by monitoring the volume of drilling fluid in the mud tank, highlighted in (Anfinsen and Rommetveit, 1992). It is a straightforward way to monitor kick/loss but is not always reliable as discussed in (Cayeux and Daireaux, 2013). Interpreting the active mud tank volume may be difficult if a significant amount of the circulating mud is buffered in the return flow lines, shale shakers and other transfer tanks.…”

“…The usage of the travel time of pressure waves through the drill string and annulus to identify kick/loss is presented in (Codazzi et al, 1992;Stokka et al, 1993). (Hargreaves, Jardine, and Jeffryes, 2001;Kamyab et al, 2010;Cayeux and Daireaux, 2013) presented different numerical methods for kick/loss detections. Compared to conventional drilling, MPD provides significantly better kick detection.…”

“…Different types of kick/loss detection methods 1.2. Early Kick/Loss Detection 5 used in both conventional drilling and managed pressure drilling (MPD) are presented in (Cayeux and Daireaux, 2013;Johnson et al, 2014;Ayesha, Venkatesan, and Khan, 2016). However, the focus of the study is on early kick/loss detection for conventional drilling operations.…”

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“…In both these cases the pressure changes were described as hardly discernable. Technology limitations make it difficult to distiguish a trend from data noise even with the application of physics based models for detecting small deviations and distinguishing these from other background noise, (Cayeaux and Daireaux, 2013). In smaller hole sizes the low annular clearances makes the equivalent circulating density (ECD) sensitive to the pipe reciprocation rate.…”